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Subscribe / Log in / New account Weekly Edition for September 1, 2011

Catching up with Calibre

By Jonathan Corbet
August 31, 2011
Last week's Edition contained an interview with Kovid Goyal, the maintainer of the Calibre electronic book manager, but it did not look deeply at the application itself. Coincidentally, your editor has been playing with Calibre with renewed interest recently. This application has made considerable progress since your editor's last look at it, so a look at where it has gone is called for. Calibre is not perfect, but it is a useful tool for a somewhat unwilling newcomer to electronic books.

Your editor is not one to resist progress; the transition from vinyl to compact disks was handled with no reservations, despite the fact that there is still something special about those old analog platters. How can one resist a medium that is bulky and heavy, limited to 30 minutes of play time, and which degrades with every playing? When CDs, in turn, started to [Books] go away barely a tear was shed. There has been no pining for 8" floppies, eight-track tapes - or for tape in general. Technology moves forward, and things get better.

But books are special. They represent an old technology well optimized for its intended task and are a thing of beauty. Your editor's love of books has swallowed up vast amounts of time and crowded the house with dead trees; Cicero's classic proverb ("a room without books is like a body without a soul") is well respected here. That occasionally leads to certain amounts of marital stress, but we digress. The point is that the movement of the written word to an increasingly digital-only form is something that has been resisted in these parts for some time.

But the writing is on the wall cloud-based persistent storage device: books as physical objects are on their way out. Once your editor got past the denial phase, it became clear that there were even some advantages to ebooks. They are often cheaper, which is nice. Certain science fiction authors would appear to be paid by the kilogram; reading them in electronic form yields the same entertainment value without the kilograms. Electronic books are especially advantageous when traveling; the weight involved in carrying sufficient reading material for a family vacation was, once again, a source of a certain amount of familial disagreement. Searchability can be a useful feature at times. There is still nothing like a real book, but the electronic version is not entirely without its charms.

One does not need to accumulate many ebooks before it becomes clear that some sort of management scheme is required. Simply keeping books on a reader device is not really an option; that device may well not be entirely under the owner's control, its capacity is limited, it can be lost or damaged, and it eventually will need to be replaced. Just dumping them on a disk somewhere has problems of its own; some sort of management tool is needed. For now, in the free software world, Calibre seems to be that tool.


As of this writing, the current version of Calibre is 0.8.16. Releases are frequent - about one week apart - and each release adds bug fixes and new features. The web site recommends installing binary releases directly from there because distributors tend to fall behind that schedule; Rawhide did not let your editor down, though. Interestingly, those looking for the source on the Calibre web site can search for a long time; there are no easily-found pointers to the SourceForge directory where the source can be found. The program is written in Python.

One thing first-time users won't necessarily notice is that Calibre phones home when it starts. The ostensible purpose is to check for new releases, but, in the process, it reports the current running version, the operating system it is running under (Linux is reported as "oth") and a unique ID generated when the program is installed - along with the IP address, naturally. It is not a huge amount of information to report - users of proprietary reader devices have much larger information disclosure issues to be concerned about - but it's [Calibre] still a bit of a privacy violation. Programs that communicate with the mother ship in this way should really inform their users of the fact and give them the opportunity to opt out.

The main Calibre window provides a list of books in the library, an animated "cover browser," a list of metadata types, and a pane for information about the selected book. By default, somebody just wanting to look through the books in the library will find less than 1/4 of the available space dedicated to that task. However, one cannot fault Calibre for lacking configurability; there are few aspects of the interface that cannot be tweaked at will. Unwanted stuff is easily gotten rid of.

There is a toolbar across the top with a large number of entries; they do not all fit unless the window is made quite wide. Some of them can be a bit confusing; should one import a book with "Add books" or "Get books"? The icon labeled "N books" (for some value of N) is actually the way to switch between libraries. "Save to disk" is a bit strange for books in the library, which are already on disk; it seems to be a way to save a book in a different format, though how that relates to the "convert books" operation is not entirely clear. With a bit of time and experimentation, though, it's not too hard to figure out how things work.

[Calibre reader] There is a basic reader application built into Calibre; it works well enough, though, likely as not, few users actually read their books in this application. Some of its more obnoxious behaviors (the 1/2 second animated page flip, for example) can be disabled. One thing that cannot be turned off, though, is the obnoxious "tooltips" that show up on everything. Your editor has noticed a trend toward these annoyances in a number of applications; when one can't see the interface through the tips, something is wrong. As can be seen in the associated screenshot, the "next page" tooltip obscures the text of the book itself.

Calibre's management of devices seems to work well; when a recognized device is plugged in, a separate pane showing the contents of that device is created. Books can be copied between the library and the device at will; if needed, Calibre will convert the book to a different format on the way. Your editor's Kindle device Just Works with Calibre; all that was needed was to plug it in. Android devices also work nicely. The Calibre site recommends installing WordPlayer on Android, but interoperation with the open-source FBReader application works well. Aldiko can also be used, though it is necessary to manually import the book files into the application after Calibre has placed them on the device.

Naturally, when working with a Kindle, one quickly runs into DRM issues; Calibre will put up a dialog saying that it cannot work with a locked file and wish you luck. As it happens, there is a plugin out there that can decrypt books from a Kindle and store them in a more accessible format. The Calibre project itself won't go near such plugins, but they are not hard to find. Whether one sees unlocking an ebook as an exercise of fair-use rights on a text that one has purchased or as an act of piracy will depend on one's viewpoint and, perhaps, local law. Your editor can only say that, if he were able to store his purchased ebooks in a format that does not require a functioning Kindle or Amazon's continuing cooperation, he would be much more inclined to buy more such books in the future.

(The Kindle, incidentally, will eventually be replaced with a more open device; selecting that device is likely to be the topic of a future article).

[Calibre search] The "Get books" option pops up a dialog that, seemingly, will search every bookstore on the planet for a given string. Results are listed with their price, format, and DRM status. The process tends to be slow - not surprising, given how many sites must be queried; one will want to trim down the number of sites to speed things up and eliminate results in undesired languages. The Calibre developers have clearly been busy setting up affiliate arrangements with as many of those bookstores as possible. The proceeds support ongoing development of the code, which seems like a good cause, certainly.

Another interesting feature is the ability to download articles from various news sources, format them appropriately, and send them to the device. In the case of the Kindle, that sending happens immediately over the Kindle's cellular connection; there is no need to plug the device into the computer first. Over 1,000 different news sources are supported at this point. If Calibre is left running, downloads can be scheduled to run at regular intervals. The value of this feature arguably drops as always-connected devices take over, but it's easy to see how it could be indispensable for those who do a fair amount of offline reading.

Wishlist and conclusion

There is a fairly well developed search feature clearly designed with the idea that there will be thousands of books in the library. Searches can key on almost any metadata, but there does not seem to be any way to search for books based on their contents. If you cannot remember which book introduced the concept of "thalience," Calibre, it seems, will not be able to help you find it. Indexing a large library to the point where it can be efficiently searched is not a small task, of course, but there are times when it would be nice.

Closer integration between Calibre and the reader devices would be useful. For example, all readers have a concept of bookmarks, or, at least, the current position within a given book. Imagine having a copy of one's current book on a phone handset; it would always be at hand when one finds oneself with an unexpected half hour to kill somewhere. Later, when curling up by the fire with the spouse, the dog, a glass of wine, and the real reader, said reader would already know the new position to start from. No such luck with the reader, alas; even the spouse and the dog can't always be counted upon. Calibre can't fix the latter, but it could convey that kind of information between reader devices.

Even nicer, someday, might be to run an application like Calibre directly on the reader devices, backed up by a library found in personally-controlled storage on the net somewhere. Google's Books offering is aiming at that sort of functionality, without the "personally-controlled" part, but books are too important to leave in some company's hands. Until such a time arrives, we'll be left managing our books on a local system and copying them to devices as needed. Calibre seems to be the best option there is for that management; it is a capable tool that does almost everything a reader could want. It definitely helps to make the transition away from real books a bit less painful.

Comments (28 posted)

LinuxCon: Mobile network management with ConnMan

By Jake Edge
August 31, 2011

For handling network management tasks, at least on the desktop, most distributions (and thus Linux users) rely on NetworkManager. But, there is an alternative, called ConnMan, that was originally created as part of Intel's Moblin effort. ConnMan has found its way into Moblin's successor, MeeGo, which is no surprise, but it is also suited to smaller embedded Linux systems as well. ConnMan's creator, Marcel Holtmann, gave a talk at LinuxCon to describe ConnMan, along with some of the challenges faced in creating a compact network management tool that is targeted at mobile devices.

[Marcel Holtmann]

Holtmann started out by describing the "wishlist" for mobile devices that he came up with when he started working on ConnMan three years ago. Mobile phones were the first use-case he considered because they are complex devices with limited battery life. Also, "if you solve the phone case, you solve the tablet and netbook problem as well", he said. In addition, the needs of televisions are a subset of those needed for mobile phones.

But, other use-cases are different. Cars have different requirements, as do robots, sensors, and medical devices. The only use-case that was left out was the data center because it is "simple and pretty much static", he said.

So, after considering those use-cases, Holtmann came up with a wishlist that consisted of a handful of high-level constraints. It should be a simple and small solution, "but at the same time, really powerful". It should be automated so that it didn't have to ask the user what to do "over and over again if we knew what to do". It should have minimal dependencies so that it could run on memory-constrained devices. It should also support customization so that vendors could create their own UI on top of the core. ConnMan sprang out of that wishlist.

There were also a common set of problems that a network management application needs to deal with including IP address assignment, which is "quite complicated actually", especially when considering IPv6, he said. Dealing with network proxy support is another problem area because the "settings are really hard to explain", so there is a need to handle it automatically. DNS handling can be problematic as well.

There are interaction problems too. "Are we on the internet?" is a surprisingly hard question to answer as the system could be connected to a hotspot that requires a login for example. There is a need to make applications aware of internet connectivity—gain or loss—as well. In addition, time synchronization is important, but even more important sometimes is determining the correct timezone. All of this stuff needs to be sorted out before telling applications that the internet is available, Holtmann said.

Beyond that, there are some additional features required for mobile devices today, including a flight (airplane) mode, tethering, and statistics gathering. The latter is particularly important for devices where different kinds of connections have different costs.

Design principles

Holtmann said that he looked at how other network management applications are designed and saw a fundamental problem. Instead of keeping the policy and configuration in the low-level connection manager, those parts live in the UI, he said. He thinks this is the "wrong approach" and that policy and configuration should live in the connection manager so that experts can deal with the hard problems, rather than making users figure them out. In addition, it allows UI developers to change the interface easily, because they don't have to change the policy/configuration handling as part of that.

There are three principles that governed the design of ConnMan from a user interaction perspective. The first is to ask users "only questions they can answer". If there are questions that a user will have trouble answering, the program should try to figure them out for itself. For example, users don't know or care about the various kinds of wireless keys required, so don't ask a bunch of technical questions about WEP vs. WPA vs. pre-shared keys, just ask for the password for the wireless network. The underlying connection manager should recognize what type is required by the wireless network automatically.

The second is to only show current and valid information to the user so that they aren't overwhelmed with useless information. Don't tell them that the Ethernet cable is not plugged in, he said, "they are sitting in front of it". Hide WiFi networks that have too weak of a signal rather than showing a bunch of "<unknown>" access points. The emphasis should be on previous connections that the user has made, because the chances that "the user wants to use it again are really high".

Lastly, interact with the user only when it's needed. Part of the solution is to remember things from previous connections and configurations, but there is more. If ConnMan doesn't make connections quickly enough, users will start to think something is wrong and start "messing with things". Also, use error notifications to tell the user something useful, not just propagating the error message from the underlying code. It was difficult to keep to the principles, Holtmann said, but that was the goal.

Reducing time-to-connect

In keeping with the last principle, ConnMan has done some things differently to try to reduce the time it takes to establish a connection. As Holtmann mentioned earlier, connection establishment for IP is rather complicated with multiple pieces required to get to a point where applications can start using the internet. First there is the low-level IPv4 and IPv6 address and proxy configuration (which includes DHCP, web proxy auto-discovery (WPAD), and IPv6 auto-configuration). After that, it may need to do a WISPr (wireless internet service provider roaming) hotspot login, followed by time synchronization.

That all takes a fair amount of time largely because of various inefficiencies in the current implementations. For one thing, IPv4 and IPv6 discovery and configuration should be done in parallel, rather than serially. Arbitrary timeouts should also be eliminated.

One of the biggest problem areas was DHCP. In current Linux systems, there are multiple levels of D-Bus messages and callout scripts to handle DHCP. There are at least three script/program executions and 2 D-Bus messages, sometimes with arbitrary waits between them, to handle getting an address via DHCP. "Time is just wasted", Holtmann said.

But DHCP only requires 4 UDP messages of 300-600 bytes each, which "can be done a lot faster than you think", he said. ConnMan implemented its own DHCP library that significantly reduced the amount of time it took to get an IP address, while also reducing memory consumption. The time reduction results in "approximately 1-2 seconds that can be given back to users", while the runtime memory savings is very important for some embedded devices.

ConnMan features

The feature list for ConnMan is quite large already, and Holtmann went through a laundry list of them. Obviously, support for WiFi, Bluetooth, Ethernet, and WiMAX are "have to have" features, he said, but ConnMan provides quite a bit more than just the connectivity options. There are various low-level features that were mentioned earlier like DHCP (both client and server), WPAD and WISPr, and support for timezone switching. In addition, support for iptables, 6to4 tunnels, DNS resolver and proxy/cache, an HTTP client, tethering support, and more are available. There is also a "personal firewall" feature that is "under discussion right now", he said.

Beyond that, there are two different APIs available for different kinds of applications to use. The Service API is for configuration and is used by the ConnMan UI. It unifies the configuration for all of the different connection options (WiFi, Bluetooth, etc.) as well as providing a single signal-strength API.

The Session API is meant for applications to use to monitor the internet connection. Each application can have one or more sessions that correspond to different connections they are making. The API provides IP address change notifications, so that the application can transparently reconnect. It also allows applications to give priority information regarding how quickly its data needs to be handled (for "realtime" audio vs. background network syncing for example). It was designed with handset and in-vehicle-infotainment (IVI) needs in mind, Holtmann said.

Hotspot login "drove me crazy for a really long time", he said, but ConnMan now has WISPr 1.0 support that works correctly, unlike many other implementations (including the iPhone). It doesn't use a browser but does require an HTTP client. With ConnMan, a device can roam between different WISPr-supporting hotspots using a password agent to provide the proper credentials.

ConnMan also supports WISPr 2.0, but none of the hotspot providers do, so he has been unable to test it. This will support "real" WiFi offloading, and it doesn't require a username/password because the SIM card credentials are used to authenticate.

Proxy support is another problem area that has been solved in ConnMan, Holtmann said. A user's device may need a proxy to reach the internet when they are at work and either need a different proxy or none at all when at home. Changing proxies is difficult to do under Linux, he said. Proxy auto-configuration (PAC) is one solution, but it is JavaScript-based. Since they don't want a JavaScript interpreter in every system, a separate solution was needed.

PAC files can be large (he mentioned Intel's being 4M) and must be downloaded each time a connection is made on networks that use it. To avoid each application requiring its own PAC support, ConnMan centralizes that information, but calls out over D-Bus to the pacrunner daemon to get the required configuration. The implementation is "a little bit nasty, but it works pretty well" in practice, he said, and it alleviates users from having to fiddle with proxy configuration.

Full Network Time Protocol (NTP) support is really only needed for data centers, so ConnMan uses Simple NTP (SNTP) instead. That reduced the footprint and external dependencies required while still providing reasonable time synchronization.

ConnMan had full support for tethering via USB, WiFi, and Bluetooth before either Android or iOS, Holtmann said. It integrates with wpa_supplicant, BlueZ, and the USB gadget subsystem. In addition, there is internal iptables handling as well as DHCP and DNS proxy handling support for ConnMan tethering.

The final feature that Holtmann described is the statistics gathering for ConnMan. Different connection types have different limits, especially when roaming, so it is important for users to know what they have used. Also, some connection types should only be allowed for certain applications, he said. IVI systems may have a SIM, but the car manufacturer may only want that used for certain critical functions (navigation, system updates, etc.). There is Session API support for per-application statistics, but there is still more work to do on that.

In answer to audience questions, Holtmann noted that MeeGo is the driving force behind ConnMan, but that others use it too, including the GENIVI Alliance for IVI applications as well as manufacturers of other small embedded Linux devices. ChromeOS uses a version of ConnMan that was forked over a year ago—which is a bit surprising: "do they want the new features or not?". For those who want to try it on the desktop, he said that Ubuntu is the only regular distribution that currently has ConnMan packages.

In summary, ConnMan is "fast and simple" and does what users expect it to do, Holtmann said. The Session API is unique to ConnMan as far as he knows, and will be very useful to applications. There will be more advanced features coming in the future, he said. Overall, Holtmann made a pretty compelling argument for looking at ConnMan as an alternative to NetworkManager (though he largely avoided talking about the latter), especially for the mobile device use-cases that it targets.

[ I would like to thank the Linux Foundation for travel assistance to attend LinuxCon. ]

Comments (17 posted)

LinuxCon: The mobile Linux patent landscape

By Jake Edge
August 31, 2011

It will come as no surprise to regular LWN readers that the patent situation for mobile Linux (and mobile devices in general) is an enormous mess. Open Invention Network CEO Keith Bergelt spoke at LinuxCon to outline how he sees the current landscape and to impart some thoughts on where he sees things going from here. In addition, he described several ways that the community can get involved to help beat back the patent threat, which is most prominent in the mobile space, but certainly not limited to that particular sphere.

Android rising

[Keith Bergelt]

Bergelt said that his talk would center around Android, because it is the "focus of a lot of ire from Microsoft", but that the same threats exist against any mobile Linux system that becomes popular. The "threat landscape" is very dynamic, he said, because it is constantly changing as various players acquire more patents. Google's move to acquire Motorola Mobility is a "very significant" move that could also change things.

Clearly, Linux is on the rise in the mobile space. Right now it is Android that is leading the way, but he is "hopeful there will be more", citing webOS, LiMo, and MeeGo as possibilities. It is "really a two-horse race" at the moment, between iOS and Android, but others may come along. That would be good because it would offer more freedom of choice, he said.

The rise of Android has been "unprecedented". If you were looking forward from 18 months ago, you couldn't imagine that something would displace iOS on mobile devices, but that's what Android has done. Android now has an "irreversible position in the mobile space", he said.

[Android 'infographic']

He put up a famous (or infamous) graphic that circulated earlier this year (at right) which showed all of the different patent lawsuits currently pending against Android devices. While many may have seen that graphic elsewhere, Bergelt said, he credits Microsoft for it. We should credit who created the graphic "rather than who is pushing it", he said. When something is successful, it attracts attention, and that is what is happening with Android right now, and graphics like this one are evidence of that.

Are the current lawsuits a Linux concern or just an Android concern, he asked. It would be easy to see them as only a problem for Android itself, because, other than the kernel, Android shares little with a traditional Linux platform. But you rarely will see an actual Linux lawsuit, Bergelt said, because it has been developed for 20 years in the open. Instead, opponents have "patents on adjacent technologies" that are used to go after Linux-based systems.

Until MeeGo or webOS mature and get significant market share, "mobile Linux is Android". Whether one thinks that Android is the "perfect implementation" of Linux or not, the community needs to "be in support of the mobile Linux that's out there", he said. When other mobile Linux systems mature, "we should support them equally as well".

It is important to "ensure that Android is not pulled off the shelves", Bergelt said. Microsoft and Apple would like to see Android pulled and are using their patent portfolios to "slow or stall the commercial success of Linux". Until other mobile platforms emerge, threats against Android equate to threats against Linux. Android's viability is needed to prove that there is a market for Linux-based platforms, he said.

Secondary market for patents

The stakes are so high that the secondary market for patents is "overheated", Bergelt said. The "per patent price has risen to astronomical levels", which is well beyond any reasonable level for acquiring purely defensive patents. It is not about acquiring patents for licensing revenue either: "You are not going to get your money back from licensing them; that's ridiculous", he said. Companies are recognizing that this "land grab for patents" provides an opportunity to get more for their patents than they would be able to otherwise, which is putting more patents on the market.

The Nortel patents (which recently sold for $4.5 billion to a consortium including Apple and Microsoft) are particularly worrisome, Bergelt said, because they cover mobile communications and network management. The US Department of Justice (DoJ) is looking into that transaction, and members of the community can help inform the agency that there are concerns about those patents being used in anti-competitive ways. A resolution like what occurred with the Novell patents, where OIN can license them indefinitely, would be good. That particular outcome deprived Microsoft of the ability to own the Novell patents because of its history of anti-competitive behavior, he said.

Bergelt said that he has some empathy for Microsoft, because the company's history is weighing it down. "If the only thing you've known is being a monopolist, that's how you are going to work", he said. But the DoJ needs accurate information about previous and current behaviors of the purchasers of the Nortel patents. He encouraged those in the audience who knew of such behaviors to report them to the agency so that it could have a "balanced view" of the situation. The DoJ employees are "bright and accomplished", but that patent-based anti-competitive behavior is not something they normally consider, he said.

Companies that are pursuing the strategy of using patents to slow or stall competitors aren't trying to educate anyone, they are, instead, "interested in threatening people". But, "illegal behavior is illegal behavior, and that's what they're practicing", he said. Microsoft and Apple would much rather have it be a duopoly, rather than dealing with the "disruptive situation" that Linux brings. Neither of those two companies "have the ability to compete with Linux in the long term", Bergelt said.

The idea is to "tax" Linux heavily with licensing fees. Microsoft has pursued a "totem-building strategy", where it gets companies to license its "Linux patents", often by throwing those patent licenses into other, unrelated deals. This "creates a presumption" that the licenses have value. There is also a more targeted component where the company uses the other licensees—who may be price-insensitive and thus willing to sign suboptimal agreements—as a weapon against smaller, more price-sensitive companies. Microsoft will also use its patents on a particular technology as the centerpiece and throw in other patent licenses as part of any deal. The FAT filesystem patents, which expire soon, have been used that way. More recently, "active sync" is being used as a centerpiece, and the company claims ten patents on that technology.

But Microsoft cannot use the Novell patents in this way, and that's what Bergelt would like to see happen with the Nortel patents as well. Right now, the licensing fee that is being charged is $15 per mobile device, but Microsoft would like to get that up to $30-40 by adding on other patents. Apple's "touch" patents—which were mostly acquired, not developed by Apple—are being used in this way as well. This can change the decisions that vendors and mobile carriers make because at some point it becomes uneconomical to pay higher per unit royalties, he said.

There is also the problem of "opportunistic patent aggressors", which are typically "non-practicing entities" (NPEs), also known as "patent trolls". These organizations are focused on generating a return. He pointed to Intellectual Ventures (IV) as the "largest patent troll in the world". IV has used investment from universities and foundations—fooled by misleading information into investing in the company—to amass an enormous patent portfolio of 34,000 worldwide patents in 9,000 patent families, he said. IV is "not an innovation company", but is, instead, a "business designed to use patents to drive return".

The market for patents has led companies like InterDigital to put themselves on sale, Bergelt said. That company has 2500+ patents that "almost exclusively relate to mobile communication", and have generated billions of dollars in traditional licensing revenue. Their patents still have life left, but the overheated market provides a way to "cash out" their portfolio. In addition, financial services firms are pouring "billions" into patent companies, and they are looking for a return on those investments, he said.

Fighting the good fight

"Things are going to get worse before they get better", Bergelt said, which echoes numerous observers of the patent mess. He sees a need for "more people to work together" to try to, eventually, fix the problem. There are so many patents that shouldn't have been issued, "free radicals" he called them, that it will take a long time to undo that. Part of the problem is that "code is not searchable in a way that's useful" to determine "prior art", so patent examiners don't have an easy way to disallow patents based on earlier implementations of the idea.

There are several defensive patent pools that have spent "billions to acquire patents". These include RPX, which has 100 members, and AlliedSecurityTrust (AST), which has 22 members, as well as OIN itself. OIN is a "very peculiar company" in that has six members but is "tasked with protecting the community". OIN and its members know that the community is "where new innovation is coming from", Bergelt said, and those innovations can be used to build billion dollar companies.

There is work to be done on mobilizing the open source software community to help fight these patents, he said. There is a "tremendous amount of prior art" that has not been identified, so OIN and others have been working on "structures" where developers can document their ideas in ways that can be used by the patent office. One of those is the "defensive publication", which is like a "patent without claims". OIN has spent "tens of thousands of dollars" to try to educate developers on how to defensively publish their ideas. In addition, there are opportunities for the community to identify existing prior art that can limit the claims or possibly invalidate patents that are in the examination process.

Unlike a technology platform that can be "overtaken by events", open source is a social phenomenon that is unstoppable, Bergelt said; we are not going back to the siloed world. Collaboration "low in the stack", while competing high in the stack, where companies may have intellectual property interests, is the way new systems will be developed.

Bergelt also gave an overview of the work that the Linux Defenders project is doing with help from the community. It is highlighting patent applications that shouldn't go forward by pointing out prior art. That means that the community "saves us the problem of having another free radical". After patents are issued, the Post-Issue Peer to Patent initiative allows the community to potentially invalidate or limit the scope of bad patents. But in order for those projects to work, more community involvement is needed, he said.

The "stakes have been raised", Bergelt said, and the computing landscape is being reshaped by smartphones. New technologies are going to allow these devices to go way beyond where they are today, he said, and that's why he's excited to see things like MeeGo and webOS. Microsoft is now recognizing that personal computing is undergoing a major shift, and it (and others) are fighting the competition in the mobile space with any weapons they can find.

Community engagement is needed in several areas, but identifying and codifying prior art is the biggest piece. We will see lots of bidding for the InterDigital portfolio over the next several months, there will be more IP speculators and trolls trying to cash in, and anti-competitive actions from larger companies will take place. We should support Android and the platforms that come after it and remember that our opponents "are going to fight like hell", Bergelt said.

After Bergelt finished, the Linux Foundation's legal counsel, Karen Copenhaver, amplified one part of Bergelt's message. The DoJ, she said, is waiting to let things play out with the Nortel patents to see if there is a big lawsuit or International Trade Commission (ITC) action using those patents. But the impact of the patents happens "long before that" in meetings between the patent consortium and vendors. So it is imperative that we provide the DoJ information on how these patents affect Linux well before any litigation occurs, she said. Both Copenhaver and Bergelt were clearly reaching out to vendors and others who have been threatened with patent actions by Microsoft, Apple, or other members of the patent-purchasing consortium.

[ I would like to thank the Linux Foundation for travel assistance to attend LinuxCon. ]

Comments (9 posted)

Next week's edition will be published on September 9

The US Labor Day holiday is September 5. In celebration, we will attempt to labor a bit less than usual, with the result that the Weekly Edition that would normally come out on September 8 will be published on the 9th instead.

Comments (1 posted)

Page editor: Jonathan Corbet


Apache range request denial of service

By Jake Edge
August 31, 2011

A rather potent denial of service (DoS) vulnerability in the Apache HTTP server has dominated the security news over the last week. It was first reported by way of a proof-of-concept posted to the full-disclosure mailing list on August 20. The problem itself is due to a bug in the way that Apache implemented HTTP Range headers, but there is also an underlying problem in the way those HTTP headers are defined.

The proof-of-concept (posted by "Kingcope") is a fairly simple Perl script that makes multiple connections to a web host, each with a long and, arguably, incorrectly redundant Range specified in the headers. Only a small number of these connections can cause enormous memory and CPU usage on the web host. This is a classic "amplification" attack, where a small amount of resources on the attacker side can lead to consuming many more victim-side resources. In some sense, normal HTTP requests are amplifications, because a few bytes of request can lead to a multi-megabyte response (a large PDF for example), but this attack is different. A single request can lead to multiple partial responses, each with their own header and, importantly, server overhead. It is the resources required to create the responses that leads to the DoS.

The Range header is meant to be used to request just a portion of the resource, but, as we see here, it can be abused. The idea is that a streaming client or other application can request chunks of the resource as it plays or displays them. An HTTP request with the following:

    Range: bytes=512-1023
would be asking for 512 bytes starting at the 513th (it is zero-based). But it is not just a single range that can be specified:
    Range: bytes=512-1023,1024-2047
would request two ranges, each of which would be sent in either a separate response (each with a Content-Range header) or in a multipart response (i.e. with a multipart/byteranges Content-Type).

Each of those examples is fairly benign. The problem stems from requests that look like:

    Range: bytes=0-,5-0,5-1,...,5-6,5-7,5-8,5-9,5-10,...
which requests the whole file (0-) along with several nonsensical ranges (5-0,5-1,...) as well as a bunch of overlapping ranges. The example is taken from the proof-of-concept code (which creates 1300 ranges for each request), and other kinds of lengthy range requests will also cause the DoS.

When it receives range requests, Apache dutifully creates pieces of a multipart response for each range specified. That eats up both memory and CPU on the server, and doing so tens or hundreds of times for multiple attacker connections is enough to exhaust the server resources and cause the DoS. The range requests in the attack are obviously not reasonable, but they are legal according to the HTTP specification. There is discussion of changing the specification, but that doesn't help right now.

An obvious solution would be to sort the ranges (as they don't have to be in any specific order) and coalesce those that are adjacent or overlap. If the range turned out to correspond to the entire file, the server could just send that instead. Unfortunately, (arguably) badly written applications or browsers may be expecting to get multipart responses in the same order, and with the same lengths, as specified in the request. In addition, the HTTP specification does not allow that kind of reordering.

So the Apache solution is to look at the sum of the lengths of the ranges in a request and if that's greater than the size of the requested file, just send the whole file. That will defeat the proof-of-concept and drastically reduce the amplification factor that any particular request can cause. It doesn't completely solve the problem, but it alleviates the worst part. Attackers can still craft nonsensical range requests, but the number of responses they can generate is vastly reduced.

While Apache's implementation of range requests is fairly resource-hungry, which makes it easier to cause the DoS, the HTTP protocol bears some of the blame here too. Allowing multiple overlapping ranges does not really make any sense, and not allowing servers to reorder and coalesce adjacent ranges seems poorly thought-out as well. No matter how efficiently implemented, allowing arbitrary ranges of that sort is going to lead to some sort of amplification effect.

Apache's fix is for the stable 2.2 series, so it is necessarily fairly conservative. There are ongoing discussions going on in the Apache dev mailing list that indicate a more robust fix—probably following the proposed changes to the HTTP specification—is in the works for the 2.3 development branch (which will eventually become the stable 2.4 release).

As of this writing, only Debian has released a fix for the problem (which it did based on the patch while it was being tested and before Apache announced its fix). Other distributions are sure to follow. Since it is trivially easy to make an unpatched server unresponsive, it probably makes sense to use one of the mitigation techniques suggested by Apache until a server update is available.

[ A word of warning to those who may be tempted to try the proof-of-concept code: while limiting the number-of-forks command-line parameter to 1 may seem like a good idea for testing purposes, it doesn't actually work in practice. If that parameter is <= 1, the code sets it to 50, which is enough to DoS a server—trust me on that last part. ]

Comments (4 posted)

Brief items

Security quotes of the week

On July 19th 2011, DigiNotar detected an intrusion into its Certificate Authority (CA) infrastructure, which resulted in the fraudulent issuance of public key certificate requests for a number of domains, including Once it detected the intrusion, DigiNotar has acted in accordance with all relevant rules and procedures. At that time, an external security audit concluded that all fraudulently issued certificates were revoked. Recently, it was discovered that at least one fraudulent certificate had not been revoked at the time. After being notified by Dutch government organization Govcert, DigiNotar took immediate action and revoked the fraudulent certificate.
-- DigiNotar 'fesses up

Diginotar indeed was hacked, on the 19th of July, 2011. The attackers were able to generate several fraudulent certificates, including possibly also EVSSL certificates. But while Diginotar revoked the other rogue certificates, they missed the one issued to Google. Didn't Diginotar think it's a tad weird that Google would suddenly renew their SSL certificate, and decide to do it with a mid-sized Dutch CA, of all places? And when Diginotar was auditing their systems after the breach, how on earth did they miss the Iranian defacement discussed above?
-- F-Secure is not so sure we have the full DigiNotar story

None of the recipients were people who would normally be considered high-profile or high-value targets, such as an executive or an IT administrator with special network privileges. But that didn't matter. When one of the four recipients clicked on the attachment, the attachment used a zero-day exploit targeting a vulnerability in Adobe Flash to drop another malicious file — a backdoor — onto the recipient's desktop computer. This gave the attackers a foothold to burrow farther into the network and gain the access they needed.
-- Wired on an RSA phishing attack that may have led to the SecurID disclosure

I remember back at the government fear mongering after 9/11. How there were hundreds of sleeper cells in the U.S. How terrorism would become the new normal unless we implemented all sorts of Draconian security measures. You'd think that -- if this were even remotely true -- we would have seen more attempted terrorism in the U.S. over the past decade.
-- Bruce Schneier

Comments (1 posted)

Fraudulent * certificate issued

The Mozilla Security Blog carries an advisory that DigiNotar has revoked a fake digital certificate it issued for Google's domain. "Users on a compromised network could be directed to sites using a fraudulent certificate and mistake them for the legitimate sites. This could deceive them into revealing personal information such as usernames and passwords. It may also deceive users into downloading malware if they believe it's coming from a trusted site. We have received reports of these certificates being used in the wild." Updates to Firefox, Thunderbird, and SeaMonkey are being released in response.

Update: see this EFF release for a lot more information; it does not look good. "Certificate authorities have been caught issuing fraudulent certificates in at least half a dozen high-profile cases in the past two years and EFF has voiced concerns that the problem may be even more widespread. But this is the first time that a fake certificate is known to have been successfully used in the wild. Even worse, the certificate in this attack was issued on July 10th 2011, almost two months ago, and may well have been used to spy on an unknown number of Internet users in Iran from the moment of its issuance until it was revoked earlier today."

Comments (89 posted)

An updated Apache DOS advisory

The Apache project has updated its advisory on the recently-disclosed denial-of-service vulnerability. The news is not good: the scope of the vulnerability has grown, the workarounds have become more complex, and there is still no fix available. "There are two aspects to this vulnerability. One is new, is Apache specific; and resolved with this server side fix. The other issue is fundamentally a protocol design issue dating back to 2007."

Full Story (comments: 7)

Apache HTTP Server 2.2.20 Released

Apache has released an update to its HTTP server that fixes the denial of service problem that was reported on August 24 (and updated on August 26). We should see updates from distributions soon, though it should be noted that Debian put out an update on August 29. "Fix handling of byte-range requests to use less memory, to avoid denial of service. If the sum of all ranges in a request is larger than the original file, ignore the ranges and send the complete file."

Full Story (comments: 3)

New vulnerabilities

apache2: denial of service

Package(s):apache2 CVE #(s):CVE-2011-3192
Created:August 30, 2011 Updated:October 14, 2011
Description: From the Debian advisory:

A vulnerability has been found in the way the multiple overlapping ranges are handled by the Apache HTTPD server. This vulnerability allows an attacker to cause Apache HTTPD to use an excessive amount of memory, causing a denial of service.

Gentoo 201206-25 apache 2012-06-24
openSUSE openSUSE-SU-2011:1217-1 apache2 2011-11-04
SUSE SUSE-SU-2011:1215-1 Apache2 2011-11-04
SUSE SUSE-SU-2011:1216-1 Apache 2 2011-11-04
SUSE SUSE-SU-2011:1229-1 apache2 2011-11-09
Scientific Linux SL-http-20111020 httpd 2011-10-20
Scientific Linux SL-http-20111020 httpd 2011-10-20
Red Hat RHSA-2011:1369-01 httpd 2011-10-13
Mandriva MDVSA-2011:130-1 apache 2011-09-17
Fedora FEDORA-2011-12715 httpd 2011-09-14
Red Hat RHSA-2011:1300-01 httpd 2011-09-15
Red Hat RHSA-2011:1294-01 httpd 2011-09-14
Slackware SSA:2011-252-01 httpd 2011-09-09
SUSE SUSE-SU-2011:1010-1 Apache 2011-09-06
SUSE SUSE-SU-2011:1007-1 Apache 2011-09-06
SUSE SUSE-SU-2011:1000-1 Apache 2011-09-06
Mandriva MDVSA-2011:130 apache 2011-09-04
Debian DSA-2298-2 apache2 2011-09-05
openSUSE openSUSE-SU-2011:0993-1 apache2 2011-09-02
CentOS CESA-2011:1245 httpd 2011-09-01
Ubuntu USN-1199-1 apache2 2011-09-01
Scientific Linux SL-http-20110831 httpd 2011-08-31
Red Hat RHSA-2011:1245-01 httpd 2011-08-31
Debian DSA-2298-1 apache2 2011-08-29

Comments (none posted)

apache-commons-daemon: remote access to superuser files/directories

Package(s):apache-commons-daemon CVE #(s):CVE-2011-2729
Created:August 29, 2011 Updated:December 12, 2011
Description: From the CVE entry:

native/unix/native/jsvc-unix.c in jsvc in the Daemon component 1.0.3 through 1.0.6 in Apache Commons, as used in Apache Tomcat 5.5.32 through 5.5.33, 6.0.30 through 6.0.32, and 7.0.x before 7.0.20 on Linux, does not drop capabilities, which allows remote attackers to bypass read permissions for files via a request to an application.

Gentoo 201206-24 tomcat 2012-06-24
Ubuntu USN-1298-1 commons-daemon 2011-12-12
openSUSE openSUSE-SU-2011:1062-1 jakarta-commons-daemon 2011-09-23
Fedora FEDORA-2011-10936 apache-commons-daemon 2011-08-17

Comments (none posted)

hplip: remote code execution

Package(s):hplip CVE #(s):CVE-2004-0801
Created:August 25, 2011 Updated:August 31, 2011

From the Novell vulnerability entry:

Unknown vulnerability in foomatic-rip in Foomatic before 3.0.2 allows local users or remote attackers with access to CUPS to execute arbitrary commands.

openSUSE openSUSE-SU-2011:0950-1 hplip 2011-08-25

Comments (none posted)

pidgin: possible buffer overflows

Package(s):pidgin CVE #(s):
Created:August 31, 2011 Updated:August 31, 2011
Description: The pidgin 2.10.0 release features the removal of a lot of calls to unsafe string functions, closing a number of potential buffer overflows. See the changelog for details.
Fedora FEDORA-2011-11544 pidgin 2011-08-26

Comments (none posted)

selinux-policy: policy updates

Package(s):selinux-policy CVE #(s):
Created:August 25, 2011 Updated:August 31, 2011

From the Scientific Linux advisory:

* Prior to this update, the SELinux policy package did not allow the RHEV agent to execute. This update adds the policy for RHEV agents, so that they can be executed as expected.

* Previously, several labels were incorrect and rules for creating new 389-ds instances were missing. As a result, access vector caches (AVC) appeared when a new 389-ds instance was created through the 389-console. This update fixes the labels and adds the missing rules. Now, new 389-ds instances are created without further errors.

* Prior to this update, AVC error messages occurred in the audit.log file. With this update, the labels causing the error messages have been fixed, thus preventing this bug.

Scientific Linux SL-NotF-20110822 selinux-policy 2011-08-22

Comments (none posted)

vpnc: remote command injection

Package(s):vpnc CVE #(s):CVE-2011-2660
Created:August 31, 2011 Updated:August 31, 2011
Description: The modify_resolvconf_suse script packaged with vpnc contains a flaw that could enable command injection attacks via specially-crafted DNS entries.
SUSE SUSE-SU-2011:0979-1 vpnc 2011-08-31
SUSE SUSE-SU-2011:0980-1 vpnc 2011-08-31

Comments (none posted)

xen: denial of service

Package(s):xen CVE #(s):CVE-2011-3131
Created:August 31, 2011 Updated:September 1, 2011
Description: A xen virtual machine given control of a PCI device can cause it to issue invalid DMA requests, potentially overwhelming the host with interrupts from the IOMMU. See this advisory for details.
Debian DSA-2582-1 xen 2012-12-07
Oracle ELSA-2012-0150 kernel 2012-03-07
Scientific Linux SL-kern-20111020 kernel 2011-10-20
CentOS CESA-2011:1386 kernel 2011-10-21
Red Hat RHSA-2011:1386-01 kernel 2011-10-20
SUSE SUSE-SU-2011:0983-1 Xen 2011-09-01
Fedora FEDORA-2011-10942 xen 2011-08-17

Comments (none posted)

Page editor: Jake Edge

Kernel development

Brief items

Kernel release status

The current development kernel is 3.1-rc4, released on August 28. "Anyway, go wild and please do test. The appended shortlog gives a reasonable idea of the changes, but they really aren't that big. So I definitely *am* hoping that -rc5 will be smaller. But at the same time, I continue to be pretty happy about the state of 3.1 so far. But maybe it's just that my meds are finally working." See the full changelog for all the details.

Stable updates: the,, and 3.0.4 updates were released on August 29 with the usual set of important fixes.

Comments (none posted)

Quotes of the week

POSIX has been wrong before. Sometimes the solution really is to say "sorry, you wrote that 20 years ago, and things have changed".
-- Linus Torvalds

It only takes a little multicast to mess up your whole day.
-- Dave Täht

For the last ~6 months the Broadcom team has been working on getting their driver out of staging. I have to believe that they would have rather been working on updating device support during that time. I can only presume that they would make that a priority in the long run.

How many times has b43 been > ~6 months behind on its hardware support? Despite Rafał's recent heroic efforts at improving that, I can't help but wonder how long will it be before b43 is again dreadfully behind?

-- John Linville

Bad English and a github address makes me unhappy.
-- Linus Torvalds

Comments (4 posted) compromised

The main page is currently carrying a notice that the site has suffered a security breach. "Earlier this month, a number of servers in the infrastructure were compromised. We discovered this August 28th. While we currently believe that the source code repositories were unaffected, we are in the process of verifying this and taking steps to enhance security across the infrastructure." As the update mentions, there's little to be gained by tampering with the git repositories there anyway.

Comments (71 posted)

Kernel development news

The x32 system call ABI

By Jonathan Corbet
August 29, 2011
The 32-bit x86 architecture has a number of well-known shortcomings. Many of these were addressed when this architecture was extended to 64 bits by AMD, but running in 64-bit mode is not without problems either. For this reason, a group of GCC, kernel, and library developers has been working on a new machine model known as the "x32 ABI." This ABI is getting close to ready, but, as a recent discussion shows, wider exposure of x32 is bringing some new issues to the surface.

Classic 32-bit x86 has easily-understood problems: it can only address 4GB of memory and its tiny set of registers slows things considerably. Running a current processor in the 64-bit mode fixes both of those problems nicely, but at a cost: expanding variables and pointers to 64 bits leads to expanded memory use and a larger cache footprint. It's also not uncommon (still) to find programs that simply do not work properly on a 64-bit system. Most programs do not actually need 64-bit variables or the ability to address massive amounts of memory; for that code, the larger data types are a cost without an associated benefit. It would be really nice if those programs could take advantage of the 64-bit architecture's additional registers and instructions without simultaneously paying the price of increased memory use.

That best-of-both-worlds situation is exactly what the x32 ABI is trying to provide. A program compiled to this ABI will run in native 64-bit mode, but with 32-bit pointers and data values. The full register set will be available, as will other advantages of the 64-bit architecture like the faster SYSCALL64 instruction. If all goes according to plan, this ABI should be the fastest mode available on 64-bit machines for a wide range of programs; it is easy to see x32 widely displacing the 32-bit compatibility mode.

One should note that the "if" above is still somewhat unproven: actual benchmarks showing the differences between x32 and the existing pure modes are hard to come by.

One outstanding question - and the spark for the current discussion - has to do with the system call ABI. For the most part, this ABI looks similar to what is used by the legacy 32-bit mode: the 32-bit-compatible versions of the system calls and associated data structures are used. But there is one difference: the x32 developers want to use the SYSCALL64 instruction just like native 64-bit applications do for the performance benefits. That complicates things a bit, since, to know what data size to expect, the kernel needs to be able to distinguish system calls made by true 64-bit applications from those running in the x32 mode, regardless of the fact that the processor is running in the same mode in both cases. As an added challenge, this distinction needs to be made without slowing down native 64-bit applications.

The solution involves using an expanded version of the 64-bit system call table. Many system calls can be called directly with no compatibility issues at all - a call to fork() needs little in the translation of data structures. Others do need the compatibility layer, though. Each of those system calls (92 of them) is assigned a new number starting at 512. That leaves a gap above the native system calls for additions over time. Bit 30 in the system call number is also set whenever an x32 binary calls into the kernel; that enables kernel code that cares to implement "compatibility mode" behavior.

Linus didn't seem to mind the mechanism used to distinguish x32 system calls in general, but he hated the use of compatibility mode for the x32 ABI. He asked:

I think the real question is "why?". I think we're missing a lot of background for why we'd want yet another set of system calls at all, and why we'd want another state flag. Why can't the x32 code just use the native 64-bit system calls entirely?

There are legitimate reasons why some of the system calls cannot be shared between the x32 and 64-bit modes. Situations where user space passes structures containing pointers to the kernel (ioctl() and readv() being simple examples) will require special handling since those pointers will be 32-bit. Signal handling will always be special. Many of the other system calls done specially for x32, though, are there to minimize the differences between x32 and the legacy 32-bit mode. And those calls are the ones that Linus objects to most strongly.

It comes down, for the most part, to the format of integer values passed to the kernel in structures. The legacy 32-bit mode, naturally, uses 32-bit values in most cases; the x32 mode follows that lead. Linus is saying, though, that the 64-bit versions of the structures - with 64-bit integer values - should be used instead. At a minimum, doing things that way would minimize the differences between the x32 and native 64-bit modes. But there is also a correctness issue involved.

One place where the 32- and 64-bit modes differ is in their representation of time values; in the 32-bit world, types like time_t, struct timespec, and struct timeval are 32-bit quantities. And 32-bit time values will overflow in the year 2038. If the year-2000 issue showed anything, it's that long-term drop-dead days arrive sooner than one tends to think. So it's not surprising that Linus is unwilling to add a new ABI that would suffer from the 2038 issue:

2038 is a long time away for legacy binaries. It's *not* all that long away if you are introducing a new 32-bit mode for performance.

The width of time_t cannot change for legacy 32-bit binaries. But x32 is an entirely new ABI with no legacy users at all; it does not have to retain any sort of past compatibility at this point. Now is the only time that this kind of issue can be fixed. So it is probably entirely safe to say that an x32 ABI will not make it into the mainline as long as it has problems like the year-2038 bug.

At this point, the x32 developers need to review their proposed system call ABI and find a way to rework it into something closer to Linus's taste; that process is already underway. Then developers can get into the serious business of building systems under that ABI and running benchmarks to see whether it is all worth the effort. Convincing distributors (other than Gentoo, of course) to support this ABI will take a fairly convincing story, but, if this mode lives up to its potential, that story might just be there.

Comments (58 posted)

No-I/O dirty throttling

By Jonathan Corbet
August 31, 2011
"Writeback" is the process of writing dirty pages back to persistent storage, allowing those pages to be reclaimed for other uses. Making writeback work properly has been one of the more challenging problems faced by kernel developers in the last few years; systems can bog down completely (or even lock up) when writeback gets out of control. Various approaches to improving the situation have been discussed; one of those is Fengguang Wu's I/O-less throttling patch set. These changes have been circulating for some time; they are seen as having potential - if only others could actually understand them. Your editor doesn't understand them either, but that has never stopped him before.

One aspect to getting a handle on writeback, clearly, is slowing down processes that are creating more dirty pages than the system can handle. In current kernels, that is done through a call to balance_dirty_pages(), which sets the offending process to work writing pages back to disk. This "direct reclaim" has the effect of cleaning some pages; it also keeps the process from dirtying more pages while the writeback is happening. Unfortunately, direct reclaim also tends to create terrible I/O patterns, reducing the bandwidth of data going to disk and making the problem worse than it was before. Getting rid of direct reclaim has been on the "to do" list for a while, but it needs to be replaced by another means for throttling producers of dirty pages.

That is where Fengguang's patch set comes in. He is attempting to create a control loop capable of determining how many pages each process should be allowed to dirty at any given time. Processes exceeding their limit are simply put to sleep for a while to allow the writeback system to catch up with them. The concept is simple enough, but the implementation is less so. Throttling is easy; performing throttling in a way that keeps the number of dirty pages within reasonable bounds and maximizes backing store utilization while not imposing unreasonable latencies on processes is a bit more difficult.

If all pages in the system are dirty, the system is probably dead, so that is a good situation to avoid. Zero dirty pages is almost as bad; performance in that situation will be exceedingly poor. The virtual memory subsystem thus aims for a spot in the middle where the ratio of dirty to clean pages is deemed to be optimal; that "setpoint" varies, but comes down to tunable parameters in the end. Current code sets a simple threshold, with throttling happening when the number of dirty pages exceeds that threshold; Fengguang is trying to do something more subtle.

Since developers have complained that his work is hard to understand, Fengguang has filled out the code with lots of documentation and diagrams. This is how he depicts the goal of the patch set:

  ^ task rate limit
  |            *
  |             *
  |              *
  |[free run]      *      [smooth throttled]
  |                  *
  |                     *
  |                         *
  |                               .     *
  |                               .          *
  |                               .              *
  |                               .                 *
  |                               .                    *
                          setpoint^                  limit^  dirty pages

The goal of the system is to keep the number of dirty pages at the setpoint; if things get out of line, increasing amounts of force will be applied to bring things back to where they should be. So the first order of business is to figure out the current status; that is done in two steps. The first is to look at the global situation: how many dirty pages are there in the system relative to the setpoint and to the hard limit that we never want to exceed? Using a cubic polynomial function (see the code for the grungy details), Fengguang calculates a global "pos_ratio" to describe how strongly the system needs to adjust the number of dirty pages.

This ratio cannot really be calculated, though, without taking the backing device (BDI) into account. A process may be dirtying pages stored on a given BDI, and the system may have a surfeit of dirty pages at the moment, but the wisdom of throttling that process depends also on how many dirty pages exist for that BDI. If a given BDI is swamped with dirty pages, it may make sense to throttle a dirtying process even if the system as a whole is doing OK. On the other hand, a BDI with few dirty pages can clear its backlog quickly, so it can probably afford to have a few more, even if the system is somewhat more dirty than one might like. So the patch set tweaks the calculated pos_ratio for a specific BDI using a complicated formula looking at how far that specific BDI is from its own setpoint and its observed bandwidth. The end result is a modified pos_ratio describing whether the system should be dirtying more or fewer pages backed by the given BDI, and by how much.

In an ideal world, throttling would match the rate at which pages are being dirtied to the rate that each device can write those pages back; a process dirtying pages backed by a fast SSD would be able to dirty more pages more quickly than a process writing to pages backed by a cheap thumb drive. The idea is simple: if N processes are dirtying pages on a BDI with a given bandwidth, each process should be throttled to the extent that it dirties 1/N of that bandwidth. The problem is that processes do not register with the kernel and declare that they intend to dirty lots of pages on a given BDI, so the kernel does not really know the value of N. That is handled by carrying a running estimate of N. An initial per-task bandwidth limit is established; after a period of time, the kernel looks at the number of pages actually dirtied for a given BDI and divides it by that bandwidth limit to come up with the number of active processes. From that estimate, a new rate limit can be applied; this calculation is repeated over time.

That rate limit is fine if the system wants to keep the number of dirty pages on that BDI at its current level. If the number of dirty pages (for the BDI or for the system as a whole) is out of line, though, the per-BDI rate limit will be tweaked accordingly. That is done through a simple multiplication by the pos_ratio calculated above. So if the number of dirty pages is low, the applied rate limit will be a bit higher than what the BDI can handle; if there are too many dirty pages, the per-BDI limit will be lower. There is some additional logic to keep the per-BDI limit from changing too quickly.

Once all that machinery is in place, fixing up balance_dirty_pages() is mostly a matter of deleting the old direct reclaim code. If neither the global nor the per-BDI dirty limits have been exceeded, there is nothing to be done. Otherwise the code calculates a pause time based on the current rate limit, the pos_ratio, and number of pages recently dirtied by the current task and sleeps for that long. The maximum sleep time is currently set to 200ms. A final tweak tries to account for "think time" to even out the pauses seen by any given process. The end result is said to be a system which operates much more smoothly when lots of pages are being dirtied.

Fengguang has been working on these patches for some time and would doubtless like to see them merged. That may yet happen, but adding core memory management code is never an easy thing to do, even when others can easily understand the work. Introducing regressions in obscure workloads is just too easy to do. That suggests that, among other things, a lot of testing will be required before confidence in these changes will be up to the required level. But, with any luck, this work will eventually result in better-performing systems for us all.

Comments (9 posted)

Broadcom's wireless drivers, one year later

By Jonathan Corbet
August 29, 2011
On September 9, 2010, Broadcom announced that it was releasing an open source driver for its wireless networking chipsets. Broadcom had long resisted calls for free drivers for this hardware, so this announcement was quite well received in the community, despite the fact that the quality of the code itself was not quite up to contemporary kernel standards. One year later, this driver is again under discussion, but the tone of the conversation has changed somewhat. After a year of work, Broadcom's driver may never see a mainline release.

Broadcom's submission was actually two drivers: brcmsmac for software-MAC chipsets, and brcmfmac for "FullMAC" chipsets with hardware MAC support. These drivers were immediately pulled into the staging tree with the understanding that there were a lot of things needing fixing before they could make the move to the mainline proper. In the following year, developers dedicated themselves to the task of cleaning up the drivers; nearly 900 changes have been merged in this time. The bulk of the changes came from Broadcom employees, but quite a few others have contributed fixes to the drivers as well.

This work has produced a driver that is free of checkpatch warnings, works on both small-endian and big-endian platforms, uses kernel libraries where appropriate, and generally looks much better than it originally did. On August 24, Broadcom developer Henry Ptasinski decided that the time had come: he posted a patch moving the Broadcom drivers into the mainline. Greg Kroah-Hartman, maintainer of the staging tree, said that he was fine with the driver moving out of staging if the networking developers agreed. Some of those developers came up with some technical issues, but it appeared that these drivers were getting close to ready to make the big move out of staging.

That was when Rafał Miłecki chimed in: "Henry: a simple question, please explain it to me, what brcmsmac does provide that b43 doesn't?" Rafał, naturally, is the maintainer of the b43 driver; b43, which has been in the mainline for years, is a driver for Broadcom chipsets developed primarily from reverse-engineered information. It has reached a point where, Rafał claims, it supports everything Broadcom's driver does with one exception (BCM4313 chipsets) that will be fixed soon. Rafał also claims that the b43 driver performs better, supports hardware that brcmsmac does not, and is, in general, a better piece of code.

So Rafał was clear on what he thought of the brcmsmac driver (brcmfmac didn't really enter into the discussion); he was also quite clear on what he would like to see happen:

We would like to have b43 supported by Broadcom. It sounds much better, I've shown you a lot of advantages of such a choice. Switching to brcmsmac on the other hand needs a lot of work and improvements.

On one hand, Rafał is in a reasonably strong position. The b43 driver is in the mainline now; there is, in general, a strong resistance to the merging of duplicate drivers for the same hardware. Code quality is, to some extent, in the eye of the beholder, but there have been few beholders who have gone on record to say that they like Broadcom's driver better. Looking at the situation with an eye purely on the quality of the kernel's code base in the long term, it is hard to make an argument that the brcmsmac driver should move into the mainline.

On the other hand, if one considers the feelings of developers and the desire to have more hardware companies supporting their products with drivers in the Linux kernel, one has to ask why Broadcom was allowed to put this driver into staging and merge hundreds of patches improving it if that driver was never going to make it into the mainline. Letting Broadcom invest that much work into its driver, then asking it to drop everything and support the reverse-engineered driver that it declined to support one year ago seems harsh. It's not a story that is likely to prove inspirational for developers in other companies who are considering trying to work more closely with the kernel community.

What seems to have happened here (according mainly to a history posted by Rafał, who is not a disinterested observer) is that, one year ago, the brcmsmac driver supported hardware that had no support in b43. Since then, b43 has gained support for that additional hardware; nobody objected to the addition of duplicated driver support at that time (as one would probably expect, given that the Broadcom driver was in staging). Rafał doesn't say whether the brcmsmac driver was helpful to him in filling out hardware support in the b43 driver. In the end, it doesn't matter; it would appear that the need for brcmsmac has passed.

One of the most important lessons for kernel developers to learn is that one should focus on the end result rather than on the merging of a specific piece of code. One can argue that Broadcom has what it wanted now: free driver support for its hardware in the mainline kernel. One could also argue that Broadcom should have worked on adding support to b43 from the beginning rather than posting a competing driver. Or, failing that, one could say that the Broadcom developers should have noticed the improvements going into b43 and thought about the implications for their own work. But none of that is going to make the Broadcom developers feel any better about how things have turned out. They might come around to working on b43, but one expects that it is not a hugely appealing alternative at the moment.

The kernel process can be quite wasteful - in terms of code and developer time lost - at times. Any kernel developer who has been in the community for a significant time will have invested significant time into code that went straight into the bit bucket at some time or other. But that doesn't mean that this waste is good or always necessary. There would be value in finding more reliable ways to warn developers when they are working on code that is unlikely to be merged. Kernel development is distributed, and there are no managers paying attention to how developers spend their time; it works well in general, but it can lead to situations where developers work at cross purposes and somebody, eventually, has to lose out.

That would appear to have happened here. In the short term, the kernel and its users have come out ahead: we have a choice of drivers for Broadcom wireless chipsets and can pick the best one to carry forward. Even Broadcom can be said to have come out ahead if it gains better support for its hardware under Linux. Whether we will pay a longer-term cost in developers who conclude that the kernel community is too hard to work with is harder to measure. But it remains true that the kernel community can, at times, be a challenging place to work.

Comments (73 posted)

Patches and updates

Kernel trees


Core kernel code

Development tools

Device drivers

Filesystems and block I/O

Memory management



Benchmarks and bugs


Page editor: Jonathan Corbet


Misadventures in GUI package-building

August 31, 2011

This article was contributed by Nathan Willis

In recent weeks I have begun to delve into the exciting world of packaging — mostly to work on font packages, which are among the simplest bits of software that one can install. The dependencies and possible conflicts are few, the payload is small, and getting the package metadata right is arguably the most important part of the process. When I spotted a news item in my feed reader about a "GUI package creator," I was curious enough to take it for a test drive. The experience itself was underwhelming, but after some digging around what I found truly perplexing is that this is an application category that seems to continually spawn new, independent development efforts, all of which result in short-lived projects.

First run

The application that I first took notice of is called Ubucompilator, a GTK+ front end for creating and modifying Debian packages. In spite of the name, it is not Ubuntu-specific, and can help you create packages for any Debian-based system. Ubucompilator has been in development since December 2009, but made its 1.0 release in May 2011, which sparked a flurry of news items in the Ubuntu blog circles.


The bulk of those stories linked to a short YouTube video showing the program in action at the hands of its creator. Unfortunately, however, the video includes no narration, which makes it difficult to follow the on-screen action (shrunk down to YouTube size as it is). There is also no documentation available, either at the main project domain or at the Who's Who of hosting services where Ubucompilator maintains a presence: Google Code, Launchpad, SourceForge, Softpedia, and

The Launchpad project pages have the most recent builds of the code, the 1.0 source package from May. It requires a runtime for Gambas2, the Visual-Basic-like language, and compiles cleanly with GNU autotools. The interface consists of a filesystem browser on the left, a textarea on the right, and a series of labeled buttons beneath, reading: "Autogen," "./Configure," "Make," "Make install," "Dh_make," "edit control file," and "Make .deb." Just above the bottom row sits a text-entry field labeled "email."

The aesthetics of the interface received more than a fair share of criticism from commenters in the blog stories. Setting that aside, what Ubucompilator appears to actually do is allow you to navigate to a directory containing buildable source code (such as an unpacked upstream package), and punch through the basic build steps with button clicks rather than shell commands. The output of each command is piped into the textarea on the right hand side of the window.

From the perspective of a packaging-newbie, I can see some value to this approach. Obviously, the configuration and make steps are there for convenience's sake only, because if the package fails to compile, you must debug and fix it using other tools. But it ought to be assumed that any user who knows how to use GNU autotools is already familiar with these steps. On the other hand, packaging is another process entirely, so how (and, more importantly, when) to make use of dh_make may not be intuitive.

Unfortunately, this is the stage of the process where Ubucompilator breaks down. Using dh_make to convert the working source code directory into a properly Debian-formatted form requires making some changes and calling some package-dependent options, and Ubucompilator does not expose any of this functionality. In addition, the "edit control file" button simply opens the ./debian/control file (only if it already exists) in an external editor. Building the actual Debian package (for which Ubucompilator calls dpkg-buildpackage) may also require passing arguments, which is not configurable in the interface.

The result is that Ubucompilator is useful for making modifications to a source package that is already in canonical Debian form, but it does not simplify the process of building anything new, nor help with the potentially-tricky steps like determining dependencies and fixing permissions. However, as commenter mikeru observed on one blog post, the bigger problem is that the interface does not reflect the ordered steps that a user must walk through in order to build a valid package. In Ubucompilator's toolbar-like layout, all of the commands are accessible at the same time, although in order to function, they must be executed in a fixed sequence. A "wizard"-like approach would better reflect the workflow and be more effective.

Other players

Interestingly enough, the "guided steps" approach that mikeru advocated is taken by at least two other GUI Debian-package-creator tools: Debreate and Packin. Nevertheless, neither of those two projects are still actively developed. Both are still installable and at least partially usable on a modern desktop, however, so I decided to explore them to see how they compared.


Debreate is a Python application that wraps a GUI around most of the same functionality as Ubucompilator, with optional support for problem-detection using Lintian, and Debian-to-RPM conversion with Alien. The last release was 0.7alpha6 from September 2010.

Debreate splits the package-construction process into discrete steps, with one page devoted to each and forward/back buttons to navigate between them. Its visuals border on the headache-inducing thanks to some odd color choices (alternating red and blue colored text fields and widgets), and not every page fits onto the default window size, but it does at least present all of the necessary options to the user, clearly labeled. It even allows you to preview how settings will be saved in the control file, and provides a decent interface for maintaining a package changelog, adding scripts, and creating .desktop menu entries.

You still need to have a basic understanding of Debian packaging in order to use Debreate, because there is little in the way of built-in help. I admit, it is probably impossible to provide a "help" menu entry that explains how to write pre- and post-install scripts, but some terminology (such as "pre-depends") would benefit from tooltips.

The same goes for the interface itself: it generally makes sense at first glance, but there are scattered checkboxes and radio-buttons whose immediate effects are unclear, particularly on those pages where there is a split-pane. For example, take the editable script window and the separate add/remove script buttons: by experimentation you learn to paste your script into the window and then click the "add" button, but there are plenty of GUI applications where you would be required to add the script before you could enter its contents; both are defensible.

Still, what Debreate does a good job of is visually tracking the settings that you make to a package-in-the-rough. For example, the "Files," "Scripts," and "Changelog" pages all include editors with which you can directly make changes. The other GUI packager-builders I looked at rely on calling external editing applications, and as a result, the changes that you make (including accidents) are not visible within the interface itself.


Packin is a Java application. The last release was in July 2009, and in an excellent display of irony, the Debian package on the download site is not installable, but I had no trouble extracting the .jar file within, and coaxing it to run under the OpenJDK runtime. Like Debreate, it adopts a step-by-step "wizard" approach to package construction, although it is significantly more compact. Not as many control file fields are supported, and you get only a single line to enter dependencies and conflicts (as opposed to Debreate's complete graphical tool with its fancy pull-down menu to select between =, >=, <=, and the other version-number operators).

It also does not have an interface to attach change-logs or scripts. Unlike Debreate, you do not add individual files or folders to the package — instead you point Packin to a properly-formatted directory. To take care of the other steps, you would still need to call on an external tool like debhelper. Between the two, Debreate is definitely the more complete tool, provided that you can read through the oddly-colored UI widgets well enough to use it.

Simplifying what can't be simplified

Debreate and Packin both require you to configure and successfully compile your source code before you begin building it into a Debian package. In that sense, the two of them and Ubucompilator stake off opposite ends of the process, and none of them covers it completely. There are potential uses for both. With Ubucompilator you could quickly patch an existing Debian package and rebuild it. With Debreate you can create a basic skeleton structure for a new package, taking advantage of the built-in guidance provided by the "wizard" approach. But neither one will work in a vacuum.

The naïve solution might be to suggest combining the two, but having spent some time with them, I am not convinced that a start-to-finish Debian package builder would have a market. The root of the problem is that even with an amalgam of Debreate and Ubucompilator's GUI tools, you will always need to drop out of the point-and-click environment to troubleshoot — either to debug the code or to edit scripts, permissions, and other package errors — and troubleshooting is inherently an un-simplifiable task. It is un-simplifiable because it consists primarily of the developer's own mental energy, and not repetitive processes that can be automated, or deterministic problems that can be caught and solved.

This is not news to anyone in the software engineering field, of course, but I was left wondering why so many people over the years have set out to build GUI interfaces for the task of package creation. Since the complete process cannot be reduced to point-and-click simplicity, eventually users become comfortable enough with the CLI and editor-based tools involved in the rest of the activity, and the GUI loses its appeal. It appears that each of the applications has a two-or-three year active lifespan before it slips into obscurity, yet new ones are always in development.

My guess is that packaging is perceived by people just starting out as having a significant barrier-to-entry, thanks to its box of specialized tools and its distinct nomenclature. To a new user, that can seem intimidating, but at the same time it is clearly a task that involves clear logic and understandable rules. Consequently, wrapping a GUI around them probably seems like a building a much-needed access ramp over that barrier — even though everyone who takes the ramp eventually no longer needs it. A similar argument could be made for other recurring "simplify it with a GUI" projects, such as graphical front-ends to version control systems, or graphical SQL explorers.

Ubucompilator, Debreate, and Packin could use some improvement, but ultimately I do not see anyone who gets into packaging using them for very long. Thus, rather than "how can we build the perfect GUI packaging tool?" perhaps better questions to ask are "how can we better integrate package-building into the development environment" and "how can we best cultivate new packagers?" The first question is up to the IDE- and SDK-makers to answer; the second is up to everyone, but the answer is probably a hard one — time, documentation, and an endless supply of patience to answer questions.

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Brief items

Distribution quote of the week

My interest is less in what the DPL is doing during his DPL term. I am much more interested in what the DPL, commonly a strong personality and well connected, is doing afterwards. Luckily, that "afterwards" time is much longer than his/her active duty. The profile of a DPL certainly helps a reach out, like "ah, one of us is strong in Debian, so Debian must be good for us". This will then help our development. So, I want the DPLs to change reasonably often. Annually sounds good to me.
-- Steffen Möller

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Mandriva 2011 released

The Mandriva 2011 "Hydrogen" release has been announced. There are lots of changes in this release, including the switch to RPM5. See the release notes and the Mandriva 2011 Tour page for more information.

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Distribution News

Debian GNU/Linux

debian-services-admin list created

The debian-services-admin list has been created. "The intent of the list is to be a single point of contact for issues with services deployed on Debian infrastructure. It is intended as a reasonably low-traffic list where everyone who's working on any such services should hang out."

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Red Hat Enterprise Linux

Red Hat Expands Customer Involvement in Red Hat Enterprise Linux 7 Development

Red Hat has issued an invitation to Red Hat Enterprise Linux users to help discuss features for Red Hat Enterprise Linux 7. "The Red Hat Enterprise Linux 7 Ideas discussion group on the Red Hat Customer Portal is now open to all Red Hat subscribers - users and partners - to share use cases and discuss features. The Red Hat Enterprise Linux 7 Ideas discussion group is an extension to the interactive processes already underway with partners, customers and contributors in the open source community. It provides a venue for sharing thoughts and use cases and is invaluable to Red Hat engineering development groups. Access to the Red Hat Customer Portal, which includes a wealth of Red Hat Enterprise Linux information and knowledge, is provided as an important component of every Red Hat subscription."

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Ubuntu family

Call for votes: Vacant Ubuntu Developer Membership Board seat

The Ubuntu Developer Membership Board has started a vote to fill a vacant position. The candidates are Stefano Rivera, Dave Walker, Micah Gersten, and Charlie Smotherman. Voting closes September 6.

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Other distributions

Scientific Linux developer Troy Dawson leaves

Troy Dawson has been very active in the Scientific Linux community. That will be coming to a close soon as Troy has accepted a job at Red Hat. "Thank you to everyone who has encouraged, thanked, and helped me over the past 8 years that I have worked on Scientific Linux. I have said it before, and I'll say it now, The Scientific Linux community is one of the best communities there is."

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Newsletters and articles of interest

Distribution newsletters

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Digging deeper with Gentoo Linux (The H)

The H has a fairly in-depth history of Gentoo Linux. It goes back to Gentoo's origins in Stampede Linux and Enoch, notes some GCC woes, looks at the development of Portage, as well as some of the more recent struggles for the distribution. "In contrast, most of the key Gentoo packages are compiled from source to the specification of the user and the hardware, and every installation is unique. A well-driven installation will result in faster code with less fluff and bloat. The installation may take hours or days but the pay off is that it only happens once. Gentoo is a rolling release and 'version-less', and package updates are 'emerged' from the portage system on the fly."

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Ubuntu 11.10 (So Far) Screenshot Tour

Jono Bacon has put up a tour of the Ubuntu 11.10 desktop for those who would like to see what it is going to look like. "As you can see, Unity provides a lot of workable space and the shell just wraps around the app in the most minimal way possible to give you as much space as possible for the app. You can also see that when maximized the window buttons and menus are not shown; they only appear if you hover the window title with the mouse. This actually makes the desktop feel much nicer and less cluttered."

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Page editor: Rebecca Sobol


Ebook editing with Sigil

August 31, 2011

This article was contributed by Nathan Willis

Although most software and hardware ebook readers can cope with standard PDF documents, text-based formats like HTML and EPUB make life easier for the author and reader due to their flexibility and editability. They can re-flow text to fit varying screen sizes and orientations, for example, and better cope with missing fonts. But historically ebook authors and editors have not had a good open source option, which meant anyone wishing to pitch in at Project Gutenberg or start an original book had to stick with a generic text editor or word processor. The creators of Sigil are attempting to change that by building a free book editor tailored to the recurring tasks in preparing a text for ebook publication.

Sigil has been in development since late 2009, and the current release is version 0.4.1. Releases are made simultaneously for Linux, Mac OS X, and Windows, with 32-bit and 64-bit versions for Linux and Windows. John Schember assumed maintainership of the project in July 2011 after founder Strahinja Marković decided to step down.

Schember pushed out the 0.4 release that had been in beta-and-RC limbo since Marković finished graduate school and work began consuming his time. There is also a degree of overlap (including Schember himself) between the Sigil development community and the Calibre ebook-manager project — which is good, considering the their shared and complementary concerns. The 0.4.1 release dropped on August 26. As Schember explained it on the development blog, in his numbering scheme an N.0 release is unstable and the N.1 release indicates that the application is now ready for public use.

Sigil uses Qt as its application framework and embeds WebKit to render HTML book contents. However, the Linux downloads are InstallJammer installers rather than standard RPM or Debian packages, and they bundle their own copy of the necessary .so files, placing everything in /opt/sigil/. Presumably this installation choice is the result of structuring the code to produce cross-platform packages for those OSes that cannot simply fetch the necessary dependencies through their package managers. As a result of that choice, though, the installer weighs in at 20.5MB and you end up with some duplicate libraries. Hopefully distributions will eventually start packaging Sigil themselves to avoid that duplication.

The installer does create .desktop launcher files on the Desktop and in the system's "Applications -> Office" menu, however. On the down side, it also registers itself as the default file-helper for EPUB downloads in Firefox, which may not be the desired behavior.

Getting around the ebook


Sigil's interface resembles a cross between a lightweight HTML editor and an ebook reader — the main content is in the center pane of the window, and you can toggle between rendered, source, and split views on the text, while navigation tools sit in side panes to either side.

On the left is a "book browser." The EPUB format consists of a ZIP file with nested folders containing XHTML text, images, CSS stylesheets, embedded fonts, and two metadata files. The .opf file includes publication metadata (author, copyright, etc.) and a manifest of the book's other content files, and the .ncx file contains an XML version of the table of contents (TOC). Sigil can edit any of the text-based files; double-clicking on one in the book browser opens it in a new tab. But you also use the book browser to add, remove, and manipulate extra media, such as images and fonts. On the right is a table-of-contents list, which automatically loads the TOC from an EPUB's .ncx file. You can jump between TOC entries by clicking on them in the list.

Basic text editing is self-explanatory. Sigil provides a word-processor-like toolbar for cutting, pasting, and basic formatting, plus shortcuts to validate the HTML and insert chapter break markers. The edit menus allow you to jump to specific lines by number, and the find-and-replace function is beefy enough to accept standard wildcard characters and Perl-like regular expressions.

When it comes to formatting, however, the need for the source code and split views becomes more clear. Basic HTML tags are good enough for text formatting, but the structure of EPUB files depends on its own set of conventions. For example, I tested several Project Gutenberg EPUBs in Sigil, and noticed that it showed numerous erroneous chapter breaks. Investigating the source, I found that the .ncx file flagged every headline HTML tag as a chapter break.

According to the documentation, Sigil evidently expects headline tags only to be used to mark structural divisions in the text, and also interprets them as a nested tree: H2 tags are subdivisions of H1 tags, and so on. But Project Gutenberg uses headline tags to mark other elements, such as the authors byline on the title page, and occasionally to mark up text itself, such as centered text or "inscriptions" that are separated from the main copy. When brought through to Sigil, these tags are inserted into the TOC. If the text merely uses different levels of headline tag for different display styles, they get nested into a hierarchical TOC anyway.

Editing — and grappling — with EPUB

Correcting this sort of problem requires re-formatting the HTML, perhaps even munging about in the CSS — such as using <DIV> or <SPAN> tags to apply styles within the text. While paragraph indentation and text weight are simple enough for WYSIWYG editing, both of those more complex tasks are better done in a proper code editor. Fortunately Sigil's code view includes syntax highlighting, parenthesis matching, and cleanup courtesy of HTML Tidy.

Changes you make to the CSS files are instantly picked up in the rendered HTML view, which is essential. What seems to be missing, however, is an interface to work with the other structural elements, starting with element ID attributes. Sigil's TOC generator creates these automatically when creating the TOC and inserts them into the text. Element IDs are the preferred method for linking to content within a page (replacing older anchor tags), but Sigil assigns them automatically, using a mnemonically unfriendly number scheme. It would be helpful to allow some control over this process, particularly for those working on very long texts.

Sigil even actively discourages you from directly editing the .ncx and .opf files in the editor, popping up a scary warning dialog that you must dismiss to continue. Perhaps that is wise, and without it too many users would foul up their TOC. But considering that Sigil can re-generate a new TOC with one button click, it seems like an unnecessary red flag.

It is also possible to break your text up into multiple XHTML files, and use multiple CSS files, but the Sigil editor offers little in the way of managing them. The convention is to use a separate XHTML file for each chapter in a long work, and while you can right-click in the book editor and create a new file, the only management options are "merge with previous" and an "Add Semantics" sub-menu where you can check special pages such as introductions or glossaries.

[Metadata editor]

Beyond the text itself, Sigil allows you to edit an EPUB's metadata (which is stored inside the book's .opf file). You do this with the "Tools -> Meta Editor" window, which provides a structured editor for key:value metadata pairs. The list of supported metadata properties is long; the editor breaks it into "basic" and "advanced" groupings. ISBN, Publisher, Author, Subject and so forth are "basic," while "advanced" contains several hundred possibilities, from "Actor" and "Adapter" all the way to "Woodcutter" and "Writer of accompanying material."

The tool is simple enough to use, particularly since each metadata property comes with a brief explanation. Otherwise I might not have guessed my way to the correct definitions of obscure properties like "Respondent-appellee" or "Electrotyper." Scanning through the list, it is clear that the EPUB community has far more than generic novels in mind for its document format: everything from screenplays to academic dissertations to legal filings are supported. In my experience, though, most ebooks take little advantage of the rich metadata options available — and free ebooks even less so than commercial ones.

[Adding semantics]

You can also add images and fonts to the ebook by right-clicking in the book browser, although doing so only adds the files to the browser. You still must manually insert images into the text editor, and reference the fonts in the CSS in order to take advantage of them. Whenever your editing session is complete, Sigil's "Validate Epub" tool will look for errors using a side-project validator called FlightCrew (although which errors it looks for are not documented), and "File -> Save As" will generate an EPUB output file.

Old books and new books

At the moment EPUB is the only output format supported, although Sigil can also import HTML text and PDFs. The use cases I looked at first were editing existing ebooks — such as fixing formatting problems in Project Gutenberg books. Ideally, Sigil will someday be useful for other tasks, such as converting an HTML or MOBI-formatted work into a proper EPUB, or writing a new ebook from scratch.

Calibre can perform format conversions, although it does so automatically. In order to edit the result, you must convert it first and then open the result in Sigil. That is not too time-consuming, although it would help matters if Calibre's conversion function could be called from within Sigil at import-time — as it stands, Calibre's main focus is indexing one's ebook library, which makes converting a single file tedious.

More importantly, Sigil allows you to create a "new" ebook project, and will automatically generate empty .ncx and .opf skeleton files. But here the book-management shortcomings mentioned earlier come right to the forefront. Working on any kind of multi-file document is awkward, as is changing CSS formatting to perfect the layout and look. Hopefully future revisions of the application will build more tools for authors, taking care of some of the predictable but still manual-only tasks. For example, if you add a font to an EPUB package, it would be nice to be able highlight text in the editor and choose that font from the Format menu, or even to set it as the default for the entire book.


Perhaps dedicated EPUB editors are not the wave of the future, and in a few years managing an ebook text will be a simple task in normal word processors, or simply a "print-to-file" style option in every application. For now, however, if you want e-reader output, you need an application that understands the formats explicitly. In that regard, Sigil is vastly superior to using an HTML editor, or generating PDFs and hoping for the best.

Now that a new maintainer is driving development, the pace at which it advances should pick up, including the weak points mentioned above. There are other nitpicks in 0.4.1, such as the number of windows that require re-sizing in order for the user to read their contents, and the fact that opening a file from the File menu closes the current editing session (although it warns about this first with a dialog box). I was greatly relieved to find that Sigil uses standard system icons and widgets throughout its UI, unlike its cousin Calibre, which tends towards the garish.

I spent some time reading about the EPUB format itself, and although it is free, a major new revision is due shortly (for some value of "shortly"). The Sigil team is following the specification process, which is good, although there does not seem to be much interest in supporting other ebook formats, such as FictionBook, Plucker, or the Kindle format.

No doubt EPUB has plenty of life left in it, but as electronic publishing consumes more and more of the publishing industry, other formats are going to become just as important (if not more so). EPUB is not well suited for documents that rely on controlled layout, such as magazines or textbooks, nor does it handle math. Closed and proprietary formats are going to make a play for those documents; with luck Sigil — and other open source tools — will be ready. If you need to edit an EPUB today, Sigil is just what you want. If you are writing from scratch, however, you might find it easier to crank out your tome in another editor, and turn to Sigil for the final formatting.

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Brief items

Quotes of the week

In hindsight however, I think the complexity of Swig has exceeded anyone's ability to fully understand it (including my own). For example, to even make sense of what's happening, you have to have a pretty solid grasp of the C/C++ type system (easier said than done). Couple that with all sorts of crazy pattern matching, low-level code fragments, and a ton of macro definitions, your head will literally explode if you try to figure out what's happening. So far as I know, recent versions of Swig have even combined all of this type-pattern matching with regular expressions. I can't even fathom it.
-- David Beazley

But if you want to be taken seriously as a researcher, you should publish your code! Without publication of your *code* research in your area cannot be reproduced by others, so it is not science.
-- Guido van Rossum

It's downright absurd for there to be a known and understood crasher bug, affecting all users, in such a critical component for so long without any acknowledgment or response by upstream or the Fedora maintainers. This and the Flash audio corruption mess make it fairly clear that glibc maintenance is not what it should be for such a crucial package. Given that, the only sensible approach seems to be to go ahead and Just Fix It.
-- Adam Williamson

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bzr 2.4.0

Version 2.4.0 of the bzr version control system is out. "This is a bugfix and polish release over the 2.3 series, with a large number of bugs fixed (>150 for the 2.4 series alone), and some performance improvements. Support for python 2.4 and 2.5 has been dropped, many large working tree operations have been optimized as well as some stacked branches operations."

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GNOME Shell 3.1.90

A new version of GNOME Shell is available. "While there are many substantial features in this release, it's particular worth pointing out the changes contributed by our Summer of Code Students: Nohemi Fernandez's onscreen keyboard, Morten Mjelva's contact search, and Neha Doijode's work on getting cover art and other images to display in notifications."

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An LLVM backend for Sparse

The sparse C parser has long been used to run certain types of static analysis checks on the kernel source. It has been a slow-moving project for some time. Now, however, Pekka Enberg and Jeff Garzik have announced a project to couple sparse and the LLVM backend to produce a working C compiler. The eventual goal is to compile the kernel; for now, they seem to be reasonably happy with a working "hello world" example.

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The Opa language

The Opa language project has announced its existence. "Opa is a new member in the family of languages aiming to make web programming transparent by automatically generating client-side Javascript and handling communication and session control. Opa is written in OCaml. A hierarchical database and web server are integrated with the language. The distribution model is based on a notion of a session, a construct roughly comparable to process definitions in the join-calculus or to concurrent objects in a number of formalisms." See this introduction for lots of information about Opa.

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Newsletters and articles

Development newsletters from the last week

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Free as in sake: The story of Koji (

Over at, Red Hat's Mike McLean looks at the history of the Koji build system, starting from when it was an internal tool through the freeing of the code (at the Fedora Core 6 to Fedora 7 transition) to the present. "Of course, this newly unified Fedora would need a build system and it quickly became apparent that Koji was the right tool for the job. While Fedora Extras was already using Plague, it did not satisfy the requirements for building the entire distribution. So, after much discussion, Red Hat released Koji under an open source license. Koji became a key part of Fedora's new end-to-end, free and open infrastructure."

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GIMP 2.7.3 adds Single Window Mode (Linux Journal)

Michael Reed looks at GIMP 2.7.3 which now has Single Window Mode. "GIMP 2.7.3 has added one of the most requested features in the program's history: a single window mode. Version 2.7 is part of the development branch, so unfortunately, the feature wont hit most distro repositories for a while. If you want to have a sneak peek at the new development features, you'll probably have to compile from scratch."

Comments (21 posted)

Williams: When the Sun Shines We'll Shine Together

NetworkManager hacker Dan Williams has an overview of the new features in NetworkManager 0.9 on his blog. Among them: "When connected to a large unified WiFi network, like a workplace, university, or hotel, NetworkManager 0.9 enhances roaming behavior as you move between locations. By using the background scanning and nl80211 features in wpa_supplicant 0.7 and later, you'll notice fewer drops in connectivity and better signal quality in large networks. Most kernel drivers will now provide automatic updates of new access points and enhanced connection quality reporting, allowing wpa_supplicant to quickly roam to the best access point when the current access point's quality degrades and not before."

Comments (26 posted)

Page editor: Jonathan Corbet


Brief items

20th anniversary of the first Linux post

On August 25, 1991, Linus Torvalds made a now-famous post to the comp.os.minix newsgroup that announced a new free operating system. We have certainly come a long way since then (note the "bang" (!) path in the headers in the posting for instance). "I'm doing a (free) operating system (just a hobby, won't be big and professional like gnu) for 386(486) AT clones. This has been brewing since april, and is starting to get ready. I'd like any feedback on things people like/dislike in minix, as my OS resembles it somewhat (same physical layout of the file-system (due to practical reasons) among other things)."

Comments (28 posted)

Articles of interest

10th Circuit Affirms in All Respects (Groklaw)

In case anybody was worried about the SCO Group's appeal with regard to ownership of the Unix copyrights: Groklaw carries the news that the US 10th Circuit Court of Appeals has affirmed the lower court judgment in all respects. "So, SCO loses again, and likely this is as far as it will go. Technically, SCO can ask the US Supreme Court to hear a further appeal, but that is very unlikely to happen and even less likely to be granted were it to happen." After all these years, it's hard to say that it is over, but, just maybe, it's over.

Comments (1 posted)

Education and Certification

LPI Hosts Exam Labs at Ohio LinuxFest 2011

The Linux Professional Institute (LPI) will be hosting exams at Ohio LinuxFest on September 11, 2011.

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Calls for Presentations

The SCALE CFP is opening

The Linux Exposition of Southern California has announced the 10th annual Southern California Linux Expo (SCALE 10x) will be held January 20-22, 2012 in Los Angeles, California. November 17 is the deadline for abstract and proposal submissions.

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Upcoming Events

O'Reilly's Android Open lineup

O'Reilly's Android Open Conference will be held October 9-11, 2011 in San Francisco, California. Click below for a list of confirmed speakers.

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LinuxCon Europe 2011 Keynotes Announced

The Linux Foundation has announced the keynotes for LinuxCon Europe which will take place alongside the Embedded Linux Conference Europe in Prague, Czech Republic October 26-28, 2011.

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Linux Users' Group of Davis, September 19

The Linux Users' Group of Davis (LUGOD) will be meeting on September 19 with a presentation on "Full Scale Flight Simulators" [rescheduled from March 2011].

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Events: September 8, 2011 to November 7, 2011

The following event listing is taken from the Calendar.

September 6
September 8
Conference on Domain-Specific Languages Bordeaux, France
September 7
September 9
Linux Plumbers' Conference Santa Rosa, CA, USA
September 8 Linux Security Summit 2011 Santa Rosa, CA, USA
September 8
September 9
Italian Perl Workshop 2011 Turin, Italy
September 8
September 9
Lua Workshop 2011 Frick, Switzerland
September 9
September 11
State of the Map 2011 Denver, Colorado, USA
September 9
September 11
Ohio LinuxFest 2011 Columbus, OH, USA
September 10
September 11
PyTexas 2011 College Station, Texas, USA
September 10
September 11
SugarCamp Paris 2011 - "Fix Sugar Documentation!" Paris, France
September 11
September 14
openSUSE Conference Nuremberg, Germany
September 12
September 14
X.Org Developers' Conference Chicago, Illinois, USA
September 14
September 16
Postgres Open Chicago, IL, USA
September 14
September 16
GNU Radio Conference 2011 Philadelphia, PA, USA
September 15 Open Hardware Summit New York, NY, USA
September 16 LLVM European User Group Meeting London, United Kingdom
September 16
September 18
Creative Commons Global Summit 2011 Warsaw, Poland
September 16
September 18
Pycon India 2011 Pune, India
September 18
September 20
Strange Loop St. Louis, MO, USA
September 19
September 22
BruCON 2011 Brussels, Belgium
September 22
September 25
Pycon Poland 2011 Kielce, Poland
September 23
September 24
Open Source Developers Conference France 2011 Paris, France
September 23
September 24
PyCon Argentina 2011 Buenos Aires, Argentina
September 24
September 25
PyCon UK 2011 Coventry, UK
September 27
September 30
PostgreSQL Conference West San Jose, CA, USA
September 27
September 29
Nagios World Conference North America 2011 Saint Paul, MN, USA
September 29
October 1
Python Brasil [7] São Paulo, Brazil
September 30
October 3
Fedora Users and Developers Conference: Milan 2011 Milan, Italy
October 1
October 2
WineConf 2011 Minneapolis, MN, USA
October 1
October 2
Big Android BBQ Austin, TX, USA
October 3
October 5
OpenStack "Essex" Design Summit Boston, MA, USA
October 4
October 9
PyCon DE Leipzig, Germany
October 6
October 9
EuroBSDCon 2011 Netherlands
October 7
October 9
Linux Autumn 2011 Kielce, Poland
October 7
October 10
Open Source Week 2011 Malang, Indonesia
October 8
October 9
PyCon Ireland 2011 Dublin, Ireland
October 8
October 9
Pittsburgh Perl Workshop 2011 Pittsburgh, PA, USA
October 8 PHP North West Conference Manchester, UK
October 8
October 10
GNOME "Boston" Fall Summit 2011 Montreal, QC, Canada
October 8 FLOSSUK / UKUUG's 2011 Unconference Manchester, UK
October 9
October 11
Android Open San Francisco, CA, USA
October 11 PLUG Talk: Rusty Russell Perth, Australia
October 12
October 15
LibreOffice Conference Paris, France
October 14
October 16
MediaWiki Hackathon New Orleans New Orleans, Louisiana, USA
October 14 Workshop Packaging BlankOn Jakarta , Indonesia
October 15 Packaging Debian Class BlankOn Surabaya, Indonesia
October 17
October 18
PyCon Finland 2011 Turku, Finland
October 18
October 21
PostgreSQL Conference Europe Amsterdam, The Netherlands
October 19
October 21
13th German Perl Workshop Frankfurt/Main, Germany
October 19
October 21
Latinoware 2011 Foz do Iguaçu, Brazil
October 20
October 22
13th Real-Time Linux Workshop Prague, Czech Republic
October 21
October 23
PHPCon Poland 2011 Kielce, Poland
October 21 PG-Day Denver 2011 Denver, CO, USA
October 23
October 25
Kernel Summit Prague, Czech Republic
October 24
October 28
18th Annual Tcl/Tk Conference (Tcl'2011) Manassas, Virgina, USA
October 24
October 25
GitTogether 2011 Mountain View, CA, USA
October 24
October 25
GStreamer Conference 2011 Prague, Czech Republic
October 26
October 28
Embedded Linux Conference Europe Prague, Czech Republic
October 26
October 28
LinuxCon Europe 2011 Prague, Czech Republic
October 28
October 30
MiniDebConf Mangalore India Mangalore, India
October 29 buildroot + crosstool-NG Developers' Day Prague, Czech Republic
October 31
November 4
Ubuntu Developer Summit Orlando, FL, USA
October 31
November 4
Linux on ARM: Linaro Connect Q4.11 Orlando, FL, USA
November 1
November 3
oVirt Workshop and Initial Code Release San Jose, CA, USA
November 1
November 8
2011 Plone Conference San Francisco, CA, USA
November 4
November 6
Fedora Users and Developer's Conference : India 2011 Pune, India
November 4
November 6
Mozilla Festival -- Media, Freedom and the Web London, United Kingdom
November 5
November 6
Technical Dutch Open Source Event Eindhoven, The Netherlands
November 5
November 6
OpenFest 2011 Sofia, Bulgaria

If your event does not appear here, please tell us about it.

Page editor: Rebecca Sobol

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