LWN.net Weekly Edition for May 27, 2010

The road forward for systemd

At the end of April, Lennart Poettering announced the initial availability of systemd, a new system initialization and session management daemon. This announcement caused a bit of surprise and concern for those who didn't know it was coming. Lennart's work with PulseAudio remains a bit of a difficult memory for some users (though it seems to be working well for most people now), and some people had thought that the initialization problem was solved with the growing adoption of upstart. Systemd is a different approach, though, which may yet prove sufficiently compelling to motivate another big change.

There are many new features in systemd, but the core change is a concept stolen from the MacOS launchd daemon - and from others that came before launchd. There are (at least) two ways to ensure that a service is available when it is needed: (1) try to keep track of all other services which may need it and be sure to start things in the right order, or (2) just wait until somebody tries to connect to the service and start it on demand. Traditional Linux init systems - and upstart too - use the first approach. Systemd, instead, goes for the second. Rather than concern itself with dependencies, it simply creates the sockets that system daemons will use to communicate with their clients. When a connection request arrives on a specific socket, the associated daemon will be started.

This approach simplifies the system configuration process because there is no longer any need to worry about dependencies between services. It holds out the promise of a faster bootstrap process because nothing is started before it is actually needed (plus a fair amount of other work has been done to improve boot time). The systemd approach to managing daemons allows a fair amount of boilerplate code to be removed, at least under the difficult assumption that the daemon no longer needs to work with other initialization systems. Lennart clearly thinks that it is a better way to manage system processes, and a number of others seem to agree.

That said, there are some obstacles to the widespread adoption of systemd by distributors. To begin with, a number of them are just now beginning to use upstart in its native mode; the idea of jumping into another transition is not necessarily all that appealing. Daemons must be patched to work optimally with systemd; otherwise the socket-based activation scheme is not available. The patching is a relatively simple task, but it must be done with a number of daemons and the result accepted back upstream. There are also concerns about how well some types of services (CUPS was mentioned) will work under systemd, but Lennart seems to think there will not be troubles there.

Another area of concern, strangely enough, is the use of control groups (cgroups) by systemd. Cgroups are a Linux-specific feature initially created for use with containers; they allow the grouping of processes under the control of one or more modules which can restrict their behavior. Systemd uses cgroups to track daemon processes that it has created; they allow these processes to be monitored even if they use the familiar daemon tricks for detaching themselves from their parents. So if systemd is told to shut down Apache, it can do a thorough job of it - even to the point of cleaning up leftovers of rogue CGI scripts and such.

Cgroups would also make it easy for system administrators to set up specialized sandboxes for daemons to run in. The problem there is that there is no easy way for systemd to pick up a cgroup setup already created by somebody else; there is no transparent inheritance for cgroups now. So Lennart is asking for that type of inheritance to be added.

Beyond that, though, some people have concerns about the use of cgroups in the first place. Peter Zijlstra worries about adding yet another feature which must be built into the kernel for the system to even boot. The Debian community does not like the use of the "debug" group, which is not currently configured into its kernels. Systemd may eventually get a more appropriately-named cgroup subsystem for its use, but it is not going to work without the cgroup feature at all. So people wanting to boot systems with systemd will need to have cgroups built in. Lennart has this message for people who don't like that:

There are also claims that work on systemd is primarily motivated by antipathy toward Ubuntu and, especially, its copyright assignment policies. There can only be a bit of truth in some of that; hearing early talk about the work which became systemd is part of what inspired this article on assignment policies back in October. That said, Lennart insists that the motivations behind systemd are technical, and he asks that it be judged on its technical merits.

So where do things stand with regard to adoption of systemd?

• There is an intent to package bug filed for Debian; the packager plans to make it easy to switch between sysvinit and systemd at boot time.

• Lennart plans to have a systemd package ready for Fedora 14, saying "whether we can have it as default is to be seen". Given that the Fedora 14 cycle has already begun, even thinking about adding a change that fundamental as the default seems ambitious. So it may be a hard sell, but Lennart would like to see it: "It would certainly be a shame though if other distros would ship systemd by default before we do."

• Gentoo has an experimental systemd package available, but it has not found its way into the main distribution yet.

• openSUSE is apparently (according to Lennart's original announcement) discussing it internally, but, as is often the case with openSUSE, there is no public indication that it is being considered.

• Ubuntu seems unlikely to consider a change anytime soon.

So it is not clear that any distribution will make the jump to systemd. But, then, even the above is a fair amount of attention for a project which has been public for less than one month. This program has reopened the discussion on how our systems should initialize themselves, and things may go on from there: there is talk of using systemd to take over the tasks of processes like cron and gnome-session. Regardless of who ends up running systemd, the ideas it expresses are likely to influence development for some time.

Comments (200 posted)

Interesting times for Linux Flash support

Although many proponents of free software and an open web don't like Flash, the multimedia platform has become so ubiquitous that it is difficult to imagine the web without it. However, Flash support has always been a challenge for Linux distributions. Adobe has had a proprietary Linux release of its Flash player software for years now, but only for the x86 processor architecture. Meanwhile, open source projects trying to recreate Flash functionality are lagging behind and struggling with lack of manpower. Luckily, there are also some interesting new technical developments in the open source Flash world. One that sparked our interest recently is Lightspark, which was written from scratch based on the SWF documentation Adobe published in June 2009 as part of the Open Screen Project.

The official Flash player

For years, Adobe treated Linux as a second-class citizen. As recently as 2007, Linux users had to wait six months after the Windows release for their version of Adobe Flash 9. At the end of 2008, that changed: with the release of Flash Player 10, Adobe released versions for Windows, MacOS X and Linux on the same day. However, that's not to say there are no problems with the proprietary Flash player. 64-bit support is still a sore point: although it's possible to use Adobe Flash player on a x86_64 Linux system using a 32-bit emulation layer such as nspluginwrapper, native 64-bit support is only available as an alpha version that was first released in November 2008.

In hindsight, it's ironic that, as late as it may come to the party, Linux is the first platform that gets a peek at a 64-bit Adobe Flash player. In its FAQ for the 64-bit prerelease, Adobe writes:

Open source approaches to Flash

But x86 and preliminary x86_64 support for Flash obviously isn't enough in the open source world. Granted, Adobe is or has been working with some mobile phone manufacturers to offer a version for ARM (for example on MeeGo or Android), but people running a Linux desktop system on a non-Intel processor are left in the cold. Until last year, your author was in exactly this position, running Debian on a PowerMac G5. If non-Intel users want to run the official Flash player they have to use ugly solutions such as running Flash in an x86 emulator.

Luckily there are some open source programs recreating Flash functionality, of which the most well-known is Gnash ("GNU Flash"), which also runs on PowerPC, ARM and MIPS processors. It's not even limited to Linux: Gnash also supports FreeBSD, NetBSD, and OpenBSD, so it pleases a lot of people that don't want to run proprietary software on their open source operating system but have to be able to see Flash content. In March we looked at the current state of affairs of Gnash when project lead Rob Savoye talked about the project at SCALE 8x.

Although Gnash has been progressing well, the nature of the project means that it will always be chasing Adobe. Moreover, Gnash is facing some manpower challenges. The Open Media Now! foundation was started in 2008 to fund Gnash development, but, because of the economic crisis, the four full-time developers were cut back to zero, Gnash developer Bastiaan Jacques said last year. Recently, another issue appeared: a growing disagreement between the two top contributors Benjamin Wolsey and Sandro Santilli on the one hand, and Rob Savoye on the other hand.

Different development styles

It all started with a message by Benjamin Wolsey to the Gnash-dev mailing list on Friday 21 May:

At the end of his message, Benjamin announced that he would start his own stable branch of Gnash if another commit of this sort appeared, implicitly threatening a fork. Benjamin's accusations seemed to be primarily aimed at Rob, who answered that the usual policy of free software projects is that frequent checkins are good. However, Sandro Santilli added that this policy would only work if the checkins are small and do not break the test suite. Then the discussion became somewhat nasty with general accusations thrown back and forth, but Rob soon pinpointed the central point of disagreement:

Rob also defended himself against the accusation that he doesn't consider testing important: "Remember, I wrote the majority of our testsuite, so I think it's fair to say I consider testing important." But he also wants to focus on new features and he has the impression that this doesn't work when the "stable branch" has to remain stable all the time:

John Gilmore tried to get the two parties back together behind their common cause ("We need each other, guys"), and Sandro suggested to use an experimental branch for code that breaks things.

However, because Benjamin reverted one of Rob's commits and threatened to do it again in the future, Rob removed Benjamin's commit rights to the Savannah repository for Gnash, because he doesn't want to "allow a power-hungry developer to continue to reverting my changes." In the meantime, Sandro worked on some improvements and asked where he should commit the code: to the Gnash trunk where Benjamin couldn't review it and Rob maybe wouldn't accept the changes, or to a fork, which would make the project diverge? Sandro obviously still cares for the Gnash project and rightly fears that a fork will not be good for the common cause.

After a few nights of sleep, Benjamin, Sandro, and Rob seem to acknowledge that they have different development, project management, and communication styles, that they all made mistakes, and were too rude in their responses at some times. At the time of this writing, they were still on speaking terms on the #gnash irc channel on Freenode and were actively trying to reach a consensus and drafting some new commit rules (including "Commits shall not be reverted except as a last resort." and "No code shall be committed that causes failures in existing tests."), so this whole crisis may well result in a better development process for the project.

The death of Swfdec

Another Flash decoder, Swfdec, has silently stopped development a while ago. The last stable release, 0.8.4, is from December 2008, and the last commits are from December 2009. Swfdec has been primarily run by one person, Benjamin Otte, but he seems to have lost interest, although he is still occasionally answering questions on the Swfdec mailing list. In response to a question by Puppy Linux developer Barry Kauler in January of this year, Benjamin announced the death of his project in one sentence:

The fact that Benjamin started a new job in Red Hat's desktop team in January of this year is surely no coincidence: it should remind us that a project with just one core developer always has a fragile future because big changes in the developer's life can result in less time to work on the project.

A new open source Flash player

Development of Gnash and Swfdec was done using reverse engineering because Adobe only offered the SWF specification with a license that forbids the use of the specification to create programs that play Flash files. In June 2009, Adobe launched the Open Screen Project which made the SWF specification available without these restrictions. This made it possible for Alessandro Pignotti to work on a new open source Flash player, entirely based on this official SWF documentation. A part of this project is based on his bachelor's thesis at the university of Pisa, called An efficient ActionScript 3.0 Just-In-Time compiler implementation [PDF].

The result is Lightspark, which includes OpenGL-based rendering, a mostly complete implementation of Adobe's ActionScript 3.0 using the LLVM compiler, and a Mozilla-compatible browser plug-in. Because Lightspark has been designed and written from scratch based on Adobe's documentation, it promises a clean code base optimized for modern hardware.

By using OpenGL instead of XVideo, Lightspark allows for hardware-accelerated rendering using OpenGL shaders. Moreover, this opens the path for supporting blur and other effects that are implemented by efficient shaders. Another possibility is using OpenGL textures to display video frames, which is less efficient than XVideo but more flexible. For example, it makes it possible to implement the overlay and transformation effects that Flash supports.

For ActionScript 3.0 (introduced in Flash 9), Lightspark has both an interpreter and a JIT compiler that uses LLVM to compile ActionScript to native x86 code. However, because the previous ActionScript versions run on a completely different virtual machine, Alessandro has decided to not support them. This means that currently it's not really possible to compare the performance of Lightspark with that of Gnash: while Lightspark only supports ActionScript 3.0, Gnash only supports previous versions of the scripting language.

For people that want to try Lightspark in their browser, Alessandro has released a Mozilla-compatible plug-in. When encountering an unsupported Flash file, the plug-in should fail gracefully. For now, there's only a PPA (Personal Package Archive) for Ubuntu users, but packages are being created for Arch Linux and Debian. In this alpha phase of development, the current release is more of a technological demo. Alessandro is currently the only developer, although some external contributions have started trickling in.

After the first wave of testing, Alessandro published some information on the plan for the next releases. A stability release with no new features is planned for the first week of June, while release 0.5.0 will be focused on YouTube support. He also clarified that his current implementation only works on x86/x86_64 because of some assembly code, but he welcomes ports to other architectures:

The Gnash developers have been talking with Alessandro about joining their efforts, but he decided to work on Lightspark because it was very difficult to include an optimizing JIT compiler into the existing Gnash architecture. That said, code sharing or even a closer collaboration between the two projects certainly seems possible. Alessandro has already said that Lightspark's code could be integrated with Gnash in time when it's good enough, and Rob would like to add support for using Lightspark in Gnash to handle AVM2, the ActionScript virtual machine that Adobe introduced in Flash 9. If this idea is implemented, Gnash could essentially hand off all ActionScript 3 functionality to Lightspark.

Conclusion

Although most free and open source proponents agree that Flash is a bad thing and that it should be replaced by open web technologies such as HTML 5, the transition to an open web will happen slowly as all evolutions in the computer world do. Moreover, we are stuck with a lot of existing Flash content that should remain accessible. Therefore, open source Flash projects like Gnash and Lightspark will remain important for many Linux users for years. There is hope that the Gnash developers will reach a consensus on their development model and hopefully Lightspark will not face the same fate as Swfdec. For something as critical as Flash is to many users, more developers for both projects could certainly help.

Comments (15 posted)

Swift and predictable reactions to WebM

On May 19, Google unveiled something that many in the open source community had been expecting (and which the Free Software Foundation asked for in March): it made the VP8 video codec available to the public under a royalty-free, open source BSD-style license. Simultaneously, it introduced WebM, an HTML5-targeted open source audio-and-video delivery system using VP8, and announced a slew of corporate and open source WebM partners supporting the format, including web browsers and video sites such as its own YouTube property.

Dueling assessments, interested parties

The move was not unexpected. Google began trying to acquire VP8's creator, the codec shop On2, months ago, and speculation began even before the acquisition was final. The public reaction to the WebM launch was not unexpected, either. MPEG-LA, the commercial sellers of license for the competitor H.264 codec, suggested that anyone who used VP8 would get sued for patent infringement. An independent H.264 hacker quickly attacked VP8 as inferior on all technical counts, and surely in violation of multiple H.264 patents as well. H.264 proponents and general news sites began circulating that blog post, more so when Apple's Steve Jobs allegedly forwarded a link to it in response to an email asking his opinion on VP8.

Responses from the open source community itself have come in two flavors. The first was a long line of multimedia projects and companies announcing support for VP8 and WebM; some (like Mozilla and Collabora) were in the know before the deal was made public and working on their code, while others just reacted swiftly following the unveiling.

The second took on the opposition, rebutting both the MPEG-LA's public statements and the attacks of the H.264 hacker, Jason Garrett-Glaser. Many pointed out Garrett-Glaser's vested interest in H.264 being regarded as the technically best codec, given that he develops the x264 encoder project, and suggested that he was prejudiced against VP8 before even examining the release. StreamingMedia.com compared the codecs side-by-side, encoding the same source media at the same audio and video data rates, which Garrett-Glaser did not do, and concluded that there was no noticeable difference for most applications. Theora hacker Gregory Maxwell addressed the technical issues in an email to the Wikitech list, arguing that the initial release of Google's VP8 encoder represents a starting point ripe for optimization.

Other naysayers dismissed VP8 on the grounds that H.264 is already widely supported in hardware devices. That may be true, but most of this hardware support is in the form of embedded digital signal processor (DSP) code, and DSP ports of Theora were already in the works. Considering that Google has already funded ARM optimizations of Theora, there is grounds to believe it will push DSP playback of VP8 as well, and the company's Android platform is a likely place for it to make an appearance.

Patents and ambiguity

More important than the current (or even the potential-future) technical performance of VP8 is the question of whether it can legally be used under the terms spelled out in the WebM license and patent grant. It is clearly a technical improvement over Theora, but if the competition proved a genuine instance of patent infringement, the codec would need to be changed before it could be safely used.

On this point, again, there are two main threads of discussion. The first boils down to debate over the belief that VP8 must surely infringe on patents used in H.264 because the codecs share such a similar structure. Garrett-Glaser takes this stance, pointing out similarities in the algorithms. Xiph.org's Christopher "Monty" Montgomery dismissed that assessment as "serious hyperbole," and others in web article comment threads pointed out that all discrete cosine transform (DCT)-based codecs utilize the same basic steps; those steps are not what video codec patents cover.

Maxwell rebuffs the similarity argument as well, saying that Garrett-Glaser "has no particular expertise with patents, and even fairly little knowledge of the specific H.264 patents" due to the fact that x264 ignores them when implementing H.264 itself. He continued:

The second discussion thread amounts to divining whether H.264's patent licensor MPEG-LA will actually sue over a patent infringement charge against VP8. Here again, the public debate is dominated by assumptions: surely Google did a patent search that completely exonerated VP8; surely On2's patent lawyers knew what they were doing as they developed VP8 — and, alternatively, surely VP8 infringes somewhere, because there are just so many patents in H.264; surely VP8 infringes somewhere, because H.264 was created by the best codec authors using the best technologies.

To get out of the "surely" mire, consider the actual possibilities case by case. It is logical to suggest that if MPEG-LA has a genuine case, it will sue. If it does not have a genuine case, the question is whether the consortium will sue anyway to cause market confusion and buy time to continue selling H.264 patent licenses. But either way, the risks in filing a lawsuit are extraordinarily high — because Google could easily counter-sue.

Despite MPEG-LA's promotional material suggesting that blanket rights to use H.264 come with a license, the actual guarantee of the patent pool is quite weak:

Clarity, please

In other words, submarine patents and patent trolls can threaten H.264 — and in theory, On2 and Google may hold such patents. So what will MPEG-LA do? CEO Larry Horn already suggested, without directly claiming, that it believes it has a genuine case against VP8. Whether it does or doesn't, actually filing an infringement lawsuit could gamble away the H.264 cash cow. The far safer route is to make noise in public, pursue licensing deals with software and hardware vendors as long as possible, and work on the next codec licensing bundle. For its part, Google has done little in public other than express its confidence that there is no patent issue.

That sounds unsatisfying to the left-brained software developer, who would prefer a clear, bright line to be drawn with VP8 either on the "safe" or "unsafe" side. Unfortunately, the modern patent game does not work that way. In practice, patents are hidden weapons that can be used to sue (and threaten to sue) opponents. All commercial players hold them, and due to the vast number of patents granted — as well as the unknown reach of those patents — many are effectively hidden away until used in an attack.

Still, some have already suggested that Google can and should provide some level of increased clarity by publicly and transparently documenting the patents it now owns on VP8, and the patent search process it used to determine that nothing in VP8 infringed on a competitor's patents. Florian Mueller of FOSS Patents commented:

Rob Glidden, formerly of Sun, contrasted Google's one-shot announcement of VP8 with the process Sun used when working on the now-shuttered Open Media Stack video codec project, which "based their work on identifiable IPR [intellectual property rights] foundations, documented their patent strategy, and [was] willing to work with bona-fide standards groups to address and resolve IPR issues." By choosing to "go on their own," he added, Google actually undermines the open standards process the web relies on.

On the other hand, Google might consider it to be to its own advantage to keep the company's VP8 patent research secret, in order to force potential attackers to do more work looking for an infringement. No one does (nor should they) expect MPEG-LA to act with the clarity being asked of Google. At times MPEG-LA likes to present itself as if it is a standards body — one that produces technical work reflecting the consensus of industry, and ratifying the best possible ideas into global specifications. But that simply is not true. MPEG-LA is a for-profit business, selling its products and marketing them on behalf of its members and against all competitors.

Since its product is protection from a lawsuit by MPEG-LA itself, it gains nothing by drawing clear, bright lines. Even Horn's comment about creating a VP8 patent pool is couched in qualifiers and vague language: "there have been expressions of interest" and "we are looking into the prospects of doing so."

Of course, this is all really about HTML5 ... and money

Behind this entire fight is the availability of a free-to-implement video codec for HTML5. MPEG-LA and its pool members fought against Theora, and they will now do the same against VP8. Do not expect MPEG-LA to change its tune and support a completely free codec, ever; if it did the organization would have no reason to exist. MPEG-LA wants H.264 to win, not because it is better technically, but because it is their product.

Open source software is in a weird position in relation to MPEG-LA's licensing model. Even though it is the end users who infringe on the patents by watching H.264 content, the MPEG-LA requires anyone distributing codecs, like browser vendors, to pay for a license. That's just not possible for free software.

MPEG-LA has pushed back the date at which it will start charging royalty fees for streaming H.264 on the Internet until 2015, and even then there is a chance that they will push it back again. It does not explicitly care about the open source browser market itself; it has simply set up a fee structure that puts free software in an awkward position. The real money comes from video production and editing suites, and from large video hosting sites that transcode millions of videos.

Consequently, the real battle for VP8 adoption may be there as well. Google put out a long list of WebM-supporting partners when it unveiled the project, including several important proprietary software companies like creative-application-juggernaut Adobe and Quicktime's former star Sorenson. While MPEG-LA has more to lose than to gain by suing Google over VP8 today, that could change if these video production pipeline players start to shift over to WebM in a big way. If that happens, it might be the final straw which causes MPEG-LA to resort to the courtroom.

Comments (58 posted)

Page editor: Jonathan Corbet

Inside this week's LWN.net Weekly Edition

• Security: Tabnabbing; New vulnerabilities in barnowl, cacti, ghostscript, kernel,...
• Kernel: Suspend blocker suspense; 2.6.35 merge window part 2; 2.6.35 Video4Linux2 enhancements; One ring buffer to rule them all?
• Distributions: De-bashing Debian; lots of new releases; reviews of Android, Mint, Puppy, and SimplyMEPIS.
• Development: Diaspora: toward free social networking; Ktorrent, MyTracks, Pascal Brisset, Voltdb, ...
• Announcements: Software patents in the news; articles on Google I/O, uTP, WebM, Android, Qbo robot...

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