User-space device enumeration [LWN.net]

Mark Bellon recently announced the first release of a tool called "User-Space Device Enumeration," or "uSDE". uSDE maintains a directory full of device nodes based on hotplug events and information found in sysfs. It is thus intended to be a user-space replacement for the devfs filesystem.

Few doubt that the objectives for uSDE make sense. But quite a few developers have asked why the uSDE developers went off and created their own system, rather than working on udev (which recently released version 005). Given that the two projects appear to be trying to do exactly the same thing, it seems strange that the work is being done twice.

According to Mr. Bellon, uSDE was developed because udev wasn't up to the needs of Carrier Grade Linux. What needs they were trying to meet are not entirely clear; his posting is full of language like "Aggressive device enumeration. Multiple concurrent policy execution and management." In fact, the actual requirements imposed by the CGL specification are minimal; as posted by Greg Kroah-Hartman:

OSDL CGL specifies that carrier grade Linux shall provide functionality such that a device's identity shall be maintained when it is removed and reinstalled even if it is plugged into a different bus, slot, or adapter. "Device identity" is the name of the device presented to user space, and this identity is assigned based on policies set by the administrator, e.g., based on location or hardware identification information.

Meeting this requirement with existing tools is not that hard to do.

uSDE appears to be the result of a different design approach. It uses a complicated plugin architecture to implement different device naming policies. As a whole, it is rather larger and more complex than udev. It does provide some functionality that udev is still lacking, including a devfs emulation module. In general, it shows the signs of having had more developer time put into it than udev.

But, while uSDE may be a little further developed than udev, it looks set to lose the fight for developer support and mindshare. The development of udev has followed the informal rules of kernel hacking: it has been done in the open, with feedback received along the way. It also doesn't hurt that udev is the project of a core kernel developer. uSDE, instead, has been developed in isolation, in competition to an established project, and was late to enter the public arena. Whether or not uSDE is, in fact, a better solution, the way in which it has been developed has put it at a disadvantage relative to its competition.

to post comments

User-space device enumeration

Posted Nov 5, 2003 12:32 UTC (Wed) by cloose (guest, #5066) [Link] (1 responses)

Iff uSDE is better solution than udev, I think, it would be really sad (and stupid) to see it not included. I always thought that Linux is about the best solution to a problem and not how or by whom it was developed.

Christian

User-space device enumeration

Posted Nov 7, 2003 5:42 UTC (Fri) by turpie (guest, #5219) [Link]

Linus has always favoured the simplest solution.
In this case it sounds like the simpler udev can be easily expanded to include the missing functionality that uSDE has.

User-space device enumeration

Posted Nov 27, 2003 0:19 UTC (Thu) by obituary (guest, #17248) [Link]

Well anyway both of them are just a bunch of junk. Devfs is better.