The return of devfs [LWN.net]

The return of devfs

Posted May 8, 2009 11:24 UTC (Fri) by pli (guest, #45060)
Parent article: The return of devfs

The day devfs was removed from mainline was a sad day. Yes, the devfs implementation had its problems, some major ones, but those could have been fixed (and were fixed by e.g. mini-devfs but was never merged). The whole thing about letting the kernel dynamically manage /dev is a sound, elegant and proven strategy. The udev debacle has been a mess from day one and now they want to save their crappy idea by re-introducing a semi-half-devfs that is in fact a udev-helper-devfs, with some terribly odd and confusing device node life-cycle handling. Part of me is happy though, because the udev people realize that this should be done in the kernel, but I'm worried that this is just a continuation of the udev madness.

I hope the submission of devtmpfs can restart the general devfs-discussion and lead to the implementation of a real and proper devfs (e.g. let's start from mini-devfs) so that we once and for all can leave udev behind us.

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The return of devfs

Posted May 8, 2009 13:35 UTC (Fri) by incase (guest, #37115) [Link]

Oh well, sure udev has quite a few problems, but in my experience, it provides a much cleaner interface to device node (or symlink to device node) creation then hotplug ever did.
And I have quite a number of places where I need it:
Give serial USB devices consistent names, even when plugged in later, in another order or whatever.
Give different usb thumb drives consistent device names (as they mount at different places and are access restricted to specific users) etc...

I never managed to achieve this consistently with the old devfs/hotplug combo. Especially since it made a difference with that combo when a device was connected (before or after hotplug was first run)..

However, this concerns basically only the hotplug functions of udev, not the coldplug functions in their current full extend. This basically means I'm all for devtmpfs as a helper to make the device nodes that udev coldplug would create available before it finished running, so that other userspace processes could already start before udev coldplug finished.

regards,
Sven

The return of devfs

Posted May 8, 2009 14:21 UTC (Fri) by nix (subscriber, #2304) [Link]

Please no. devfs was an abomination.

The lifetime rules of objects in devtmpfs are simple: the nodes are
created by the kernel, and that's all. It's just a bunch of automatic
mknod()s. Everything else is handled by udev, as now.