udev reorders assignment [was Re: Solved Debian update - keyboard responsive, Lennart Sorrenson not so much]

[D. Hugh Redelmeier]

| From: Russell Reiter <rreiter91-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org>

| <snip previous>
| > worse off (I am not sure loosing udev after booting is really that huge
| > a deal, but could be annoying).
|
| That's where I'm stuck on this. Unless you have a solid set of rules,
| devices re polled by udev seem to be reordered in assignment. That's a
| major complaint I see in the various blog's about udev. Udev
| diagnostic tools have improved but there are still some gaps and
| people still encounter problems.

What do you mean by "devices re polled by udev seem to be reordered in
assignment"?

Are you talking about /dev entries for similar devices having unstable
names?  For example, /dev/sda and /dev/sdb might switch between
devices in different boots?  Or eth0 vs eth1?  Or something else?

Name instability seems to be an outcome of doing things in parallel (at 
least at at abstract level).  The kernel folks think that this is a win 
(speed, elegance, and moving things out of the kernel, if I remember 
correctly).

There are many workarounds.

In the case of disks, /etc/fstab entries should now use UUIDs (or LABELs) 
to refer to partitions.  Nicer in a lot of ways.

In the case of TV tuner cards (my problem on my MythTV boxes), 
there are interesting entries in /dev that allow you to address them
by PCI slot.

Do "ls -d /dev/*/by-*" to see how you can get at particular devices by
UUID or LABEL or PCI slot or whatever.

In the case of ethernet interfaces (not in /dev, thanks to BSD brain
damage 30 years ago), you can discriminate by way of MAC address, but
I don't think that that is satisfactory since a card's MAC addresses
can be changed.  I've not yet bumped hard into this problem so I
haven't searched for a better technique.  I guess if the hardware is
different you could discriminate via PCI device IDs.  Any better
solutions?  I sure want my router to know very early in the boot
sequence which interfaces are inward facing and which are outward
facing.  Heck, I'm so behind the times I still use ifconfig etc. that
are long obsolete.
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