[gentoo-amd64] Changes to device order

[Richard Freeman]

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Hmm - after a reboot yesterday the order of my various /dev/video#'s
have changed.  I'm guessing this was related to the recent baselayout
update (one of those reasons I always reboot within a few days after a
baselayout change - I want to make sure I can reboot at all lest the
system be down while I'm out of town).  Or maybe it was due to this
monthly udev update cron job that seems to get triggered nowadays.

Any ideas what might cause this to happen?

It took a while to figure out what was happening - I run myth and all it
knew is that the device it was trying to access wasn't initializing
correctly.  I figured the card had some issue, but it eventually turned
out that I was addressing the wrong card and doing it in the wrong way.

This seems to be one of those potential unix achilles-heels.  Devices
just have those generic /dev/devicename mknods, but there isn't anything
that uniquely identifies a specific device.  If these mknods change
order then everything gets confused.  I guess a solution would be to
assign some kind of GUID to each device and use that to address them -
but that of course gets rid of the elegance of the everything-is-a-file
philosophy.  Maybe create two links to the device - one with a classic
name, and another which is a GUID-based filename, and software can use
either one.

I had a similar issue with a pair of USB serial ports I bought.  Now,
this is probably not linux's fault - but the devices had NO uniquely
identifying info embedded in them as far as I could tell.  So, I was
very nervous about them switching around their mknods after reboots,
after moving them around, etc.  In the end I edited the udev
configuration to create a second mknod for each device that was
associated with the specific USB port they were plugged into (so much
for plug-and-play).  My understanding is that windows has the same
problem with these sorts of devices - they work real great until you
have a bunch of them.

Does anybody know if a generic solution exists to these sorts of
problems in linux, or how to mitigate these sorts of issues?  With the
increased usage of USB I'd think that situations like this will only
come up more often...
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