Bug#991639: udev: 80-debian-compat.rules can yield non-stable and inconsistent symlinks

[Vincent Lefevre]

On 2021-07-29 16:20:48 +0200, Michael Biebl wrote:
> Am 29.07.21 um 15:07 schrieb Vincent Lefevre:
> > Package: udev
> > Version: 247.3-6
> > Severity: normal
> > 
> > My machine has 2 DVD-RW drives, and /lib/udev/rules.d/80-debian-compat.rules
> > sometimes yields the following symlinks:
> > 
> > lrwxrwxrwx 1 root root 3 2021-07-29 14:25:55 /dev/cdrw -> sr1
> > lrwxrwxrwx 1 root root 3 2021-07-29 14:25:55 /dev/dvd -> sr0
> > lrwxrwxrwx 1 root root 3 2021-07-29 14:25:55 /dev/dvdrw -> sr0
> > 
> > instead of /dev/cdrw -> sr0 for the first one, to be consistent with
> > the other symlinks.
> > 
> > I already reported the issue in 2017 (4 years ago!), but nothing has
> > been done yet. See
> > 
> > * Initial message:
> >    https://lists.debian.org/debian-user/2017/04/msg00789.html
> 
> 
> And the comment from 2017 still holds true:
> https://lists.debian.org/debian-user/2017/04/msg00790.html
> 
> "
> See the comment in there:
> 
> # These rules will create symlinks for CD/DVD drives, to help old
> # programs which are unable to automatically discover the devices.
> # The first detected device gets the symlink, but this is not stable across
> # reboots.
> 
> So, yes, what you see can happen depending on the order devices are
> discovered.
> "
> 
> The kernel hasn't changed. It still probes devices asynchronously.
> There is not much we can do about that.

The comment says: "The first detected device gets the symlink".
If this were true, all symlinks would be the same (even though
this would not be stable), which is not the case.

BTW, aren't the devices numbered 0, 1, etc. in the order they are
detected, so that one would expect always sr0 here?

(What would be unstable would be what sr0 and sr1 physically are.)

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