udev by-label/by-uuid vs. lvm2

udev by-label/by-uuid vs. lvm2

[Andreas Jellinghaus]

Hi,

not sure if this is an ubuntu issue:
at least on ubuntu edgy udev creates the
usual /dev/disk/by-uuid and by-label directories
with links for all filesystems/disks/partitions.

but with lvm2 vg's are only created in
/dev/<foo>/<bar> and /dev/mapper/<foo>-<bar>.
that is ok, <foo> is the pv and <bar> the vg.

still the filesystem on <bar> has a uuid and
a label, and neither is found in /dev/disk/by-*/
as link. As a result booting with LABEL or UUID
doesn't work in the initramfs either (UUID is
the default config as far as I know).

can someone tell me if this problem is
a) wontfix/by design
b) kernel too old problem (maybe lvm2 doesn't
    create events for udev?)
c) udev out of date or misconfigured (so I will
    file a bug with ubuntu to let them know)
d) something else

Thanks, Andreas

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Re: udev by-label/by-uuid vs. lvm2

[Bryan Kadzban]

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On Thu, Nov 02, 2006 at 06:05:10PM +0100, Andreas Jellinghaus wrote:
> still the filesystem on <bar> has a uuid and
> a label, and neither is found in /dev/disk/by-*/
> as link. As a result booting with LABEL or UUID
> doesn't work in the initramfs either (UUID is
> the default config as far as I know).
> 
> can someone tell me if this problem is
> a) wontfix/by design

At the moment, I think it's by design, but I'm not sure if that makes it
a won't fix.  I suspect it is, though.

The "standard" udev persistent-storage.rules file has a rule that
ignores dm-* devices (which I think includes these).  This is probably
so that you don't have multiple programs trying to handle device node
creation for LVM devices.  AFAIK there's no way to have udev create a
symlink to a device that it doesn't know anything about.

You probably want to have whatever tool handles LVM devices create the
symlink, if it can.  It could use udev's vol_id program to find out the
UUID and label strings for each partition-equivalent.  (I don't think
LVM calls them partitions, but I don't know what it does call them.
Whatever device contains the filesystem is what vol_id should be run
on.)


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