Get rid of /etc/mtab and store userspace options in /run

[Martin Pitt]

/etc/mtab has always been a bit of a wart, as it's potentially broken to put information about mounted file system on a mountedfile system. It is out of date in rescue mode when / is read-only (but "mount" output won't tell you), and leads to bugs like bug 891688 or bug 13131.

The only reason why we still have it is that /proc/mounts is not able to store userspace-only extra options which e. g. udisks (uhelper=udisks), pm-utils (commit=XXX), or NFS use.

These days there is a better option for this. Copying response from util-linux upstream Karel Zak:

  "When linked with libmount (--enable-libmount-mount) then the userspace options (and only the options) are maintained by library in userspace in /run/mount/utab. The mount, umount and findmnt are able to see these options from by libmount. It's also supported by the latest mount.nfs (as NFS requires some userspace stuff too)..

 See Fedora, we don't use mtab any more. (Well, some utils like df have problem to de-duplicate list of mounted filesystems, but all
 basic things works as expected.)"

This is worth investigating for the Q cycle.

[Martin Pitt (pitti)]

Subscribing Foundations team for comments/input, but assigning to myself for now.

[Steve Langasek (vorlon)]

Certainly sounds to me like a reasonable change for Q, if this is the direction upstream is going in order to solve the problem.

[Martin Pitt (pitti)]

Assigning to c-foundations for consideration. Please feel free to unassign again if you consider it inappropriate.

[Martin Pitt (pitti)]

This has happened a fair while ago already.