Use device number to find uuid

[Random-Liu]

Use linux device number from mount.Lookup to look for uuid.

This may be able to fix #325.

And I also see the Ubuntu used by GKE, rootfs is mounted from /dev/root, which doesn't have real corresponding device file.

With this fix, we get device number from mount directly, and find uuid with the device number. This doesn't assume that the mount source has to be a existing file.

Signed-off-by: Lantao Liu [email protected]

[Random-Liu]

@ijc Could you take a look?

[abhi]

Looks fine to me.

[mikebrow]

/LGTM

[ijc]

LookupMount has a comment in it:

  // Note that m.{Major, Minor} are generally unreliable for our purpose here
  // https://www.spinics.net/lists/linux-btrfs/msg58908.html

But we are now using exactly those fields below.

[ijc]

Actually, we don't seem to rely on these any more or less than we did before, so I guess this is fine.

[mikebrow]

@Random-Liu @ijc Interesting.. if "generally unreliable" maybe we should do it both ways and compare results then return the best result. Just thinking out loud and now worrying about what was meant by generally unreliable.

[metahertz]

Thanks for taking this one on @Random-Liu!
Will test if this fixes #325 and report back.

[metahertz]

Hey @Random-Liu
Sadly this doesn't fix the ZFS issues in #325. For the same reason as the previous code, ZFS manages it's own volumes/filesystems/mounts etc, so the rest of the linux kernel (IIUC) doesn't know which disks are part of a ZFS pool (think LVM/RAID/etc) and which aren't.

If dealing with ZFS, the "truest" way to get a unique identifier which will ALWAYS identify that pool is the GUID property of the pool itself, so for the given mounts (from #325)

tmpfs on /var type tmpfs (rw,nosuid,nodev,noexec,relatime,size=1023524k,mode=755)
testpool/nextnas/containerd-vol on /var/lib/containerd/io.containerd.snapshotter.v1.zfs type zfs (rw,xattr,noacl)
testpool on /var/zpool type zfs (rw,xattr,noacl)
testpool/nextnas on /var/zpool/nextnas type zfs (rw,xattr,noacl)

the "pool name" is always the first word before the first / for a zfs mount, in our case, testpool.
Running the ZFS userspace tools;

zpool get guid testpool

gives us a UUID which will always identify that pool.
UUID/nextnas would always identify the other mount (as it's in the pool 'testpool').

Error received for current master of cri-containerd as follows;