Re: [PATCH] tests: add btrfs mount tests (fails!)

[Stanislav Brabec <sbrabec@suse.cz>]

Stanislav Brabec wrote:
> Coverage:

I just found a bug in my testcase:
To prevent race bind-mnt has to be created in time of fs creation.

  btrfs subvol create s3 >/dev/null
+mkdir -p s3/bind-mnt
  popd >/dev/null

But, what is worse, I found a problem in previous patches.

Things are even more complicated than I thought, and patches still not 
cover all cases.

Up to now, I have been thinking that device + subvolid is unique 
identifier in the mountinfo. But it is not true, at least not when bind 
mounts take its role.

Using bind mounts that point to a sub-directory of a subvolume of btrfs 
results in two lines in mountinfo that have the same subvolid but 
different subvol.

Second "mount -a" then fails badly. Not only that it mounts the bind 
mount second time, it also mistakenly mounts another volume over a 
previously mounted volume.

dev/loop0 on 
/home/sbrabec/VCS/util-linux/tests/output/mount/fstab-btrfs-mnt-subvol 
type btrfs 
(rw,relatime,space_cache,subvolid=258,subvol=/d0/dd0/ddd0/d2/dd2/ddd2/s3/bind-mnt)
=> totally wrong

We are back on the beginning.

I have to re-evaluate all patches I sent up to now.

TODO:

Check whether it is possible to directly mount sub-directory of 
sub-volume that is not a subvolume per self.

If yes:
- We will need to introduce full path evaluation of btrfs sub-volume, 
and always compare it with mountinfo.

If not:
- We will have to search the whole mountinfo for a particular subvolid 
and and find a shortest subvol string.

David, could you bring some light into it?

-- 
Best Regards / S pozdravem,

Stanislav Brabec
software developer
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