Nikolay,
This is intended. Otherwise it's an open avenue for the user to shoot
themselves in the foot.
I don't understand how?
Again. Any idea how? Is there any test case?
<snip>
UUID, by definition, are Unique. What you want to is
to toss the Unique part, meaning we'll really be left with some sort of
ID. What's more - the UUID is used by libblkid to populate the available
devices so not making it unique can cause subtle bugs.
- Irrespective of the fstype, when fs image file is copied/snapshot-ed
the fsid is indeed going to be duplicate.
- xfs and btrfs kernel doesn't allow duplicate fsid to be mounted which
is fair and accepted. (I remember fixing the duplicate fsid bugs in
the kernel, just fyi if you are concerned about them).
- ext4 kernel does allow duplicate fsid to be mounted.
- btrfstume -M <uuid> isn't the place to check if the fsid is a
duplicate. Because, libblkid will be unaware of the complete list of
fs images with its fsid.
- As I said before, its a genuine use-case here where the user wants to
revert the fsid change, so that btrfs fs root image can be booted.
Its up-to the user if fsid is duplicate in the user space, as btrfs
kernel rightly fails the mount if its duplicate fsid anyways.
Thanks, Anand
