Revert "btrfs: canonicalize the device path before adding it"

commit 8fb1dcbb upstream.

This reverts commit 7e06de7c.

Commit 7e06de7c ("btrfs: canonicalize the device path before adding
it") tries to make btrfs to use "/dev/mapper/*" name first, then any
filename inside "/dev/" as the device path.

This is mostly fine when there is only the root namespace involved, but
when multiple namespace are involved, things can easily go wrong for the
d_path() usage.

As d_path() returns a file path that is namespace dependent, the
resulted string may not make any sense in another namespace.

Furthermore, the "/dev/" prefix checks itself is not reliable, one can
still make a valid initramfs without devtmpfs, and fill all needed
device nodes manually.

Overall the userspace has all its might to pass whatever device path for
mount, and we are not going to win the war trying to cover every corner
case.

So just revert that commit, and do no extra d_path() based file path
sanity check.

CC: stable@vger.kernel.org # 6.12+
Link: https://lore.kernel.org/linux-fsdevel/20250115185608.GA2223535@zen.localdomain/


Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>