statx: stx_subvol

statx: stx_subvol

Add a new statx field for (sub)volume identifiers, as implemented by
btrfs and bcachefs.

This includes bcachefs support; we'll definitely want btrfs support as
well.

Link: https://lore.kernel.org/linux-fsdevel/2uvhm6gweyl7iyyp2xpfryvcu2g3padagaeqcbiavjyiis6prl@yjm725bizncq/
Signed-off-by: Kent Overstreet <[email protected]>
Cc: Josef Bacik <[email protected]>
Cc: Miklos Szeredi <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: David Howells <[email protected]>
Signed-off-by: Kent Overstreet <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Johannes Thumshirn <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>