On Tue, Feb 06, 2024 at 10:24:45AM +0200, Amir Goldstein wrote: > On Tue, Feb 6, 2024 at 12:49 AM Kent Overstreet > <kent.overstreet@xxxxxxxxx> wrote: > > > > On Tue, Feb 06, 2024 at 09:17:58AM +1100, Dave Chinner wrote: > > > On Mon, Feb 05, 2024 at 03:05:13PM -0500, Kent Overstreet wrote: > > > > Add a new generic ioctls for querying the filesystem UUID. > > > > > > > > These are lifted versions of the ext4 ioctls, with one change: we're not > > > > using a flexible array member, because UUIDs will never be more than 16 > > > > bytes. > > > > > > > > This patch adds a generic implementation of FS_IOC_GETFSUUID, which > > > > reads from super_block->s_uuid; FS_IOC_SETFSUUID is left for individual > > > > filesystems to implement. > > > > > > It's fine to have a generic implementation, but the filesystem should > have the option to opt-in for a specific implementation. > > There are several examples, even with xfs and btrfs where ->s_uuid > does not contain the filesystem's UUID or there is more than one > uuid and ->s_uuid is not the correct one to expose to the user. Yeah, some of you were smoking some good stuff from the stories I've been hearing... > A model like ioctl_[gs]etflags() looks much more appropriate > and could be useful for network filesystems/FUSE as well. A filesystem needs to store two UUIDs (that identify the filesystem as a whole). - Your internal UUID, which can never change because it's referenced in various other on disk data structures - Your external UUID, which identifies the filesystem to the outside world. Users want to be able to change this - which is why it has to be distinct from the internal UUID. The internal UUID must never be exposed to the outside world, and that includes the VFS; storing your private UUID in sb->s_uuid is wrong - separation of concerns. yes, I am aware of fscrypt, and yes, someone's going to have to fix that. This interface is only for the external/public UUID.
