Unverified Commit d9c37a49 authored Jul 14, 2025 by Qu Wenruo Committed by Christian Brauner Jul 15, 2025

fs: add a new remove_bdev() callback



Currently all filesystems which implement super_operations::shutdown()
can not afford losing a device.

Thus fs_bdev_mark_dead() will just call the ->shutdown() callback for the
involved filesystem.

But it will no longer be the case, as multi-device filesystems like
btrfs and bcachefs can handle certain device loss without the need to
shutdown the whole filesystem.

To allow those multi-device filesystems to be integrated to use
fs_holder_ops:

- Add a new super_operations::remove_bdev() callback

- Try ->remove_bdev() callback first inside fs_bdev_mark_dead()
  If the callback returned 0, meaning the fs can handling the device
  loss, then exit without doing anything else.

  If there is no such callback or the callback returned non-zero value,
  continue to shutdown the filesystem as usual.

This means the new remove_bdev() should only do the check on whether the
operation can continue, and if so do the fs specific handlings.
The shutdown handling should still be handled by the existing
->shutdown() callback.

For all existing filesystems with shutdown callback, there is no change
to the code nor behavior.

Btrfs is going to implement both the ->remove_bdev() and ->shutdown()
callbacks soon.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Link: https://lore.kernel.org/09909fcff7f2763cc037fec97ac2482bdc0a12cb.1752470276.git.wqu@suse.com


Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

parent 19272b37

fs/super.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -1457,6 +1457,17 @@ static void fs_bdev_mark_dead(struct block_device *bdev, bool surprise)
		if (!sb)
		return;

		if (sb->s_op->remove_bdev) {
		int ret;

		ret = sb->s_op->remove_bdev(sb, bdev);
		if (!ret) {
		super_unlock_shared(sb);
		return;
		}
		/* Fallback to shutdown. */
		}

		if (!surprise)
		sync_filesystem(sb);
		shrink_dcache_sb(sb);

include/linux/fs.h

+9 −0

Original line number	Diff line number	Diff line
		@@ -2363,6 +2363,15 @@ struct super_operations {
		struct shrink_control *);
		long (free_cached_objects)(struct super_block ,
		struct shrink_control *);
		/*
		* If a filesystem can support graceful removal of a device and
		* continue read-write operations, implement this callback.
		*
		* Return 0 if the filesystem can continue read-write.
		* Non-zero return value or no such callback means the fs will be shutdown
		* as usual.
		*/
		int (remove_bdev)(struct super_block sb, struct block_device *bdev);
		void (shutdown)(struct super_block sb);
		};