On Mon 14-07-25 14:55:57, Qu Wenruo wrote:
> 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
^^^ handle
> 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
^^^^ I'd remove this word.
> ->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@xxxxxxxx>
Besides the spelling fixes looks good to me. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> fs/super.c | 11 +++++++++++
> include/linux/fs.h | 9 +++++++++
> 2 files changed, 20 insertions(+)
>
> diff --git a/fs/super.c b/fs/super.c
> index 80418ca8e215..7f876f32343a 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -1459,6 +1459,17 @@ 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);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index b085f161ed22..6a8a5e63a5d4 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2367,6 +2367,15 @@ 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);
> };
>
> --
> 2.50.0
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
