On Wed, Mar 05, 2025 at 10:48:34AM -0800, Darrick J. Wong wrote:
> On Wed, Mar 05, 2025 at 09:04:50AM -0800, Luis Chamberlain wrote:
> > On Wed, Mar 05, 2025 at 02:15:47PM +0000, Matthew Wilcox wrote:
> > > On Tue, Mar 04, 2025 at 10:33:30PM -0800, Darrick J. Wong wrote:
> > > > > So this is expedient because XFS happens to not call sb_set_blocksize()?
> > > > > What is the path forward for filesystems which call sb_set_blocksize()
> > > > > today and want to support LBS in future?
> > > >
> > > > Well they /could/ set sb_blocksize/sb_blocksize_bits themselves, like
> > > > XFS does.
> > >
> > > I'm kind of hoping that isn't the answer.
> >
> > set_blocksize() can be used. The only extra steps the filesystem needs
> > to in addition is:
> >
> > sb->s_blocksize = size;
> > sb->s_blocksize_bits = blksize_bits(size);
> >
> > Which is what both XFS and bcachefs do.
> >
> > We could modify sb to add an LBS flag but that alone would not suffice
> > either as the upper limit is still a filesystem specific limit. Additionally
> > it also does not suffice for filesystems that support a different device
> > for metadata writes, for instance XFS supports this and uses the sector
> > size for set_blocksize().
> >
> > So I think that if ext4 for example wants to use LBS then simply it
> > would open code the above two lines and use set_blocksize(). Let me know
> > if you have any other recommendations.
>
> int sb_set_large_blocksize(struct super_block *sb, int size)
> {
> if (set_blocksize(sb->s_bdev_file, size))
> return 0;
> sb->s_blocksize = size;
> sb->s_blocksize_bits = blksize_bits(size);
> return sb->s_blocksize;
> }
> EXPORT_SYMBOL_GPL(sb_set_large_blocksize);
>
> int sb_set_blocksize(struct super_block *sb, int size)
> {
> if (size > PAGE_SIZE)
> return 0;
> return sb_set_large_blocksize(sb, size);
> }
> EXPORT_SYMBOL(sb_set_blocksize);
>
> Though you'll note that this doesn't help XFS, or any other filesystem
> where the bdev block size isn't set to the fs block size. But xfs can
> just be weird on its own like always. ;)
Actually, I failed to also notice XFS implicitly calls sb_set_large_blocksize()
through:
xfs_fs_get_tree() -->
get_tree_bdev() -->
get_tree_bdev_flags() -->
get_tree_bdev_flags() -->
sb_set_blocksize()
We just don't care if sb_set_blocksize() if fails inside get_tree_bdev_flags().
To be clear this has been the case since we added and tested LBS on XFS.
So if we wanted something more automatic, how about:
diff --git a/block/bdev.c b/block/bdev.c
index 3bd948e6438d..4844d1e27b6f 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -181,6 +181,8 @@ EXPORT_SYMBOL(set_blocksize);
int sb_set_blocksize(struct super_block *sb, int size)
{
+ if (!(sb->s_type->fs_flags & FS_LBS) && size > PAGE_SIZE)
+ return 0;
if (set_blocksize(sb->s_bdev_file, size))
return 0;
/* If we get here, we know size is validated */
diff --git a/fs/bcachefs/fs.c b/fs/bcachefs/fs.c
index 90ade8f648d9..e99e378d68ea 100644
--- a/fs/bcachefs/fs.c
+++ b/fs/bcachefs/fs.c
@@ -2396,7 +2396,7 @@ static struct file_system_type bcache_fs_type = {
.name = "bcachefs",
.init_fs_context = bch2_init_fs_context,
.kill_sb = bch2_kill_sb,
- .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP,
+ .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP | FS_LBS,
};
MODULE_ALIAS_FS("bcachefs");
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index d92d7a07ea89..3d8b80165d48 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -2118,7 +2118,8 @@ static struct file_system_type xfs_fs_type = {
.init_fs_context = xfs_init_fs_context,
.parameters = xfs_fs_parameters,
.kill_sb = xfs_kill_sb,
- .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP | FS_MGTIME,
+ .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP | FS_MGTIME |
+ FS_LBS,
};
MODULE_ALIAS_FS("xfs");
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 2c3b2f8a621f..16d17bd82be0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2616,6 +2616,7 @@ struct file_system_type {
#define FS_DISALLOW_NOTIFY_PERM 16 /* Disable fanotify permission events */
#define FS_ALLOW_IDMAP 32 /* FS has been updated to handle vfs idmappings. */
#define FS_MGTIME 64 /* FS uses multigrain timestamps */
+#define FS_LBS 128 /* FS supports LBS */
#define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */
int (*init_fs_context)(struct fs_context *);
const struct fs_parameter_spec *parameters;
