On Thu, Mar 06, 2025 at 01:39:49PM -0500, Kent Overstreet wrote:
> On Tue, Mar 04, 2025 at 05:53:01PM -0800, Luis Chamberlain wrote:
> > The commit titled "block/bdev: lift block size restrictions to 64k"
> > lifted the block layer's max supported block size to 64k inside the
> > helper blk_validate_block_size() now that we support large folios.
> > However in lifting the block size we also removed the silly use
> > cases many filesystems have to use sb_set_blocksize() to *verify*
> > that the block size < PAGE_SIZE. The call to sb_set_blocksize() can
> > happen in-kernel given mkfs utilities *can* create for example an
> > ext4 32k block size filesystem on x86_64, the issue we want to prevent
> > is mounting it on x86_64 unless the filesystem supports LBS.
> >
> > While, we could argue that such checks should be filesystem specific,
> > there are much more users of sb_set_blocksize() than LBS enabled
> > filesystem on linux-next, so just do the easier thing and bring back
> > the PAGE_SIZE check for sb_set_blocksize() users.
> >
> > This will ensure that tests such as generic/466 when run in a loop
> > against say, ext4, won't try to try to actually mount a filesystem with
> > a block size larger than your filesystem supports given your PAGE_SIZE
> > and in the worst case crash.
> >
> > Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> > Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
>
> bcachefs doesn't use sb_set_blocksize() - but it appears it should, and
> it does also support bs > ps in -next.
>
> Can we get a proper helper for lbs filesystems?
What do you think of this last recommention I had?
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;
