[PATCH v2 1/3] btrfs: Set qgroup inherit size limit to SZ_4K instead of page size

[Qu Wenruo <wqu@suse.com>]

Change btrfs_qgroup_inherit maximum size from PAGE_SIZE to SZ_4K to make
it consistent across different architectures.

This change will only affect architectures whose page size is not
(larger than) 4K, and will only affect how many qgroups can exist in
btrfs_qgroup_inherit structure:

Before: (64K page size)
8183

After: (fixed to 4K btrfs_qgroup_inherit size)
503

Although in theory this could lead to incompatibility, but considering
how rare btrfs_qgroup_inherit is used, it's still not too late to change
it without impacting a large user base.

And passing over 100 qgroups in one btrfs_qgroup_inherit structure is
already insane.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/ioctl.c           | 2 +-
 include/uapi/linux/btrfs.h | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 63600dc2ac4c..5db8680b40a9 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1811,7 +1811,7 @@ static noinline int btrfs_ioctl_snap_create_v2(struct file *file,
 	if (vol_args->flags & BTRFS_SUBVOL_RDONLY)
 		readonly = true;
 	if (vol_args->flags & BTRFS_SUBVOL_QGROUP_INHERIT) {
-		if (vol_args->size > PAGE_SIZE) {
+		if (vol_args->size > BTRFS_QGROUP_INHERIT_MAX_SIZE) {
 			ret = -EINVAL;
 			goto free_args;
 		}
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 5ca1d21fc4a7..311edb65567c 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -82,6 +82,7 @@ struct btrfs_qgroup_limit {
  */
 #define BTRFS_QGROUP_INHERIT_SET_LIMITS	(1ULL << 0)
 
+#define BTRFS_QGROUP_INHERIT_MAX_SIZE	(SZ_4K)
 struct btrfs_qgroup_inherit {
 	__u64	flags;
 	__u64	num_qgroups;
-- 
2.18.0