[PATCH] btrfs: fix GET_SUBVOL_INFO after compat refactor

[Daan De Meyer via B4 Relay <devnull+daan.amutable.com@kernel.org>]

From: Daan De Meyer <daan@amutable.com>

btrfs_search_slot() returns a positive value when the search key does
not exactly match an item. This is expected here, since offset 0 is used
to find the first ROOT_BACKREF for the subvolume and the actual key has
the parent root ID as its offset.

Before the compat ioctl refactoring, the native handler still copied the
filled structure to userspace when the search returned 1. After the
lookup was moved to a shared helper, both native and compat callers
treat the positive return value as a failure and skip copy_to_user(),
leaving BTRFS_IOC_GET_SUBVOL_INFO unusable for non-top-level
subvolumes.

Reset ret after successfully validating and reading the ROOT_BACKREF so
the helper reports success and both callers copy the result to
userspace.

Fixes: 538e5bdbc899 ("btrfs: add 32-bit compat ioctl for BTRFS_IOC_GET_SUBVOL_INFO")
Signed-off-by: Daan De Meyer <daan@amutable.com>
---
Fix BTRFS_IOC_GET_SUBVOL_INFO for non-top-level subvolumes after the
recent 32-bit compat ioctl refactor.
---
 fs/btrfs/ioctl.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 9d47d16394fc..ab6c17716026 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2042,6 +2042,7 @@ static int _btrfs_ioctl_get_subvol_info(struct inode *inode,
 			ret = -ENOENT;
 			goto out;
 		}
+		ret = 0;
 	}
 
 out:

---
base-commit: cab9e339cfbc1a4e075e53e281dfb00391e1a6bb
change-id: 20260713-btrfs-get-subvol-info-fix-e93803926554

Best regards,
--  
Daan De Meyer <daan@amutable.com>