[PATCH] ovl: fix wrong detection of 32bit inode numbers

[PATCH] ovl: fix wrong detection of 32bit inode numbers

[Amir Goldstein]

The implicit FILEID_INO32_GEN encoder was changed to be explicit,
so we need to fix the detection.

When mounting overlayfs with upperdir and lowerdir on different ext4
filesystems, the expected kmsg log is:

  overlayfs: "xino" feature enabled using 32 upper inode bits.

But instead, since the regressing commit, the kmsg log was:

  overlayfs: "xino" feature enabled using 2 upper inode bits.

Fixes: e21fc2038c1b9 ("exportfs: make ->encode_fh() a mandatory method for NFS export")
Cc: stable@vger.kernel.org # v6.7+
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---

Miklos,

I have queued up this fix.
The regression has no serious impact on most users, because xino
works pretty well either way.

A nested overlayfs, where the lower overlayfs is nonsamefs ext4
would have less xino overflows, but this is a very corner case.

Thanks,
Amir.

 fs/overlayfs/util.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 3f1b763a8bb4c..2ea769f311c34 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -85,7 +85,10 @@ int ovl_can_decode_fh(struct super_block *sb)
 	if (!exportfs_can_decode_fh(sb->s_export_op))
 		return 0;
 
-	return sb->s_export_op->encode_fh ? -1 : FILEID_INO32_GEN;
+	if (sb->s_export_op->encode_fh == generic_encode_ino32_fh)
+		return FILEID_INO32_GEN;
+
+	return -1;
 }
 
 struct dentry *ovl_indexdir(struct super_block *sb)
-- 
2.53.0

Re: [PATCH] ovl: fix wrong detection of 32bit inode numbers

[Miklos Szeredi]

On Tue, 24 Mar 2026 at 16:22, Amir Goldstein <amir73il@gmail.com> wrote:
>
> The implicit FILEID_INO32_GEN encoder was changed to be explicit,
> so we need to fix the detection.
>
> When mounting overlayfs with upperdir and lowerdir on different ext4
> filesystems, the expected kmsg log is:
>
>   overlayfs: "xino" feature enabled using 32 upper inode bits.
>
> But instead, since the regressing commit, the kmsg log was:
>
>   overlayfs: "xino" feature enabled using 2 upper inode bits.
>
> Fixes: e21fc2038c1b9 ("exportfs: make ->encode_fh() a mandatory method for NFS export")
> Cc: stable@vger.kernel.org # v6.7+
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
>
> Miklos,
>
> I have queued up this fix.
> The regression has no serious impact on most users, because xino
> works pretty well either way.
>
> A nested overlayfs, where the lower overlayfs is nonsamefs ext4
> would have less xino overflows, but this is a very corner case.

LGTM, thanks.

Miklos