The filesystem UUID was only being loaded into super_block sb when an
external journal device was in use. When mounting without an external
journal, the UUID remained unset, which prevented the computation of
a filesystem ID (fsid), which could be confirmed via `stat -f -c "%i"`
and thus user space could not use fanotify correctly.

A missing filesystem ID causes fanotify to return ENODEV when marking
the filesystem for events like FAN_CREATE, FAN_DELETE, FAN_MOVED_TO,
and FAN_MOVED_FROM. As a result, applications relying on fanotify
could not monitor these events on JFS filesystems without an external
journal.

Moved the UUID initialization so it is always performed during mount,
ensuring the superblock UUID is consistently available.

Signed-off-by: João Paredes <joaommp@yahoo.com>
---
 fs/jfs/jfs_mount.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/jfs/jfs_mount.c b/fs/jfs/jfs_mount.c
index 52e6b58c5dbd..dac822f15070 100644
--- a/fs/jfs/jfs_mount.c
+++ b/fs/jfs/jfs_mount.c
@@ -378,11 +378,12 @@ static int chkSuper(struct super_block *sb)
 	sbi->nbperpage = PSIZE >> sbi->l2bsize;
 	sbi->l2nbperpage = L2PSIZE - sbi->l2bsize;
 	sbi->l2niperblk = sbi->l2bsize - L2DISIZE;
+	uuid_copy(&sbi->uuid, &j_sb->s_uuid);
+
 	if (sbi->mntflag & JFS_INLINELOG)
 		sbi->logpxd = j_sb->s_logpxd;
 	else {
 		sbi->logdev = new_decode_dev(le32_to_cpu(j_sb->s_logdev));
-		uuid_copy(&sbi->uuid, &j_sb->s_uuid);
 		uuid_copy(&sbi->loguuid, &j_sb->s_loguuid);
 	}
 	sbi->fsckpxd = j_sb->s_fsckpxd;
-- 
2.53.0

On 3/1/26 8:55PM, João Paredes wrote:
> The filesystem UUID was only being loaded into super_block sb when an
> external journal device was in use. When mounting without an external
> journal, the UUID remained unset, which prevented the computation of
> a filesystem ID (fsid), which could be confirmed via `stat -f -c "%i"`
> and thus user space could not use fanotify correctly.
> 
> A missing filesystem ID causes fanotify to return ENODEV when marking
> the filesystem for events like FAN_CREATE, FAN_DELETE, FAN_MOVED_TO,
> and FAN_MOVED_FROM. As a result, applications relying on fanotify
> could not monitor these events on JFS filesystems without an external
> journal.
> 
> Moved the UUID initialization so it is always performed during mount,
> ensuring the superblock UUID is consistently available.
> 
> Signed-off-by: João Paredes <joaommp@yahoo.com>

Applied to jfs-next.

Thanks!
Shaggy

> ---
>   fs/jfs/jfs_mount.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/jfs/jfs_mount.c b/fs/jfs/jfs_mount.c
> index 52e6b58c5dbd..dac822f15070 100644
> --- a/fs/jfs/jfs_mount.c
> +++ b/fs/jfs/jfs_mount.c
> @@ -378,11 +378,12 @@ static int chkSuper(struct super_block *sb)
>   	sbi->nbperpage = PSIZE >> sbi->l2bsize;
>   	sbi->l2nbperpage = L2PSIZE - sbi->l2bsize;
>   	sbi->l2niperblk = sbi->l2bsize - L2DISIZE;
> +	uuid_copy(&sbi->uuid, &j_sb->s_uuid);
> +
>   	if (sbi->mntflag & JFS_INLINELOG)
>   		sbi->logpxd = j_sb->s_logpxd;
>   	else {
>   		sbi->logdev = new_decode_dev(le32_to_cpu(j_sb->s_logdev));
> -		uuid_copy(&sbi->uuid, &j_sb->s_uuid);
>   		uuid_copy(&sbi->loguuid, &j_sb->s_loguuid);
>   	}
>   	sbi->fsckpxd = j_sb->s_fsckpxd;