shmem: allow reporting fanotify events with file handles on tmpfs

Since kernel v5.1, fanotify_init(2) supports the flag FAN_REPORT_FID
for identifying objects using file handle and fsid in events.

fanotify_mark(2) fails with -ENODEV when trying to set a mark on
filesystems that report null f_fsid in stasfs(2).

Use the digest of uuid as f_fsid for tmpfs to uniquely identify tmpfs
objects as best as possible and allow setting an fanotify mark that
reports events with file handles on tmpfs.

Link: https://lore.kernel.org/r/20210322173944.449469-3-amir73il@gmail.com
Acked-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/mm/shmem.c b/mm/shmem.c
index b2db4ed0fbc7c936b2603dc1a2dfcef3bbeae088..162d8f8993bbf4b8ae49cdc89cc3fb29d6806dd0 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2846,6 +2846,9 @@ static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
                buf->f_ffree = sbinfo->free_inodes;
        }
        /* else leave those fields 0 like simple_statfs */
+
+       buf->f_fsid = uuid_to_fsid(dentry->d_sb->s_uuid.b);
+
        return 0;
 }