# \[PATCH v6 11/21\] fanotify: Allow file handle encoding for unhashed events

- From: Gabriel Krisman Bertazi \<hidden\>
- Date: 2021-08-12 21:41:12 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2021/08/212293
- Thread: https://ratatoskr.run/linux-api/2021/08/212282/t.md

```text
FAN_FS_ERROR will report a file handle, but it is an unhashed event.
Allow passing a NULL hash to fanotify_encode_fh and avoid calculating
the hash if not needed.

Signed-off-by: Gabriel Krisman Bertazi <redacted>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 fs/notify/fanotify/fanotify.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index acf78c0ed219..50fce4fec0d6 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -403,8 +403,12 @@ static int fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode,
 	fh->type = type;
 	fh->len = fh_len;
 
-	/* Mix fh into event merge key */
-	*hash ^= fanotify_hash_fh(fh);
+	/*
+	 * Mix fh into event merge key.  Hash might be NULL in case of
+	 * unhashed FID events (i.e. FAN_FS_ERROR).
+	 */
+	if (hash)
+		*hash ^= fanotify_hash_fh(fh);
 
 	return FANOTIFY_FH_HDR_LEN + fh_len;
 
-- 
2.32.0

```