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

- From: Amir Goldstein \<amir73il@gmail.com\>
- Date: 2021-08-13 08:00:07 
- List: linux-ext4
- Page: https://ratatoskr.run/linux-ext4/2021/08/212336
- Thread: https://ratatoskr.run/linux-api/2021/08/212282/t.md

```text
On Fri, Aug 13, 2021 at 12:41 AM Gabriel Krisman Bertazi
[ref] wrote:
>
> 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>

Reviewed-by: Amir Goldstein <amir73il@gmail.com>

> ---
>  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
>
```