Re: [PATCH v9 24/31] fanotify: Report fid entry even for zero-length file_handle

On Mon, Oct 25, 2021 at 10:30 PM Gabriel Krisman Bertazi
[off-list ref] wrote:

Non-inode errors will reported with an empty file_handle.  In
preparation for that, allow some events to print the FID record even if
there isn't any file_handle encoded

Even though FILEID_ROOT is used internally, make zero-length file
handles be reported as FILEID_INVALID.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Gabriel Krisman Bertazi <redacted>

---
Changes since v8:
  - Move fanotify_event_has_object_fh check here (jan)

Logically, this move is wrong, because after this patch,
copy_fid_info_to_user() can theoretically be called with NULL fh in the
existing construct of:
  if (fanotify_event_has_object_fh(event)) {
  ...
    ret = copy_fid_info_to_user(fanotify_event_fsid(event),

fanotify_event_object_fh(event),

The thing that prevents this case in effect is that FAN_FS_ERROR
is not yet wired, but I am not sure if leaving this theoretic bisect
issue is a good idea.

Anyway, that's a very minor theoretic issue and I am sure Jan can
decide whether to deal with it and how (no need to post v10 IMO).

Thanks,
Amir.