Re: [PATCH v4 08/15] fanotify: enable FAN_REPORT_FID init flag

[Matthew Bobrowski <mbobrowski@mbobrowski.org>]

On Mon, Dec 10, 2018 at 05:20:38PM +0100, Jan Kara wrote:
> On Sat 08-12-18 11:26:38, Amir Goldstein wrote:
> > On Sun, Dec 2, 2018 at 1:38 PM Amir Goldstein <amir73il@gmail.com> wrote:
> > >
> > > When setting up an fanotify listener, user may request to get fid
> > > information in event instead of an open file descriptor.
> > >
> > > The fid obtained with event on a watched object contains the file
> > > handle returned by name_to_handle_at(2) and fsid returned by statfs(2).
> > >
> > > When setting a mark, we need to make sure that the filesystem
> > > supports encoding file handles with name_to_handle_at(2) and that
> > > statfs(2) encodes a non-zero fsid.
> > >
> > 
> > Jan,
> > 
> > On a discussion with Matthew about tests he is writing for FAN_REPORT_TID,
> > the issue of permission events came up.
> > Since I am not aware of any specific benefit that FAN_REPORT_TID could
> > bring to users of permission events, I think the best course of action is to
> > limit the use of FAN_REPORT_TID to group with priority FAN_CLASS_NOTIF.
> > That would simplify tests and man page and if we ever see a use case for
> > anything else, we can add that in the future.
> > 
> > If you agree, we should add something like this to this patch:
> 
> Yeah, that's a good point. Agreed.

OK, good to know. I will continue to write the FAN_REPORT_FID tests based on
Amir's fanotify_dirent branch, which contains the amendment suggested below. 

Amir, presumably we should also have a separate test that covers the expected
error result when FAN_REPORT_FID is supplied with invalid class bits? 

> > --- a/fs/notify/fanotify/fanotify_user.c
> > +++ b/fs/notify/fanotify/fanotify_user.c
> > @@ -768,6 +768,10 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int,
> > flags, unsigned int, event_f_flags)
> >                 return -EINVAL;
> >         }
> > 
> > +       if ((flags & FAN_REPORT_FID) &&
> > +           (flags & FANOTIFY_CLASS_BITS) != FAN_CLASS_NOTIF)
> > +               return -EINVAL;
> > +
> >         user = get_current_user();
> >         if (atomic_read(&user->fanotify_listeners) >
> > FANOTIFY_DEFAULT_MAX_LISTENERS) {
> >                 free_uid(user);

-- 
Matthew Bobrowski