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List:       linux-api
Subject:    Re: [PATCH 2/2] fanotify: Add pidfd support to the fanotify API
From:       Matthew Bobrowski <repnop () google ! com>
Date:       2021-04-28 22:53:31
Message-ID: YInna8fT/WfUkV6+ () google ! com
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On Tue, Apr 27, 2021 at 08:14:05AM +0300, Amir Goldstein wrote:
> On Tue, Apr 27, 2021 at 6:35 AM Matthew Bobrowski <repnop@google.com> wrote:
> >
> > On Mon, Apr 26, 2021 at 02:11:30PM +0300, Amir Goldstein wrote:
> > > > Amir, I was just thinking about this a little over the weekend and I
> > > > don't think we discussed how to handle the FAN_REPORT_PIDFD |
> > > > FAN_REPORT_FID and friends case? My immediate thought is to make
> > > > FAN_REPORT_PIDFD mutually exclusive with FAN_REPORT_FID and friends,
> > > > but then again receiving a pidfd along with FID events may be also
> > > > useful for some? What are your thoughts on this? If we don't go ahead
> > > > with mutual exclusion, then this multiple event types alongside struct
> > > > fanotify_event_metadata starts getting a little clunky, don't you
> > > > think?
> > > >
> > >
> > > The current format of an fanotify event already supports multiple info records:
> > >
> > > [fanotify_event_metadata]
> > > [[fanotify_event_info_header][event record #1]]
> > > [[fanotify_event_info_header][event record #2]]...
> > >
> > > (meta)->event_len is the total event length including all info records.
> > >
> > > For example, FAN_REPORT_FID | FAN_REPORT_DFID_MAME produces
> > > (for some events) two info records, one FAN_EVENT_INFO_TYPE_FID
> > > record and one FAN_EVENT_INFO_TYPE_DFID_NAME record.
> >
> > Ah, that's right! I now remember reviewing some patches associated
> > with the FID change series which mentioned the possibility of
> > receiving multiple FID info records. As the implementation currently
> > stands, AFAIK there's not possibility for fanotify to ever return more
> > than two info records, right?
> >
> > Is there any preference in terms of whether the new FAN_REPORT_PIDFD
> > info records precede or come after FAN_REPORT_FID/FAN_REPORT_DFID_NAME
> > info records in FAN_REPORT_FID or FAN_REPORT_FID |
> > FAN_REPORT_DFID_NAME configurations?
>
> Doesn't matter.

OK, fair.

> Your typical application would first filter by pid/pidfd and only if process
> matches the filters would it care to examine the event fid info, correct?

Not necessarily, but you're right, the ordering doesn't really matter
too much.

/M
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