Re: Kernel bugzilla 198569: fanotify_mark() and FAN_Q_OVERFLOW

["Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>]

Hello Amir, Jan,

On Thu, 23 Apr 2020 at 14:19, Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Thu, Apr 23, 2020 at 2:23 PM Jan Kara <jack@suse.cz> wrote:
> >
> > Hi Michael!
> >
> > On Thu 23-04-20 12:36:26, Michael Kerrisk (man-pages) wrote:
> > > Would you be able to take a look at
> > > https://bugzilla.kernel.org/show_bug.cgi?id=198569
> > >
> > > It relates to some text you added to the fanotify_mark(2) manual page:
> > >
> > >        FAN_Q_OVERFLOW
> > >               Create an event when an overflow of the event queue occurs.
> > >               The size of the event queue is limited to 16384 entries  if
> > >               FAN_UNLIMITED_QUEUE is not set in fanotify_init(2).
> > >
> > > This was in the following commit
> > >
> > > [[
> > > commit 5d730f864a6603b090cd1078668cede05d02b8c4
> > > Author: Heinrich Schuchardt <xypron.glpk@gmx.de>
> > > Date:   Tue Nov 8 23:13:38 2016 +0100
> > >
> > >     fanotify_mark.2: Mention FAN_Q_OVERFLOW
> > >
> > >     To receive overflow events it is necessary to set this bit
> > >     in fanotify_mark().
> > > ]]
> > >
> > > As far as I can see, FAN_Q_OVERFLOW (test program, reading the kernel
> > > source) is only an output flag. But on the other hand, I know you are
> > > generally careful, so I wonder if something changed (though, at a
> > > quick glance, I could not see evidence that it has).
> >
> > Yeah, the manpage is wrong AFAICT. FAN_Q_OVERFLOW is not accepted in the
> > input mask. It is only output event flag.
> >
>
> Right.
>
> Note that fanotify.7 documents FAN_Q_OVERFLOW as part of event output mask
> so perhaps the FAN_Q_OVERFLOW entry for fanotify_mark.2 input mask should
> just be removed?

Yes, I'll just remove that piece from fanotify_mark.2.
>
> Similarly, the input only flag FAN_EVENT_ON_CHILD is documented in
> fanotify_mark.2, but not in fanotify.7.
>
> FAN_ONDIR has been input only until v5.1 and since then it can also be
> in output mask for group with FAN_REPORT_FID.
> This is documented in fanotify_mark.2, but not in fanotify.7.

I'm overlooking something: where is this detail documented in
fanotify_mark.2? (I mean, I see mention of FAN_ONDIR, but no mention
of a change in v5.1.)

And would you be willing to write a small patch for fanotify.7 :-) ?

Thanks,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/