linux-kernel - Re: [PATCH] ioctl_userfaultfd.2: Corrections for returned .ioctls members

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Date:   Tue, 22 Mar 2022 09:36:32 -0700
From:   Axel Rasmussen <axelrasmussen@...gle.com>
To:     "Alejandro Colomar (man-pages)" <alx.manpages@...il.com>
Cc:     Peter Xu <peterx@...hat.com>, Ian Abbott <abbotti@....co.uk>,
        linux-man@...r.kernel.org,
        Michael Kerrisk <mtk.manpages@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ioctl_userfaultfd.2: Corrections for returned .ioctls members

On Tue, Mar 22, 2022 at 9:23 AM Axel Rasmussen <axelrasmussen@...gle.com> wrote:
>
> On Tue, Mar 22, 2022 at 5:32 AM Alejandro Colomar (man-pages)
> <alx.manpages@...il.com> wrote:
> >
> > Hi Ian and Peter,
> >
> > On 3/21/22 07:10, Peter Xu wrote:
> > > On Fri, Mar 18, 2022 at 07:13:43PM +0000, Ian Abbott wrote:
> > >> Support for the `UFFDIO_WRITEPROTECT` operation is not indicated in the
> > >> `ioctls` member of `struct uffdio_api`.  It is indicated in the `ioctls`
> > >> member of `struct uffdio_register` along with indications of support for
> > >> the `UFFDIO_COPY`, `UFFDIO_WAKE` and `UFFDIO_ZEROPAGE` operations (and
> > >> also the `UFFDIO_CONTINUE` operation supported since Linux 5.13 but
> > >> that is not documented by this man page yet.)
> > >
> > > I thought it should have landed but indeed it's not.  Copying Axel.
>
> Ah, I mistakenly thought it got merged, but there were a few remaining
> issues Alejandro wanted addressed first. I'll send a v3 of it later
> today.
>
> For what it's worth, as part of adding minor fault handling, we pretty
> significantly change the ioctl field's behavior, and I rewrote a lot
> of the documentation around it. So, it may conflict with this patch.
> :/ Sorry about that.

Heh, I spoke too soon. My patch doesn't touch this after all, I think
the patches don't conflict. :) It's been a while since I looked at
it...

>
> > >
> > >>
> > >> Fixes: f559fa36a678 ("ioctl_userfaultfd.2: Add write-protect mode docs")
> > >> Signed-off-by: Ian Abbott <abbotti@....co.uk>
> >
> > Patch applied.
> >
> > >
> > > The patch looks correct to me, thanks for fixing it.
> > >
> > > Acked-by: Peter Xu <peterx@...hat.com>
> >
> > And tag appended.
> >
> > Thank you both!
> >
> > Alex
> >
> > >
> > >> ---
> > >>   man2/ioctl_userfaultfd.2 | 27 ++++++++++++++++++++-------
> > >>   1 file changed, 20 insertions(+), 7 deletions(-)
> > >>
> > >> diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2
> > >> index 504f61d4b..e930af520 100644
> > >> --- a/man2/ioctl_userfaultfd.2
> > >> +++ b/man2/ioctl_userfaultfd.2
> > >> @@ -235,11 +235,6 @@ operation is supported.
> > >>   The
> > >>   .B UFFDIO_UNREGISTER
> > >>   operation is supported.
> > >> -.TP
> > >> -.B 1 << _UFFDIO_WRITEPROTECT
> > >> -The
> > >> -.B UFFDIO_WRITEPROTECT
> > >> -operation is supported.
> > >>   .PP
> > >>   This
> > >>   .BR ioctl (2)
> > >> @@ -333,8 +328,26 @@ If the operation is successful, the kernel modifies the
> > >>   bit-mask field to indicate which
> > >>   .BR ioctl (2)
> > >>   operations are available for the specified range.
> > >> -This returned bit mask is as for
> > >> -.BR UFFDIO_API .
> > >> +This returned bit mask can contain the following bits:
> > >> +.TP
> > >> +.B 1 << _UFFDIO_COPY
> > >> +The
> > >> +.B UFFDIO_COPY
> > >> +operation is supported.
> > >> +.TP
> > >> +.B 1 << _UFFDIO_WAKE
> > >> +The
> > >> +.B UFFDIO_WAKE
> > >> +operation is supported.
> > >> +.TP
> > >> +.B 1 << _UFFDIO_WRITEPROTECT
> > >> +The
> > >> +.B UFFDIO_WRITEPROTECT
> > >> +.TP
> > >> +.B 1 << _UFFDIO_ZEROPAGE
> > >> +The
> > >> +.B UFFDIO_ZEROPAGE
> > >> +operation is supported.
> > >>   .PP
> > >>   This
> > >>   .BR ioctl (2)
> > >> --
> > >
> >
> > --
> > Alejandro Colomar
> > Linux man-pages comaintainer; http://www.kernel.org/doc/man-pages/
> > http://www.alejandro-colomar.es/