linux-kernel - Re: [PATCH v2 2/6] userfaultfd: add /dev/userfaultfd for fine grained access control

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Date:   Tue, 26 Apr 2022 09:00:26 -0700
From:   Axel Rasmussen <axelrasmussen@...gle.com>
To:     "Dmitry V. Levin" <ldv@...linux.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Charan Teja Reddy <charante@...eaurora.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Gleb Fotengauer-Malinovskiy <glebfm@...linux.org>,
        Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
        Peter Xu <peterx@...hat.com>, Shuah Khan <shuah@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        zhangyi <yi.zhang@...wei.com>, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Linuxkselftest <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v2 2/6] userfaultfd: add /dev/userfaultfd for fine grained
 access control

You're right, [1] says _IO is appropriate for ioctls which only take
an integer argument. I'll send a v3 with this fix, although I might
wait a bit for any other review comments before doing so. Thanks for
taking a look!

https://www.kernel.org/doc/html/latest/driver-api/ioctl.html

On Mon, Apr 25, 2022 at 1:32 PM Dmitry V. Levin <ldv@...linux.org> wrote:
>
> On Fri, Apr 22, 2022 at 02:29:41PM -0700, Axel Rasmussen wrote:
> [...]
> > --- a/include/uapi/linux/userfaultfd.h
> > +++ b/include/uapi/linux/userfaultfd.h
> > @@ -12,6 +12,10 @@
> >
> >  #include <linux/types.h>
> >
> > +/* ioctls for /dev/userfaultfd */
> > +#define USERFAULTFD_IOC 0xAA
> > +#define USERFAULTFD_IOC_NEW _IOWR(USERFAULTFD_IOC, 0x00, int)
>
> Why this new ioctl is defined using _IOWR()?  Since it neither reads from
> user memory nor writes into user memory, it should rather be defined using
> _IO(), shouldn't it?
>
>
> --
> ldv