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From:   Axel Rasmussen <axelrasmussen@google.com>
Date:   Tue, 26 Apr 2022 09:00:26 -0700
Message-ID: <CAJHvVchLSpbKXn6u451pjaRpW=SwbOFSdpQpaC47WBFa0660xw@mail.gmail.com>
Subject: Re: [PATCH v2 2/6] userfaultfd: add /dev/userfaultfd for fine grained
 access control
To:     "Dmitry V. Levin" <ldv@altlinux.org>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Charan Teja Reddy <charante@codeaurora.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>,
        Hugh Dickins <hughd@google.com>, Jan Kara <jack@suse.cz>,
        Jonathan Corbet <corbet@lwn.net>,
        Mel Gorman <mgorman@techsingularity.net>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@kernel.org>, Nadav Amit <namit@vmware.com>,
        Peter Xu <peterx@redhat.com>, Shuah Khan <shuah@kernel.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        zhangyi <yi.zhang@huawei.com>, linux-api@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        Linuxkselftest <linux-kselftest@vger.kernel.org>
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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@altlinux.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