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

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Message-ID: <20220425203249.GA5814@altlinux.org>
Date:   Mon, 25 Apr 2022 23:32:49 +0300
From:   "Dmitry V. Levin" <ldv@...linux.org>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
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,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 2/6] userfaultfd: add /dev/userfaultfd for fine
 grained access control

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