linux-kernel - Re: [PATCH v2 3/5] mm: userfaultfd: combine 'mode' and 'wp

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Date:   Thu, 23 Feb 2023 09:31:26 -0800
From:   James Houghton <jthoughton@...gle.com>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
        Muchun Song <muchun.song@...ux.dev>,
        Nadav Amit <namit@...are.com>, Peter Xu <peterx@...hat.com>,
        Shuah Khan <shuah@...nel.org>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 3/5] mm: userfaultfd: combine 'mode' and 'wp_copy' arguments

On Wed, Feb 22, 2023 at 4:58 PM Axel Rasmussen <axelrasmussen@...gle.com> wrote:
>
> Many userfaultfd ioctl functions take both a 'mode' and a 'wp_copy'
> argument. In future commits we plan to plumb the flags through to more
> places, so we'd be proliferating the very long argument list even
> further.
>
> Let's take the time to simplify the argument list. Combine the two
> arguments into one - and generalize, so when we add more flags in the
> future, it doesn't imply more function arguments.
>
> Since the modes (copy, zeropage, continue) are mutually exclusive, store
> them as an integer value (0, 1, 2) in the low bits. Place combine-able
> flag bits in the high bits.
>
> Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>

Acked-by: James Houghton <jthoughton@...gle.com>

I don't see anything wrong with this patch. Thanks, Axel.