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

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Date:   Thu, 23 Feb 2023 11:03:58 -0800
From:   Axel Rasmussen <axelrasmussen@...gle.com>
To:     Nadav Amit <namit@...are.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>,
        Peter Xu <peterx@...hat.com>, Shuah Khan <shuah@...nel.org>,
        James Houghton <jthoughton@...gle.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v2 3/5] mm: userfaultfd: combine 'mode' and 'wp_copy' arguments

On Thu, Feb 23, 2023 at 10:51 AM Nadav Amit <namit@...are.com> wrote:
>
>
>
> > On Feb 22, 2023, at 4:57 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>
>
> Hi Axel,
>
> I sent a patch a long time ago called “userfaultfd: introduce uffd_flags”.
> For some reason it does not appear on lore, but you were a recipient.
>
> It was pretty similar, but one thing that I preferred in my version is
> that it defined a different type to avoid confusion. Since “flags” is
> a very generic name, perhaps you’d like to adapt this approach.

Oh! I must have missed it, or just forgot. I'll take a look and see
about making some improvements. I'll also be sure to credit you in the
commit message.

>