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From:   Ilya Dryomov <idryomov@gmail.com>
Date:   Mon, 26 Jun 2023 23:01:37 +0200
Message-ID: <CAOi1vP8nbP93SyjhN4uJDaKEFKmsBcOKH6iGjpt3Qbj8n7CapQ@mail.gmail.com>
Subject: Re: [PATCH net-next] libceph: Partially revert changes to support MSG_SPLICE_PAGES
To:     David Howells <dhowells@redhat.com>
Cc:     netdev@vger.kernel.org, Xiubo Li <xiubli@redhat.com>,
        Jeff Layton <jlayton@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Matthew Wilcox <willy@infradead.org>,
        ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org
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On Mon, Jun 26, 2023 at 10:44=E2=80=AFPM David Howells <dhowells@redhat.com=
> wrote:
>
> Ilya Dryomov <idryomov@gmail.com> wrote:
>
> >   if (sendpage_ok(bv.bv_page))
> >           msg.msg_flags |=3D MSG_SPLICE_PAGES;
> >   else
> >           msg.msg_flags &=3D ~MSG_SPLICE_PAGES;
>
> Hmmm...  I'm not sure there's any guarantee that msg, including msg_flags=
,
> won't get altered by ->sendmsg().

If this is indeed an issue, do_sendmsg() should be fixed too.  I would
like to avoid having do_try_sendpage() do one thing and do_sendmsg() do
something subtly different.

But then, even with the current patch, only msg_flags is reinitialized
on the next loop iteration, not the entire message.  Should the entire
message be reinitialized?

Thanks,

                Ilya