netdev - Re: [PATCH net-next] libceph: Partially revert changes to support MSG_SPLICE

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Date: Mon, 26 Jun 2023 23:01:37 +0200
From: Ilya Dryomov <idryomov@...il.com>
To: David Howells <dhowells@...hat.com>
Cc: netdev@...r.kernel.org, Xiubo Li <xiubli@...hat.com>, 
	Jeff Layton <jlayton@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Jens Axboe <axboe@...nel.dk>, Matthew Wilcox <willy@...radead.org>, ceph-devel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] libceph: Partially revert changes to support MSG_SPLICE_PAGES

On Mon, Jun 26, 2023 at 10:44 PM David Howells <dhowells@...hat.com> wrote:
>
> Ilya Dryomov <idryomov@...il.com> wrote:
>
> >   if (sendpage_ok(bv.bv_page))
> >           msg.msg_flags |= MSG_SPLICE_PAGES;
> >   else
> >           msg.msg_flags &= ~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