netdev - Re: [PATCH net-next v3 01/18] net: Copy slab data for sendmsg(MSG_SPLICE

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Date: Fri, 23 Jun 2023 10:08:18 +0100
From: David Howells <dhowells@...hat.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: dhowells@...hat.com, Eric Dumazet <edumazet@...gle.com>,
    netdev@...r.kernel.org, Alexander Duyck <alexander.duyck@...il.com>,
    "David S. Miller" <davem@...emloft.net>,
    Paolo Abeni <pabeni@...hat.com>,
    Willem de Bruijn <willemdebruijn.kernel@...il.com>,
    David Ahern <dsahern@...nel.org>,
    Matthew Wilcox <willy@...radead.org>, Jens Axboe <axboe@...nel.dk>,
    linux-mm@...ck.org, linux-kernel@...r.kernel.org,
    Menglong Dong <imagedong@...cent.com>
Subject: Re: [PATCH net-next v3 01/18] net: Copy slab data for sendmsg(MSG_SPLICE_PAGES)

Jakub Kicinski <kuba@...nel.org> wrote:

> If we can't reach instant agreement --
> can you strategically separate out the minimal set of changes required
> to just kill MSG_SENDPAGE_NOTLAST. IMHO it's worth getting that into
> 6.5.

Paolo Abeni <pabeni@...hat.com> wrote:

> Given all the above, and the late stage of the current devel cycle,
> would you consider slicing down this series to just kill
> MSG_SENDPAGE_NOTLAST, as Jakub suggested?

I could do that.

There is also another alternative.  I could just push the sendpage wrappers up
the stack into the higher-level callers.  Basically this:

int udp_sendpage(struct sock *sk, struct page *page, int offset,
		 size_t size, int flags)
{
	struct bio_vec bvec;
	struct msghdr msg = { .msg_flags = flags | MSG_SPLICE_PAGES };

	if (flags & MSG_SENDPAGE_NOTLAST)
		msg.msg_flags |= MSG_MORE;

	bvec_set_page(&bvec, page, size, offset);
	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);
	return udp_sendmsg(sk, &msg, size);
}

and kill off sendpage and MSG_SENDPAGE_NOTLAST.

David