From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D6427C636D7 for ; Mon, 13 Feb 2023 09:44:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230421AbjBMJo0 (ORCPT ); Mon, 13 Feb 2023 04:44:26 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53302 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229821AbjBMJoY (ORCPT ); Mon, 13 Feb 2023 04:44:24 -0500 Received: from formenos.hmeau.com (167-179-156-38.a7b39c.syd.nbn.aussiebb.net [167.179.156.38]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D20D7C65B; Mon, 13 Feb 2023 01:44:16 -0800 (PST) Received: from loth.rohan.me.apana.org.au ([192.168.167.2]) by formenos.hmeau.com with smtp (Exim 4.94.2 #2 (Debian)) id 1pRV8C-00AXUe-BO; Mon, 13 Feb 2023 17:28:17 +0800 Received: by loth.rohan.me.apana.org.au (sSMTP sendmail emulation); Mon, 13 Feb 2023 17:28:16 +0800 Date: Mon, 13 Feb 2023 17:28:16 +0800 From: Herbert Xu To: Linus Torvalds Cc: david@fromorbit.com, metze@samba.org, axboe@kernel.dk, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, samba-technical@lists.samba.org Subject: Re: copy on write for splice() from file to pipe? Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Newsgroups: apana.lists.os.linux.kernel Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org Linus Torvalds wrote: > > Ok, so I decided to try to take a look. > > Somebody who actually does networking (and drivers in particular) > should probably check this, but it *looks* like the IPv4 TCP case > (just to pick the ony I looked at) gores through > tcp_sendpage_locked(), which does > > if (!(sk->sk_route_caps & NETIF_F_SG)) > return sock_no_sendpage_locked(sk, page, offset, size, flags); > > which basically says "if you can't handle fragmented socket buffers, > do that 'no_sendpage' case". > > So that will basically end up just falling back to a kernel > 'sendmsg()', which does a copy and then it's stable. > > But for the networks that *can* handle fragmented socket buffers, it > then calls do_tcp_sendpages() instead, which just creates a skb > fragment of the page (with tcp_build_frag()). > > I wonder if that case should just require NETIF_F_HW_CSUM? NETIF_F_SG already depends on checksum offload (either via NETIF_F_HW_CSUM or something else that is equivalent). So are you guys just imagining non-existant problems? Cheers, -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt