From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from shards.monkeyblade.net ([184.105.139.130]:59648 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754026AbeCRUai (ORCPT ); Sun, 18 Mar 2018 16:30:38 -0400 Date: Sun, 18 Mar 2018 16:30:36 -0400 (EDT) Message-Id: <20180318.163036.2130452319233778270.davem@davemloft.net> To: john.fastabend@gmail.com Cc: davejwatson@fb.com, daniel@iogearbox.net, ast@kernel.org, netdev@vger.kernel.org Subject: Re: [bpf-next PATCH v3 06/18] bpf: sockmap, add bpf_msg_apply_bytes() helper From: David Miller In-Reply-To: <20180318195715.14466.28900.stgit@john-Precision-Tower-5810> References: <20180318195501.14466.25366.stgit@john-Precision-Tower-5810> <20180318195715.14466.28900.stgit@john-Precision-Tower-5810> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org List-ID: From: John Fastabend Date: Sun, 18 Mar 2018 12:57:15 -0700 > A single sendmsg or sendfile system call can contain multiple logical > messages that a BPF program may want to read and apply a verdict. But, > without an apply_bytes helper any verdict on the data applies to all > bytes in the sendmsg/sendfile. Alternatively, a BPF program may only > care to read the first N bytes of a msg. If the payload is large say > MB or even GB setting up and calling the BPF program repeatedly for > all bytes, even though the verdict is already known, creates > unnecessary overhead. > > To allow BPF programs to control how many bytes a given verdict > applies to we implement a bpf_msg_apply_bytes() helper. When called > from within a BPF program this sets a counter, internal to the > BPF infrastructure, that applies the last verdict to the next N > bytes. If the N is smaller than the current data being processed > from a sendmsg/sendfile call, the first N bytes will be sent and > the BPF program will be re-run with start_data pointing to the N+1 > byte. If N is larger than the current data being processed the > BPF verdict will be applied to multiple sendmsg/sendfile calls > until N bytes are consumed. > > Note1 if a socket closes with apply_bytes counter non-zero this > is not a problem because data is not being buffered for N bytes > and is sent as its received. > > Signed-off-by: John Fastabend Acked-by: David S. Miller