From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f65.google.com ([209.85.160.65]:38903 "EHLO mail-pl0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751714AbeCOV7t (ORCPT ); Thu, 15 Mar 2018 17:59:49 -0400 Received: by mail-pl0-f65.google.com with SMTP id m22-v6so4630755pls.5 for ; Thu, 15 Mar 2018 14:59:48 -0700 (PDT) Subject: Re: [bpf-next PATCH v2 06/18] bpf: sockmap, add bpf_msg_apply_bytes() helper To: Alexei Starovoitov Cc: davem@davemloft.net, ast@kernel.org, daniel@iogearbox.net, davejwatson@fb.com, netdev@vger.kernel.org References: <20180312192034.8039.70022.stgit@john-Precision-Tower-5810> <20180312192334.8039.98220.stgit@john-Precision-Tower-5810> <20180315214554.2gspfp255qqxbjcb@ast-mbp> From: John Fastabend Message-ID: Date: Thu, 15 Mar 2018 14:59:33 -0700 MIME-Version: 1.0 In-Reply-To: <20180315214554.2gspfp255qqxbjcb@ast-mbp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org List-ID: On 03/15/2018 02:45 PM, Alexei Starovoitov wrote: > On Mon, Mar 12, 2018 at 12:23:34PM -0700, John Fastabend wrote: >> 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. >> >> Note2 if this is operating in the sendpage context the data >> pointers may be zeroed after this call if the apply walks beyond >> a msg_pull_data() call specified data range. (helper implemented >> shortly in this series). > > instead of 'shortly in this seris' you meant 'implemented earlier'? > patch 5 handles it, but it's set here, right? > Yep just a hold-over from an earlier patch description. I'll remove that entire note2 and fixup a couple small things Daniel noticed with a v3. > The semantics of the helper looks great. > Great!