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 X-Spam-Level: X-Spam-Status: No, score=-9.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 491B9C2B9F4 for ; Fri, 25 Jun 2021 13:17:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2290461963 for ; Fri, 25 Jun 2021 13:17:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231405AbhFYNTj (ORCPT ); Fri, 25 Jun 2021 09:19:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41234 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230151AbhFYNTi (ORCPT ); Fri, 25 Jun 2021 09:19:38 -0400 Received: from mail-wm1-x334.google.com (mail-wm1-x334.google.com [IPv6:2a00:1450:4864:20::334]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B9086C061574 for ; Fri, 25 Jun 2021 06:17:17 -0700 (PDT) Received: by mail-wm1-x334.google.com with SMTP id o35-20020a05600c5123b02901e6a7a3266cso3436344wms.1 for ; Fri, 25 Jun 2021 06:17:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=jMnrxOarW2WsI7LAJ6IVtiCjQzECm0F5WAlu5kIUqiU=; b=rJG58dPIzcSEpKxo/rE6kJvXz9NG9Yj4sWLSW9rtBtWXCbX6q3gH5KU/A4bgRSIN6V vh4g0/EblNqD8RWT1K0JCuu570RrMwRzh8C42miUkT1hU8UGmxW5+4T1Zek2WRnXsjGm GOG8emNqydgXpOjk3oq8vLL67CLWXfKIY/J7dJqQPEoDxs1wdxoxw/6Fr5s5JUldEFAT pXBH/nxqUL7ggLXnPDciycsbcnnVbufW6dO63g3qFFVHoAR3B3BpuRLBkpjH6dTaaIEJ o3k4N2l2SasERLkfLzLzDbNtxINK5mgZgpYJYQ1epb/KC0AhIlWyTfb6CezYEGudvS09 +yuw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=jMnrxOarW2WsI7LAJ6IVtiCjQzECm0F5WAlu5kIUqiU=; b=thMzK8k1QVj6KI9N7ElWGjmqbamfN5lTYS0V2ZlXrgryYL0xAFbFzgiThkEz2nhSb9 NuJ1a7/NACa2kU3xbZlXg2iTRowkRNFR5zlT+kN/31+3IhEy6hazUdrIK1u7v3cJVncn AmA9sDdwdYFHoiXYmLlbpBYrnk1DvBgjoPJoZdZHWFjmQ/eiK2gj7/yS3J1TSFC4sz7K Zn8zSJoMb3XrhCupObo+dzeXimm3Jf59TuF33cxQSSPHlG53nBCQ4baEdhtW5QK4ChKw xBSByjpw+ohZRgFmEfknfe/XJy/z4ogZDMrmfQ5cT7dhZxEJhaTTQCZINLORgNvD0dgZ 5qvQ== X-Gm-Message-State: AOAM533jeMJRiVKLa/p6hCMMwDK2a6j170eMMwECcP/sbSAhCzlwnYL7 UAxR6zXUsvuvEhEPToWo6h46LT/K8l4= X-Google-Smtp-Source: ABdhPJyv8Gg1Jm87fd1MuvOEC2HvwJM/nhk55SgRUFvmXlF88QkNRcMISGHtjgDEqSBiKw0jorvPPg== X-Received: by 2002:a05:600c:3b28:: with SMTP id m40mr10528138wms.99.1624627036163; Fri, 25 Jun 2021 06:17:16 -0700 (PDT) Received: from [10.93.98.252] ([146.247.46.131]) by smtp.gmail.com with ESMTPSA id c8sm5914819wri.91.2021.06.25.06.17.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Jun 2021 06:17:15 -0700 (PDT) Subject: Re: [PATCH v3] libtracefs: Add APIs for data streaming To: Steven Rostedt Cc: linux-trace-devel@vger.kernel.org References: <20210624145101.87233-1-y.karadz@gmail.com> <20210624124542.5ca75fe3@oasis.local.home> From: Yordan Karadzhov Message-ID: <835ff5f9-5fed-0dfb-2d75-dd9158fb63a7@gmail.com> Date: Fri, 25 Jun 2021 16:17:14 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210624124542.5ca75fe3@oasis.local.home> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-trace-devel@vger.kernel.org On 24.06.21 г. 19:45, Steven Rostedt wrote: > On Thu, 24 Jun 2021 17:51:01 +0300 > "Yordan Karadzhov (VMware)" wrote: > >> The new APIs can be used to dump the content of "trace_pipe" into a >> file or directly to "stdout". The "splice" system call is used to >> moves the data without copying. The new functionality is essentially >> identical to what 'trace-cmd show -p' does. >> >> Signed-off-by: Yordan Karadzhov (VMware) >> > > So I did some investigations here, and found that splice() is not > guaranteed to work on a terminal output. > > To overcome this, I decided to have the print create another pipe, and > pass that to the stream code. The if something was read, it would read > the pipe. > > It required changing the return of the functions to return the amount > transferred, so that I can differentiate between "EOF" with nothing > read, and something read. Because I couldn't get the pipe to not block > on read if there was no content in it. :-/ > > Anyway, I submitted a v4 with the changes I made, and it appears to > work. I haven't tested it that much, so it may still have bugs. > Hi Steve, I tested v4 of the patch that you submitted and it doesn't work correct in my use case. Also it seems greatly over-complicated to me. Note that when you call tracefs_trace_pipe_stream() inside a loop you will keep opening and closing the "trace_pipe" and the pipe over and over again. See the example code below. Is this what you are aiming? Also is this guaranteed to always work? Thanks! Yordan #define _GNU_SOURCE #include #include #include #include #include #include volatile bool keep_going = true; static void finish(int sig) { keep_going = false; } int main(int argc, char **argv) { int splice_flags = SPLICE_F_MORE | SPLICE_F_MOVE; int brass1[2], brass2[2], fd, ret; char buf[BUFSIZ]; signal(SIGINT, finish); fd = open(argv[1], O_RDONLY); if (fd < 0) { perror("open"); return 1; } if (pipe(brass1) < 0){ perror("pipe A"); return 1; } if (pipe(brass2) < 0){ perror("pipe B"); return 1; } errno = 0; while (keep_going) { ret = splice(fd, NULL, brass1[1], NULL, BUFSIZ, splice_flags); if (ret < 0) { perror("splice A"); return 1; } ret = splice(brass1[0], NULL, brass2[1], NULL, BUFSIZ, splice_flags); if (ret < 0) { perror("splice B"); return 1; } ret = read(brass2[0], buf, BUFSIZ); if (ret < 0) { perror("read"); return 1; } ret = write(STDOUT_FILENO, buf, ret); if (ret < 0) { perror("write"); return 1; } } close(fd); close(brass1[0]); close(brass1[1]); close(brass2[0]); close(brass2[1]); return 0; } > We could optimize it to just use the splice output first (stream > first), and if that returns with EINVAL, which is the expected error on > a non functioning stdout, we could then switch to this alternate method. > > Although, the stream would have read some of the pipe and lost the > data, which is not what we want, so a test of stdout would need to be > made with splice first. :-/ > > -- Steve >