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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 363ABC43603 for ; Mon, 9 Dec 2019 09:35:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 078262073D for ; Mon, 9 Dec 2019 09:35:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727494AbfLIJfT (ORCPT ); Mon, 9 Dec 2019 04:35:19 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:38054 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727160AbfLIJfT (ORCPT ); Mon, 9 Dec 2019 04:35:19 -0500 Received: from localhost ([127.0.0.1] helo=vostro.local) by Galois.linutronix.de with esmtp (Exim 4.80) (envelope-from ) id 1ieFRV-0005eV-BF; Mon, 09 Dec 2019 10:35:01 +0100 From: John Ogness To: Sergey Senozhatsky Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Petr Mladek , Steven Rostedt , Linus Torvalds , Greg Kroah-Hartman , Andrea Parri , Thomas Gleixner , Sergey Senozhatsky , Brendan Higgins , kexec@lists.infradead.org Subject: Re: [RFC PATCH v5 1/3] printk-rb: new printk ringbuffer implementation (writer) References: <20191128015235.12940-1-john.ogness@linutronix.de> <20191128015235.12940-2-john.ogness@linutronix.de> <20191209092756.GH88619@google.com> Date: Mon, 09 Dec 2019 10:34:59 +0100 In-Reply-To: <20191209092756.GH88619@google.com> (Sergey Senozhatsky's message of "Mon, 9 Dec 2019 18:27:56 +0900") Message-ID: <87muc1zvss.fsf@linutronix.de> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019-12-09, Sergey Senozhatsky wrote: >> + * Sample reader code:: >> + * >> + * struct printk_info info; >> + * char text_buf[32]; >> + * char dict_buf[32]; >> + * u64 next_seq = 0; >> + * struct printk_record r = { >> + * .info = &info, >> + * .text_buf = &text_buf[0], >> + * .dict_buf = &dict_buf[0], >> + * .text_buf_size = sizeof(text_buf), >> + * .dict_buf_size = sizeof(dict_buf), >> + * }; >> + * >> + * while (prb_read_valid(&rb, next_seq, &r)) { >> + * if (info.seq != next_seq) >> + * pr_warn("lost %llu records\n", info.seq - next_seq); >> + * >> + * if (info.text_len > r.text_buf_size) { >> + * pr_warn("record %llu text truncated\n", info.seq); >> + * text_buf[sizeof(text_buf) - 1] = 0; >> + * } >> + * >> + * if (info.dict_len > r.dict_buf_size) { >> + * pr_warn("record %llu dict truncated\n", info.seq); >> + * dict_buf[sizeof(dict_buf) - 1] = 0; >> + * } >> + * >> + * pr_info("%llu: %llu: %s;%s\n", info.seq, info.ts_nsec, >> + * &text_buf[0], info.dict_len ? &dict_buf[0] : ""); >> + * >> + * next_seq = info.seq + 1; >> + * } >> + */ > > Will this loop ever end? :) > > pr_info() adds data to ringbuffer, which prb_read_valid() reads, so > pr_info() can add more data, which prb_read_valid() will read, so > pr_info()... The sample code is assuming that @rb is not the same ringbuffer used by kernel/printk/printk.c. (For example, the test module is doing that to stress test the ringbuffer code without actually affecting printk.) I can add a sentence to clarify that. John Ogness