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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 D854CC169C4 for ; Fri, 8 Feb 2019 22:08:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AFBF421924 for ; Fri, 8 Feb 2019 22:08:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726997AbfBHWIl (ORCPT ); Fri, 8 Feb 2019 17:08:41 -0500 Received: from mail.kernel.org ([198.145.29.99]:57690 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726788AbfBHWIl (ORCPT ); Fri, 8 Feb 2019 17:08:41 -0500 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1E09A20811; Fri, 8 Feb 2019 22:08:40 +0000 (UTC) Date: Fri, 8 Feb 2019 17:08:38 -0500 From: Steven Rostedt To: Tzvetomir Stoyanov Cc: linux-trace-devel@vger.kernel.org Subject: Re: [PATCH v3 3/7] trace-cmd: Fixed logic in tracecmd_read_page_record() Message-ID: <20190208170838.5f0faa1f@gandalf.local.home> In-Reply-To: <20190208134918.5618-4-tstoyanov@vmware.com> References: <20190208134918.5618-1-tstoyanov@vmware.com> <20190208134918.5618-4-tstoyanov@vmware.com> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-trace-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-trace-devel@vger.kernel.org On Fri, 8 Feb 2019 15:49:14 +0200 Tzvetomir Stoyanov wrote: > Fixed the logic in tracecmd_read_page_record() when > searching for the next event in the event from the > ring buffer. In the current logic, in the case when > last_record is not NULL (we are searching for the second one) > the check "if (ptr != last_record->data)" always fails. > Nice catch. Let's change the change log and subject: Subject trace-cmd: Fix tracecmd_read_page_record() to read more than one event The kbuffer_next_event() will return the next event on the sub buffer. If we pass in the last_record to tracecmd_read_page_record(), it initializes the sub buffer, and by calling kbuffer_next_event() (instead of kbuffer_read_event()), the second event on the sub buffer is returned. This causes the match of the last_record not to match if the last_record happens to be the first event on the sub buffer. > Signed-off-by: Tzvetomir Stoyanov > --- > lib/trace-cmd/trace-input.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/lib/trace-cmd/trace-input.c b/lib/trace-cmd/trace-input.c > index 33ad7d1..5d64ca8 100644 > --- a/lib/trace-cmd/trace-input.c > +++ b/lib/trace-cmd/trace-input.c > @@ -1688,18 +1688,22 @@ tracecmd_read_page_record(struct tep_handle *pevent, void *page, int size, > goto out_free; > } > > - do { > + ptr = kbuffer_read_event(kbuf, &ts); > + while (ptr < last_record->data) { > ptr = kbuffer_next_event(kbuf, NULL); > if (!ptr) > break; > - } while (ptr < last_record->data); > + if (ptr == last_record->data) > + break; > + } > if (ptr != last_record->data) { > warning("tracecmd_read_page_record: could not find last_record"); > goto out_free; > } > - } > + ptr = kbuffer_next_event(kbuf, &ts); > + } else > + ptr = kbuffer_read_event(kbuf, &ts); > > - ptr = kbuffer_read_event(kbuf, &ts); Also, instead of the above "} else" clause, we can just move the ptr = kbuffer_read_event(kbuf, &ts); before the if condition testing last_record. -- Steve > if (!ptr) > goto out_free; >