From patchwork Thu Sep 22 08:40:45 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= X-Patchwork-Id: 673231 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3sfr7K0kMMz9sC7 for ; Thu, 22 Sep 2016 19:00:45 +1000 (AEST) Received: from localhost ([::1]:32906 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bmzs2-0003l3-IT for incoming@patchwork.ozlabs.org; Thu, 22 Sep 2016 05:00:42 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55162) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bmzZG-0001iS-1r for qemu-devel@nongnu.org; Thu, 22 Sep 2016 04:41:18 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bmzZC-000733-K7 for qemu-devel@nongnu.org; Thu, 22 Sep 2016 04:41:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43922) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bmzZC-00072w-EG for qemu-devel@nongnu.org; Thu, 22 Sep 2016 04:41:14 -0400 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id EAF3F8F29E; Thu, 22 Sep 2016 08:41:13 +0000 (UTC) Received: from t530wlan.home.berrange.com.com (vpn1-7-180.ams2.redhat.com [10.36.7.180]) by int-mx14.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u8M8evGi003239; Thu, 22 Sep 2016 04:41:12 -0400 From: "Daniel P. Berrange" To: qemu-devel@nongnu.org Date: Thu, 22 Sep 2016 09:40:45 +0100 Message-Id: <1474533652-31170-11-git-send-email-berrange@redhat.com> In-Reply-To: <1474533652-31170-1-git-send-email-berrange@redhat.com> References: <1474533652-31170-1-git-send-email-berrange@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.27 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Thu, 22 Sep 2016 08:41:13 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH v4 10/17] trace: don't abort qemu if ftrace can't be initialized X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?UTF-8?q?Llu=C3=ADs=20Vilanova?= , Stefan Hajnoczi Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" If the ftrace backend is compiled into QEMU, any attempt to start QEMU while non-root will fail due to the inability to open /sys/kernel/debug/tracing/trace_on. Add a fallback into the code so that it connects up the trace_marker_fd variable to /dev/null when setting EACCESS on the 'trace_on' file. This allows QEMU to run, with ftrace turned into a no-op. Signed-off-by: Daniel P. Berrange --- trace/ftrace.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/trace/ftrace.c b/trace/ftrace.c index e953922..3588bb0 100644 --- a/trace/ftrace.c +++ b/trace/ftrace.c @@ -51,6 +51,12 @@ bool ftrace_init(void) snprintf(path, PATH_MAX, "%s/tracing/tracing_on", debugfs); trace_fd = open(path, O_WRONLY); if (trace_fd < 0) { + if (errno == EACCES) { + trace_marker_fd = open("/dev/null", O_WRONLY); + if (trace_marker_fd != -1) { + return true; + } + } perror("Could not open ftrace 'tracing_on' file"); return false; } else {