From mboxrd@z Thu Jan 1 00:00:00 1970 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 From: "Daniel P. Berrange" 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> Subject: [Qemu-devel] [PATCH v4 10/17] trace: don't abort qemu if ftrace can't be initialized List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: =?UTF-8?q?Llu=C3=ADs=20Vilanova?= , Eric Blake , Stefan Hajnoczi , "Daniel P. Berrange" 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 { -- 2.7.4