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Re: [Qemu-devel] [PATCH v6 12/20] trace: don't abort qemu if ftrace can'
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH v6 12/20] trace: don't abort qemu if ftrace can't be initialized |
Date: |
Tue, 4 Oct 2016 15:12:31 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 |
On 10/04/2016 08:35 AM, Daniel P. Berrange wrote:
> 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/tracing_on.
>
> Add a fallback into the code so that it connects up the
> trace_marker_fd variable to /dev/null when setting
s/setting/getting/ ?
> EACCESS on the 'trace_on' file. This allows QEMU to
s/EACCESS/EACCES/
> run, with ftrace turned into a no-op.
>
> Signed-off-by: Daniel P. Berrange <address@hidden>
> ---
> 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);
Unrelated, but it would be nice to get rid of the PATH_MAX stack
allocation, and instead use g_strdup_printf() or similar in a followup
patch.
> 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 {
>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- [Qemu-devel] [PATCH v6 02/20] trace: remove double-underscore in event name, (continued)
- [Qemu-devel] [PATCH v6 02/20] trace: remove double-underscore in event name, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 01/20] trace: move colo trace events to net/ sub-directory, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 03/20] trace: add trace event iterator APIs, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 05/20] trace: remove some now unused functions, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 06/20] trace: remove global 'uint16 dstate[]' array, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 07/20] trace: remove duplicate control.h includes in generated-tracers.h, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 08/20] trace: break circular dependency in event-internal.h, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 09/20] trace: give each trace event a named TraceEvent struct, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 10/20] trace: remove the TraceEventID and TraceEventVCPUID enums, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 12/20] trace: don't abort qemu if ftrace can't be initialized, Daniel P. Berrange, 2016/10/04
- Re: [Qemu-devel] [PATCH v6 12/20] trace: don't abort qemu if ftrace can't be initialized,
Eric Blake <=
- [Qemu-devel] [PATCH v6 13/20] trace: provide mechanism for registering trace events, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 11/20] trace: emit name <-> ID mapping in simpletrace header, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 14/20] trace: dynamically allocate trace_dstate in CPUState, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 15/20] trace: dynamically allocate event IDs at runtime, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 16/20] trace: get rid of generated-events.h/generated-events.c, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 17/20] trace: rename _read_events to read_events, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 19/20] trace: pass trace-events to tracetool as a positional param, Daniel P. Berrange, 2016/10/04
- [Qemu-devel] [PATCH v6 18/20] trace: push reading of events up a level to tracetool main, Daniel P. Berrange, 2016/10/04