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 <berra...@redhat.com>
> ---
> 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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