On 10/12/20 3:53 PM, Steven Rostedt wrote: > On Mon, 12 Oct 2020 10:26:42 +0200 > Peter Enderborg <peter.enderb...@sony.com> wrote: > >> When there is no clients listening on event the trace return >> EBADF. The file is not a bad file descriptor and to get the >> userspace able to do a proper error handling it need a different >> error code that separate a bad file descriptor from a empty listening. > I have no problem with this patch, but your description is incorrect. And > before making this change, I want to make sure that what you think is > happening is actually happening. > > This has nothing to do with "clients listening". This happens when the ring > buffer is disabled for some reason. The most likely case of this happening > is if someone sets /sys/kernel/tracing/tracing_on to zero.
I see that as no one is listening. You start to listen by setting this tracing on some instance, but that is for trace_pipe. Is it the same flag for raw access and all ways you can invoke a trace? Would "When there is no instances listening on events the trace return EBADF, it is when the tracing_on is off globally. The file is not a bad file descriptor and to get the userspace able to do a proper error handling it need a different error code that separate a bad file descriptor from a empty listening." be a ok? > If this is still something you want applied, please update the change log > to a more accurate scenario. > > Thanks, > > -- Steve > > >> Signed-off-by: Peter Enderborg <peter.enderb...@sony.com> >> --- >> kernel/trace/trace.c | 8 ++++---- >> 1 file changed, 4 insertions(+), 4 deletions(-) >> >> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c >> index d3e5de717df2..6e592bf736df 100644 >> --- a/kernel/trace/trace.c >> +++ b/kernel/trace/trace.c >> @@ -6651,8 +6651,8 @@ tracing_mark_write(struct file *filp, const char >> __user *ubuf, >> event = __trace_buffer_lock_reserve(buffer, TRACE_PRINT, size, >> irq_flags, preempt_count()); >> if (unlikely(!event)) >> - /* Ring buffer disabled, return as if not open for write */ >> - return -EBADF; >> + /* Ring buffer disabled, return as if not connected */ >> + return -ENOTCONN; >> >> entry = ring_buffer_event_data(event); >> entry->ip = _THIS_IP_; >> @@ -6731,8 +6731,8 @@ tracing_mark_raw_write(struct file *filp, const char >> __user *ubuf, >> event = __trace_buffer_lock_reserve(buffer, TRACE_RAW_DATA, size, >> irq_flags, preempt_count()); >> if (!event) >> - /* Ring buffer disabled, return as if not open for write */ >> - return -EBADF; >> + /* Ring buffer disabled, return not connected */ >> + return -ENOTCONN; >> >> entry = ring_buffer_event_data(event); >>