[ltt-dev] [UST PATCH] Request: Make wait_for_buffer_consumption visible

[Paul Wögerer]

Hi,

I'm trying to use LTTng UST as a backend for function call tracing. The 
following pseudocode shows what we basically to:

ustcmd_set_marker_state( "call_trace", call, enter, 1, pid );
ustcmd_set_marker_state( "call_trace", call, inside, 1, pid );
ustcmd_set_marker_state( "call_trace", call, exit, 1, pid );

ustcmd_create_trace( "call_trace", pid );
ustcmd_start_trace( "call_trace", pid );

...
... Lots of auto-generated code that makes use of call.enter/inside/exit 
markers
...

ustcmd_stop_trace( "call_trace", pid );
ustcmd_destroy_trace( "call_trace", pid );

This works very well in general but whenever an executable runs only for 
a very short amount of time I run into troubles with stopping/destroying 
my "call_trace" properly.

This is caused by the fact that stop/destroy_trace runs before buffer 
consumption completed on the ust-consumerd side. This is easy to prevent 
by some code that implements waiting for buffer consumption. Fortunately 
this is already available in tracectl.c keepalive().

The following patch puts the "waiting for buffer consumption" code into 
its own function and makes it visible externally via ust/ustctl.h. Using 
function wait_for_buffer_consumption() before stop/destroy_trace solves 
the problem for me.

Please apply the patch from the attachment to the ust trunk to make 
wait_for_buffer_consumption()available for everyone.

Thanks,
Paul

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