Hi Tom, On Sun, 4 Oct 2020 17:14:06 -0500 Tom Zanussi <zanu...@kernel.org> wrote:
> Currently, sythetic events only support static string fields such as: > > # echo 'test_latency u64 lat; char somename[32]' > > /sys/kernel/debug/tracing/synthetic_events > > Which is fine, but wastes a lot of space in the event. > > It also prevents the most commonly-defined strings in the existing > trace events e.g. those defined using __string(), from being passed to > synthetic events via the trace() action. > > With this change, synthetic events with dynamic fields can be defined: > > # echo 'test_latency u64 lat; char somename[]' > > /sys/kernel/debug/tracing/synthetic_events > > And the trace() action can be used to generate events using either > dynamic or static strings: > > # echo > 'hist:keys=name:lat=common_timestamp.usecs-$ts0:onmatch(sys.event).test_latency($lat,name)' > > /sys/kernel/debug/tracing/events > > The synthetic event dynamic strings are implemented in the same way as > the existing __data_loc strings and appear as such in the format file. > > [ <rost...@goodmis.org>: added __set_synth_event_print_fmt() changes: > > I added the following to make it work with trace-cmd. Dynamic strings > must have __get_str() for events in the print_fmt otherwise it can't be > parsed correctly. ] I confirmed this works, but have some questions; - It seems no error message when we failed to define with wrong syntax /sys/kernel/debug/tracing # echo 'myevent char name []' >> synthetic_events sh: write error: Invalid argument /sys/kernel/debug/tracing # cat error_log /sys/kernel/debug/tracing # - what we write and what we see in synthetic_events are different /sys/kernel/debug/tracing # echo 'myevent char name[]' >> synthetic_events /sys/kernel/debug/tracing # cat synthetic_events myevent __data_loc char[] name - And it is not able to re-define with that syntax /sys/kernel/debug/tracing # echo > synthetic_events /sys/kernel/debug/tracing # echo 'myevent __data_loc char[] name' >> synthetic_events sh: write error: Invalid argument /sys/kernel/debug/tracing # - It seems to accept wrong name for variables /sys/kernel/debug/tracing # echo 'myevent char name]' >> synthetic_events /sys/kernel/debug/tracing # echo 'myevent2 char name;[]' >> synthetic_events /sys/kernel/debug/tracing # cat synthetic_events myevent char name] myevent2 __data_loc char[] name; Some of those issues are not introduced from this series. I think we'd better fix those before introducing this series so that we can backport it to stable kernels. Thank you, -- Masami Hiramatsu <mhira...@kernel.org>
