tracing: Add variable support to hist triggers
Add support for saving the value of a current event's event field by assigning it to a variable that can be read by a subsequent event. The basic syntax for saving a variable is to simply prefix a unique variable name not corresponding to any keyword along with an '=' sign to any event field. Both keys and values can be saved and retrieved in this way: # echo 'hist:keys=next_pid:vals=$ts0:ts0=common_timestamp ... # echo 'hist:timer_pid=common_pid:key=$timer_pid ...' If a variable isn't a key variable or prefixed with 'vals=', the associated event field will be saved in a variable but won't be summed as a value: # echo 'hist:keys=next_pid:ts1=common_timestamp:... Multiple variables can be assigned at the same time: # echo 'hist:keys=pid:vals=$ts0,$b,field2:ts0=common_timestamp,b=field1 ... Multiple (or single) variables can also be assigned at the same time using separate assignments: # echo 'hist:keys=pid:vals=$ts0:ts0=common_timestamp:b=field1:c=field2 ... Variables set as above can be used by being referenced from another event, as described in a subsequent patch. Link: http://lkml.kernel.org/r/fc93c4944d9719dbcb1d0067be627d44e98e2adc.1516069914.git.tom.zanussi@linux.intel.com Signed-off-by:Tom Zanussi <tom.zanussi@linux.intel.com> Signed-off-by:
Baohong Liu <baohong.liu@intel.com> Signed-off-by:
Steven Rostedt (VMware) <rostedt@goodmis.org>
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