tracing: add TRACE_FIELD_SPECIAL to record complex entries
Tom Zanussi pointed out that the simple TRACE_FIELD was not enough to record trace data that required memcpy. This patch addresses this issue by adding a TRACE_FIELD_SPECIAL. The format is similar to TRACE_FIELD but looks like so: TRACE_FIELD_SPECIAL(type_item, item, cmd) What TRACE_FIELD gave was: TRACE_FIELD(type, item, assign) The TRACE_FIELD would be used in declaring a structure: struct { type item; }; And later assign it via: entry->item = assign; What TRACE_FIELD_SPECIAL gives us is: In the declaration of the structure: struct { type_item; }; And the assignment: cmd; This change log will explain the one example used in the patch: TRACE_EVENT_FORMAT(sched_switch, TPPROTO(struct rq *rq, struct task_struct *prev, struct task_struct *next), TPARGS(rq, prev, next), TPFMT("task %s:%d ==> %s:%d", prev->comm, prev->pid, next->comm, next->pid), TRACE_STRUCT( TRACE_FIELD(pid_t, prev_pid, prev->pid) TRACE_FIELD(int, prev_prio, prev->prio) TRACE_FIELD_SPECIAL(char next_comm[TASK_COMM_LEN], next_comm, TPCMD(memcpy(TRACE_ENTRY->next_comm, next->comm, TASK_COMM_LEN))) TRACE_FIELD(pid_t, next_pid, next->pid) TRACE_FIELD(int, next_prio, next->prio) ), TPRAWFMT("prev %d:%d ==> next %s:%d:%d") ); The struct will be create as: struct { pid_t prev_pid; int prev_prio; char next_comm[TASK_COMM_LEN]; pid_t next_pid; int next_prio; }; Note the TRACE_ENTRY in the cmd part of TRACE_SPECIAL. TRACE_ENTRY will be set by the tracer to point to the structure inside the trace buffer. entry->prev_pid = prev->pid; entry->prev_prio = prev->prio; memcpy(entry->next_comm, next->comm, TASK_COMM_LEN); entry->next_pid = next->pid; entry->next_prio = next->prio Reported-by: Tom Zanussi <tzanussi@gmail.com> Signed-off-by: Steven Rostedt <srostedt@redhat.com>
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@ -71,10 +71,15 @@ TRACE_EVENT_FORMAT(sched_switch,
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TRACE_STRUCT(
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TRACE_FIELD(pid_t, prev_pid, prev->pid)
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TRACE_FIELD(int, prev_prio, prev->prio)
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TRACE_FIELD_SPECIAL(char next_comm[TASK_COMM_LEN],
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next_comm,
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TPCMD(memcpy(TRACE_ENTRY->next_comm,
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next->comm,
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TASK_COMM_LEN)))
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TRACE_FIELD(pid_t, next_pid, next->pid)
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TRACE_FIELD(int, next_prio, next->prio)
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),
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TPRAWFMT("prev %d:%d ==> next %d:%d")
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TPRAWFMT("prev %d:%d ==> next %s:%d:%d")
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);
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TRACE_EVENT_FORMAT(sched_migrate_task,
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@ -30,5 +30,7 @@
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#define TRACE_FIELD(type, item, assign) \
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type item;
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#define TRACE_FIELD_SPECIAL(type_item, item, cmd) \
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type_item;
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#include <trace/trace_event_types.h>
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@ -39,6 +39,10 @@
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#define TRACE_FIELD(type, item, assign) \
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field->item,
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#undef TRACE_FIELD_SPECIAL
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#define TRACE_FIELD_SPECIAL(type_item, item, cmd) \
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field->item,
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#undef TPRAWFMT
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#define TPRAWFMT(args...) args
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@ -147,6 +147,20 @@ __attribute__((section("_ftrace_events"))) event_##call = { \
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#define TRACE_FIELD(type, item, assign)\
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entry->item = assign;
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#undef TRACE_FIELD
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#define TRACE_FIELD(type, item, assign)\
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entry->item = assign;
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#undef TPCMD
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#define TPCMD(cmd...) cmd
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#undef TRACE_ENTRY
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#define TRACE_ENTRY entry
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#undef TRACE_FIELD_SPECIAL
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#define TRACE_FIELD_SPECIAL(type_item, item, cmd) \
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cmd;
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#undef TRACE_EVENT_FORMAT
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#define TRACE_EVENT_FORMAT(call, proto, args, fmt, tstruct, tpfmt) \
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_TRACE_FORMAT(call, PARAMS(proto), PARAMS(args), PARAMS(fmt)) \
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