Re: [PATCH v2 7/7] tools/testing/selftests/bpf: replace open-coded 16 with TASK_COMM_LEN

[Yafang Shao <laoar.shao@gmail.com>]

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On Sun, Feb 12, 2023 at 3:00 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Wed, 8 Feb 2023 21:33:43 -0500
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > OK, so it doesn't break perf, trace-cmd and rasdaemon, because the enum is
> > only needed in the print_fmt part. It can handle it in the field portion.
> >
> > That is:
> >
> >
> > system: sched
> > name: sched_switch
> > ID: 285
> > format:
> >       field:unsigned short common_type;       offset:0;       size:2; signed:0;
> >       field:unsigned char common_flags;       offset:2;       size:1; signed:0;
> >       field:unsigned char common_preempt_count;       offset:3;       size:1; signed:0;
> >       field:int common_pid;   offset:4;       size:4; signed:1;
> >
> >       field:char prev_comm[TASK_COMM_LEN];    offset:8;       size:16;        signed:0;
> >                              ^^^^^^^^^^^^^^                          ^^
> >                             is ignored                             is used
> >
> >
> >       field:pid_t prev_pid;   offset:24;      size:4; signed:1;
> >       field:int prev_prio;    offset:28;      size:4; signed:1;
> >       field:long prev_state;  offset:32;      size:8; signed:1;
> >       field:char next_comm[TASK_COMM_LEN];    offset:40;      size:16;        signed:0;
> >       field:pid_t next_pid;   offset:56;      size:4; signed:1;
> >       field:int next_prio;    offset:60;      size:4; signed:1;
> >
> > print fmt: "prev_comm=%s prev_pid=%d prev_prio=%d prev_state=%s%s ==> next_comm=%s next_pid=%d next_prio=%d", REC->prev_comm, REC->prev_pid, REC->prev_prio, (REC->prev_state & ((((0x00000000 | 0x00000001 | 0x00000002 | 0x00000004 | 0x00000008 | 0x00000010 | 0x00000020 | 0x00000040) + 1) << 1) - 1)) ? __print_flags(REC->prev_state & ((((0x00000000 | 0x00000001 | 0x00000002 | 0x00000004 | 0x00000008 | 0x00000010 | 0x00000020 | 0x00000040) + 1) << 1) - 1), "|", { 0x00000001, "S" }, { 0x00000002, "D" }, { 0x00000004, "T" }, { 0x00000008, "t" }, { 0x00000010, "X" }, { 0x00000020, "Z" }, { 0x00000040, "P" }, { 0x00000080, "I" }) : "R", REC->prev_state & (((0x00000000 | 0x00000001 | 0x00000002 | 0x00000004 | 0x00000008 | 0x00000010 | 0x00000020 | 0x00000040) + 1) << 1) ? "+" : "", REC->next_comm, REC->next_pid, REC->next_prio
> >
> >    ^^^^^^^
> >
> > Is what requires the conversions. So I take that back. It only breaks
> > perfetto, and that's because it writes its own parser and doesn't use
> > libtraceevent.
>
> Actually, there are cases that this needs to be a number, as b3bc8547d3be6
> ("tracing: Have TRACE_DEFINE_ENUM affect trace event types as well") made
> it update fields as well as the printk fmt.
>

It seems that TRACE_DEFINE_ENUM(TASK_COMM_LEN) in the trace events
header files would be a better fix.

> I think because libtraceevent noticed that it was a "char" array, it just
> defaults to "size". But this does have meaning for all other types, and I
> can see other parsers requiring that.
>
> -- Steve


-- 
Regards
Yafang

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diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index 7f4dfbd..97cf6c2 100644
--- a/include/trace/events/block.h
+++ b/include/trace/events/block.h
@@ -12,6 +12,8 @@
 
 #define RWBS_LEN	8
 
+TRACE_DEFINE_ENUM(TASK_COMM_LEN);
+
 DECLARE_EVENT_CLASS(block_buffer,
 
 	TP_PROTO(struct buffer_head *bh),
diff --git a/include/trace/events/oom.h b/include/trace/events/oom.h
index 26a11e4..19de9a8 100644
--- a/include/trace/events/oom.h
+++ b/include/trace/events/oom.h
@@ -7,6 +7,8 @@
 #include <linux/tracepoint.h>
 #include <trace/events/mmflags.h>
 
+TRACE_DEFINE_ENUM(TASK_COMM_LEN);
+
 TRACE_EVENT(oom_score_adj_update,
 
 	TP_PROTO(struct task_struct *task),
diff --git a/include/trace/events/osnoise.h b/include/trace/events/osnoise.h
index 82f741e..ac3c0ab 100644
--- a/include/trace/events/osnoise.h
+++ b/include/trace/events/osnoise.h
@@ -6,6 +6,8 @@
 #define _OSNOISE_TRACE_H
 
 #include <linux/tracepoint.h>
+TRACE_DEFINE_ENUM(TASK_COMM_LEN);
+
 TRACE_EVENT(thread_noise,
 
 	TP_PROTO(struct task_struct *t, u64 start, u64 duration),
diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index fbb99a6..57ec09e 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -216,6 +216,7 @@ static inline long __trace_sched_switch_state(bool preempt,
 }
 #endif /* CREATE_TRACE_POINTS */
 
+TRACE_DEFINE_ENUM(TASK_COMM_LEN);
 /*
  * Tracepoint for task switches, performed by the scheduler:
  */
diff --git a/include/trace/events/signal.h b/include/trace/events/signal.h
index 1db7e4b..3b1cdb6 100644
--- a/include/trace/events/signal.h
+++ b/include/trace/events/signal.h
@@ -9,6 +9,8 @@
 #include <linux/sched.h>
 #include <linux/tracepoint.h>
 
+TRACE_DEFINE_ENUM(TASK_COMM_LEN);
+
 #define TP_STORE_SIGINFO(__entry, info)				\
 	do {							\
 		if (info == SEND_SIG_NOINFO) {			\
diff --git a/include/trace/events/task.h b/include/trace/events/task.h
index 64d1609..0a9e03a7 100644
--- a/include/trace/events/task.h
+++ b/include/trace/events/task.h
@@ -6,6 +6,7 @@
 #define _TRACE_TASK_H
 #include <linux/tracepoint.h>
 
+TRACE_DEFINE_ENUM(TASK_COMM_LEN);
 TRACE_EVENT(task_newtask,
 
 	TP_PROTO(struct task_struct *task, unsigned long clone_flags),