[RFC][PATCH 00/17 v2] tracing: Use TRACE_DEFINE_ENUM() to show enum values

[Steven Rostedt]

As there are many tracepoints that use __print_symbolic() to translate
numbers into ASCII strings, and several of these translate enums as
well, it causes a problem for user space tools that read the tracepoint
format files and have to translate the binary data to their associated
strings.

For example, with the tlb_flush tracepoint, we have this in the format
file:

print fmt: "pages:%ld reason:%s (%d)", REC->pages,
 __print_symbolic(REC->reason,
   { TLB_FLUSH_ON_TASK_SWITCH, "flush on task switch" },
   { TLB_REMOTE_SHOOTDOWN, "remote shootdown" },
   { TLB_LOCAL_SHOOTDOWN, "local shootdown" },
   { TLB_LOCAL_MM_SHOOTDOWN, "local mm shootdown" }), REC->reason

Now, userspace does not know what the value of TLB_REMOTE_SHOOTDOWN is.
To solve this, a new macro is created as a helper to allow tracepoints
to export enums they use to userspace. This macro is called,
TRACE_DEFINE_ENUM(), such that

 TRACE_DEFINE_ENUM(TLB_REMOTE_SHOOTDOWN);

will convert the "print fmt"s in the format files to its actual value
and no longer display the enum name.

On boot up (or module load), the enums saved via TRACE_DEFINE_ENUM()
will be searched for in the TP_printk()s of the tracepoints. Logic
knows enough to ignore quoted text.

For debugging, a new file is still added in the tracing directory
to show what enums were added, their values and the TRACE_SYSTEM that
added them:

 # cat /sys/kernel/debug/tracing/enum_map
TLB_LOCAL_MM_SHOOTDOWN 3 (tlb)
TLB_LOCAL_SHOOTDOWN 2 (tlb)
TLB_REMOTE_SHOOTDOWN 1 (tlb)
TLB_FLUSH_ON_TASK_SWITCH 0 (tlb)

And the output of the tlb_flush format is now:

print fmt: "pages:%ld reason:%s (%d)", REC->pages,
 __print_symbolic(REC->reason,
   { 0, "flush on task switch" },
   { 1, "remote shootdown" },
   { 2, "local shootdown" },
   { 3, "local mm shootdown" }), REC->reason

And userspace tools can easily parse that without special handling.

Local SHA1: a6862181206543b6493c73690f322868c86de0ea


Steven Rostedt (Red Hat) (17):
      tracing: Add TRACE_SYSTEM_VAR to intel-sst
      tracing: Add TRACE_SYSTEM_VAR to kvm-s390
      tracing: Add TRACE_SYSTEM_VAR to xhci-hcd
      tracing: Give system name a pointer
      tracing: Update trace-event-sample with TRACE_SYSTEM_VAR documentation
      tracing: Add TRACE_DEFINE_ENUM() macro to map enums to their values
      tracing: Allow for modules to export their trace enums as well
      tracing/samples: Update the trace-event-sample.h with TRACE_DEFINE_ENUM()
      tracing: Show the mapped enums in enum_map file
      x86/tlb/trace: Export enums in used by tlb_flush tracepoint
      net/9p/tracing: Export enums in tracepoints to userspace
      f2fs: Export the enums in the tracepoints to userspace
      irq/tracing: Export enums in tracepoints to user space
      mm: tracing: Export enums in tracepoints to user space
      SUNRPC: Export enums in tracepoints to user space
      v4l: Export enums used by tracepoints to user space
      writeback: Export enums used by tracepoint to user space

----
 arch/s390/kvm/trace-s390.h                 |   7 +
 drivers/usb/host/xhci-trace.h              |   7 +
 include/asm-generic/vmlinux.lds.h          |   5 +-
 include/linux/ftrace_event.h               |   4 +-
 include/linux/module.h                     |   2 +
 include/linux/tracepoint.h                 |   8 +
 include/trace/events/9p.h                  | 157 ++++++++--------
 include/trace/events/f2fs.h                |  30 ++++
 include/trace/events/intel-sst.h           |   7 +
 include/trace/events/irq.h                 |  39 ++--
 include/trace/events/migrate.h             |  42 +++--
 include/trace/events/sunrpc.h              |  62 +++++--
 include/trace/events/tlb.h                 |  30 +++-
 include/trace/events/v4l2.h                |  75 +++++---
 include/trace/events/writeback.h           |  33 +++-
 include/trace/ftrace.h                     |  41 ++++-
 kernel/module.c                            |   3 +
 kernel/trace/trace.c                       | 276 ++++++++++++++++++++++++++++-
 kernel/trace/trace.h                       |   2 +
 kernel/trace/trace_events.c                |  98 +++++++++-
 samples/trace_events/trace-events-sample.h |  84 ++++++++-
 21 files changed, 853 insertions(+), 159 deletions(-)
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