Re: [RFC][PATCH 00/10] tracing: Use TRACE_DEFINE_ENUM() to show enum values

[Masami Hiramatsu]

(2015/03/28 6:37), Steven Rostedt wrote:
> 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

Hmm, would user-space application really need to know the symbol name of enums?
If not, the event format files would better export the number(value) instead of
the enum name, like below.

 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

I'm still not sure how we can code it :( (It seems that some trick we need when
showing the print fmt.)

> 
> 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 export the TLB_REMOTE_SHOOTDOWN enum to use space.
> 
> How that is done is with a new file in the debugfs tracing directory.
> 
>  # cat /sys/kernel/debug/tracing/enum_map
> TLB_LOCAL_MM_SHOOTDOWN 3
> TLB_LOCAL_SHOOTDOWN 2
> TLB_REMOTE_SHOOTDOWN 1
> TLB_FLUSH_ON_TASK_SWITCH 0

BTW, if we can show the enum_map, can we also show the "symbolic" map
instead of using the __print_symbolic() ? :)

Thank you,

> 
> Now userspace, when seeing TLB_REMOTE_SHOOTDOWN in the format, knows
> that represents "1", and can do the conversions properly.
> 
> 
> Local SHA1: 6115e48a506e738f0f24771b4c87e4ba90d3d1c2
> 
> 
> Steven Rostedt (Red Hat) (10):
>       tracing: Add TRACE_DEFINE_ENUM() macro to map enums to their values
>       tracing: Allow for modules to export their trace enums as well
>       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
> 
> ----
>  include/asm-generic/vmlinux.lds.h |   5 +-
>  include/linux/module.h            |   2 +
>  include/linux/tracepoint.h        |   7 +
>  include/trace/events/9p.h         | 157 +++++++++++++----------
>  include/trace/events/f2fs.h       |  21 +++
>  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            |  11 ++
>  kernel/module.c                   |   3 +
>  kernel/trace/trace.c              | 260 +++++++++++++++++++++++++++++++++++++-
>  14 files changed, 598 insertions(+), 149 deletions(-)
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> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx


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