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tracing: add __print_flags for events

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Developers have been asking for the ability in the ftrace event tracer
to display names of bits in a flags variable.

Instead of printing out c2, it would be easier to read FOO|BAR|GOO,
assuming that FOO is bit 1, BAR is bit 6 and GOO is bit 7.

Some examples where this would be useful are the state flags in a context
switch, kmalloc flags, and even permision flags in accessing files.

[
  v2 changes include:

  Frederic Weisbecker's idea of using a mask instead of bits,
  thus we can output GFP_KERNEL instead of GPF_WAIT|GFP_IO|GFP_FS.

  Li Zefan's idea of allowing the caller of __print_flags to add their
  own delimiter (or no delimiter) where we can get for file permissions
  rwx instead of r|w|x.
]

[
  v3 changes:

   Christoph Hellwig's idea of using an array instead of va_args.
]

[ Impact: better displaying of flags in trace output ]

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
This commit is contained in:
Steven Rostedt
2009-05-26 20:25:22 +02:00
committed by Frederic Weisbecker
parent 0e907c9939
commit be74b73a57
3 changed files with 65 additions and 1 deletions
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13
include/linux/ftrace_event.h
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@@ -3,12 +3,23 @@
#include <linux/trace_seq.h>
#include <linux/ring_buffer.h>
#include <linux/percpu.h>
struct trace_array;
struct tracer;
struct dentry;
DECLARE_PER_CPU(struct trace_seq, ftrace_event_seq);
struct trace_print_flags {
unsigned long mask;
const char *name;
};
const char *ftrace_print_flags_seq(struct trace_seq *p, const char *delim,
unsigned long flags,
const struct trace_print_flags *flag_array);
/*
* The trace entry - the most basic unit of tracing. This is what
* is printed in the end as a single line in the trace output, such as: