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    Subject[PATCH 1/3] tracing: add __print_flags for events
    From: Steven Rostedt <srostedt@redhat.com>

    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.

    I included 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.

    I also included 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.

    [ Impact: better displaying of flags in trace output ]

    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    include/linux/ftrace_event.h | 6 +++++-
    include/trace/ftrace.h | 10 ++++++++++
    kernel/trace/trace_output.c | 38 ++++++++++++++++++++++++++++++++++++++
    3 files changed, 53 insertions(+), 1 deletions(-)

    diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
    index bae51dd..253c3d0 100644
    --- a/include/linux/ftrace_event.h
    +++ b/include/linux/ftrace_event.h
    @@ -3,12 +3,16 @@

    #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);
    +const char *ftrace_print_flags_seq(struct trace_seq *p, const char *delim,
    + unsigned long flags, ...);
    +
    /*
    * 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:
    diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
    index edb02bc..9b79c7c 100644
    --- a/include/trace/ftrace.h
    +++ b/include/trace/ftrace.h
    @@ -87,6 +87,7 @@
    * struct trace_seq *s = &iter->seq;
    * struct ftrace_raw_<call> *field; <-- defined in stage 1
    * struct trace_entry *entry;
    + * struct trace_seq *p;
    * int ret;
    *
    * entry = iter->ent;
    @@ -98,7 +99,9 @@
    *
    * field = (typeof(field))entry;
    *
    + * p = get_cpu_var(ftrace_event_seq);
    * ret = trace_seq_printf(s, <TP_printk> "\n");
    + * put_cpu();
    * if (!ret)
    * return TRACE_TYPE_PARTIAL_LINE;
    *
    @@ -119,6 +122,10 @@
    #undef __get_str
    #define __get_str(field) ((char *)__entry + __entry->__str_loc_##field)

    +#undef __print_flags
    +#define __print_flags(flag, delim, x...) \
    + ftrace_print_flags_seq(p, delim, flag, x , 0)
    +
    #undef TRACE_EVENT
    #define TRACE_EVENT(call, proto, args, tstruct, assign, print) \
    enum print_line_t \
    @@ -127,6 +134,7 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags) \
    struct trace_seq *s = &iter->seq; \
    struct ftrace_raw_##call *field; \
    struct trace_entry *entry; \
    + struct trace_seq *p; \
    int ret; \
    \
    entry = iter->ent; \
    @@ -138,7 +146,9 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags) \
    \
    field = (typeof(field))entry; \
    \
    + p = &get_cpu_var(ftrace_event_seq); \
    ret = trace_seq_printf(s, #call ": " print); \
    + put_cpu(); \
    if (!ret) \
    return TRACE_TYPE_PARTIAL_LINE; \
    \
    diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
    index 489c0e8..f730de5 100644
    --- a/kernel/trace/trace_output.c
    +++ b/kernel/trace/trace_output.c
    @@ -14,6 +14,8 @@
    /* must be a power of 2 */
    #define EVENT_HASHSIZE 128

    +DEFINE_PER_CPU(struct trace_seq, ftrace_event_seq);
    +
    static DEFINE_MUTEX(trace_event_mutex);
    static struct hlist_head event_hash[EVENT_HASHSIZE] __read_mostly;

    @@ -212,6 +214,42 @@ int trace_seq_path(struct trace_seq *s, struct path *path)
    return 0;
    }

    +const char *
    +ftrace_print_flags_seq(struct trace_seq *p, const char *delim,
    + unsigned long flags, ...)
    +{
    + const char *str;
    + va_list args;
    + unsigned long mask;
    +
    + trace_seq_init(p);
    + va_start(args, flags);
    + for (mask = va_arg(args, unsigned long); mask && flags;
    + mask = va_arg(args, unsigned long)) {
    + str = va_arg(args, const char *);
    +
    + if ((flags & mask) != mask)
    + continue;
    +
    + flags &= ~mask;
    + if (p->len && delim)
    + trace_seq_puts(p, delim);
    + trace_seq_puts(p, str);
    + }
    + va_end(args);
    +
    + /* check for left over flags */
    + if (flags) {
    + if (p->len && delim)
    + trace_seq_puts(p, delim);
    + trace_seq_printf(p, "0x%lx", flags);
    + }
    +
    + trace_seq_putc(p, 0);
    +
    + return p->buffer;
    +}
    +
    #ifdef CONFIG_KRETPROBES
    static inline const char *kretprobed(const char *name)
    {
    --
    1.6.2.4
    --


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