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    Subject[PATCH 4/7] tracing/function: Introduce persistent trace option
    Date
    This patch introduces 'func_ptrace' option, now available in
    /sys/kernel/debug/tracing/options when function tracer
    is selected.

    The patch also adds some tiny code that calls back to pstore
    to record the trace. The callback is no-op when PSTORE=n.

    Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
    ---
    kernel/trace/trace_functions.c | 25 ++++++++++++++++++++-----
    1 file changed, 20 insertions(+), 5 deletions(-)

    diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
    index c7b0c6a..269627c 100644
    --- a/kernel/trace/trace_functions.c
    +++ b/kernel/trace/trace_functions.c
    @@ -13,6 +13,7 @@
    #include <linux/debugfs.h>
    #include <linux/uaccess.h>
    #include <linux/ftrace.h>
    +#include <linux/pstore.h>
    #include <linux/fs.h>

    #include "trace.h"
    @@ -74,6 +75,14 @@ function_trace_call_preempt_only(unsigned long ip, unsigned long parent_ip)
    preempt_enable_notrace();
    }

    +/* Our two options */
    +enum {
    + TRACE_FUNC_OPT_STACK = 0x1,
    + TRACE_FUNC_OPT_PSTORE = 0x2,
    +};
    +
    +static struct tracer_flags func_flags;
    +
    static void
    function_trace_call(unsigned long ip, unsigned long parent_ip)
    {
    @@ -97,6 +106,12 @@ function_trace_call(unsigned long ip, unsigned long parent_ip)
    disabled = atomic_inc_return(&data->disabled);

    if (likely(disabled == 1)) {
    + /*
    + * So far tracing doesn't support multiple buffers, so
    + * we make an explicit call for now.
    + */
    + if (unlikely(func_flags.val & TRACE_FUNC_OPT_PSTORE))
    + pstore_ftrace_call(ip, parent_ip);
    pc = preempt_count();
    trace_function(tr, ip, parent_ip, flags, pc);
    }
    @@ -158,15 +173,13 @@ static struct ftrace_ops trace_stack_ops __read_mostly =
    .flags = FTRACE_OPS_FL_GLOBAL,
    };

    -/* Our two options */
    -enum {
    - TRACE_FUNC_OPT_STACK = 0x1,
    -};
    -
    static struct tracer_opt func_opts[] = {
    #ifdef CONFIG_STACKTRACE
    { TRACER_OPT(func_stack_trace, TRACE_FUNC_OPT_STACK) },
    #endif
    +#ifdef CONFIG_PSTORE_FTRACE
    + { TRACER_OPT(func_pstore, TRACE_FUNC_OPT_PSTORE) },
    +#endif
    { } /* Always set a last empty entry */
    };

    @@ -219,6 +232,8 @@ static int func_set_flag(u32 old_flags, u32 bit, int set)

    return 0;
    }
    + if (bit == TRACE_FUNC_OPT_PSTORE)
    + return 0;

    return -EINVAL;
    }
    --
    1.7.10.4


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