trace_nop.c

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/*
 * nop tracer
 *
 * Copyright (C) 2008 Steven Noonan <[email protected]>
 *
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/debugfs.h>
#include <linux/ftrace.h>

#include "trace.h"

/* Our two options */
enum {
    TRACE_NOP_OPT_ACCEPT = 0x1,
    TRACE_NOP_OPT_REFUSE = 0x2
};

/* Options for the tracer (see trace_options file) */
static struct tracer_opt nop_opts[] = {
    /* Option that will be accepted by set_flag callback */
    { TRACER_OPT(test_nop_accept, TRACE_NOP_OPT_ACCEPT) },
    /* Option that will be refused by set_flag callback */
    { TRACER_OPT(test_nop_refuse, TRACE_NOP_OPT_REFUSE) },
    { } /* Always set a last empty entry */
};

static struct tracer_flags nop_flags = {
    /* You can check your flags value here when you want. */
    .val = 0, /* By default: all flags disabled */
    .opts = nop_opts
};

static struct trace_array   *ctx_trace;

static void start_nop_trace(struct trace_array *tr)
{
    /* Nothing to do! */
}

static void stop_nop_trace(struct trace_array *tr)
{
    /* Nothing to do! */
}

static int nop_trace_init(struct trace_array *tr)
{
    ctx_trace = tr;
    start_nop_trace(tr);
    return 0;
}

static void nop_trace_reset(struct trace_array *tr)
{
    stop_nop_trace(tr);
}

/* It only serves as a signal handler and a callback to
 * accept or refuse tthe setting of a flag.
 * If you don't implement it, then the flag setting will be
 * automatically accepted.
 */
static int nop_set_flag(u32 old_flags, u32 bit, int set)
{
    /*
     * Note that you don't need to update nop_flags.val yourself.
     * The tracing Api will do it automatically if you return 0
     */
    if (bit == TRACE_NOP_OPT_ACCEPT) {
        printk(KERN_DEBUG "nop_test_accept flag set to %d: we accept."
            " Now cat trace_options to see the result\n",
            set);
        return 0;
    }

    if (bit == TRACE_NOP_OPT_REFUSE) {
        printk(KERN_DEBUG "nop_test_refuse flag set to %d: we refuse."
            "Now cat trace_options to see the result\n",
            set);
        return -EINVAL;
    }

    return 0;
}


struct tracer nop_trace __read_mostly =
{
    .name       = "nop",
    .init       = nop_trace_init,
    .reset      = nop_trace_reset,
    .wait_pipe  = poll_wait_pipe,
#ifdef CONFIG_FTRACE_SELFTEST
    .selftest   = trace_selftest_startup_nop,
#endif
    .flags      = &nop_flags,
    .set_flag   = nop_set_flag
};