// SPDX-License-Identifier: GPL-2.0
/*
 * nop tracer
 *
 * Copyright (C) 2008 Steven Noonan <steven@uplinklabs.net>
 *
 */

#include <linux/module.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 the setting of a flag.
 * If you don't implement it, then the flag setting will be
 * automatically accepted.
 */
static int nop_set_flag(struct trace_array *tr, 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,
#ifdef CONFIG_FTRACE_SELFTEST
        .selftest       = trace_selftest_startup_nop,
#endif
        .flags          = &nop_flags,
        .set_flag       = nop_set_flag,
        .allow_instances = true,
};