1/* 2 * nop tracer 3 * 4 * Copyright (C) 2008 Steven Noonan <steven@uplinklabs.net> 5 * 6 */ 7 8#include <linux/module.h> 9#include <linux/fs.h> 10#include <linux/debugfs.h> 11#include <linux/ftrace.h> 12 13#include "trace.h" 14 15/* Our two options */ 16enum { 17 TRACE_NOP_OPT_ACCEPT = 0x1, 18 TRACE_NOP_OPT_REFUSE = 0x2 19}; 20 21/* Options for the tracer (see trace_options file) */ 22static struct tracer_opt nop_opts[] = { 23 /* Option that will be accepted by set_flag callback */ 24 { TRACER_OPT(test_nop_accept, TRACE_NOP_OPT_ACCEPT) }, 25 /* Option that will be refused by set_flag callback */ 26 { TRACER_OPT(test_nop_refuse, TRACE_NOP_OPT_REFUSE) }, 27 { } /* Always set a last empty entry */ 28}; 29 30static struct tracer_flags nop_flags = { 31 /* You can check your flags value here when you want. */ 32 .val = 0, /* By default: all flags disabled */ 33 .opts = nop_opts 34}; 35 36static struct trace_array *ctx_trace; 37 38static void start_nop_trace(struct trace_array *tr) 39{ 40 /* Nothing to do! */ 41} 42 43static void stop_nop_trace(struct trace_array *tr) 44{ 45 /* Nothing to do! */ 46} 47 48static int nop_trace_init(struct trace_array *tr) 49{ 50 ctx_trace = tr; 51 start_nop_trace(tr); 52 return 0; 53} 54 55static void nop_trace_reset(struct trace_array *tr) 56{ 57 stop_nop_trace(tr); 58} 59 60/* It only serves as a signal handler and a callback to 61 * accept or refuse tthe setting of a flag. 62 * If you don't implement it, then the flag setting will be 63 * automatically accepted. 64 */ 65static int nop_set_flag(u32 old_flags, u32 bit, int set) 66{ 67 /* 68 * Note that you don't need to update nop_flags.val yourself. 69 * The tracing Api will do it automatically if you return 0 70 */ 71 if (bit == TRACE_NOP_OPT_ACCEPT) { 72 printk(KERN_DEBUG "nop_test_accept flag set to %d: we accept." 73 " Now cat trace_options to see the result\n", 74 set); 75 return 0; 76 } 77 78 if (bit == TRACE_NOP_OPT_REFUSE) { 79 printk(KERN_DEBUG "nop_test_refuse flag set to %d: we refuse." 80 "Now cat trace_options to see the result\n", 81 set); 82 return -EINVAL; 83 } 84 85 return 0; 86} 87 88 89struct tracer nop_trace __read_mostly = 90{ 91 .name = "nop", 92 .init = nop_trace_init, 93 .reset = nop_trace_reset, 94 .wait_pipe = poll_wait_pipe, 95#ifdef CONFIG_FTRACE_SELFTEST 96 .selftest = trace_selftest_startup_nop, 97#endif 98 .flags = &nop_flags, 99 .set_flag = nop_set_flag 100}; 101