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 */ 16 enum { 17 TRACE_NOP_OPT_ACCEPT = 0x1, 18 TRACE_NOP_OPT_REFUSE = 0x2 19 }; 20 21 /* Options for the tracer (see trace_options file) */ 22 static 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 30 static 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 36 static struct trace_array *ctx_trace; 37 38 static void start_nop_trace(struct trace_array *tr) 39 { 40 /* Nothing to do! */ 41 } 42 43 static void stop_nop_trace(struct trace_array *tr) 44 { 45 /* Nothing to do! */ 46 } 47 48 static int nop_trace_init(struct trace_array *tr) 49 { 50 ctx_trace = tr; 51 start_nop_trace(tr); 52 return 0; 53 } 54 55 static 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 */ 65 static int nop_set_flag(struct trace_array *tr, 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 89 struct tracer nop_trace __read_mostly = 90 { 91 .name = "nop", 92 .init = nop_trace_init, 93 .reset = nop_trace_reset, 94 #ifdef CONFIG_FTRACE_SELFTEST 95 .selftest = trace_selftest_startup_nop, 96 #endif 97 .flags = &nop_flags, 98 .set_flag = nop_set_flag, 99 .allow_instances = true, 100 }; 101 102