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