linux/include/trace/boot.h

#ifndef _LINUX_TRACE_BOOT_H
#define _LINUX_TRACE_BOOT_H

/*
 * Structure which defines the trace of an initcall
 * while it is called.
 * You don't have to fill the func field since it is
 * only used internally by the tracer.
 */
struct boot_trace_call {
	pid_t			caller;
	char			func[KSYM_SYMBOL_LEN];
};

/*
 * Structure which defines the trace of an initcall
 * while it returns.
 */
struct boot_trace_ret {
	char			func[KSYM_SYMBOL_LEN];
	int				result;
	unsigned long long	duration;		/* nsecs */
};

#ifdef CONFIG_BOOT_TRACER
/* Append the traces on the ring-buffer */
extern void trace_boot_call(struct boot_trace_call *bt, initcall_t fn);
extern void trace_boot_ret(struct boot_trace_ret *bt, initcall_t fn);

/* Tells the tracer that smp_pre_initcall is finished.
 * So we can start the tracing
 */
extern void start_boot_trace(void);

/* Resume the tracing of other necessary events
 * such as sched switches
 */
extern void enable_boot_trace(void);

/* Suspend this tracing. Actually, only sched_switches tracing have
 * to be suspended. Initcalls doesn't need it.)
 */
extern void disable_boot_trace(void);
#else
static inline
void trace_boot_call(struct boot_trace_call *bt, initcall_t fn) { }

static inline
void trace_boot_ret(struct boot_trace_ret *bt, initcall_t fn) { }

static inline void start_boot_trace(void) { }
static inline void enable_boot_trace(void) { }
static inline void disable_boot_trace(void) { }
#endif /* CONFIG_BOOT_TRACER */

#endif /* __LINUX_TRACE_BOOT_H */