Re: [PATCH 7/7] V2 add syscall tracepoints

[Li Zefan]

>  #endif /* _TRACE_SYSCALL_H */
> diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> index 08aed43..cc283d6 100644
> --- a/kernel/trace/trace_syscalls.c
> +++ b/kernel/trace/trace_syscalls.c
> @@ -1,15 +1,16 @@
>  #include <trace/syscall.h>
>  #include <linux/kernel.h>
> +#include <linux/ftrace.h>
>  #include <asm/syscall.h>
>  
>  #include "trace_output.h"
>  #include "trace.h"
>  
> -/* Keep a counter of the syscall tracing users */
> -static int refcount;
> -
> -/* Prevent from races on thread flags toggling */
>  static DEFINE_MUTEX(syscall_trace_lock);
> +static int sys_refcount_enter;
> +static int sys_refcount_exit;
> +static DECLARE_BITMAP(enabled_enter_syscalls, FTRACE_SYSCALL_MAX + 1);
> +static DECLARE_BITMAP(enabled_exit_syscalls, FTRACE_SYSCALL_MAX + 1);

Why "+ 1" ?

> -static int init_syscall_tracer(struct trace_array *tr)
> +int reg_event_syscall_enter(char *name)
>  {
> -	start_ftrace_syscalls();
> +	int ret = 0;
> +	int num;
>  
> -	return 0;
> +	num = syscall_name_to_nr(name);
> +	if (num < 0 || num > FTRACE_SYSCALL_MAX)
> +		return -ENOSYS;

syscall_name_to_nr() returns [0, FTRACE_SYSCALL_MAX) or -1,
so you don't need to check num > MAX, instead it should be
WAR_ON(num >= MAX).

> +	mutex_lock(&syscall_trace_lock);
> +	if (!sys_refcount_enter)
> +		ret = register_trace_syscall_enter(ftrace_syscall_enter);
> +	if (ret) {
> +		pr_info("event trace: Could not activate"
> +				"syscall entry trace point");

Should be:

+		pr_info("event trace: Could not activate "
+				"syscall entry trace point");

> +	} else {
> +		set_bit(num, enabled_enter_syscalls);
> +		sys_refcount_enter++;
> +	}
> +	mutex_unlock(&syscall_trace_lock);
> +	return ret;
>  }

> +int reg_event_syscall_exit(char *name)
>  {
> -	int ret;
> +	int ret = 0;
> +	int num;
>  
> -	ret = register_ftrace_event(&syscall_enter_event);
> -	if (!ret) {
> -		printk(KERN_WARNING "event %d failed to register\n",
> -		       syscall_enter_event.type);
> -		WARN_ON_ONCE(1);
> +	num = syscall_name_to_nr(name);
> +	if (num < 0 || num > FTRACE_SYSCALL_MAX)
> +		return -ENOSYS;

ditto

> +	mutex_lock(&syscall_trace_lock);
> +	if (!sys_refcount_exit)
> +		ret = register_trace_syscall_exit(ftrace_syscall_exit);
> +	if (ret) {
> +		pr_info("event trace: Could not activate"
> +				"syscall exit trace point");

ditto

> +	} else {
> +		set_bit(num, enabled_exit_syscalls);
> +		sys_refcount_exit++;
>  	}
> +	mutex_unlock(&syscall_trace_lock);
> +	return ret;
> +}
>  
> -	ret = register_ftrace_event(&syscall_exit_event);
> -	if (!ret) {
> -		printk(KERN_WARNING "event %d failed to register\n",
> -		       syscall_exit_event.type);
> -		WARN_ON_ONCE(1);
> -	}
> +void unreg_event_syscall_exit(char *name)
> +{
> +	int num;
>  
> -	return register_tracer(&syscall_tracer);
> +	num = syscall_name_to_nr(name);
> +	if (num < 0 || num > FTRACE_SYSCALL_MAX)
> +		return;

ditto

> +	mutex_lock(&syscall_trace_lock);
> +	sys_refcount_exit--;
> +	clear_bit(num, enabled_exit_syscalls);
> +	if (!sys_refcount_exit)
> +		unregister_trace_syscall_exit(ftrace_syscall_exit);
> +	mutex_unlock(&syscall_trace_lock);
>  }
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