Re: [PATCH 07/10] trace_syscalls: init print_fmt

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 2009-12-09 at 15:15 +0800, Lai Jiangshan wrote:
> Init print_fmt for trace_syscalls.
> It will be used for replacing ->show_format().

This needs more explanation too.

> 
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> index 75289f3..dcd8699 100644
> --- a/kernel/trace/trace_syscalls.c
> +++ b/kernel/trace/trace_syscalls.c
> @@ -191,6 +191,61 @@ int syscall_enter_format(struct ftrace_event_call *call, struct trace_seq *s)
>  	return trace_seq_putc(s, '\n');
>  }
>  
> +static
> +int  __set_enter_print_fmt(struct syscall_metadata *entry, char *buf, int len)
> +{
> +	int i;
> +	int pos = 0;
> +
> +	pos += snprintf(buf + pos, len > pos ? len - pos : 0, "\"");
> +	for (i = 0; i < entry->nb_args; i++) {
> +		pos += snprintf(buf + pos, len > pos ? len - pos : 0,
> +				"%s: 0x%%0%zulx%s", entry->args[i],
> +				sizeof(unsigned long),
> +				i == entry->nb_args - 1 ? "" : ", ");
> +	}
> +	pos += snprintf(buf + pos, len > pos ? len - pos : 0, "\"");
> +
> +	for (i = 0; i < entry->nb_args; i++) {
> +		pos += snprintf(buf + pos, len > pos ? len - pos : 0,
> +				", ((unsigned long)(REC->%s))", entry->args[i]);

Yuck! 4 snprintf(buf + pos, len > pos ? len - pos: 0 ...

Please make a wrapper for that.

Actually, this could use the new trace_seq code if I separate the
buffer. You would just need to do:

	struct trace_seq s;

	trace_seq_init(&s, buf, len);

	trace_seq_putc(&s, '"');
	for (i = 0; i < entry->nb_args; i++)
		trace_seq_printf(&s, "%s: 0x%%0%zulx%s", entry->args[i],
				sizeof(unsigned long),
				i == entry->nb_args - 1 ? "" : ", ");

	trace_seq_putc(&s, '"');

	for (i = 0; i < entry->nb_args; i++)
		trace_seq_printf(&s, ", ((unsigned long)(REC->%s)",
				entry->args[i]);

	return s.len;


Looks much better, and less error prone.

-- Steve

> +	}
> +
> +	/* return the length of print_fmt */
> +	return pos;
> +}
> +
> +static int set_syscall_print_fmt(struct ftrace_event_call *call)
> +{
> +	char *print_fmt;
> +	int len;
> +	struct syscall_metadata *entry = call->data;
> +
> +	if (entry->enter_event != call) {
> +		call->print_fmt = "\"0x%lx\", REC->ret";
> +		return 0;
> +	}
> +
> +	len = __set_enter_print_fmt(entry, NULL, 0);
> +
> +	print_fmt = kmalloc(len + 1, GFP_KERNEL);
> +	if (!print_fmt)
> +		return -ENOMEM;
> +
> +	__set_enter_print_fmt(entry, print_fmt, len + 1);
> +	call->print_fmt = print_fmt;
> +
> +	return 0;
> +}
> +
> +static void free_syscall_print_fmt(struct ftrace_event_call *call)
> +{
> +	struct syscall_metadata *entry = call->data;
> +
> +	if (entry->enter_event == call)
> +		kfree(call->print_fmt);
> +}
> +
>  int syscall_exit_format(struct ftrace_event_call *call, struct trace_seq *s)
>  {
>  	int ret;
> @@ -386,9 +441,14 @@ int init_syscall_trace(struct ftrace_event_call *call)
>  {
>  	int id;
>  
> +	if (set_syscall_print_fmt(call) < 0)
> +		return -ENOMEM;
> +
>  	id = register_ftrace_event(call->event);
> -	if (!id)
> +	if (!id) {
> +		free_syscall_print_fmt(call);
>  		return -ENODEV;
> +	}
>  	call->id = id;
>  	INIT_LIST_HEAD(&call->fields);
>  	return 0;
> 
>