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

Steven Rostedt
2009-12-11T00:35:02Z

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;
>
>