Re: [PATCH] tracing - support multiple pids in set_pid_ftrace file

Li Zefan
2009-09-15T09:41:27Z

jolsa@redhat.com wrote:
> Adding the possibility to set more than 1 pid in the set_pid_ftrace file,
> thus allowing to trace more than 1 independent processes.
>
> Usage:
>
> sh-4.0# echo 284 > ./set_ftrace_pid
> sh-4.0# cat ./set_ftrace_pid
> 284
> sh-4.0# echo 1 >> ./set_ftrace_pid
> sh-4.0# echo 0 >> ./set_ftrace_pid
> sh-4.0# cat ./set_ftrace_pid
> swapper tasks
> 1
> 284
> sh-4.0# echo 4 > ./set_ftrace_pid
> sh-4.0# cat ./set_ftrace_pid
> 4
> sh-4.0# echo > ./set_ftrace_pid
> sh-4.0# cat ./set_ftrace_pid
> no pid
> sh-4.0#
>
>
> wbr,
> jirka
>
> Signed-off-by: Jiri Olsa <jolsa@redhat.com>
> ---
> kernel/trace/ftrace.c | 226 +++++++++++++++++++++++++++++++++++--------------
> kernel/trace/trace.h | 4 +-
> 2 files changed, 164 insertions(+), 66 deletions(-)
>
...
> +static void ftrace_pid_reset(void)
> +{
> + struct ftrace_pid *fpid, *safe;
> +
> + mutex_lock(&ftrace_lock);
> + list_for_each_entry_safe(fpid, safe, &ftrace_pids, list) {
> + struct pid *pid = fpid->pid;
> +
> + clear_ftrace_pid_task(&pid);

Now we can change clear_ftrace_pid_task() to take struct pid *
instead of struct pid**.

> +
> + if (pid != ftrace_swapper_pid)
> + put_pid(pid);
> +

clear_ftrace_pid_task() already called put_pid().

> + list_del(&fpid->list);
> + kfree(fpid);
> + }
> +
> + ftrace_update_pid_func();
> + ftrace_startup_enable(0);
> +
> + mutex_unlock(&ftrace_lock);
> +}
> +
...
> static ssize_t
> ftrace_pid_write(struct file *filp, const char __user *ubuf,
> size_t cnt, loff_t *ppos)
> {
> - struct pid *pid;
> char buf[64];
> long val;
> int ret;
> @@ -2897,57 +3016,36 @@ ftrace_pid_write(struct file *filp, const char __user *ubuf,
>
> buf[cnt] = 0;
>
> + /*
> + * Allow the "echo > set_ftrace_pid" to clean
> + * the pids quietly.
> + */
> + if (!*ppos && *buf == '\n' && cnt == 1)
> + return 1;
> +

How about:
strstrip(buf);
if (strlen(buf) == 0)
return 1;

So "echo -n '' > set_ftrace_pid" works too.

> ret = strict_strtol(buf, 10, &val);
> if (ret < 0)
> return ret;
>