Re: [PATCH] synth_events: Do not block other dyn_event systems during create

Re: [PATCH] synth_events: Do not block other dyn_event systems during create

[Masami Hiramatsu]

Hi Beau,

On Thu, 30 Sep 2021 15:38:21 -0700
Beau Belgrave <beaub@linux.microsoft.com> wrote:

> synth_events is returning -EINVAL if the dyn_event create command does
> not contain ' \t'. This prevents other systems from getting called back.
> synth_events needs to return -ECANCELED in these cases when the command
> is not targeting the synth_event system.

Thanks for clean up the synthetic event!
This looks good to me.

Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>

So now are you trying to reuse synth event for user event?
Then I think you need to register a new dyn_event ops so
that histogram will not submit the event.

BTW, how do you filter an event written by a user process?
Will you add an array of event id for the file data structure?

Thank you,

> 
> Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
> ---
>  kernel/trace/trace_events_synth.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
> index 9315fc03e303..08b7ea639cea 100644
> --- a/kernel/trace/trace_events_synth.c
> +++ b/kernel/trace/trace_events_synth.c
> @@ -2051,6 +2051,13 @@ static int create_synth_event(const char *raw_command)
>  
>  	last_cmd_set(raw_command);
>  
> +	name = raw_command;
> +
> +	/* Don't try to process if not our system */
> +	if (name[0] != 's' || name[1] != ':')
> +		return -ECANCELED;
> +	name += 2;
> +
>  	p = strpbrk(raw_command, " \t");
>  	if (!p) {
>  		synth_err(SYNTH_ERR_INVALID_CMD, 0);
> @@ -2059,12 +2066,6 @@ static int create_synth_event(const char *raw_command)
>  
>  	fields = skip_spaces(p);
>  
> -	name = raw_command;
> -
> -	if (name[0] != 's' || name[1] != ':')
> -		return -ECANCELED;
> -	name += 2;
> -
>  	/* This interface accepts group name prefix */
>  	if (strchr(name, '/')) {
>  		len = str_has_prefix(name, SYNTH_SYSTEM "/");
> -- 
> 2.17.1
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>

Re: [PATCH] synth_events: Do not block other dyn_event systems during create

[Beau Belgrave]

> Thanks for clean up the synthetic event!
> This looks good to me.
> 
> Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
No problem, thanks for the review!

> So now are you trying to reuse synth event for user event?
> Then I think you need to register a new dyn_event ops so
> that histogram will not submit the event.
A user events patch will get sent out soon, I'm finalizing some testing.
User events will register it's own dyn_event ops and allow users the
option to create, delete and view status of user events via the
dynamic_events tracefs file (in addition to the user mode IOCTL/ABI).

As probes attach to the user events the status of this is reflected in
dynamic_events, which makes it easy for admins to see why one is busy,
etc. It also makes it easy to verifying the system is working as
expected with just a terminal.

> BTW, how do you filter an event written by a user process?
> Will you add an array of event id for the file data structure?
The filtering would happen at the trace_event level, the only filtering
at the user event level is if a probe has been enabled on the underlying
trace_event or not. That is done via the shared page bits being cleared
or set. Bits are updated as probe un/registrations occur.

Users can advertise field values, offsets, etc as well as the print_fmt
in the newer ABI/patch based on the feedback from LPC2021. These land in
the trace_event fields and are viewable via tracefs like any other
evnet. I hope that is enough to light up the history feature of trace_event.
I am not familiar with it as much as you all.

Thanks,
-Beau