linux-kernel - Re: [PATCH v4 04/10] user_events: Handle matching arguments from dyn

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Date:   Mon, 8 Nov 2021 17:05:53 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Beau Belgrave <beaub@...ux.microsoft.com>
Cc:     mhiramat@...nel.org, linux-trace-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 04/10] user_events: Handle matching arguments from
 dyn_events

On Thu,  4 Nov 2021 10:04:27 -0700
Beau Belgrave <beaub@...ux.microsoft.com> wrote:

> Ensures that when dynamic events requests a match with arguments that
> they match what is in the user_event.
> 
> Signed-off-by: Beau Belgrave <beaub@...ux.microsoft.com>
> ---
>  kernel/trace/trace_events_user.c | 67 +++++++++++++++++++++++++++++++-
>  1 file changed, 66 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> index 479a9ced3281..cd78cc481557 100644
> --- a/kernel/trace/trace_events_user.c
> +++ b/kernel/trace/trace_events_user.c
> @@ -662,13 +662,78 @@ static int user_event_free(struct dyn_event *ev)
>  	return destroy_user_event(user);
>  }
>  
> +static int user_field_match(struct ftrace_event_field *field, int argc,
> +			    const char **argv, int *iout)
> +{
> +	char field_name[256];
> +	char arg_name[256];

I'm a bit nervous about allocating that much on the stack. This isn't a
critical function. I think it is best to just kmalloc it, and fail in the
unlikely event that the kmalloc fails. It should never fail unless there's
major memory issues with the system.

-- Steve


> +	int len, pos, i = *iout;
> +	bool colon = false;
> +
> +	if (i >= argc)
> +		return false;
> +
> +	len = sizeof(arg_name);
> +	pos = 0;
> +
> +	for (; i < argc; ++i) {
> +		if (i != *iout)
> +			pos += snprintf(arg_name + pos, len - pos, " ");
> +
> +		pos += snprintf(arg_name + pos, len - pos, argv[i]);
> +
> +		if (strchr(argv[i], ';')) {
> +			++i;
> +			colon = true;
> +			break;
> +		}
> +	}
> +
> +	len = sizeof(field_name);
> +	pos = 0;
> +
> +	pos += snprintf(field_name + pos, len - pos, field->type);
> +	pos += snprintf(field_name + pos, len - pos, " ");
> +	pos += snprintf(field_name + pos, len - pos, field->name);
> +
> +	if (colon)
> +		pos += snprintf(field_name + pos, len - pos, ";");
> +
> +	*iout = i;
> +
> +	return strcmp(arg_name, field_name) == 0;
> +}
> +
> +static bool user_fields_match(struct user_event *user, int argc,
> +			      const char **argv)
> +{
> +	struct ftrace_event_field *field, *next;
> +	struct list_head *head = &user->fields;
> +	int i = 0;
> +
> +	list_for_each_entry_safe_reverse(field, next, head, link)
> +		if (!user_field_match(field, argc, argv, &i))
> +			return false;
> +
> +	if (i != argc)
> +		return false;
> +
> +	return true;
> +}
> +
>  static bool user_event_match(const char *system, const char *event,
>  			     int argc, const char **argv, struct dyn_event *ev)
>  {
>  	struct user_event *user = container_of(ev, struct user_event, devent);
> +	bool match;
>  
> -	return strcmp(EVENT_NAME(user), event) == 0 &&
> +	match = strcmp(EVENT_NAME(user), event) == 0 &&
>  		(!system || strcmp(system, USER_EVENTS_SYSTEM) == 0);
> +
> +	if (match && argc > 0)
> +		match = user_fields_match(user, argc, argv);
> +
> +	return match;
>  }
>  
>  static struct dyn_event_operations user_event_dops = {