Re: [PATCH v4 04/12] tracing: Add dynamic event command creation interface

[Masami Hiramatsu <mhiramat@kernel.org>]

Hi Tom

On Wed, 29 Jan 2020 12:59:24 -0600
Tom Zanussi <zanussi@kernel.org> wrote:

> Add an interface used to build up dynamic event creation commands,
> such as synthetic and kprobe events.  Interfaces specific to those
> particular types of events and others can be built on top of this
> interface.
> 
> Command creation is started by first using the dynevent_cmd_init()
> function to initialize the dynevent_cmd object.  Following that, args
> are appended and optionally checked by the dynevent_arg_add() and
> dynevent_arg_pair_add() functions, which use objects representing
> arguments and pairs of arguments, initialized respectively by
> dynevent_arg_init() and dynevent_arg_pair_init().  Finally, once all
> args have been successfully added, the command is finalized and
> actually created using dynevent_create().
> 
> The code here for actually printing into the dyn_event->cmd buffer
> using snprintf() etc was adapted from v4 of Masami's 'tracing/boot:
> Add synthetic event support' patch.
> 
> Signed-off-by: Tom Zanussi <zanussi@kernel.org>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  include/linux/trace_events.h  |  23 ++++
>  kernel/trace/trace_dynevent.c | 240 ++++++++++++++++++++++++++++++++++++++++++
>  kernel/trace/trace_dynevent.h |  33 ++++++
>  3 files changed, 296 insertions(+)
> 
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index 25fe743bcbaf..651b03d5e272 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -354,6 +354,29 @@ extern struct trace_event_file *trace_get_event_file(const char *instance,
>  						     const char *event);
>  extern void trace_put_event_file(struct trace_event_file *file);
>  
> +#define MAX_DYNEVENT_CMD_LEN	(2048)
> +
> +enum dynevent_type {
> +	DYNEVENT_TYPE_NONE,
> +};
> +
> +struct dynevent_cmd;
> +
> +typedef int (*dynevent_create_fn_t)(struct dynevent_cmd *cmd);
> +
> +struct dynevent_cmd {
> +	char			*buf;
> +	const char		*event_name;
> +	int			maxlen;
> +	int			remaining;
> +	unsigned int		n_fields;
> +	enum dynevent_type	type;
> +	dynevent_create_fn_t	run_command;
> +	void			*private_data;
> +};
> +
> +extern int dynevent_create(struct dynevent_cmd *cmd);
> +
>  extern int synth_event_delete(const char *name);
>  
>  /*
> diff --git a/kernel/trace/trace_dynevent.c b/kernel/trace/trace_dynevent.c
> index 89779eb84a07..6ffdbc4fda53 100644
> --- a/kernel/trace/trace_dynevent.c
> +++ b/kernel/trace/trace_dynevent.c
> @@ -223,3 +223,243 @@ static __init int init_dynamic_event(void)
>  	return 0;
>  }
>  fs_initcall(init_dynamic_event);
> +
> +/**
> + * dynevent_arg_add - Add an arg to a dynevent_cmd
> + * @cmd: A pointer to the dynevent_cmd struct representing the new event cmd
> + * @arg: The argument to append to the current cmd
> + *
> + * Append an argument to a dynevent_cmd.  The argument string will be
> + * appended to the current cmd string, followed by a separator, if
> + * applicable.  Before the argument is added, the check_arg()
> + * function, if defined, is called.
> + *
> + * The cmd string, separator, and check_arg() function should be set
> + * using the dynevent_arg_init() before any arguments are added using
> + * this function.
> + *
> + * Return: 0 if successful, error otherwise.
> + */
> +int dynevent_arg_add(struct dynevent_cmd *cmd,
> +		     struct dynevent_arg *arg)
> +{
> +	int ret = 0;
> +	int delta;
> +	char *q;
> +
> +	if (arg->check_arg) {
> +		ret = arg->check_arg(arg);

Hmm, this seems a bit odd. The check_arg() arg object member check
the validity of the object itself. What about moving those checker
into dynevent_cmd instead of dynevent_arg?
(Or, just pass the appropriate checker as the 3rd parameter of
 this function)

> +		if (ret)
> +			return ret;
> +	}
> +
> +	q = cmd->buf + (cmd->maxlen - cmd->remaining);
> +
> +	delta = snprintf(q, cmd->remaining, " %s%c", arg->str, arg->separator);
> +	if (delta >= cmd->remaining) {
> +		pr_err("String is too long: %s\n", arg->str);
> +		return -E2BIG;
> +	}
> +	cmd->remaining -= delta;
> +
> +	return ret;
> +}
> +
> +/**
> + * dynevent_arg_pair_add - Add an arg pair to a dynevent_cmd
> + * @cmd: A pointer to the dynevent_cmd struct representing the new event cmd
> + * @arg_pair: The argument pair to append to the current cmd
> + *
> + * Append an argument pair to a dynevent_cmd.  An argument pair
> + * consists of a left-hand-side argument and a right-hand-side
> + * argument separated by an operator, which can be whitespace, all
> + * followed by a separator, if applicable.  This can be used to add
> + * arguments of the form 'type variable_name;' or 'x+y'.
> + *
> + * The lhs argument string will be appended to the current cmd string,
> + * followed by an operator, if applicable, followd by the rhs string,
> + * followed finally by a separator, if applicable.  Before anything is
> + * added, the check_arg() function, if defined, is called.
> + *
> + * The cmd strings, operator, separator, and check_arg() function
> + * should be set using the dynevent_arg_pair_init() before any arguments
> + * are added using this function.
> + *
> + * Return: 0 if successful, error otherwise.
> + */
> +int dynevent_arg_pair_add(struct dynevent_cmd *cmd,
> +			  struct dynevent_arg_pair *arg_pair)
> +{
> +	int ret = 0;
> +	int delta;
> +	char *q;
> +
> +	if (arg_pair->check_arg) {
> +		ret = arg_pair->check_arg(arg_pair);

Ditto.

> +		if (ret)
> +			return ret;
> +	}
> +
> +	q = cmd->buf + (cmd->maxlen - cmd->remaining);
> +
> +	delta = snprintf(q, cmd->remaining, " %s%c", arg_pair->lhs,
> +			 arg_pair->operator);
> +	if (delta >= cmd->remaining) {
> +		pr_err("field string is too long: %s\n", arg_pair->lhs);
> +		return -E2BIG;
> +	}
> +	cmd->remaining -= delta; q += delta;
> +
> +	delta = snprintf(q, cmd->remaining, "%s%c", arg_pair->rhs,
> +			 arg_pair->separator);
> +	if (delta >= cmd->remaining) {
> +		pr_err("field string is too long: %s\n", arg_pair->rhs);
> +		return -E2BIG;
> +	}
> +	cmd->remaining -= delta; q += delta;

Here, q += delta is redundant, because q is not used anymore.

> +
> +	return ret;
> +}
> +

Thank you,


-- 
Masami Hiramatsu <mhiramat@kernel.org>