linux-kernel - Re: [PATCH v3 04/12] tracing: Add dynamic event command creation interface

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Date:   Wed, 29 Jan 2020 13:00:18 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Tom Zanussi <zanussi@...nel.org>
Cc:     artem.bityutskiy@...ux.intel.com, mhiramat@...nel.org,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
        ndesaulniers@...gle.com
Subject: Re: [PATCH v3 04/12] tracing: Add dynamic event command creation
 interface

On Fri, 24 Jan 2020 16:56:15 -0600
Tom Zanussi <zanussi@...nel.org> wrote:

> +/**
> + * 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);
> +		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;

This looks like you can take advantage of the seq_buf code
(see /lib/seq_buf.c), as that handles a lot of this for you.

As I'm trying to get this into the merge window, I won't delay this for
that (unless I find something else to delay this for), but this should
definitely incorporate seq_buf and not handle its own buffering.

-- Steve



> +
> +	return ret;
> +}