Date:   Mon, 13 Dec 2021 14:21:19 -0600
From:   Tom Zanussi <zanussi@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     rostedt@...dmis.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/4] tracing: Add helper functions to simplify
 event_command.parse() callback handling

Hi Masami,

On Mon, 2021-12-13 at 22:46 +0900, Masami Hiramatsu wrote:
> Hi Tom,
> 
> On Fri, 10 Dec 2021 15:16:24 -0600
> Tom Zanussi <zanussi@...nel.org> wrote:
> 
> > +/*
> > + * Event trigger parsing helper functions.
> > + *
> > + * These functions help make it easier to write an event trigger
> > + * parsing function i.e. the struct event_command.parse() callback
> > + * function responsible for parsing and registering a trigger
> > command
> > + * written to the 'trigger' file.
> > + *
> > + * A trigger command (or just 'trigger' for short) takes the form:
> > + *   [trigger] [if filter]
> > + *
> > + * The struct event_command.parse() callback (and other struct
> > + * event_command functions) refer to several components of a
> > trigger
> > + * command.  Those same components are referenced by the event
> > trigger
> > + * parsing helper functions defined below.  These components are:
> > + *
> > + *   cmd     - the trigger command name
> > + *   glob    - the trigger command name optionally prefaced with
> > '!'
> > + *   param   - text remaining after the command is stripped of cmd
> > and ':'
> > + *   filter  - the optional filter text following (and including)
> > 'if'
> > + *
> > + * To illustrate the use of these componenents, here are some
> > concrete
> > + * examples. For the following triggers:
> > + *
> > + *   echo 'traceon:5 if pid == 0' > trigger
> > + *     - 'traceon' is both cmd and glob
> > + *     - '5 if pid == 0' is the param
> > + *     - 'if pid == 0' is the filter
> 
> I would like to know why both 'param' and 'filter' has "if pid == 0".
> I thought that part is (generic) filter and not a parameter.
> 
> If I missed any discussion on this point, sorry about that.

No discussion about this in particular, but from Steve's review I did
change 'param' to 'param_and_filter' in the code.  So I guess I should
change these to strip the filter from the param when describing them,
and then it's obvious that param_and_filter refers to the combination. 
I'll change that in the next version.

> 
> > + *
> > + *   echo 'enable_event:sys:event:n' > trigger
> > + *     - 'enable_event' is both cmd and glob
> > + *     - 'sys:event:n' is the param
> > + *     - there is no filter
> > + *
> > + *   echo 'hist:keys=pid if prio > 50' > trigger
> > + *     - 'hist' is both cmd and glob
> > + *     - 'keys=pid if prio > 50' is the param
> > + *     - 'if prio > 50' is the filter
> > + *
> > + *   echo '!enable_event:sys:event:n' > trigger
> > + *     - 'enable_event' the cmd
> > + *     - '!enable_event' is the glob
> > + *     - 'sys:event:n' is the param
> > + *     - there is no filter
> > + *
> > + *   echo 'traceoff' > trigger
> > + *     - 'traceoff' is both cmd and glob
> > + *     - there is no param
> > + *     - there is no filter
> > + *
> > + * There are a few different categories of event trigger covered
> > by
> > + * these helpers:
> > + *
> > + *  - triggers that don't require a parameter e.g. traceon
> > + *  - triggers that do require a parameter e.g. enable_event and
> > hist
> > + *  - triggers that though they may not require a param may
> > support an
> > + *    optional 'n' param (n = number of times the trigger should
> > fire)
> > + *    e.g.: traceon:5 or enable_event:sys:event:n
> > + *  - triggers that do not support an 'n' param e.g. hist
> > + *
> > + * These functions can be used or ignored as necessary - it all
> > + * depends on the complexity of the trigger, and the granularity
> > of
> > + * the functions supported reflects the fact that some
> > implementations
> > + * may need to customize certain aspects of their implementations
> > and
> > + * won't need certain functions.  For instance, the hist trigger
> > + * implementation doesn't use event_trigger_separate_filter()
> > because
> > + * it has special requirements for handling the filter.
> > + */
> > +
> > +/**
> > + * event_trigger_check_remove - check whether an event trigger
> > specifies remove
> > + * @glob: The trigger command string, with optional remove(!)
> > operator
> > + *
> > + * The event trigger callback implementations pass in 'glob' as a
> > + * parameter.  This is the command name either with or without a
> > + * remove(!)  operator.  This function simply parses the glob and
> > + * determines whether the command corresponds to a trigger removal
> > or
> > + * a trigger addition.
> > + *
> > + * Return: true if this is a remove command, false otherwise
> > + */
> > +bool event_trigger_check_remove(const char *glob)
> > +{
> > +	return (glob && glob[0] == '!') ? true : false;
> > +}
> > +
> > +/**
> > + * event_trigger_empty_param - check whether the param is empty
> > + * @param: The trigger param string
> > + *
> > + * The event trigger callback implementations pass in 'param' as a
> > + * parameter.  This corresponds to the string following the
> > command
> > + * name minus the command name.  This function can be called by a
> > + * callback implementation for any command that requires a param;
> > a
> > + * callback that doesn't require a param can ignore it.
> > + *
> > + * Return: true if this is an empty param, false otherwise
> > + */
> > +bool event_trigger_empty_param(const char *param)
> > +{
> > +	return !param;
> > +}
> > +
> > +/**
> > + * event_trigger_separate_filter - separate an event trigger from
> > a filter
> > + * @param: The param string containing trigger and possibly filter
> > + * @trigger: outparam, will be filled with a pointer to the
> > trigger
> > + * @filter: outparam, will be filled with a pointer to the filter
> > + * @param_required: Specifies whether or not the param string is
> > required
> > + *
> > + * Given a param string of the form '[trigger] [if filter]', this
> > + * function separates the filter from the trigger and returns the
> > + * trigger in *trigger and the filter in *filter.  Either the
> > *trigger
> > + * or the *filter may be set to NULL by this function - if not set
> > to
> > + * NULL, they will contain strings corresponding to the trigger
> > and
> > + * filter.
> > + *
> > + * There are two cases that need to be handled with respect to the
> > + * passed-in param: either the param is required, or it is not
> > + * required.  If @param_required is set, and there's no param, it
> > will
> > + * return -EINVAL.  If @param_required is not set and there's a
> > param
> > + * that starts with a number, that corresponds to the case of a
> > + * trigger with :n (n = number of times the trigger should fire)
> > and
> > + * the parsing continues normally; otherwise the function just
> > returns
> > + * and assumes param just contains a filter and there's nothing
> > else
> > + * to do.
> > + *
> > + * Return: 0 on success, errno otherwise
> > + */
> > +int event_trigger_separate_filter(char *param_and_filter, char
> > **param,
> > +				  char **filter, bool param_required)
> > +{
> > +	int ret = 0;
> > +
> > +	*param = *filter = NULL;
> > +
> > +	if (!param_and_filter) {
> > +		if (param_required)
> > +			ret = -EINVAL;
> > +		goto out;
> > +	}
> > +
> > +	/*
> > +	 * Here we check for an optional param. The only legal
> > +	 * optional param is :n, and if that's the case, continue
> > +	 * below. Otherwise we assume what's left is a filter and
> > +	 * return it as the filter string for the caller to deal with.
> > +	 */
> > +	if (!param_required && param_and_filter &&
> > !isdigit(param_and_filter[0])) {
> > +		*filter = param_and_filter;
> > +		goto out;
> > +	}
> > +
> > +	/*
> > +	 * Separate the param from the filter (param [if filter]).
> > +	 * Here we have either an optional :n param or a required
> > +	 * param and an optional filter.
> > +	 */
> > +	*param = strsep(&param_and_filter, " \t");
> > +	if (!*param) {
> > +		ret = -EINVAL;
> 
> This seems not happen because this means "!param_and_filter" and
> that is already checked at the entry of this function.

Yes, I think you're correct.  I can just remove that check.

> 
> > +		goto out;
> > +	}
> > +
> > +	/*
> > +	 * Here we have a filter, though it may be empty.
> > +	 */
> > +	if (param_and_filter) {
> > +		*filter = skip_spaces(param_and_filter);
> > +		if (!**filter)
> > +			*filter = NULL;
> > +	}
> > +out:
> > +	return ret;
> > +}
> > +
> > +/**
> > + * event_trigger_alloc - allocate and init event_trigger_data for
> > a trigger
> > + * @cmd_ops: The event_command operations for the trigger
> > + * @cmd: The cmd string
> > + * @param: The param string
> > + * @private_data: User data to associate with the event trigger
> > + *
> > + * Allocate an event_trigger_data instance and initialize it.  The
> > + * @cmd_ops are used along with the @cmd and @param to get the
> > + * trigger_ops to assign to the event_trigger_data.  @private_data
> > can
> > + * also be passed in and associated with the event_trigger_data.
> > + *
> > + * Use event_trigger_free() to free an event_trigger_data object.
> > + *
> > + * Return: The trigger_data object success, NULL otherwise
> > + */
> > +struct event_trigger_data *event_trigger_alloc(struct
> > event_command *cmd_ops,
> > +					       char *cmd,
> > +					       char *param,
> > +					       void *private_data)
> > +{
> > +	struct event_trigger_data *trigger_data;
> > +	struct event_trigger_ops *trigger_ops;
> > +
> > +	trigger_ops = cmd_ops->get_trigger_ops(cmd, param);
> > +
> > +	trigger_data = kzalloc(sizeof(*trigger_data), GFP_KERNEL);
> > +	if (!trigger_data)
> > +		return NULL;
> > +
> > +	trigger_data->count = -1;
> > +	trigger_data->ops = trigger_ops;
> > +	trigger_data->cmd_ops = cmd_ops;
> > +	trigger_data->private_data = private_data;
> > +
> > +	INIT_LIST_HEAD(&trigger_data->list);
> > +	INIT_LIST_HEAD(&trigger_data->named_list);
> > +	RCU_INIT_POINTER(trigger_data->filter, NULL);
> > +
> > +	return trigger_data;
> > +}
> > +
> > +/**
> > + * event_trigger_parse_num - parse and return the number param for
> > a trigger
> > + * @trigger: The trigger string
> 
> Does this mean trigger parameter?

Yes, I'll change this to 'param'.

> 
> > + * @trigger_data: The trigger_data for the trigger
> > + *
> > + * Parse the :n (n = number of times the trigger should fire)
> > param
> > + * and set the count variable in the trigger_data to the parsed
> > count.
> > + *
> > + * Return: 0 on success, errno otherwise
> > + */
> > +int event_trigger_parse_num(char *trigger,
> > +			    struct event_trigger_data *trigger_data)
> > +{
> > +	char *number;
> > +	int ret = 0;
> > +
> > +	if (trigger) {
> > +		number = strsep(&trigger, ":");
> > +
> > +		if (!strlen(number))
> > +			return -EINVAL;
> > +
> > +		/*
> > +		 * We use the callback data field (which is a pointer)
> > +		 * as our counter.
> > +		 */
> > +		ret = kstrtoul(number, 0, &trigger_data->count);
> > +	}
> > +
> > +	return ret;
> > +}
> 
> Does this work with '!enable_event:sys:event:n' case?
> (we need to find the last parameter.)

Yes, because :n isn't used in that case. Since you can't have multiple
'enable_event:sys:event:n' where sys:event are the same, whether using
:n or not, it suffices for delete to use only sys:event and ignore :n.

Thanks,

Tom

> 
> Thank you,
> 
> 

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