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From: sameeruddin shaik <sameeruddin.shaik8@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>, linux-trace-devel@vger.kernel.org
Subject: Re: [PATCH 0/7] libtracfes: Add tracefs_function_filter()
Date: Fri, 26 Mar 2021 05:55:46 +0530
Message-ID: <743080c8-6b22-83b7-6b2b-0221c2ee945b@gmail.com> (raw)
In-Reply-To: <20210323085220.6e20d125@gandalf.local.home>


On 23/03/21 6:22 pm, Steven Rostedt wrote:
> On Mon, 22 Mar 2021 21:27:55 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
>> This adds a new API tracefs_function_filter() as described in:
>>
>>   https://bugzilla.kernel.org/show_bug.cgi?id=210643
>>
>> It will use regular expressions against available_filter_functions (or even
>> the kernel glob expression) to enable the function by the index method if it
>> is supported. If it is not supported, it will go back to the writing of the
>> filter strings directly into the set_ftrace_filter file.
>>
>>
> Playing with the interface some more, I feel it's not quite adequate.
>
> The returning the negative number of filters that failed, isn't very
> useful. Having the errs array that points to those filters gives us that
> information.
Yeah, Anyway we are pointing the failed filters using the errs pointer. 
But to differentiate

the failed filters from the general errors, we can return -1, what you say?
>
> Also, because of the way that file works in the kernel, we need to be able
> to call this function several times without closing the file. That's
> because the actions take place when the file is closed, *not* when a write
> is made. Having the interface return errors without closing the file would
> allow the user to fix the failed filters and try again.
>
> I plan on committing this patch series, so any new changes will be done on
> top of them. But here's what I think needs to be done to make the interface
> more usable.
>
>   - Create a tracefs_function_filter_commit(instance) API that will close
>     the file and commit the changes.
>
>   - Have the tracefs_function_filter() open the set_ftrace_filter file if it
>     is not already opened. This will allow for the function to be called
>     multiple times. The file descriptor will be part of the instance
>     descriptor or a global variable for the top level instance. The opening
>     of the files will need to be protected by a pthread mutex.
>     Note, the "reset" parameter is only applicable if the file is not
>     already opened.
>
>   - On success, return 0 and tracefs_function_filter_commit() must be called.
>
>   - If the file descriptor is opened and an error happens, return 1, and the
>     tracefs_function_filter_commit() still needs to be called, but the user
>     can call tracefs_function_filter() again to try to fix the problem.
>
>   - If an error is found before the file descriptor is opened, then
>     tracefs_function_filter_commit() does not need to be called.
>
> That is:
>
> 	ret = tracefs_function_filter(...);
> 	if (ret >= 0)
> 		tracefs_function_filter_commit();
>
>   - Now for errs, it will be allocated if a problem happened on a filter,
>     and may be set if the return value is non zero (1 or -1). The user can
>     use it to know if the problem happened on a filter as well as find out
>     which filter had the problem.
>
>   - We can have a tracefs_read_function_filter() that returns an array of
>     strings which ends with a NULL pointer (and needs to be freed with
>     tracefs_list_free(), and have this:
>
>     save_filters = tracefs_read_function_filter(instance);
>
>     ret = tracefs_function_filter(instance, filters, NULL, true, &errs);
>     if (ret > 0 && errs) {
> 	/* Modified but failed */
> 	int i, j;
> 	for (i = 0; filters[i]; i++)
> 		;
> 	for (j = 0; errs[i]; j++)
> 		;
> 	if (i == j)
> 		/* all filters failed! Put back the original */
> 		tracefs_function_filter(instance, save_filters, NULL, false, NULL);
>     }
>     if (ret >= 0)
> 	tracefs_function_filter_commit(instance);
>
> Another reason to have it not close the file is because we only support
> passing in one module at a time. If the user wants to enable functions in
> two modules, they would need to call this twice, and we want them to be
> able to do so and have both changes take affect at the same time.
>
> Thoughts?
>
> -- Steve

  parent reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-23  1:27 Steven Rostedt
2021-03-23  1:27 ` [PATCH 1/7] libtracefs: An API to set the filtering of functions Steven Rostedt
2021-03-23  1:27 ` [PATCH 2/7] libtracefs: Move opening of file out of controlled_write() Steven Rostedt
2021-03-23  1:27 ` [PATCH 3/7] libtracefs: Add add_errors() helper function for control_write() Steven Rostedt
2021-03-23  1:27 ` [PATCH 4/7] libtracefs: Add checking of available_filter_functions to tracefs_function_filter() Steven Rostedt
2021-03-23  1:28 ` [PATCH 5/7] libtracefs: Add write_filter() helper function Steven Rostedt
2021-03-23  1:28 ` [PATCH 6/7] libtracefs: Allow for setting filters with regex expressions Steven Rostedt
2021-03-23  1:28 ` [PATCH 7/7] libtracefs: Add indexing to set functions in tracefs_function_filter() Steven Rostedt
2021-03-23 12:52 ` [PATCH 0/7] libtracfes: Add tracefs_function_filter() Steven Rostedt
2021-03-24 10:13   ` Sameeruddin Shaik
2021-03-24 14:08     ` Steven Rostedt
2021-03-26  0:25   ` sameeruddin shaik [this message]
2021-03-25  0:35     ` Steven Rostedt

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