Re: [PATCH][WIP]libtracefs:New API to enable the filtering of functions

[Sameeruddin Shaik <sameeruddin.shaik8@gmail.com>]

Yeah steve understood,
Will try to implement the functionality in phases.

On Wed, Feb 10, 2021 at 9:08 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Thu, 11 Feb 2021 08:33:50 +0530
> Sameeruddin Shaik <sameeruddin.shaik8@gmail.com> wrote:
>
> > By this you mean to say like, we have to do the filter functions
> > validation in the API?
> > or
> > shall we continue with tzvetomir idea (I mean depending on the kernel
> > validation)?
>
> I mean write to the file, and if it errors, then do our own operations on
> it. This would need to be documented in the man page for this function.
>
>
> For example:
>
>    filter = "sched*"
>
> would write into the file, which the kernel should turn into a selection of
> all functions that start with "sched".
>
> But if you had:
>
>    filter = "sched_feat_[^w].*"
>
> Which would set "sched_feat_open" and "sched_feat_show" but not
> "sched_feat_write". Since it is a regex and not a glob expression, it will
> fail the filter.
>
>  fd = open("set_ftrace_filter", O_WRONLY);
>  write(fd, "sched_feat_[^w].*", 7);
>
> Will return an error of EINVAL. When that happens, you should run this
> through the regex exec, and then use the result to find all the matches.
>
> Note, it should be implied that if the regex does not start with "^" and
> end with "$", then that should be added too.
>
>   "sched_feat_[^w].*" turns into "^sched_feat_[^w].*$"
>
> before processing it into the regex.
>
> You may be asking, what if someone wants to add something that is a regex,
> but also acceptable as a glob?
>
> Let's say you want "_*acpi_device_uevent_modalias", where you want:
>
>  "__acpi_device_uevent_modalias" and "acpi_device_uevent_modalias"
>
> But the glob would only select "__acpi_device_uevent_modalias"
>
> To force the regex, the user should just add "^" to the beginning of the
> string.
>
> Thus "_*acpi_device_uevent_modalias" wont work as expected, but
> "^_*acpi_device_uevent_modalias" will.
>
> Make sense?
>
> -- Steve
>