Re: [PATCH] libtracefs: An API to set the filtering of functions

[Tzvetomir Stoyanov <tz.stoyanov@gmail.com>]

On Mon, Mar 1, 2021 at 10:40 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Tue,  2 Mar 2021 22:45:10 +0530
> Sameeruddin shaik <sameeruddin.shaik8@gmail.com> wrote:
>
> > This new API will write the function filters into the
> > set_ftrace_filter file, it will write only string as of now, it can't
> > handle kernel glob or regular expressions.
>
> The limitation of no glob or regular expressions is fine. We can add that
> in future patches.
>
> >
> > tracefs_function_filter()
> >
> > https://bugzilla.kernel.org/show_bug.cgi?id=210643
> >
> > Signed-off-by: Sameeruddin shaik <sameeruddin.shaik8@gmail.com>
> >
[ ... ]
>
> > +                     free(each_str);
> > +                     continue;
> > +             }
> > +             size += write(fd, each_str, write_size);
>
> Need to check errors here, and we need a way to report that an error
> happened for a string. Perhaps the API also needs to have an error message
> pointer that is passed in? Or a bitmask that lets the user know which
> filter failed?
>
> Tzvetomir, have any ideas on how to report back to the caller which filter
> failed? Could just send back an array of strings of the filters that failed.

It is very useful to have a way to report back the failed filters.
Using an array
of strings will work for this API, but I was thinking somehow to leverage the
error_log file by the ftrace itself. Currently it does not report any
error, just
returns EINVAL. In more complex filters it would be useful to log
more detailed description of the problem in the error_log file.

[ ... ]


-- 
Tzvetomir (Ceco) Stoyanov
VMware Open Source Technology Center