Re: [PATCH 08/13 v2] libtracefs: Allow for setting filters with regex expressions

[sameeruddin shaik <sameeruddin.shaik8@gmail.com>]

hi steve,

On 31/03/21 10:09 pm, Steven Rostedt wrote:
> On Thu, 1 Apr 2021 22:03:02 +0530
> sameeruddin shaik <sameeruddin.shaik8@gmail.com> wrote:
>
>> hi steve,
>>
>> On 30/03/21 6:21 am, Steven Rostedt wrote:
>>> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
>>>
>>> All for full "regex(3)" processing of setting functions in the
>>> set_ftrace_filter file. Check if the filter passed in is just a glob
>>> expression that the kernel can process, or if it is a regex that should look
>>> at the available_filter_functions list instead.
>>>
>>> If it is a regex, it will read the available_filter_functions and write in
>>> each function as it finds it.
>>>
>>> Link: https://lore.kernel.org/linux-trace-devel/20210323013225.451281989@goodmis.org
>>>
>>> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
>>> ---
>>>    Documentation/libtracefs-function-filter.txt |  10 ++
>>>    src/tracefs-tools.c                          | 139 ++++++++++++++++---
>>>    2 files changed, 128 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/Documentation/libtracefs-function-filter.txt b/Documentation/libtracefs-function-filter.txt
>>> index c0c89f372c21..88aa3b923d54 100644
>>> --- a/Documentation/libtracefs-function-filter.txt
>>> +++ b/Documentation/libtracefs-function-filter.txt
>>> @@ -32,6 +32,16 @@ _errs_, is a pointer to an array of strings, which will be allocated if
>>>    any of filters fail to match any available function, If _errs_ is NULL, it will
>>>    be ignored.
>>>    
>>> +A filter in the array of _filters_ may be either a straight match of a
>>> +function, a glob or regex(3). a glob is where '*' matches zero or more
>>> +characters, '?' will match zero or one character, and '.' only matches a
>>> +period. If the filter is determined to be a regex (where it contains
>>> +anything other than alpha numeric characters, or '.', '*', '?') the filter
>>> +will be processed as a regex(3) following the rules of regex(3), and '.' is
>>> +not a period, but will match any one character. To force a regular
>>> +expression, either prefix the filter with a '^' or append it with a '$' as
>>> +all filters will act as complete matches of functions anyway.
>>> +
>> if we give the filter as regex "^ext4*$" from user side, ideally it
>> should match the ext4 filter functions, if i am not wrong, its not
>> matching any filter in the available_filter_functions
> If you add the "^" and/or "$" it makes it into a regex. The above means
> that the filter will match "ext", "ext4", "ext44", "ext4444444"
>
> Because "*" means zero or more of the previous character. So, unless
> there's a function that matches one of the above, it wont match anything
> else.
>
> If you left off the "^" and "$" then it would be a glob, where "*" means
> zero or more of any character. But if you want the same in regex, you need
> to use:
>
>   "^ext4.*$"

IF we use the regex in filters, running time of the program is 
increasing drastically.

lets say,

if we give the kernel glob as a filter, its getting converted to regex 
and running time of program is

5 secs, in other case where we use regex, its taking 80 secs to complete.

--sameer.