Re: [PATCH v3 20/21] dyndbg: add user-flag, negating-flags, and filtering on flags

Jason Baron
2020-06-18T18:47:10Z

On 6/18/20 1:40 PM, Petr Mladek wrote:
> On Thu 2020-06-18 18:19:12, Petr Mladek wrote:
>> On Wed 2020-06-17 10:25:35, Jim Cromie wrote:
>>> 1. Add a user-flag [u] which works like the [pfmlt] flags, but has no
>>> effect on callsite behavior; it allows incremental marking of
>>> arbitrary sets of callsites.
>>>
>>> 2. Add [PFMLTU] flags, which negate their counterparts; P===!p etc.
>>> And in ddebug_read_flags():
>>> current code does: [pfmltu_] -> flags
>>> copy it to: [PFMLTU_] -> mask
>>>
>>> also disallow both of a pair: ie no 'pP', no true & false.
>>>
>>> 3. Add filtering ops into ddebug_change(), right after all the
>>> callsite-property selections are complete. These filter on the
>>> callsite's current flagstate before applying modflags.
>>>
>>> Why ?
>>>
>>> The u-flag & filter flags
>>>
>>> The 'u' flag lets the user assemble an arbitary set of callsites.
>>> Then using filter flags, user can activate the 'u' callsite set.
>>>
>>> #> echo 'file foo.c +u; file bar.c +u' > control # and repeat
>>> #> echo 'u+p' > control
>>>
>>> Of course, you can continue to just activate your set without ever
>>> marking it 1st, but you could trivially add the markup as you go, then
>>> be able to use it as a constraint later, to undo or modify your set.
>>>
>>> #> echo 'file foo.c +up' >control
>>> .. monitor, debug, finish ..
>>> #> echo 'u-p' >control
>>>
>>> # then later resume
>>> #> echo 'u+p' >control
>>>
>>> # disable some cluttering messages, and remove from u-set
>>> #> echo 'file noisy.c function:jabber_* u-pu' >control
>>>
>>> # for doc, recollection
>>> grep =pu control > my-favorite-callsites
>>>
>>> Note:
>>>
>>> Your flagstate after boot is generally not all =_. -DDEBUG will arm
>>> compiled callsites by default, $builtinmod.dyndbg=+p bootargs can
>>> enable them early, and $module.dyndbg=+p bootargs will arm them when
>>> the module is loaded. But you could manage them with u-flags:
>>>
>>> #> echo '-t' >control # clear t-flag to use it as 2ndary markup
>>> #> echo 'p+ut' >control # mark the boot-enabled set of callsites
>>> #> echo '-p' >control # clean your dmesg -w stream
>>>
>>> ... monitor, debug ..
>>> #> echo 'module of_interest $qterms +pu' >control # build your set of useful debugs
>>> #> echo 'module of_interest $qterms UT+pu' >control # same, but dont alter ut marked set
>>
>> Does anyone requested this feature, please?
>>
>> For me, it is really hard to imagine people using these complex and hacky
>> steps.
>
> I think that all this is motivated by adding support for module
> specific groups.
>
> What about storing the group as yet another information for each
> message? I mean the same way as we store module name, file, line,
> function name.
>
> Then we could add API to define group for a given message:
>
> pr_debug_group(group_id, fmt, ...);
>
> the interface for the control file might be via new keyword "group".
> You could then do something like:
>
> echo module=drm group=0x3 +p >control
>
> But more importantly you should add functions that might be called
> when the drm.debug parameter is changes. I have already mentioned
> it is another reply:
>
> dd_enable_module_group(module_name, group_id);
> dd_disable_module_group(module_name, group_id);
>
>
> It will _not_ need any new flag or flag filtering.
>
> Best Regards,
> Petr
>

Yes, I'm wondering as well if people are really going to use the
new flags and filter flags - I mentioned that here:
https://lkml.org/lkml/2020/6/12/732

The grouping stuff is already being used by lots of modules so
that seems useful.

Thanks,

-Jason