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

Petr Mladek
2020-06-18T17:41:05Z

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