dyndbg: add DECLARE_DYNDBG_CLASSMAP macro

Using DECLARE_DYNDBG_CLASSMAP, modules can declare up to 31 classnames.
By doing so, they authorize dyndbg to manipulate class'd prdbgs (ie:
__pr_debug_cls, and soon drm_*dbg), ala::

   :#> echo class DRM_UT_KMS +p > /proc/dynamic_debug/control

The macro declares and initializes a static struct ddebug_class_map::

 - maps approved class-names to class_ids used in module,
   by array order. forex: DRM_UT_*
 - class-name vals allow validation of "class FOO" queries
   using macro is opt-in
 - enum class_map_type - determines interface, behavior

Each module has its own class-type and class_id space, and only known
class-names will be authorized for a manipulation.  Only DRM modules
should know and respont to this:

  :#> echo class DRM_UT_CORE +p > control	# across all modules

pr_debugs (with default class_id) are still controllable as before.

DECLARE_DYNDBG_CLASSMAP(_var, _maptype, _base, classes...) is::

 _var: name of the static struct var. user passes to module_param_cb()
       if they want a sysfs node.

 _maptype: this is hard-coded to DD_CLASS_TYPE_DISJOINT_BITS for now.

 _base: usually 0, it allows splitting 31 classes into subranges, so
 	that multiple classes / sysfs-nodes can share the module's
 	class-id space.

 classes: list of class_name strings, these are mapped to class-ids
 	  starting at _base.  This class-names list must have a
 	  corresponding ENUM, with SYMBOLS that match the literals,
 	  and 1st enum val = _base.

enum class_map_type has 4 values, on 2 factors::

 - classes are disjoint/independent vs relative/x<y/verbosity.
   disjoint is basis, verbosity by overlay.

 - input NUMBERS vs [+-]CLASS_NAMES
   uints, ideally hex.  vs  +DRM_UT_CORE,-DRM_UT_KMS

DD_CLASS_TYPE_DISJOINT_BITS: classes are separate, one per bit.
   expecting hex input. built for drm.debug, basis for other types.

DD_CLASS_TYPE_DISJOINT_NAMES: input is a CSV of [+-]CLASS_NAMES,
   classes are independent, like DISJOINT

DD_CLASS_TYPE_LEVEL_NUM: input is numeric level, 0-N.
   0 implies silence. use printk to break that.
   relative levels applied on bitmaps.

DD_CLASS_TYPE_LEVEL_NAMES: input is a CSV of [+-]CLASS_NAMES,
   names like: ERR,WARNING,NOTICE,INFO,DEBUG
   avoiding EMERG,ALERT,CRIT,ERR - no point.

NOTES:

The macro places the initialized struct ddebug_class_map into the
__dyndbg_classes section.  That draws an 'orphan' warning which we
handle in the next commit.  The struct attributes are necessary:
__aligned(8) fixed null-ptr derefs, and __used is needed by drm
drivers, which declare class-maps, but don't also declare a
sysfs-param, and thus dont ref the classmap.  The __used insures that
the linkage is made, then the class-map is found at load-time.

While its possible to handle both NAMES and NUMBERS in the same
sys-interface, there is ambiguity to avoid, by disallowing them
together.  Later, if ambiguities are resolved, 2 new enums can permit
both inputs, on verbose & independent types separately, and authors
can select the interface style they like.

The plan is to implement LEVELS in the callbacks, outside of
ddebug_exec_query(), which for simplicity will treat the CLASSES in
the map as disjoint.  The callbacks can see map-type, and apply ++/--
loops (or bitops) to force the relative meanings across the
class-bitmap.

RFC: That leaves 2 issues:

1. doing LEVELs in callbacks means that the native >control interface
doesn't enforce the LEVELS relationship, so you could confusingly have
V3 enabled, but V1 disabled.  OTOH, the control iface already allows
infinite tweaking of the underlying callsites; sysfs node readback can
only tell the user what they previously wrote.

2. All dyndbg >control reduces to a query/command, includes +/-, which
is at-root a kernel patching operation with +/- semantics.  And the
_NAMES handling exposes it to the user, making it API-adjacent.

And its not just >control where +/- gets used (which is settled), the
new place is with sysfs-nodes exposing _*_NAMES classes, and here its
subtly different.

_DISJOINT_NAMES: is simple, independent
_LEVEL_NAMES: masks-on bits 0 .. N-1, N..max off

  # turn on L3,L2,L1 others off
  echo +L3 > /sys/module/test_dynamic_debug/parameters/p_level_names

  # turn on L2,L1 others off
  echo -L3 > /sys/module/test_dynamic_debug/parameters/p_level_names

IOW, the - changes the threshold-on bitpos by 1.

Alternatively, we could treat the +/- as half-duplex, where -L3 turns
off L>2 (and ignores L1), and +L2 would turn on L<=2 (and ignore others).

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Link: https://lore.kernel.org/r/20220904214134.408619-15-jim.cromie@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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