Describe the 3 API macros providing dynamic_debug's classmaps DYNDBG_CLASSMAP_DEFINE - create, exports a module's classmap DYNDBG_CLASSMAP_USE - refer to exported map DYNDBG_CLASSMAP_PARAM - bind control param to the classmap DYNDBG_CLASSMAP_PARAM_REF + use module's storage - __drm_debug cc: linux-doc@xxxxxxxxxxxxxxx Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx> --- v5 adjustments per Randy Dunlap v7 checkpatch fixes v8 more v9 rewords --- .../admin-guide/dynamic-debug-howto.rst | 79 ++++++++++++++++++- 1 file changed, 78 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst index 691e0f7d4de1..391e40a510c9 100644 --- a/Documentation/admin-guide/dynamic-debug-howto.rst +++ b/Documentation/admin-guide/dynamic-debug-howto.rst @@ -230,7 +230,6 @@ the ``p`` flag has meaning, other flags are ignored. Note the regexp ``^[-+=][fslmpt_]+$`` matches a flags specification. To clear all flags at once, use ``=_`` or ``-fslmpt``. - Debug messages during Boot Process ================================== @@ -380,3 +379,81 @@ just a shortcut for ``print_hex_dump(KERN_DEBUG)``. For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is its ``prefix_str`` argument, if it is constant string; or ``hexdump`` in case ``prefix_str`` is built dynamically. + +Dynamic Debug classmaps +======================= + +The "class" keyword selects prdbgs based on author supplied, +domain-oriented names. This complements the nested-scope keywords: +module, file, function, line. + +The main difference from the others: class'd prdbgs must be named to +be changed. This protects them from generic overwrite: + + # IOW this cannot undo any DRM.debug settings + :#> ddcmd -p + +So each class must be enabled individually (no wildcards): + + :#> ddcmd class DRM_UT_CORE +p + :#> ddcmd class DRM_UT_KMS +p + # or more selectively + :#> ddcmd class DRM_UT_CORE module drm +p + +Or the legacy/normal (more convenient) way: + + :#> echo 0x1ff > /sys/module/drm/parameters/debug + +Dynamic Debug Classmap API +========================== + +DRM.debug is built upon: + ~23 macros, all passing a DRM_UT_* constant as arg-1. + ~5000 calls to them, across drivers/gpu/drm/* + bits in /sys/module/drm/parameters/debug control all DRM_UT_* together + +The const short ints are good for optimizing compilers; a classmaps +design goal was to keep that. So basically .classid === category. + +And since prdbgs are cataloged with just a DRM_UT_* to identify them, +the "class" keyword maps known classnames to those reserved IDs, and +by explicitly requiring "class FOO" in queries, we protect FOO class'd +debugs from overwrite by generic queries. + +Its expected that other classmap users will also provide debug-macros +using an enum-defined categorization scheme like DRM's, and dyndbg can +be adapted under them similarly. + +DYNDBG_CLASSMAP_DEFINE(var,type,_base,classnames) - this maps +classnames onto class-ids starting at _base, it also maps the +names onto CLASSMAP_PARAM bits 0..N. + +DYNDBG_CLASSMAP_USE(var) - modules call this to refer to the var +_DEFINEd elsewhere (and exported). + +Classmaps are opt-in: modules invoke _DEFINE or _USE to authorize +dyndbg to update those classes. "class FOO" queries are validated +against the classes, this finds the classid to alter; classes are not +directly selectable by their classid. + +There are 2 types of classmaps: + + DD_CLASS_TYPE_DISJOINT_BITS: classes are independent, like DRM.debug + DD_CLASS_TYPE_LEVEL_NUM: classes are relative, ordered (V3 > V2) + +DYNDBG_CLASSMAP_PARAM - modelled after module_param_cb, it refers to a +DEFINEd classmap, and associates it to the param's data-store. This +state is then applied to DEFINEr and USEr modules when they're modprobed. + +The PARAM interface also enforces the DD_CLASS_TYPE_LEVEL_NUM relation +amongst the contained classnames; all classes are independent in the +control parser itself; there is no implied meaning in names like "V4". + +Modules or module-groups (drm & drivers) can define multiple +classmaps, as long as they share the limited 0..62 per-module-group +_class_id range, without overlap. + +``#define DEBUG`` will enable all pr_debugs in scope, including any +class'd ones. This won't be reflected in the PARAM readback value, +but the class'd pr_debug callsites can be forced off by toggling the +classmap-kparam all-on then all-off. -- 2.47.0
