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Mon, 22 Dec 2025 00:28:35 -0800 (PST) Received: from frodo ([2404:4400:417e:3d00:8b90:7f55:1261:772f]) by smtp.googlemail.com with ESMTPSA id d2e1a72fcca58-7ff7e493123sm9540699b3a.50.2025.12.22.00.28.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Dec 2025 00:28:34 -0800 (PST) From: Jim Cromie To: linux-kernel@vger.kernel.org, jbaron@akamai.com, gregkh@linuxfoundation.org, ukaszb@chromium.org, louis.chauvet@bootlin.com Cc: dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, intel-gvt-dev@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, daniel.vetter@ffwll.ch, tvrtko.ursulin@linux.intel.com, jani.nikula@intel.com, ville.syrjala@linux.intel.com, seanpaul@chromium.org, robdclark@gmail.com, groeck@google.com, yanivt@google.com, bleung@google.com, quic_saipraka@quicinc.com, will@kernel.org, catalin.marinas@arm.com, quic_psodagud@quicinc.com, maz@kernel.org, arnd@arndb.de, linux-arm-kernel@lists.infradead.org, linux-arm-msm@vger.kernel.org, mingo@redhat.com, jim.cromie@gmail.com, linux-doc@vger.kernel.org Subject: [PATCH v7 31/31] docs/dyndbg: add classmap info to howto Date: Mon, 22 Dec 2025 21:20:48 +1300 Message-ID: <20251222082049.1782440-32-jim.cromie@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251222082049.1782440-3-jim.cromie@gmail.com> References: <20251222082049.1782440-3-jim.cromie@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Describe the 3 API macros providing dynamic_debug's classmaps DYNAMIC_DEBUG_CLASSMAP_DEFINE - create & export a classmap DYNAMIC_DEBUG_CLASSMAP_USE - refer to exported map DYNAMIC_DEBUG_CLASSMAP_PARAM - bind control param to the classmap DYNAMIC_DEBUG_CLASSMAP_PARAM_REF + use module's storage - __drm_debug NB: The _DEFINE & _USE model makes the user dependent on the definer, just like EXPORT_SYMBOL(__drm_debug) already does. cc: linux-doc@vger.kernel.org Signed-off-by: Jim Cromie --- .../admin-guide/dynamic-debug-howto.rst | 135 ++++++++++++++++-- 1 file changed, 123 insertions(+), 12 deletions(-) diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst index 89ee15d7ae58..c85266ee8eed 100644 --- a/Documentation/admin-guide/dynamic-debug-howto.rst +++ b/Documentation/admin-guide/dynamic-debug-howto.rst @@ -146,6 +146,9 @@ keywords are:: "1-30" is valid range but "1 - 30" is not. +Keywords +-------- + The meanings of each keyword are: func @@ -194,16 +197,6 @@ format format "nfsd: SETATTR" // a neater way to match a format with whitespace format 'nfsd: SETATTR' // yet another way to match a format with whitespace -class - The given class_name is validated against each module, which may - have declared a list of known class_names. If the class_name is - found for a module, callsite & class matching and adjustment - proceeds. Examples:: - - class DRM_UT_KMS # a DRM.debug category - class JUNK # silent non-match - // class TLD_* # NOTICE: no wildcard in class names - line The given line number or range of line numbers is compared against the line number of each ``pr_debug()`` callsite. A single @@ -218,6 +211,25 @@ line line -1605 // the 1605 lines from line 1 to line 1605 line 1600- // all lines from line 1600 to the end of the file +class + + The given class_name is validated against each module, which may + have declared a list of class_names it accepts. If the class_name + accepted by a module, callsite & class matching and adjustment + proceeds. Examples:: + + class DRM_UT_KMS # a drm.debug category + class JUNK # silent non-match + // class TLD_* # NOTICE: no wildcard in class names + +.. note:: + + Unlike other keywords, classes are "name-to-change", not + "omitting-constraint-allows-change". See Dynamic Debug Classmaps + +Flags +----- + The flags specification comprises a change operation followed by one or more flag characters. The change operation is one of the characters:: @@ -238,11 +250,15 @@ The flags are:: s Include the source file name l Include line number +.. note:: + + * To query without changing ``+_`` or ``-_``. + * To clear all flags ``=_`` or ``-fslmpt``. + For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only the ``p`` flag has meaning, other flags are ignored. -Note the regexp ``^[-+=][fslmpt_]+$`` matches a flags specification. -To clear all flags at once, use ``=_`` or ``-fslmpt``. +The regexp ``^[-+=][fslmpt_]+$`` matches a flags specification. Debug messages during Boot Process @@ -394,3 +410,98 @@ 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. + +.. _dyndbg-classmaps: + +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: classes must be named to be +changed. This protects them from unintended overwrite:: + + # IOW this cannot undo any drm.debug settings + :#> ddcmd -p + +This protection is needed; /sys/module/drm/parameters/debug is ABI. +drm.debug is authoritative when dyndbg is not used, dyndbg-under-DRM +is an implementation detail, and must not behave erratically, just +because another admin fed >control something unrelated. + +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 + +That makes direct >control wordy and annoying, but it is a secondary +interface; it is not intended to replace the ABI, just slide in +underneath and reimplement the guaranteed behavior. So DRM would keep +using the convenient way, and be able to trust it:: + + :#> echo 0x1ff > /sys/module/drm/parameters/debug + +That said, since the sysfs/kparam is the ABI, if the author omits the +CLASSMAP_PARAM, theres no ABI to guard, and he probably wants a less +pedantic >control interface. In this case, protection is dropped. + +Dynamic Debug Classmap API +========================== + +DYNAMIC_DEBUG_CLASSMAP_DEFINE(clname,type,_base,classnames) - this maps +classnames (a list of strings) onto class-ids consecutively, starting +at _base. + +DYNAMIC_DEBUG_CLASSMAP_USE(clname) & _USE_(clname,_base) - modules +call this to refer to the var _DEFINEd elsewhere (and exported). + +DYNAMIC_DEBUG_CLASSMAP_PARAM(clname) - creates the sysfs/kparam, +maps/exposes bits 0..N as class-names. + +Classmaps are opt-in: modules invoke _DEFINE or _USE to authorize +dyndbg to update those named classes. "class FOO" queries are +validated against the classes defined or used by the module, this +finds the classid to alter; classes are not directly selectable by +their classid. + +Classnames are global in scope, so subsystems (module-groups) should +prepend a subsystem name; unqualified names like "CORE" are discouraged. + +NB: It is an inherent API limitation (due to class_id's int type) that +the following are possible: + + // these errors should be caught in review + __pr_debug_cls(0, "fake DRM_UT_CORE msg"); // this works + __pr_debug_cls(62, "un-known classid msg"); // this compiles, does nothing + +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) + +DYNAMIC_DEBUG_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" +or "PL_ERROR" vs "PL_WARNING". + +Modules or subsystems (drm & drivers) can define multiple classmaps, +as long as they (all the classmaps) share the limited 0..62 +per-module-group _class_id range, without overlap. + +If a module encounters a conflict between 2 classmaps it is _USEing or +_DEFINEing, it can invoke the extended _USE_(name,_base) macro to +de-conflict the respective ranges. + +``#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. -- 2.52.0