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Wed, 19 Nov 2025 19:08:51 -0800 (PST) Received: by archie.me (Postfix, from userid 1000) id AAB3D41D96E5; Thu, 20 Nov 2025 10:08:49 +0700 (WIB) Date: Thu, 20 Nov 2025 10:08:49 +0700 From: Bagas Sanjaya To: Jim Cromie , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, gregkh@linuxfoundation.org, jbaron@akamai.com Cc: ukaszb@chromium.org, louis.chauvet@bootlin.com, linux-doc@vger.kernel.org Subject: Re: [PATCH v6 31/31] docs/dyndbg: add classmap info to howto Message-ID: References: <20251118201842.1447666-1-jim.cromie@gmail.com> <20251118201842.1447666-32-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-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="HVQbqimanuPfAVD/" Content-Disposition: inline In-Reply-To: <20251118201842.1447666-32-jim.cromie@gmail.com> --HVQbqimanuPfAVD/ Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Nov 18, 2025 at 01:18:41PM -0700, Jim Cromie wrote: > diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Document= ation/admin-guide/dynamic-debug-howto.rst > index 1ceadf4f28f9..adac32a5cd23 100644 > --- a/Documentation/admin-guide/dynamic-debug-howto.rst > +++ b/Documentation/admin-guide/dynamic-debug-howto.rst > @@ -146,7 +146,9 @@ keywords are::: > "1-30" is valid range but "1 - 30" is not. > =20 > =20 > -The meanings of each keyword are: > +Keywords::: > + > +The meanings of each keyword are:: > =20 > func > The given string is compared against the function name > @@ -194,16 +196,6 @@ format > format "nfsd: SETATTR" // a neater way to match a format with whitespa= ce > format 'nfsd: SETATTR' // yet another way to match a format with white= space > =20 > -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 +210,24 @@ 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 > =20 > +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 +248,15 @@ The flags are:: > s Include the source file name > l Include line number > =20 > +Notes: > + > +To query without changing ``+_`` or ``-_``. > +To clear all flags ``=3D_`` or ``-fslmpt``. > + > For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only > the ``p`` flag has meaning, other flags are ignored. > =20 > -Note the regexp ``^[-+=3D][fslmpt_]+$`` matches a flags specification. > -To clear all flags at once, use ``=3D_`` or ``-fslmpt``. > +The regexp ``^[-+=3D][fslmpt_]+$`` matches a flags specification. > =20 > =20 > Debug messages during Boot Process > @@ -394,3 +408,92 @@ 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 > +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > + > +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 > +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D > + > +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 classes. "class FOO" queries are validated > +against the classes, this finds the classid to alter; classes are not > +directly selectable by their classid. > + > +NB: It is an inherent API limitation (due to int class_id defn) 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 not= hing > + > +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 module-groups (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 its _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. Hmmm... the resulting htmldocs looks messy so I clean it up: ---- >8 ---- diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentat= ion/admin-guide/dynamic-debug-howto.rst index adac32a5cd232d..fd3dbae00cfc60 100644 --- a/Documentation/admin-guide/dynamic-debug-howto.rst +++ b/Documentation/admin-guide/dynamic-debug-howto.rst @@ -146,9 +146,10 @@ keywords are::: "1-30" is valid range but "1 - 30" is not. =20 =20 -Keywords::: +Keywords +-------- =20 -The meanings of each keyword are:: +The meanings of each keyword are: =20 func The given string is compared against the function name @@ -221,12 +222,13 @@ class class JUNK # silent non-match // class TLD_* # NOTICE: no wildcard in class names =20 -.. note :: +.. note:: =20 Unlike other keywords, classes are "name-to-change", not - "omitting-constraint-allows-change". See Dynamic Debug Classmaps + "omitting-constraint-allows-change". See :ref:`dyndbg-classmaps`. =20 -Flags::: +Flags +----- =20 The flags specification comprises a change operation followed by one or more flag characters. The change operation is one @@ -248,10 +250,10 @@ The flags are:: s Include the source file name l Include line number =20 -Notes: +.. note:: =20 -To query without changing ``+_`` or ``-_``. -To clear all flags ``=3D_`` or ``-fslmpt``. + * To query without changing: ``+_`` or ``-_``. + * To clear all flags: ``=3D_`` or ``-fslmpt``. =20 For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only the ``p`` flag has meaning, other flags are ignored. @@ -409,6 +411,8 @@ 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. =20 +.. _dyndbg-classmaps: + Dynamic Debug Classmaps =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =20 @@ -417,7 +421,7 @@ domain-oriented names. This complements the nested-sco= pe keywords: module, file, function, line. =20 The main difference from the others: classes must be named to be -changed. This protects them from unintended overwrite: +changed. This protects them from unintended overwrite:: =20 # IOW this cannot undo any drm.debug settings :#> ddcmd -p @@ -427,7 +431,7 @@ drm.debug is authoritative when dyndbg is not used, dyn= dbg-under-DRM is an implementation detail, and must not behave erratically, just because another admin fed >control something unrelated. =20 -So each class must be enabled individually (no wildcards): +So each class must be enabled individually (no wildcards):: =20 :#> ddcmd class DRM_UT_CORE +p :#> ddcmd class DRM_UT_KMS +p @@ -437,7 +441,7 @@ So each class must be enabled individually (no wildcard= s): 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. +using the convenient way, and be able to trust it:: =20 :#> echo 0x1ff > /sys/module/drm/parameters/debug =20 @@ -464,7 +468,7 @@ against the classes, this finds the classid to alter; c= lasses are not directly selectable by their classid. =20 NB: It is an inherent API limitation (due to int class_id defn) that -the following are possible: +the following are possible:: =20 // these errors should be caught in review __pr_debug_cls(0, "fake DRM_UT_CORE msg"); // this works @@ -472,8 +476,8 @@ the following are possible: =20 There are 2 types of classmaps: =20 - DD_CLASS_TYPE_DISJOINT_BITS: classes are independent, like drm.debug - DD_CLASS_TYPE_LEVEL_NUM: classes are relative, ordered (V3 > V2) +* DD_CLASS_TYPE_DISJOINT_BITS: classes are independent, like drm.debug +* DD_CLASS_TYPE_LEVEL_NUM: classes are relative, ordered (V3 > V2) =20 DYNAMIC_DEBUG_CLASSMAP_PARAM - modelled after module_param_cb, it refers to a DEFINEd classmap, and associates it to the param's Thanks. --=20 An old man doll... just what I always wanted! - Clara --HVQbqimanuPfAVD/ Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQSSYQ6Cy7oyFNCHrUH2uYlJVVFOowUCaR6GPAAKCRD2uYlJVVFO o82NAP9o9bKdHzQr2WUnsmQEo2y9z1jOdX8J+HgUei4iaKFGoAEA7aYmQOKNkEme AThPfWzYb2VtrLEG2zkxC0iPslgWTAg= =vmiO -----END PGP SIGNATURE----- --HVQbqimanuPfAVD/--