From nobody Mon Feb 9 14:14:58 2026 Received: from mail-oi1-f193.google.com (mail-oi1-f193.google.com [209.85.167.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9E9A4310655 for ; Wed, 14 Jan 2026 02:00:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.167.193 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768356053; cv=none; b=rMJZA2oX0tTp9NE5QImuljcHUaWQmpwpyDYcP/pKDrA9wHjQWhSXegZeznH4J0sBc/IdoHUT0c97Ubb0bsLY6WKCAv2iWvLaCQtOrEedZ8dw9SkrH4bc99O0Q5mxt4dJoMFvvHsMe0H1uI8LGy6vPlsl9qfCRc7LuMf9lhcDnQM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768356053; c=relaxed/simple; bh=AK/bnfFexI75Q/0N26IRCouQSTxRNRsO2xPVvCV9E/E=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=iBB0RrjhKRuytKn2ykESqwA+1S96nCIB7HuRpcbVmWWYLEeDqD+8ZVYH4JZGsz7keXwsqjkEk/cxIOKmIM843DQCt1jGZ5OB+1Ibt9WcQ+9fEEMNgh0vRMc9ldGtyBYJkL3Ld3JWPDWS3CCS43ovum9R9Mm5fcfYrMcu2V9Yq4g= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=hldCFLT8; arc=none smtp.client-ip=209.85.167.193 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="hldCFLT8" Received: by mail-oi1-f193.google.com with SMTP id 5614622812f47-455a461ab6eso3314770b6e.2 for ; Tue, 13 Jan 2026 18:00:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1768356050; x=1768960850; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=/ABMBtHazCQPbXZPvqunvxRiAtO4J7KVdTol8wYfw0Q=; b=hldCFLT8KzxtynNWBK/wQ+/YnhPqHjO8UK/oC1gQT4Bsm3OOI2QSKiHP/SvMWreZAl lflyNM1yquI7Nznkv49GoXPfZzMFmelN+ei1dUqzam8Kl57yoJZH+x/MECbFBeAv7zwu 3mob23YaLWjHVIEBObe+dtuweg12d55OlRYUzPufbkTVN1c92TImyF1S+Eb9Mjnl2wQ4 izQP2ovGGrsKrws5w/GlqUf1a2ldJXpTc75l7yUGrhd08UTFI7mw7EY4h/7Aj0XG2EHk c6d7ZYcNfo6PtfQVZLrFzdc6v+i85w606EjZkffvTaToo+FSChd9Rnwr4KdeAzzCtfgt 4Ltg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1768356050; x=1768960850; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=/ABMBtHazCQPbXZPvqunvxRiAtO4J7KVdTol8wYfw0Q=; b=ROjAx4unpEFqYD3GXHd/mIQXruyi2ooj5x8iyDeP+yh4xbhE+kTKNYeJnldFAmb9Kp LjBXFsbjlzVvb2IA9r2Kv6OPryQS61gfPIP5xxm5ytrfVzU3aAVR8zJpVsHmE1JDYIjI ndVtDnlYTDYvhqurf29evNGLz+SJBhn9YcrzDYEsYe0r1w2iZqnzdvbLComY3Hr3uDsI AuKKrMESjbrLcdkAtRe5cQ93XKaBO9dSkPjaciHUIvskf1YTCwlruXu8IM13cvyaZmbE D6zigDb0SRGzQZQiqujCVgvQ5RZe5AkPe1A5/JhCsVuOf8nY/fUzdSlUwOEHm+WoU1dI sIUw== X-Forwarded-Encrypted: i=1; AJvYcCU/lJGTvj0n20Ue9aPKFYBlMEwsAjAjh11CHYNW3zx+PdSGGz5Of3fVekl+V9+XmF966rAy/vW+C/RAogw=@vger.kernel.org X-Gm-Message-State: AOJu0YwQGtAXh9G5ODJv8zL3rCO2Iyx7INjDHRoa0e239frj+W+YM8Gf b8L/AWJZ/e33Eq9DBaEZ1hE0nRru3sLzz4RARmDmwfzmWuv2f6BbRrtM X-Gm-Gg: AY/fxX4Nr/HZpiWLaX8TPUmirqHj1UmTiI6SXpcAHUHEWp7QPbo6bGztPxZjtI1MeAz EYUvWC1dT1TXeqrWcR1KUwdviLK7/g1jt+PCXlsdbjibM3IyrjaUBQ4tHCSfewk3C4eL6lVAzM6 QVS11RPopE9sTkt4M1S8OoJ0iIdr1vcvyWCYnikKqYxi2pi8+wRbTXeFj9UNtQ/drHyvgLrOeMC QKLZyA2ADoRI+fONVBhNfwvTBbE9xveBFQeuO6wwe49thldkDaESsZFHPmhfAgKxQQCawKVBh5v b+oeQBtE+eA+vjJ9JAucakrtGKuLbLpEagOVk9C7nBkUrKvMDKN4JoBOlk5BskLk3pqf6FPVQ2a AeFDhEw5aPwPaTbAmaEgPaGbJG4C4x7ii0fTsenh4DlPUFVxR8r+JCNQkQF2jsUUFJkMQJD8s6G rMxhOKihUstEqLUhA/ik0+o0eBm98OuPNEOmx5 X-Received: by 2002:a05:6808:c16c:b0:44f:6e2a:ace with SMTP id 5614622812f47-45c73e33e0amr394064b6e.52.1768356050518; Tue, 13 Jan 2026 18:00:50 -0800 (PST) Received: from frodo (c-98-38-17-99.hsd1.co.comcast.net. [98.38.17.99]) by smtp.googlemail.com with ESMTPSA id 5614622812f47-45a5e183ac3sm10223525b6e.4.2026.01.13.18.00.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Jan 2026 18:00:50 -0800 (PST) From: Jim Cromie To: gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org Cc: Jim Cromie , Jason Baron , =?UTF-8?q?=C5=81ukasz=20Bartosik?= , Louis Chauvet , Bagas Sanjaya , Dave Airlie , Daniel Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , dri-devel@lists.freedesktop.org, Petr Mladek , Shuah Khan , linux-doc@vger.kernel.org, Steven Rostedt , "Liam R. Howlett" Subject: [PATCH v8 31/31] docs/dyndbg: add classmap info to howto Date: Tue, 13 Jan 2026 18:57:47 -0700 Message-ID: <20260114015815.1565725-32-jim.cromie@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260114015815.1565725-1-jim.cromie@gmail.com> References: <20260114015815.1565725-1-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: quoted-printable Content-Type: text/plain; charset="utf-8" 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/Documentat= ion/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. =20 =20 +Keywords +-------- + The meanings of each keyword are: =20 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 whitesp= ace =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 +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 =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 +250,15 @@ The flags are:: s Include the source file name l Include line number =20 +.. note:: + + * 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 +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 +=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 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 nothi= ng + +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. --=20 2.52.0