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[147.75.80.249]) by mx.google.com with ESMTPS id a2-20020a1709065f8200b00a28716e1a2asi28112eju.611.2024.01.08.08.17.36 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Jan 2024 08:17:36 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel+bounces-19830-ouuuleilei=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249; Authentication-Results: mx.google.com; dkim=pass header.i=@posteo.net header.s=2017 header.b=HzQVztjN; spf=pass (google.com: domain of linux-kernel+bounces-19830-ouuuleilei=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) smtp.mailfrom="linux-kernel+bounces-19830-ouuuleilei=gmail.com@vger.kernel.org"; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=posteo.net Received: from smtp.subspace.kernel.org (wormhole.subspace.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by am.mirrors.kernel.org (Postfix) with ESMTPS id 8616B1F22458 for ; Mon, 8 Jan 2024 16:17:36 +0000 (UTC) Received: from localhost.localdomain (localhost.localdomain [127.0.0.1]) by smtp.subspace.kernel.org (Postfix) with ESMTP id BC5DA537E2; Mon, 8 Jan 2024 16:16:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=posteo.net header.i=@posteo.net header.b="HzQVztjN" X-Original-To: linux-kernel@vger.kernel.org Received: from mout01.posteo.de (mout01.posteo.de [185.67.36.65]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 76E5B5380D for ; Mon, 8 Jan 2024 16:16:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=posteo.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=posteo.net Received: from submission (posteo.de [185.67.36.169]) by mout01.posteo.de (Postfix) with ESMTPS id DBCD8240029 for ; Mon, 8 Jan 2024 17:16:30 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=posteo.net; s=2017; t=1704730590; bh=VhNI/VyHttpB6Dc+nOmQ0eI7dT/saNfHep5H24iJdO8=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version: Content-Transfer-Encoding:From; b=HzQVztjNExNwWDrBuHzEvHtkFFb6vD0OXysV/RE2YSQAQeRZRM4R2KPi1eqBI1IE0 BSv2xCrBjDcgcfMHIjpUhv7F7AXvuX8XRuiUkCupg5ER15Ex18/IoSvHTPiCypErA9 870DCFFhsdxf6Ku/I5Bdn4tyn4/jWmgW0j+pNBTZ19BpBQFy9thMKIBdX+Xy1LGjKn ktiSoGhu0cJbFOuiyqcWbCl5Iv5BRsQl12Bl6+IAmoxmpSpOAEKunG3bM33lUuyF6b w7VL9S2/9IFb4670o/kT67shDy+0J9nn2ZRyR2cEJqPySYA83y8pVs3zf3EgzSV+PD zV6Uyu0OElw7A== Received: from customer (localhost [127.0.0.1]) by submission (posteo.de) with ESMTPSA id 4T7zhV4n4Wz9rxN; Mon, 8 Jan 2024 17:16:26 +0100 (CET) From: Yueh-Shun Li To: Jonathan Corbet Cc: Yueh-Shun Li , Hu Haowen , Alex Shi , Yanteng Si , Randy Dunlap , workflows@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 2/4] coding-style: show how reusing macros prevents naming collisions Date: Mon, 8 Jan 2024 16:03:23 +0000 Message-ID: <20240108160746.177421-3-shamrocklee@posteo.net> In-Reply-To: <20240108160746.177421-1-shamrocklee@posteo.net> References: <107b6b5e-ca14-4b2b-ba2e-38ecd74c0ad3@infradead.org> <20240108160746.177421-1-shamrocklee@posteo.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1787539653211679118 X-GMAIL-MSGID: 1787539653211679118 In section "18) Don't re-invent the kernel macros" in "Linux kernel coding style": Show how reusing macros from shared headers prevents naming collisions using "stringify", the one of the most widely reinvented macro, as an example. This patch aims to provide a stronger reason to reuse shared macros, by showing the risk of improvised macro variants. Signed-off-by: Yueh-Shun Li --- Documentation/process/coding-style.rst | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/Documentation/process/coding-style.rst b/Documentation/process/coding-style.rst index 2504cb00a961..1e79aba4b346 100644 --- a/Documentation/process/coding-style.rst +++ b/Documentation/process/coding-style.rst @@ -1070,6 +1070,28 @@ Similarly, if you need to calculate the size of some structure member, use There are also ``min()`` and ``max()`` macros in ``include/linux/minmax.h`` that do strict type checking if you need them. +Using existing macros provided by the shared headers also prevents naming +collisions. For example, if one developer define in ``foo.h`` + +.. code-block:: c + + #define __stringify(x) __stringify_1(x) + #define __stringify_1(x) #x + +and another define in ``bar.h`` + +.. code-block:: c + + #define stringify(x) __stringify(x) + #define __stringify(x) #x + +When both headers are ``#include``-d into the same file, the facilities provided +by ``foo.h`` might be broken by ``bar.h``. + +If both ``foo.h`` and ``bar.h`` use the macro ``__stringify()`` provided by +``include/linux/stringify.h``, they wouldn't have stepped onto each other's +toes. + Feel free to search across and peruse the header files to see what else is already defined that you shouldn't reproduce in your code.