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[209.51.188.17]) by mx.google.com with ESMTPS id f29-20020a05622a1a1d00b003e4dfa86e21si7051066qtb.40.2023.04.24.02.30.48 for (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Mon, 24 Apr 2023 02:30:48 -0700 (PDT) Received-SPF: pass (google.com: domain of qemu-devel-bounces+patch=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; Authentication-Results: mx.google.com; dkim=pass header.i=@linaro.org header.s=google header.b=cWdCeBFw; spf=pass (google.com: domain of qemu-devel-bounces+patch=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom="qemu-devel-bounces+patch=linaro.org@nongnu.org"; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linaro.org Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pqsW7-0003zL-5m; Mon, 24 Apr 2023 05:29:51 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pqsVj-0003o9-D6 for qemu-devel@nongnu.org; Mon, 24 Apr 2023 05:29:29 -0400 Received: from mail-wr1-x435.google.com ([2a00:1450:4864:20::435]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1pqsVe-0006cD-DC for qemu-devel@nongnu.org; Mon, 24 Apr 2023 05:29:26 -0400 Received: by mail-wr1-x435.google.com with SMTP id ffacd0b85a97d-2f7db354092so2465916f8f.2 for ; Mon, 24 Apr 2023 02:29:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1682328560; x=1684920560; 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=b/rn85BLkY7Z2OPz7xDZllD6kTbU8YWvJhq44VxZVFA=; b=cWdCeBFwHORwSIrh3xV/ytU3JtqALq3T08Tf2im2Jdj3x4XRhiqBmltJDubRUTBGOz vxuIOf1QQFS8BEj47uBdidywyPym28gKmcXooJGHaOSXjivv9TfSkFAl4SMuBcASMcNk SPXPk9FpxtjzpBujJsucdfrW1Tz7pQp6xMk9Vr9P8qzVyCBSQYGsbat14saVL/b7DAXt 0T5hylQqJW2AGYoqZkqHO5nyvhkcG/Cbp2nYfOGXfdczWF9DRniEWrT6eta42O2JKvob A++PQuWWIMLOJLFFFyZtvjmmSFWadE3cRXBvpKniYcyvcK3fow/Ufv0s0upQZ1b5aYQZ 5qFw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1682328560; x=1684920560; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=b/rn85BLkY7Z2OPz7xDZllD6kTbU8YWvJhq44VxZVFA=; b=VLGR7KogXtRJpd9fc2Dxfw4GROdpb2i7hYSSsCyjSmNX1Jf23s+UXC84KslM3fPpNk AWwOkqt2dBsR3tEq8lCwG+rWp93TkFk3Llr0qLVLzFOuicnhO5Yls+6k5EyxZ59A4xAK mdwxU96SYJvThwn5W2GtZKvCkoqMNVzQYyuOu3b/ka3FTU3WQy4hj6MAoMFWvnLb7eJa JspTUMRhm29j4BVbUAZwrBiS9+6qwWJ50oJcwh2WLcZt+Sicpb/7pw4fiqTxlEyS3eOY 6xpUeRH4DZZh/n8mr8aKJyBBomTwsyYLCCKYizTwDOsf55rxO9eBp+MLImauhC1PPn35 a72Q== X-Gm-Message-State: AAQBX9fQ4Y1U5gMPVPIQpbFUbZzDlTXkvENiPD6D/xLUzH5ET6ZMqzHO pITsrxSbUpnrWJngFjU13wwxMA== X-Received: by 2002:a5d:4e01:0:b0:304:6715:8728 with SMTP id p1-20020a5d4e01000000b0030467158728mr5095286wrt.18.1682328560614; Mon, 24 Apr 2023 02:29:20 -0700 (PDT) Received: from zen.linaroharston ([85.9.250.243]) by smtp.gmail.com with ESMTPSA id h3-20020a5d5043000000b002c70ce264bfsm10327237wrt.76.2023.04.24.02.29.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Apr 2023 02:29:19 -0700 (PDT) Received: from zen.lan (localhost [127.0.0.1]) by zen.linaroharston (Postfix) with ESMTP id 87A481FFC8; Mon, 24 Apr 2023 10:22:51 +0100 (BST) From: =?utf-8?q?Alex_Benn=C3=A9e?= To: qemu-devel@nongnu.org Cc: Wainer dos Santos Moschetta , Beraldo Leal , Thomas Huth , =?utf-8?q?Alex_Benn=C3=A9e?= , "Edgar E. Iglesias" , Paolo Bonzini , Aurelien Jarno , Peter Maydell , Juan Quintela , =?utf-8?q?C=C3=A9dric_Le_Goater?= , Richard Henderson , Joel Stanley , Leif Lindholm , Markus Armbruster , Radoslaw Biernacki , Stefan Hajnoczi , =?utf-8?q?Marc-Andr=C3=A9_Lureau?= , John Snow , Andrew Jeffery , David Hildenbrand , Bastian Koppelmann , Max Filippov , qemu-s390x@nongnu.org, Cleber Rosa , =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , =?utf-8?q?Dani?= =?utf-8?q?el_P=2E_Berrang=C3=A9?= , qemu-arm@nongnu.org, Eduardo Habkost , Ilya Leoshkevich , Vladimir Sementsov-Ogievskiy Subject: [PATCH 18/18] docs/style: call out the use of GUARD macros Date: Mon, 24 Apr 2023 10:22:49 +0100 Message-Id: <20230424092249.58552-19-alex.bennee@linaro.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230424092249.58552-1-alex.bennee@linaro.org> References: <20230424092249.58552-1-alex.bennee@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2a00:1450:4864:20::435; envelope-from=alex.bennee@linaro.org; helo=mail-wr1-x435.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+patch=linaro.org@nongnu.org Sender: qemu-devel-bounces+patch=linaro.org@nongnu.org There use makes our code safer so we should mention them. Signed-off-by: Alex Bennée Reviewed-by: Philippe Mathieu-Daudé Reviewed-by: Juan Quintela Reviewed-by: Vladimir Sementsov-Ogievskiy Message-Id: <20230420155723.1711048-10-alex.bennee@linaro.org> --- vppr: - show example of what QEMU_LOCK_GUARD makes easier (although I didn't repeat for the WITH_ form) --- docs/devel/style.rst | 54 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 54 insertions(+) diff --git a/docs/devel/style.rst b/docs/devel/style.rst index e9fce0fc69..b97e5111fc 100644 --- a/docs/devel/style.rst +++ b/docs/devel/style.rst @@ -668,6 +668,60 @@ Note that there is no need to provide typedefs for QOM structures since these are generated automatically by the QOM declaration macros. See :ref:`qom` for more details. +QEMU GUARD macros +================= + +QEMU provides a number of ``_GUARD`` macros intended to make the +handling of multiple exit paths easier. For example using +``QEMU_LOCK_GUARD`` to take a lock will ensure the lock is released on +exit from the function. + +.. code-block:: c + + static int my_critical_function(SomeState *s, void *data) + { + QEMU_LOCK_GUARD(&s->lock); + do_thing1(data); + if (check_state2(data)) { + return -1; + } + do_thing3(data); + return 0; + } + +will ensure s->lock is released however the function is exited. The +equivalent code without _GUARD macro makes us to carefully put +qemu_mutex_unlock() on all exit points: + +.. code-block:: c + + static int my_critical_function(SomeState *s, void *data) + { + qemu_mutex_lock(&s->lock); + do_thing1(data); + if (check_state2(data)) { + qemu_mutex_unlock(&s->lock); + return -1; + } + do_thing3(data); + qemu_mutex_unlock(&s->lock); + return 0; + } + +There are often ``WITH_`` forms of macros which more easily wrap +around a block inside a function. + +.. code-block:: c + + WITH_RCU_READ_LOCK_GUARD() { + QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) { + err = do_the_thing(kid->child); + if (err < 0) { + return err; + } + } + } + Error handling and reporting ============================