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GET /api/patches/2195635/?format=api
{ "id": 2195635, "url": "http://patchwork.ozlabs.org/api/patches/2195635/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260211152508.732487-12-berrange@redhat.com/", "project": { "id": 14, "url": "http://patchwork.ozlabs.org/api/projects/14/?format=api", "name": "QEMU Development", "link_name": "qemu-devel", "list_id": "qemu-devel.nongnu.org", "list_email": "qemu-devel@nongnu.org", "web_url": "", "scm_url": "", "webscm_url": "", "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<20260211152508.732487-12-berrange@redhat.com>", "list_archive_url": null, "date": "2026-02-11T15:24:52", "name": "[v6,11/27] util: introduce some API docs for logging APIs", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "5c52795188b37690115c8eca562d2aa04cf7df08", "submitter": { "id": 2694, "url": "http://patchwork.ozlabs.org/api/people/2694/?format=api", "name": "Daniel P. Berrangé", "email": "berrange@redhat.com" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260211152508.732487-12-berrange@redhat.com/mbox/", "series": [ { "id": 491862, "url": "http://patchwork.ozlabs.org/api/series/491862/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/list/?series=491862", "date": "2026-02-11T15:24:41", "name": "util: sync error_report & qemu_log output more closely", "version": 6, "mbox": "http://patchwork.ozlabs.org/series/491862/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2195635/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2195635/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org>", "X-Original-To": "incoming@patchwork.ozlabs.org", "Delivered-To": "patchwork-incoming@legolas.ozlabs.org", "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=XGum1ddF;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)" ], "Received": [ "from lists.gnu.org (lists.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4fB2P03FZWz1xtr\n\tfor <incoming@patchwork.ozlabs.org>; Thu, 12 Feb 2026 02:27:32 +1100 (AEDT)", "from localhost ([::1] helo=lists1p.gnu.org)\n\tby lists.gnu.org with esmtp (Exim 4.90_1)\n\t(envelope-from <qemu-devel-bounces@nongnu.org>)\n\tid 1vqC6p-0006Z4-45; Wed, 11 Feb 2026 10:26:31 -0500", "from eggs.gnu.org ([2001:470:142:3::10])\n by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)\n (Exim 4.90_1) (envelope-from <berrange@redhat.com>)\n id 1vqC6o-0006WO-9X\n for qemu-devel@nongnu.org; Wed, 11 Feb 2026 10:26:30 -0500", "from us-smtp-delivery-124.mimecast.com ([170.10.133.124])\n by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)\n (Exim 4.90_1) (envelope-from <berrange@redhat.com>)\n id 1vqC6m-0005u9-6t\n for qemu-devel@nongnu.org; Wed, 11 Feb 2026 10:26:30 -0500", "from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com\n (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by\n relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3,\n cipher=TLS_AES_256_GCM_SHA384) id us-mta-306-FVN3tseiN7q5m3q1l49CNA-1; Wed,\n 11 Feb 2026 10:26:23 -0500", "from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com\n (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4])\n (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest\n SHA256)\n (No client certificate requested)\n by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS\n id 814E51955F28; Wed, 11 Feb 2026 15:26:21 +0000 (UTC)", "from toolbx.redhat.com (unknown [10.45.227.9])\n by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP\n id F3BB930001A8; Wed, 11 Feb 2026 15:26:13 +0000 (UTC)" ], "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;\n s=mimecast20190719; t=1770823587;\n h=from:from:reply-to:subject:subject:date:date:message-id:message-id:\n to:to:cc:cc:mime-version:mime-version:content-type:content-type:\n content-transfer-encoding:content-transfer-encoding:\n in-reply-to:in-reply-to:references:references;\n bh=quFtc628f984Q3yp25Wk6fR4lXqtSsXdbUO1vrf3FKQ=;\n b=XGum1ddFipUAH/hYvTHdJweaOPPGUFkBf4H8jZS9gREAgHI2pkosMQ5TowJrYQWluG3591\n yx6V73SPi/Q3f+aW9MOjmMG9Mlj3VRsl+ekm14nB1y+UY/GY3qA+0qGhXyICAcMoOTm6JW\n dR3mVPHHCxiopfwnW/JvUsASRDD9TDw=", "X-MC-Unique": "FVN3tseiN7q5m3q1l49CNA-1", "X-Mimecast-MFC-AGG-ID": "FVN3tseiN7q5m3q1l49CNA_1770823581", "From": "=?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= <berrange@redhat.com>", "To": "qemu-devel@nongnu.org", "Cc": "Manos Pitsidianakis <manos.pitsidianakis@linaro.org>,\n Stefan Weil <sw@weilnetz.de>, \"Dr. David Alan Gilbert\" <dave@treblig.org>,\n Pierrick Bouvier <pierrick.bouvier@linaro.org>, devel@lists.libvirt.org,\n\t=?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= <philmd@linaro.org>, =?utf-8?q?Marc?=\n\t=?utf-8?q?-Andr=C3=A9_Lureau?= <marcandre.lureau@redhat.com>,\n Hanna Reitz <hreitz@redhat.com>, Kevin Wolf <kwolf@redhat.com>,\n qemu-block@nongnu.org, qemu-rust@nongnu.org,\n Paolo Bonzini <pbonzini@redhat.com>, Markus Armbruster <armbru@redhat.com>,\n Gerd Hoffmann <kraxel@redhat.com>,\n =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= <berrange@redhat.com>,\n Christian Schoenebeck <qemu_oss@crudebyte.com>,\n Richard Henderson <richard.henderson@linaro.org>", "Subject": "[PATCH v6 11/27] util: introduce some API docs for logging APIs", "Date": "Wed, 11 Feb 2026 15:24:52 +0000", "Message-ID": "<20260211152508.732487-12-berrange@redhat.com>", "In-Reply-To": "<20260211152508.732487-1-berrange@redhat.com>", "References": "<20260211152508.732487-1-berrange@redhat.com>", "MIME-Version": "1.0", "Content-Type": "text/plain; charset=UTF-8", "Content-Transfer-Encoding": "8bit", "X-Scanned-By": "MIMEDefang 3.4.1 on 10.30.177.4", "Received-SPF": "pass client-ip=170.10.133.124;\n envelope-from=berrange@redhat.com;\n helo=us-smtp-delivery-124.mimecast.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, DKIMWL_WL_HIGH=-0.001,\n DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001,\n RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001,\n SPF_HELO_PASS=-0.001,\n SPF_PASS=-0.001 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": "qemu development <qemu-devel.nongnu.org>", "List-Unsubscribe": "<https://lists.nongnu.org/mailman/options/qemu-devel>,\n <mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>", "List-Archive": "<https://lists.nongnu.org/archive/html/qemu-devel>", "List-Post": "<mailto:qemu-devel@nongnu.org>", "List-Help": "<mailto:qemu-devel-request@nongnu.org?subject=help>", "List-Subscribe": "<https://lists.nongnu.org/mailman/listinfo/qemu-devel>,\n <mailto:qemu-devel-request@nongnu.org?subject=subscribe>", "Errors-To": "qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org", "Sender": "qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org" }, "content": "There is a gotcha with qemu_log() usage in a threaded process.\nIf fragments of a log message are output via qemu_log() it is\npossible for messages from two threads to get mixed up. To\nprevent this qemu_log_trylock() should be used, along with\nfprintf(f) calls.\n\nThis is a subtle problem that needs to be explained in the\nAPI docs to ensure correct usage.\n\nIn the Rust code, the log_mask_ln method which is conceptually\nequivalent to the C qemu_log() call will unconditionally append\na newline so must only ever be used for complete log messages.\n\nReported-by: Markus Armbruster <armbru@redhat.com>\nSigned-off-by: Daniel P. Berrangé <berrange@redhat.com>\n---\n include/qemu/log-for-trace.h | 17 ++++++++++++++++-\n include/qemu/log.h | 32 ++++++++++++++++++++++++++++++++\n rust/util/src/log.rs | 6 ++++++\n 3 files changed, 54 insertions(+), 1 deletion(-)", "diff": "diff --git a/include/qemu/log-for-trace.h b/include/qemu/log-for-trace.h\nindex f3a8791f1d..6861a1a4b7 100644\n--- a/include/qemu/log-for-trace.h\n+++ b/include/qemu/log-for-trace.h\n@@ -29,7 +29,22 @@ static inline bool qemu_loglevel_mask(int mask)\n return (qemu_loglevel & mask) != 0;\n }\n \n-/* main logging function */\n+/**\n+ * qemu_log: report a log message\n+ * @fmt: the format string for the message\n+ * @...: the format string arguments\n+ *\n+ * This will emit a log message to the current output stream.\n+ *\n+ * The @fmt string should normally represent a complete line\n+ * of text, and thus end with a newline character.\n+ *\n+ * While it is possible to incrementally output fragments of\n+ * a complete line using qemu_log, this is inefficient and\n+ * races with other threads. For outputting fragments it is\n+ * strongly preferred to use the qemu_log_trylock() method\n+ * combined with fprintf().\n+ */\n void G_GNUC_PRINTF(1, 2) qemu_log(const char *fmt, ...);\n \n #endif\ndiff --git a/include/qemu/log.h b/include/qemu/log.h\nindex 7effba4da4..b49a1a5fe3 100644\n--- a/include/qemu/log.h\n+++ b/include/qemu/log.h\n@@ -41,7 +41,39 @@ bool qemu_log_separate(void);\n \n /* Lock/unlock output. */\n \n+/**\n+ * Acquires a lock on the current log output stream.\n+ * The returned FILE object should be used with the\n+ * fprintf() function to output the log message, and\n+ * then qemu_log_unlock() called to release the lock.\n+ *\n+ * The primary use case is to be able to incrementally\n+ * output fragments of a complete log message in an\n+ * efficient and race free manner.\n+ *\n+ * The simpler qemu_log() method should normally only\n+ * be used to output complete log messages, and not\n+ * within scope of a qemu_log_trylock() call.\n+ *\n+ * A typical usage pattern would be\n+ *\n+ * FILE *f = qemu_log_trylock()\n+ *\n+ * fprintf(f, \"Something \");\n+ * fprintf(f, \"Something \");\n+ * fprintf(f, \"Something \");\n+ * fprintf(f, \"The end\\n\");\n+ *\n+ * qemu_log_unlock(f);\n+ *\n+ * Returns: the current FILE if available, NULL on error\n+ */\n FILE *qemu_log_trylock(void) G_GNUC_WARN_UNUSED_RESULT;\n+\n+/**\n+ * Releases the lock on the log output, previously\n+ * acquired by qemu_log_trylock().\n+ */\n void qemu_log_unlock(FILE *fd);\n \n /* Logging functions: */\ndiff --git a/rust/util/src/log.rs b/rust/util/src/log.rs\nindex 0a4bc4249a..a85db804a7 100644\n--- a/rust/util/src/log.rs\n+++ b/rust/util/src/log.rs\n@@ -134,6 +134,12 @@ fn drop(&mut self) {\n /// \"Address 0x{:x} out of range\",\n /// error_address,\n /// );\n+///\n+/// The `log_mask_ln` macro must only be used for emitting complete\n+/// log messages. Where it is required to incrementally output string\n+/// fragments to construct a complete message, `LogGuard::new()` must\n+/// be directly used in combination with `writeln()` to avoid output\n+/// races with other QEMU threads.\n /// ```\n #[macro_export]\n macro_rules! log_mask_ln {\n", "prefixes": [ "v6", "11/27" ] }