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GET /api/patches/2195643/?format=api
{ "id": 2195643, "url": "http://patchwork.ozlabs.org/api/patches/2195643/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260211152508.732487-13-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": "<20260211152508.732487-13-berrange@redhat.com>", "list_archive_url": null, "date": "2026-02-11T15:24:53", "name": "[v6,12/27] util: avoid repeated prefix on incremental qemu_log calls", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "1c99f0fd7595fec21724869399b9c637351747fd", "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/20260211152508.732487-13-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/2195643/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2195643/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=PSRRZjAO;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;\n s=mimecast20190719; t=1770823594;\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=ivMVOpUATjRZXgnDFtNQpL979jOHE0O+UHSIPG4QEn0=;\n b=PSRRZjAOxpe0vB/ATORNcG7oofo6mltJ/QulBaBQdsZ+pjmANCtOnM/d2FbafI8k2O7awC\n IyACRP1MBxlecRMDoeuRACKbtq+RphJChpo/Z9drWrjlov9s++/Urs11O4fp/inz3JvSx6\n 21LYgw6uSSh40nFlGINmoE+NOpQRbnE=", "X-MC-Unique": "W5DJzJOzM3iDuOGI-5z7AA-1", "X-Mimecast-MFC-AGG-ID": "W5DJzJOzM3iDuOGI-5z7AA_1770823586", "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 12/27] util: avoid repeated prefix on incremental qemu_log\n calls", "Date": "Wed, 11 Feb 2026 15:24:53 +0000", "Message-ID": "<20260211152508.732487-13-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 are three general patterns to QEMU log output\n\n 1. Single complete message calls\n\n qemu_log(\"Some message\\n\");\n\n 2. Direct use of fprintf\n\n FILE *f = qemu_log_trylock()\n fprintf(f, \"...\");\n fprintf(f, \"...\");\n fprintf(f, \"...\\n\");\n qemu_log_unlock(f)\n\n 3. Mixed use of qemu_log_trylock/qemu_log()\n\n FILE *f = qemu_log_trylock()\n qemu_log(\"....\");\n qemu_log(\"....\");\n qemu_log(\"....\\n\");\n qemu_log_unlock(f)\n\nWhen message prefixes are enabled, the timestamp will be\nunconditionally emitted for all qemu_log() calls. This\nworks fine in the 1st case, and has no effect in the 2nd\ncase. In the 3rd case, however, we get the timestamp\nprinted over & over in each fragment.\n\nOne can suggest that pattern (3) is pointless as it is\nfunctionally identical to (2) but with extra indirection\nand overhead. None the less we have a fair bit of code\nthat does this.\n\nThe qemu_log() call itself is nothing more than a wrapper\nwhich does pattern (2) with a single fprintf() call.\n\nOne might question whether (2) should include the message\nprefix in the same way that (1), but there are scenarios\nwhere this could be inappropriate / unhelpful such as the\nCPU register dumps or linux-user strace output.\n\nThis patch fixes the problem in pattern (3) by keeping\ntrack of the call depth of qemu_log_trylock() and then\nonly emitting the the prefix when the starting depth\nwas zero. In doing this qemu_log_trylock_context() is\nalso introduced as a variant of qemu_log_trylock()\nthat emits the prefix. Callers doing to batch output\ncan thus choose whether a prefix is appropriate or\nnot.\n\nFixes: 012842c07552 (log: make '-msg timestamp=on' apply to all qemu_log usage)\nReported-by: Richard Henderson <richard.henderson@linaro.org>\nSigned-off-by: Daniel P. Berrangé <berrange@redhat.com>\n---\n include/qemu/log.h | 7 +++++++\n util/log.c | 49 ++++++++++++++++++++++++++--------------------\n 2 files changed, 35 insertions(+), 21 deletions(-)", "diff": "diff --git a/include/qemu/log.h b/include/qemu/log.h\nindex b49a1a5fe3..92956e5d0f 100644\n--- a/include/qemu/log.h\n+++ b/include/qemu/log.h\n@@ -70,6 +70,13 @@ bool qemu_log_separate(void);\n */\n FILE *qemu_log_trylock(void) G_GNUC_WARN_UNUSED_RESULT;\n \n+/**\n+ * As qemu_log_trylock(), but will also print the message\n+ * context, if any is configured and this caused the\n+ * acquisition of the FILE lock\n+ */\n+FILE *qemu_log_trylock_with_context(void) G_GNUC_WARN_UNUSED_RESULT;\n+\n /**\n * Releases the lock on the log output, previously\n * acquired by qemu_log_trylock().\ndiff --git a/util/log.c b/util/log.c\nindex c44d66b5ce..1644e6814b 100644\n--- a/util/log.c\n+++ b/util/log.c\n@@ -127,13 +127,39 @@ static FILE *qemu_log_trylock_with_err(Error **errp)\n return logfile;\n }\n \n+/*\n+ * Zero if there's been no opening qemu_log_trylock call,\n+ * indicating the need for message context to be emitted\n+ *\n+ * Non-zero if we're in the middle of printing a message,\n+ * possibly over multiple lines and must skip further\n+ * message context\n+ */\n+static __thread uint log_depth;\n+\n FILE *qemu_log_trylock(void)\n {\n- return qemu_log_trylock_with_err(NULL);\n+ FILE *f = qemu_log_trylock_with_err(NULL);\n+ log_depth++;\n+ return f;\n+}\n+\n+FILE *qemu_log_trylock_with_context(void)\n+{\n+ FILE *f = qemu_log_trylock();\n+ if (f && log_depth == 1 && message_with_timestamp) {\n+ g_autofree const char *timestr = NULL;\n+ g_autoptr(GDateTime) dt = g_date_time_new_now_utc();\n+ timestr = g_date_time_format_iso8601(dt);\n+ fprintf(f, \"%s \", timestr);\n+ }\n+ return f;\n }\n \n void qemu_log_unlock(FILE *logfile)\n {\n+ assert(log_depth);\n+ log_depth--;\n if (logfile) {\n fflush(logfile);\n qemu_funlockfile(logfile);\n@@ -145,28 +171,9 @@ void qemu_log_unlock(FILE *logfile)\n \n void qemu_log(const char *fmt, ...)\n {\n- FILE *f;\n- g_autofree const char *timestr = NULL;\n-\n- /*\n- * Prepare the timestamp *outside* the logging\n- * lock so it better reflects when the message\n- * was emitted if we are delayed acquiring the\n- * mutex\n- */\n- if (message_with_timestamp) {\n- g_autoptr(GDateTime) dt = g_date_time_new_now_utc();\n- timestr = g_date_time_format_iso8601(dt);\n- }\n-\n- f = qemu_log_trylock();\n+ FILE *f = qemu_log_trylock_with_context();\n if (f) {\n va_list ap;\n-\n- if (timestr) {\n- fprintf(f, \"%s \", timestr);\n- }\n-\n va_start(ap, fmt);\n vfprintf(f, fmt, ap);\n va_end(ap);\n", "prefixes": [ "v6", "12/27" ] }