From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 62D3DE9A03B for ; Wed, 18 Feb 2026 09:52:44 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vseEG-00039F-Vh; Wed, 18 Feb 2026 04:52:20 -0500 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 1vseEF-00038o-A6 for qemu-rust@nongnu.org; Wed, 18 Feb 2026 04:52:19 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vseEA-0003Ni-Bd for qemu-rust@nongnu.org; Wed, 18 Feb 2026 04:52:18 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1771408333; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=p/o48FhHUtVqRP8QJE7g4XyNXIXv3G98fFT/ILWFulI=; b=PFZ6fr+nmABgYzD88qq+4Nc+COs6ybMqmwVZew8J8of0X2BZ7muYu/1Rp/Og+XtLQnQo8C K5GCootVU3uQAgueP2wWP+o9H7AuYw2hfBSHfmW69h9+01wjENPg6ERO2KYmKOWx5I41RD oO42Q/2jY6c6CG7jowWY8m9RshaEskw= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-619-yp4l4jOuP0yIkUJ0thNoWg-1; Wed, 18 Feb 2026 04:52:12 -0500 X-MC-Unique: yp4l4jOuP0yIkUJ0thNoWg-1 X-Mimecast-MFC-AGG-ID: yp4l4jOuP0yIkUJ0thNoWg_1771408330 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 604941956058; Wed, 18 Feb 2026 09:52:10 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.14]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A48ED1955F43; Wed, 18 Feb 2026 09:52:09 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 38B7021E692D; Wed, 18 Feb 2026 10:52:07 +0100 (CET) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Cc: qemu-devel@nongnu.org, Manos Pitsidianakis , Stefan Weil , "Dr. David Alan Gilbert" , Pierrick Bouvier , devel@lists.libvirt.org, Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , =?utf-8?Q?Marc-Andr?= =?utf-8?Q?=C3=A9?= Lureau , Hanna Reitz , Kevin Wolf , qemu-block@nongnu.org, qemu-rust@nongnu.org, Paolo Bonzini , Gerd Hoffmann , Christian Schoenebeck , Richard Henderson Subject: Re: [PATCH v6 12/27] util: avoid repeated prefix on incremental qemu_log calls In-Reply-To: <20260211152508.732487-13-berrange@redhat.com> ("Daniel P. =?utf-8?Q?Berrang=C3=A9=22's?= message of "Wed, 11 Feb 2026 15:24:53 +0000") References: <20260211152508.732487-1-berrange@redhat.com> <20260211152508.732487-13-berrange@redhat.com> Date: Wed, 18 Feb 2026 10:52:07 +0100 Message-ID: <87ms16e5vc.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Mimecast-MFC-PROC-ID: P29SSkULdniimCV9j84lpfp8evN-vI_38KysPPdhw3M_1771408330 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -13 X-Spam_score: -1.4 X-Spam_bar: - X-Spam_report: (-1.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.043, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, GB_FAKE_RF=0.754, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-rust@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: QEMU Rust-related patches and discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-rust-bounces+qemu-rust=archiver.kernel.org@nongnu.org Sender: qemu-rust-bounces+qemu-rust=archiver.kernel.org@nongnu.org Daniel P. Berrang=C3=A9 writes: > There are three general patterns to QEMU log output > > 1. Single complete message calls > > qemu_log("Some message\n"); > > 2. Direct use of fprintf > > FILE *f =3D qemu_log_trylock() > fprintf(f, "..."); > fprintf(f, "..."); > fprintf(f, "...\n"); > qemu_log_unlock(f) Real code needs to check @f or risk crashing. Shouldn't we show that here? > 3. Mixed use of qemu_log_trylock/qemu_log() > > FILE *f =3D qemu_log_trylock() > qemu_log("...."); > qemu_log("...."); > qemu_log("....\n"); > qemu_log_unlock(f) > > When message prefixes are enabled, the timestamp will be > unconditionally emitted for all qemu_log() calls. This > works fine in the 1st case, and has no effect in the 2nd > case. In the 3rd case, however, we get the timestamp > printed over & over in each fragment. > > One can suggest that pattern (3) is pointless as it is > functionally identical to (2) but with extra indirection > and overhead. None the less we have a fair bit of code > that does this. > > The qemu_log() call itself is nothing more than a wrapper > which does pattern (2) with a single fprintf() call. qemu_log_trylock()'s lock is recursive. Worth a comment? Not sure. > One might question whether (2) should include the message > prefix in the same way that (1), but there are scenarios > where this could be inappropriate / unhelpful such as the > CPU register dumps or linux-user strace output. > > This patch fixes the problem in pattern (3) by keeping > track of the call depth of qemu_log_trylock() and then > only emitting the the prefix when the starting depth > was zero. In doing this qemu_log_trylock_context() is > also introduced as a variant of qemu_log_trylock() > that emits the prefix. Callers doing to batch output > can thus choose whether a prefix is appropriate or > not. > > Fixes: 012842c07552 (log: make '-msg timestamp=3Don' apply to all qemu_lo= g usage) > Reported-by: Richard Henderson > Signed-off-by: Daniel P. Berrang=C3=A9 Reviewed-by: Markus Armbruster