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 0389DCA0EFA for ; Tue, 26 Aug 2025 11:59:09 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uqsJm-0002wo-Mc; Tue, 26 Aug 2025 07:58:26 -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 1uqsJj-0002vp-QI for qemu-devel@nongnu.org; Tue, 26 Aug 2025 07:58:24 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uqsJc-0004Gt-Pr for qemu-devel@nongnu.org; Tue, 26 Aug 2025 07:58:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1756209495; h=from:from:reply-to: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=djl+0gtWuuhoRTrN1ryfL+u6O00KCBccCjqe7XL3P4o=; b=GFxbw7xvr7/ArwiMBmlWTCw8em6H2KeEaLxPcB2vjMsOp38kZrLgurcG4xYfN3e7VaOkcZ LbDR76uW04UOWeiu4+fKxjy3kpwvHYhpgO/jAQikLGRqqr9laPrzyzoWyj5FfciZqzhDqJ OHvcDhZvpJAKAqsxHDr0uF7BFUHQqqw= Received: from mx-prod-mc-02.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-42-Q1Bcn1xcNGOf3JZZkqOYTA-1; Tue, 26 Aug 2025 07:58:12 -0400 X-MC-Unique: Q1Bcn1xcNGOf3JZZkqOYTA-1 X-Mimecast-MFC-AGG-ID: Q1Bcn1xcNGOf3JZZkqOYTA_1756209491 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 31758195608A; Tue, 26 Aug 2025 11:58:11 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.174]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B0BF3300146C; Tue, 26 Aug 2025 11:58:08 +0000 (UTC) Date: Tue, 26 Aug 2025 12:58:05 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Maydell Cc: Paolo Bonzini , qemu-devel@nongnu.org, tanishdesai37@gmail.com, stefanha@redhat.com, mads@ynddal.dk Subject: Re: [PATCH 03/14] trace/ftrace: move snprintf+write from tracepoints to ftrace.c Message-ID: References: <20250822122655.1353197-1-pbonzini@redhat.com> <20250822122655.1353197-4-pbonzini@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; 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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=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, T_SPF_TEMPERROR=0.01 autolearn=ham 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Aug 26, 2025 at 12:45:42PM +0100, Peter Maydell wrote: > On Tue, 26 Aug 2025 at 12:42, Daniel P. Berrangé wrote: > > > > On Fri, Aug 22, 2025 at 02:26:44PM +0200, Paolo Bonzini wrote: > > > This simplifies the Python code and reduces the size of the tracepoints. > > > > +void ftrace_write(const char *fmt, ...) > > > +{ > > > + char ftrace_buf[MAX_TRACE_STRLEN]; > > > + int unused __attribute__ ((unused)); > > > + int trlen; > > > + va_list ap; > > > + > > > + va_start(ap, fmt); > > > + trlen = vsnprintf(ftrace_buf, MAX_TRACE_STRLEN, fmt, ap); > > > + va_end(ap); > > > + > > > + trlen = MIN(trlen, MAX_TRACE_STRLEN - 1); > > > + unused = write(trace_marker_fd, ftrace_buf, trlen); > > > > You're just copying the existing code pattern which is fine for now so > > > > Reviewed-by: Daniel P. Berrangé > > > > > > More generally though, IMHO, QEMU would be better off bringing in > > gnulib's 'ignore_value' macro, but simplified since we don't care > > about ancient GCC > > > > #define ignore_value(x) \ > > (__extension__ ({ __typeof__ (x) __x = (x); (void) __x; })) > > > > so that we don't need to play games with extra variables. eg > > > > ignore_value(write(trace_marker_fd, ftrace_buf, trlen)); > > Isn't there a way to write that that explicitly tells > the compiler "this is unused" (i.e. with the 'unused' > attribute) rather than relying on a particular construct > to not trigger a warning? I think what the code is already doing is the closest to making it explicit, but that needs the extra variable which is unpleasant. It is annoyng that 'warn_unused_result' doesn't let you just cast to (void) to discard a result without warnings :-( With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|