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bh=ywrwi5unSNAlTBRP9AvE3Cqq3sK/uZ73N2XY41MTeSo=; b=RyOnfIQ/nesHJEZHFwuFiOhOOfwrAQvcXTyd4Ej7NN5pQQyoxtJ1Gse12UULEoZ+PhljZy DhpHT65CLTPMFW2pObptAFLtITdItmZMkjdUN30kYfCZO5GCDWT11bIjTM4SIDUnYbFMyD ny+PDOXpListVU9zCrVCGsO/s54wPhc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-232-3XwDkgYvOmmW_BRxlWeTQg-1; Tue, 13 Jul 2021 09:01:51 -0400 X-MC-Unique: 3XwDkgYvOmmW_BRxlWeTQg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D46208B94EA; Tue, 13 Jul 2021 13:01:36 +0000 (UTC) Received: from redhat.com (ovpn-113-49.phx2.redhat.com [10.3.113.49]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3D79010016FD; Tue, 13 Jul 2021 13:01:36 +0000 (UTC) Date: Tue, 13 Jul 2021 08:01:34 -0500 From: Eric Blake To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH 01/11] nbd/server: Remove unused variable Message-ID: <20210713130134.zfti7sgxcw4i3dbd@redhat.com> References: <20210712215535.1471256-1-richard.henderson@linaro.org> <20210712215535.1471256-2-richard.henderson@linaro.org> MIME-Version: 1.0 In-Reply-To: User-Agent: NeoMutt/20210205-569-37ed14 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.7, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Richard Henderson , qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Jul 13, 2021 at 12:27:48PM +0300, Vladimir Sementsov-Ogievskiy wrote: > 13.07.2021 00:55, Richard Henderson wrote: > > From clang-13: > > nbd/server.c:976:22: error: variable 'bitmaps' set but not used \ > > [-Werror,-Wunused-but-set-variable] > > > > +++ b/nbd/server.c > > @@ -973,7 +973,6 @@ static int nbd_negotiate_meta_queries(NBDClient *client, > > { > > int ret; > > g_autofree char *export_name = NULL; > > - g_autofree bool *bitmaps = NULL; > > NBDExportMetaContexts local_meta = {0}; > > uint32_t nb_queries; > > size_t i; > > @@ -1007,9 +1006,6 @@ static int nbd_negotiate_meta_queries(NBDClient *client, > > "export '%s' not present", sane_name); > > } > > meta->bitmaps = g_new0(bool, meta->exp->nr_export_bitmaps); > > - if (client->opt == NBD_OPT_LIST_META_CONTEXT) { > > - bitmaps = meta->bitmaps; > > - } > > ret = nbd_opt_read(client, &nb_queries, sizeof(nb_queries), false, errp); > > if (ret <= 0) { > > > > > Hm. I'm afraid, this way meta->bitmaps will be leaked in NBD_OPT_LIST_META_CONTEXT case. > > Actually, "bitmaps" _is_ used, in cleanup handler, setup by g_autofree. So it's a false positive. > Correct; this patch is wrong, and would cause a memory leak. This is a false positive in clang, and a known issue that clang is in general unable to see that g_autofree variables are used, sometimes for their intentional side effects such as easier memory cleanup as done here. I suspect that the definition of g_autofree already uses __attribute__((unused)) to work around clang's oddities, which means I'm not sure how to silence clang on this one. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org