From patchwork Wed Nov 15 17:24:37 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Woodhouse X-Patchwork-Id: 13457150 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.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 C42A2C2BB3F for ; Wed, 15 Nov 2023 17:27:57 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.633811.988880 (Exim 4.92) (envelope-from ) id 1r3Jg0-0003Jy-4R; Wed, 15 Nov 2023 17:27:44 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 633811.988880; Wed, 15 Nov 2023 17:27:44 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1r3Jfz-0003If-UV; Wed, 15 Nov 2023 17:27:43 +0000 Received: by outflank-mailman (input) for mailman id 633811; Wed, 15 Nov 2023 17:27:42 +0000 Received: from se1-gles-flk1-in.inumbo.com ([94.247.172.50] helo=se1-gles-flk1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1r3Jfy-00031y-AT for xen-devel@lists.xenproject.org; Wed, 15 Nov 2023 17:27:42 +0000 Received: from desiato.infradead.org (desiato.infradead.org [2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id 44a6bfc0-83dc-11ee-9b0e-b553b5be7939; Wed, 15 Nov 2023 18:27:38 +0100 (CET) Received: from [2001:8b0:10b:1::ebe] (helo=i7.infradead.org) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1r3Jfi-004Bc2-26; Wed, 15 Nov 2023 17:27:26 +0000 Received: from dwoodhou by i7.infradead.org with local (Exim 4.96.2 #2 (Red Hat Linux)) id 1r3Jfh-004sFL-16; Wed, 15 Nov 2023 17:27:25 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list X-Inumbo-ID: 44a6bfc0-83dc-11ee-9b0e-b553b5be7939 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description; bh=iJEkdS0pn0NaWuyuJa10RygKkR2b5taCeZjDdDEb+V8=; b=kAKl+Xku2nRKfIhSLPH3+fjd8S PIIIAjYbVjC4xBDHZaXNvD0z9x58yFQGqYFlfOnrlK+4kceqKQqBzVf/04nDaW7UNNcPAq7CN3GON 53EQfv1KL4qKFIxx1w0US+jxdYqvXc7rz+VeWnWsY6SMjejou4sfApYbzAtwVZtc+xAb7CnxLZO8h fGQ4l0vEe7cWQ+BAJAboVAzNGMLlBX3Azmy5PcL6SK0RsmpuFWKpXr02LRE5FrafLzTVJHR/q/xlr /DjObAZMr4mskpzSgSE0g6R8w8U3d6Pj9cs6eGpjrhG0hEQEBZfInO3RbFgBLxC6gPbX0LxKhDsjk P2AENoUQ==; From: David Woodhouse To: qemu-devel@nongnu.org Cc: Stefano Stabellini , Anthony Perard , Paul Durrant , Kevin Wolf , Hanna Reitz , Jason Wang , Paolo Bonzini , xen-devel@lists.xenproject.org, qemu-block@nongnu.org Subject: [PATCH 3/3] hw/xen: clean up xen_block_find_free_vdev() to avoid Coverity false positive Date: Wed, 15 Nov 2023 17:24:37 +0000 Message-ID: <20231115172723.1161679-4-dwmw2@infradead.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20231115172723.1161679-1-dwmw2@infradead.org> References: <20231115172723.1161679-1-dwmw2@infradead.org> MIME-Version: 1.0 Sender: David Woodhouse X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html From: David Woodhouse Coverity couldn't see that nr_existing was always going to be zero when qemu_xen_xs_directory() returned NULL in the ENOENT case (CID 1523906). Perhaps more to the point, neither could Peter at first glance. Improve the code to hopefully make it clearer to Coverity and human reviewers alike. Signed-off-by: David Woodhouse Reviewed-by: Paul Durrant --- hw/block/xen-block.c | 24 +++++++++++++++++++++--- 1 file changed, 21 insertions(+), 3 deletions(-) diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c index 6d64ede94f..aed1d5c330 100644 --- a/hw/block/xen-block.c +++ b/hw/block/xen-block.c @@ -91,9 +91,27 @@ static bool xen_block_find_free_vdev(XenBlockDevice *blockdev, Error **errp) existing_frontends = qemu_xen_xs_directory(xenbus->xsh, XBT_NULL, fe_path, &nr_existing); - if (!existing_frontends && errno != ENOENT) { - error_setg_errno(errp, errno, "cannot read %s", fe_path); - return false; + if (!existing_frontends) { + if (errno == ENOENT) { + /* + * If the frontend directory doesn't exist because there are + * no existing vbd devices, that's fine. Just ensure that we + * don't dereference the NULL existing_frontends pointer, by + * checking that nr_existing is zero so the loop below is not + * entered. + * + * In fact this is redundant since nr_existing is initialized + * to zero, but setting it again here makes it abundantly clear + * to Coverity, and to the human reader who doesn't know the + * semantics of qemu_xen_xs_directory() off the top of their + * head. + */ + nr_existing = 0; + } else { + /* All other errors accessing the frontend directory are fatal. */ + error_setg_errno(errp, errno, "cannot read %s", fe_path); + return false; + } } memset(used_devs, 0, sizeof(used_devs));