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 090F4C43217 for ; Tue, 1 Nov 2022 19:02:04 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1opwVh-0006Bo-W1; Tue, 01 Nov 2022 15:01:18 -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 1opwVf-0005ze-2C for qemu-devel@nongnu.org; Tue, 01 Nov 2022 15:01:15 -0400 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 1opwVW-0004LA-C4 for qemu-devel@nongnu.org; Tue, 01 Nov 2022 15:01:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1667329264; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NLagzt3b9eFE5VQap6yM2xzJT792otpID4qDi8KriWE=; b=B+RuLre0Z3tWReLKDbwrP9eb/Vu+P3pSjPk1qq4qargCJ7ZBqJCjt+ft6MzqGWMQszD8SY Ask9P361FqqNXvIKDIk623sl5fiaM1X6oEc8zqP4uNsrEstn43vSW3RxFBjKlxQ3d1YfOO c/34I6O4TELNv6d37+rCIvXF0SqUhKs= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-317-8Ks1pwd6ON69v6pwij917Q-1; Tue, 01 Nov 2022 15:00:59 -0400 X-MC-Unique: 8Ks1pwd6ON69v6pwij917Q-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 363083C02B89; Tue, 1 Nov 2022 19:00:59 +0000 (UTC) Received: from localhost (unknown [10.39.192.93]) by smtp.corp.redhat.com (Postfix) with ESMTP id B1A882028CE4; Tue, 1 Nov 2022 19:00:58 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: hreitz@redhat.com, qemu-block@nongnu.org, Kevin Wolf , nsoffer@redhat.com, Stefan Hajnoczi Subject: [PATCH 1/2] file-posix: fix Linux alignment probing when EIO is returned Date: Tue, 1 Nov 2022 15:00:30 -0400 Message-Id: <20221101190031.6766-2-stefanha@redhat.com> In-Reply-To: <20221101190031.6766-1-stefanha@redhat.com> References: <20221101190031.6766-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.051, 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_H2=-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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Qemu-devel" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Linux dm-crypt returns errno EIO from unaligned O_DIRECT pread(2) calls. Alignment probing fails on dm-crypt devices because the code expects EINVAL. Treating any errno as an "unaligned" indicator would be easy, but breaks commit 22d182e82b4b ("block/raw-posix: fix launching with failed disks"). Offline disks return EIO for correctly aligned requests and EINVAL for unaligned requests. It's possible to make both dm-crypt and offline disks work: look for the transition from EINVAL to EIO instead of for a single EINVAL value. Buglink: https://gitlab.com/qemu-project/qemu/-/issues/1290 Fixes: 22d182e82b4b ("block/raw-posix: fix launching with failed disks") Signed-off-by: Stefan Hajnoczi --- block/file-posix.c | 42 +++++++++++++++--------------------------- 1 file changed, 15 insertions(+), 27 deletions(-) diff --git a/block/file-posix.c b/block/file-posix.c index b9647c5ffc..b9d62f52fe 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -355,31 +355,6 @@ static bool raw_needs_alignment(BlockDriverState *bs) return s->force_alignment; } -/* Check if read is allowed with given memory buffer and length. - * - * This function is used to check O_DIRECT memory buffer and request alignment. - */ -static bool raw_is_io_aligned(int fd, void *buf, size_t len) -{ - ssize_t ret = pread(fd, buf, len, 0); - - if (ret >= 0) { - return true; - } - -#ifdef __linux__ - /* The Linux kernel returns EINVAL for misaligned O_DIRECT reads. Ignore - * other errors (e.g. real I/O error), which could happen on a failed - * drive, since we only care about probing alignment. - */ - if (errno != EINVAL) { - return true; - } -#endif - - return false; -} - static void raw_probe_alignment(BlockDriverState *bs, int fd, Error **errp) { BDRVRawState *s = bs->opaque; @@ -426,34 +401,47 @@ static void raw_probe_alignment(BlockDriverState *bs, int fd, Error **errp) * try to detect buf_align, which cannot be detected in some cases (e.g. * Gluster). If buf_align cannot be detected, we fallback to the value of * request_alignment. + * + * The probing loop keeps track of the last errno so that the alignment of + * offline disks can be probed. On Linux pread(2) returns with errno EINVAL + * for most file descriptors when O_DIRECT alignment constraints are unmet. + * Offline disks fail correctly aligned pread(2) with EIO. Therefore it's + * possible to detect alignment on offline disks by observing when the + * errno changes from EINVAL to something else. */ if (!bs->bl.request_alignment) { + int last_errno = 0; int i; size_t align; buf = qemu_memalign(max_align, max_align); for (i = 0; i < ARRAY_SIZE(alignments); i++) { align = alignments[i]; - if (raw_is_io_aligned(fd, buf, align)) { + if (pread(fd, buf, align, 0) >= 0 || + (errno != EINVAL && last_errno == EINVAL)) { /* Fallback to safe value. */ bs->bl.request_alignment = (align != 1) ? align : max_align; break; } + last_errno = errno; } qemu_vfree(buf); } if (!s->buf_align) { + int last_errno = 0; int i; size_t align; buf = qemu_memalign(max_align, 2 * max_align); for (i = 0; i < ARRAY_SIZE(alignments); i++) { align = alignments[i]; - if (raw_is_io_aligned(fd, buf + align, max_align)) { + if (pread(fd, buf + align, max_align, 0) >= 0 || + (errno != EINVAL && last_errno == EINVAL)) { /* Fallback to request_alignment. */ s->buf_align = (align != 1) ? align : bs->bl.request_alignment; break; } + last_errno = errno; } qemu_vfree(buf); } -- 2.38.1