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 1DCC8C3ABC3 for ; Tue, 13 May 2025 13:52:47 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uEq3E-0001Hr-9F; Tue, 13 May 2025 09:52:08 -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 1uEq37-0001Gw-LW for qemu-devel@nongnu.org; Tue, 13 May 2025 09:52:03 -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 1uEq32-0001kr-1F for qemu-devel@nongnu.org; Tue, 13 May 2025 09:51:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1747144313; 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: in-reply-to:in-reply-to:references:references; bh=u71QUGF+wv5hJ6F1s1Mid1pdlzn9vihyorwuiVBmgvc=; b=gUVsNlMQwlwAB7yQe+wqeO75iOnGvv13IckSSOJWH2iJ59zTgSQ4ioFVpGVD7A77/gnHBF LOsUWF32MwdbDGC0ZMGfne3oRNXh9+7nvj0AeP96w3/0AyyUvBedgkgSH74Gr5p8ZyxyOg 53LkjwKamOY427inlKknKo80By+0Wb0= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-353-6sudEH2DNraB5TuMurKFdQ-1; Tue, 13 May 2025 09:51:52 -0400 X-MC-Unique: 6sudEH2DNraB5TuMurKFdQ-1 X-Mimecast-MFC-AGG-ID: 6sudEH2DNraB5TuMurKFdQ_1747144311 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 07B6E180087F; Tue, 13 May 2025 13:51:51 +0000 (UTC) Received: from localhost (unknown [10.2.16.166]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 2A8661955E74; Tue, 13 May 2025 13:51:49 +0000 (UTC) Date: Tue, 13 May 2025 09:51:48 -0400 From: Stefan Hajnoczi To: Kevin Wolf Cc: qemu-block@nongnu.org, hreitz@redhat.com, pbonzini@redhat.com, bmarzins@redhat.com, qemu-devel@nongnu.org Subject: Re: [PATCH] file-posix: Probe paths and retry SG_IO on potential path errors Message-ID: <20250513135148.GB227327@fedora> References: <20250513113730.37404-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="Tb0TCTHDk9mdm4rt" Content-Disposition: inline In-Reply-To: <20250513113730.37404-1-kwolf@redhat.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 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: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.549, 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_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org --Tb0TCTHDk9mdm4rt Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, May 13, 2025 at 01:37:30PM +0200, Kevin Wolf wrote: > When scsi-block is used on a host multipath device, it runs into the > problem that the kernel dm-mpath doesn't know anything about SCSI or > SG_IO and therefore can't decide if a SG_IO request returned an error > and needs to be retried on a different path. Instead of getting working > failover, an error is returned to scsi-block and handled according to > the configured error policy. Obviously, this is not what users want, > they want working failover. >=20 > QEMU can parse the SG_IO result and determine whether this could have > been a path error, but just retrying the same request could just send it > to the same failing path again and result in the same error. >=20 > With a kernel that supports the DM_MPATH_PROBE_PATHS ioctl on dm-mpath > block devices (queued in the device mapper tree for Linux 6.16), we can > tell the kernel to probe all paths and tell us if any usable paths > remained. If so, we can now retry the SG_IO ioctl and expect it to be > sent to a working path. >=20 > Signed-off-by: Kevin Wolf > --- > block/file-posix.c | 82 +++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 81 insertions(+), 1 deletion(-) Maybe the probability of retry success would be higher with a delay so that intermittent issues have time to resolve themselves. Either way, the patch looks good. Reviewed-by: Stefan Hajnoczi --Tb0TCTHDk9mdm4rt Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQEzBAEBCgAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmgjTnQACgkQnKSrs4Gr c8gLcwgAspZ6tFEEB/fdfpGq32m61kemzNqjOSGk0SgFDeCn1yIrctb+fNCxmJW6 r9PqyXaEr3rY9jwxYOnQ5t6Pera4u/se7mX4M1Pfr4aqjDMf//NhfN+oW9tn1hhz EtDUsPP1pa2PaCc0hwlZJRSzD7Tf2dIUZCx6Gi3EdLYDUk4wlcWeexB8XTtv9PH6 jR3DzkPzYNxF8uJ+0UE4ONHGqZjBFToy+qeFR5d8lmpZ38sQbZEK5mrBBrOzTqWL bjvrT1D9IfiXlDgsmufo3hC0MfSDm7qJqcJEmWWQXw6Kvov8BTpEqMK6/7y6sNJ/ t6KhuBn9Ih8yi4PbszKRmV8DekoGIw== =nMDJ -----END PGP SIGNATURE----- --Tb0TCTHDk9mdm4rt--