From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4A2B7288DA; Fri, 16 May 2025 05:52:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747374739; cv=none; b=XqNpncfoeoIX2d3dIKLPCwoUE+23vUIlNcTrAM7PDQv1rOqA0dsEj2Y8Mc5dly6TDO4myOxU2gq+8x0+j3hqFkGPIU9ZYhMXpL6OZC9AEymdYxER6V0vrqBWmIOEvL+T18YYVgp2BpDCV2RY84KNr+M9vRnOipdGvNb5ihYJywg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747374739; c=relaxed/simple; bh=aw08LBXzt6obXPy/8Vm80GRmMC7w0UnW/0OPYmGgpZM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XB3d8h6mbDOqjzgelvLn5iN8jxjElSkbYAClfd5k20i+ZBIq2eLQ1vv45O5ht7EEuTEEb/PcAn3cyFSw4QZI3Kdpna65CVgOI7XDo62yXk9v5vcXF2USg6zoDrIRqR64qyTjVKgAnYttZfKW0THwOkifU0B99EgXelv+zbTPR/o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=IlF8fXdI; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="IlF8fXdI" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=K8UXY7rT/l3eeHRyLbzo//dG7vL4enowgat/pk9HleM=; b=IlF8fXdI+7gIwHPmL36dnwQJYA znkqyKppR4lYlt38el9ZKosOASWE4iHCifZDLGO4IKaOSkyU1ITC+e26DPAeKhH1RMgkMZw3ARfCH DrmNFEE7qFu9Q0tkHCgoo736lnxo/sCz8uBEfBZN11TIGyZ8vmobr+0E3yknxwrs+V8gNwiTyPRSW tdciEteZ7NYUsGCD0oZV7Jlj1L3x9FmxkhtF7f1UkbuPzJSlb3XJaAs4cQJtVmHbrJnVr8+IH4YvS jA0a5kfs1Gb8TfuZgadMUSw4541KHSd85QJQehpyvP6fDV8c9lKLF8QjJGvhQCk9hDGANPx5dEu7W p0nW4LuA==; Received: from hch by bombadil.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uFnzT-00000002XCz-1Gf0; Fri, 16 May 2025 05:52:15 +0000 Date: Thu, 15 May 2025 22:52:15 -0700 From: Christoph Hellwig To: Benjamin Marzinski Cc: Christoph Hellwig , Hannes Reinecke , Kevin Wolf , Martin Wilck , dm-devel@lists.linux.dev, hreitz@redhat.com, mpatocka@redhat.com, snitzer@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/2] dm mpath: Interface for explicit probing of active paths Message-ID: References: <20250429165018.112999-1-kwolf@redhat.com> <47dd225b433b0df585a25084a2e793344eeda239.camel@suse.com> <0340c51e-6f89-4799-b2f1-19c785a19ff2@suse.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Tue, May 13, 2025 at 12:29:51PM -0400, Benjamin Marzinski wrote: > On Mon, May 12, 2025 at 11:49:19PM -0700, Christoph Hellwig wrote: > > On Tue, May 13, 2025 at 08:32:12AM +0200, Hannes Reinecke wrote: > > > Reservations and stuff. > > > > They should use the kernel persistent reservation API. > > Currently QEMU isn't sending Persistent Reservation requests to > multipath devices at all. It's sending those directly to the underlying > scsi devices. The issue here is with all the other SCSI commands that > users want to send to their SCSI passthrough device that is actually a > multipath device on top of a number of SCSI paths. They expect to > get back the actual sense and status information, so QEMU needs to > send them via SG_IOs. And that's the problem. There is plenty of path (I_T_L) nexus specific information in SCSI, and just trying to glob it back together above means you'll get path specific information in something that doesn't claim to be multi-pathing and will get random and changing results depending on the underlying path selection. > Without reading that sense and status information in kernel, the > multipath target can't know if it needs to fail a path and retry the > ioctl down a different path. The blk_status_t has the information to fail over. But the whole idea of implementing SG_IO in dm-mpath or any other stacking layer is just really, really dangerous.