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 816451EB36; Wed, 14 May 2025 04:56:15 +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=1747198577; cv=none; b=AT0m3sxd39fACpDjrSixtpLw+4s9/IaN1nM6NTHit8gKvUpp0Lg2cB7SCeTcQ/mvVtp335LdT0GK4lWXEed4VPCelr4nCJgFmDVQWPc8fci0CucceB1+vVpRU39jLTzeto5sNg/KIasGwEmthqtHJpx3XQNjt8SN/N7UhCSDyic= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747198577; c=relaxed/simple; bh=qpuQoQ3WdonhF4Z9FZyaNqH6Gw0yQC7RkRBThKebTkQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=DPO24sGoSdn6RqXezQHj5/Qe3M4F3Pu6L0qgwZTkGEs93jK1cZ9lm/ZoQAud6gmKbTrEO8e+cseSB3043gYzWU4ZJBLieFPOiaKYNzDdGZy9WrpfCwO3pJ31X3LDZ7GsDs9xpWhIKbu39YqTLylL7vOKSnJVWvlaKmyGm31Z7uE= 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=4Xf0FWjk; 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="4Xf0FWjk" 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=o8R6IIGe6dhLB8MYoBo+/X39C91BPWRY/jdRNVLyMW8=; b=4Xf0FWjkitD2mfSuWsFm0YC/DT GFovwiUdxEeRSPXZhnw93K5Pwn10BQhULbNLAyXFkDT4wnOFWVY1QTxGWorLl+scFthZoh4WNO4KH 20SfgUlP5jtW/ZUz99E70D2VIvxjgE7F0zGX0USfvb3Esmu87bp/drlvIaQP89HxrXkYqCn3Cl6TL NTie5euKu8NTpG/JA6yKbb/pGPnDSX7YHefoWzkvpfAC5UD6hbN8fcDVhEEBrcmfSPnZDA9o8IpgP fM4sOencslpTav/NQIOJRWku1hgiBALqWdJ72p1TuW4ZYsIPf6+AYYEya7pCozxLCm3pmE1brgINA A49mM0pA==; Received: from hch by bombadil.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uF4AA-0000000E25P-0bGB; Wed, 14 May 2025 04:56:14 +0000 Date: Tue, 13 May 2025 21:56:14 -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: > 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. QEMU can read this information, but it > doesn't know what path the multipath device send the ioctl down. This > patch just gives users a way to check the paths in the active pathgroup > (which all should be able to handle IO) and fail those that can't. > While QEMU is the driver of this, it's completely general functionality. As just replied to Martin the problem is that this setup fundamentally can't work. Either you pass a SCSI devices through, which should (mostly, there are a few warts) work. Or you want host side multipathing, in which case you must pass through the block device abstraction and not a SCSI one, or at least do a full emulation of the SCSI interfaces instead of pretending to pass it through. The root of all evil here is that dm-multipath tries to pass through SG_IO, which is dangerous for all but the most trivial commands.