From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 F2D5026F447 for ; Mon, 19 May 2025 10:06:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747649181; cv=none; b=nfrHiLeQLO3aROL6wCSr8GZ5CN5dOUh/Rgcq7yp8Mp4J+B4lt7w7ha9AAF9ovL0xpaUrcu2nTwSeJT3x1ZJ3WGX42iWk8thKjPWy/jp1HWY2UPnLys7t1vuDStzbilxsrZd8hREJMlo5jFFYkkJClDSAkTPl5vr3MLjAjXT0liQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747649181; c=relaxed/simple; bh=WY4pVtTTZhYVG9r0kI5X0a3ASMeqcPFq3H1auY5Ce1o=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=nHQ19YdN7/Nd2g77mWn3IEoZCp9BWvPJbb4VN7EAKbRg2lUqWPZ+igkPt8Vajf64J9ayvk7Q26AhtOHpYgoskHdCYZh3IYZN3QbrenM6JaHIYWJX4dB9PQqvouBL/mTJy9//mZVtkR0yvrkwmUvVb10P7HUUbho494cFkIPcQEs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=VEI4OGWh; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="VEI4OGWh" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1747649178; 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=J8y8RvBhJowtfwrg+WUxnhDmoJuUc4fa/9tDJ52ajU4=; b=VEI4OGWhVcPu1+Hqota+aciSypAR4uv5MZkJV0WumyvJKUTsXvAeijv+DPMNM14hppqdNU S9Orw5ywWg2nUivgaqerPwW5iigyAP80omkWmPhJybY392JVA9oBEcuUMKw81H1nT02z6v oYrYvCofteRDY5LYZCIRH5hFNzprNRI= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-595-qVK8RXgdOuq2NyqG4Brs0Q-1; Mon, 19 May 2025 06:06:13 -0400 X-MC-Unique: qVK8RXgdOuq2NyqG4Brs0Q-1 X-Mimecast-MFC-AGG-ID: qVK8RXgdOuq2NyqG4Brs0Q_1747649172 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 24F0F19560AF; Mon, 19 May 2025 10:06:12 +0000 (UTC) Received: from redhat.com (unknown [10.44.34.97]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C9AD030001AB; Mon, 19 May 2025 10:06:08 +0000 (UTC) Date: Mon, 19 May 2025 12:06:05 +0200 From: Kevin Wolf To: Christoph Hellwig Cc: Martin Wilck , Benjamin Marzinski , 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> Precedence: bulk X-Mailing-List: dm-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Am 16.05.2025 um 08:00 hat Christoph Hellwig geschrieben: > On Thu, May 15, 2025 at 12:11:49PM +0200, Kevin Wolf wrote: > > If you're talking about SG_IO in dm-mpath, then PRIN/PROUT commands are > > actually the one thing that we don't need. libmpathpersist sends the > > commands to the individual path devices, so dm-mpath will never see > > those. It's mostly about getting the full results on the SCSI level for > > normal I/O commands. > > > > There has actually been a patch series on qemu-devel last year (that I > > haven't found the time to review properly yet) that would add explicit > > persistent reservation operations to QEMU's block layer that could then > > be used with the emulated scsi-hd device. On the backend, it only > > implemented it for iscsi, but I suppose we could implement it for > > file-posix, too (using the same libmpathpersist code as for > > passthrough). If that works, maybe at least some users can move away > > from SCSI passthrough. > > Please call into the kernel PR code instead of hacking up more of > this, which will just run into problems again. I agree that using kernel code is preferable to doing things behind the kernel's back. However, libmpathpersist is the official interface for doing these things with multipath devices, so I think the necessary work to make this happen should primarily be done in the library (and possibly the kernel if the existing interfaces aren't good enough). QEMU could directly call the kernel when qemu-pr-helper isn't in use. I don't know enough about how libmpathpersist works internally to tell if running it this way would be a good idea for multipath devices. Can multipathd still do its job with reservations being made behind its back? (It would probably be good to allow this eventually, but is it the case today?) Kevin