From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47881) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fxYAR-0004iS-L9 for qemu-devel@nongnu.org; Wed, 05 Sep 2018 09:48:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fxYAQ-0000hP-Of for qemu-devel@nongnu.org; Wed, 05 Sep 2018 09:48:23 -0400 References: <20180810162658.6562-1-kwolf@redhat.com> <20180810162658.6562-2-kwolf@redhat.com> <20180828142626.GM122225@angien.pipo.sk> <20180903150311.GC14463@dhcp-200-186.str.redhat.com> <20180904141730.GC3803@andariel.pipo.sk> <20180904150042.GE3803@andariel.pipo.sk> <20180904153436.GC4371@localhost.localdomain> <20180905123813.GF3803@andariel.pipo.sk> From: Eric Blake Message-ID: Date: Wed, 5 Sep 2018 08:48:15 -0500 MIME-Version: 1.0 In-Reply-To: <20180905123813.GF3803@andariel.pipo.sk> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/2] commit: Add top-node/base-node options List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Krempa , Kevin Wolf Cc: Alberto Garcia , qemu-devel@nongnu.org, qemu-block@nongnu.org, mreitz@redhat.com On 09/05/2018 07:38 AM, Peter Krempa wrote: > block-commit is able to reopen the format layers and works as expected. > > Unfortunately though the 'read-only' option is actually useful as the > curl-driver does not work without it: > > -blockdev {"driver":"http","url":"http://ftp.sjtu.edu.cn:80/ubuntu-cd/12.04/ubuntu-12.04.5-alternate-amd64.iso","node-name":"libvirt-2-storage","discard":"unmap"}: curl block device does not support writes > > We obviously can encode that knowledge into libvirt but it will be hard > to undo if qemu eventually supports writes in the curl driver. > > Which other protocol drivers don't support writes? in case we have to go > this way. When an NBD server exported an image as read-only, the NBD block client cannot request write permissions. But that's a runtime discovery process, not a limitation of the block driver itself. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org