From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59255) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WmLMJ-0003dc-F7 for qemu-devel@nongnu.org; Mon, 19 May 2014 07:04:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WmLMD-0005ID-5V for qemu-devel@nongnu.org; Mon, 19 May 2014 07:03:55 -0400 Message-ID: <5379E50B.5070607@redhat.com> Date: Mon, 19 May 2014 13:03:39 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1400410205-26152-1-git-send-email-kroosec@gmail.com> <5379BA0A.7080200@msgid.tls.msk.ru> In-Reply-To: <5379BA0A.7080200@msgid.tls.msk.ru> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [Qemu-trivial] [PATCH 1/2] nbd: Don't export a block device with no medium. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Michael Tokarev , Hani Benhabiles , qemu-devel@nongnu.org Cc: qemu-trivial@nongnu.org, kwolf@redhat.com, stefanha@redhat.com Il 19/05/2014 10:00, Michael Tokarev ha scritto: > 18.05.2014 14:50, Hani Benhabiles wrote: >> The device is exported with erroneous values and can't be read. >> >> Before the patch: >> $ sudo nbd-client localhost -p 10809 /dev/nbd0 -name floppy0 >> Negotiation: ..size = 17592186044415MB >> bs=1024, sz=18446744073709547520 bytes >> >> $ sudo mount /dev/nbd0 /mnt/tmp/ >> mount: block device /dev/nbd0 is write-protected, mounting read-only >> mount: /dev/nbd0: can't read superblock >> >> After the patch: >> (qemu) nbd_server_add ide0-hd0 >> (qemu) nbd_server_add floppy0 >> Device 'floppy0' has no medium > > I'm not sure this is the right direction. Maybe we should actually > allow exporting devices with no medium to be able to insert medium > later without re-starting the server? Especially with -t (persistent). > I dunno. At least this is the decision which should not be left to > a -trivial tree. The protocol has no support for marking a device as no-medium, or for reporting a medium change, so there's nothing sane that we can do. (Upon a medium change, for example, the embedded NBD server will shut down all connections). In particular, for qemu-nbd there is no support for named exports, so even with "-t" it makes sense to just exit with an error condition and ask the user to reinvoke qemu-nbd later. I'll revive the nbd-next branch for these two patches. Thanks Michael for carrying the other two. Paolo