From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1LBzDm-00068D-Ja for qemu-devel@nongnu.org; Sun, 14 Dec 2008 17:13:54 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1LBzDk-00066l-0U for qemu-devel@nongnu.org; Sun, 14 Dec 2008 17:13:53 -0500 Received: from [199.232.76.173] (port=34705 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LBzDj-00066i-RF for qemu-devel@nongnu.org; Sun, 14 Dec 2008 17:13:51 -0500 Received: from mx1.redhat.com ([66.187.233.31]:39942) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1LBzDj-00042l-HR for qemu-devel@nongnu.org; Sun, 14 Dec 2008 17:13:51 -0500 Date: Sun, 14 Dec 2008 22:13:46 +0000 From: "Daniel P. Berrange" Subject: Re: [Qemu-devel] [PATCH] Vmchannel PCI device. Message-ID: <20081214221346.GA16902@redhat.com> References: <20081214115027.4028.56164.stgit@dhcp-1-237.tlv.redhat.com> <20081214131247.GS5555@redhat.com> <49455B5E.8080504@codemonkey.ws> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <49455B5E.8080504@codemonkey.ws> Reply-To: "Daniel P. Berrange" , qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: qemu-devel@nongnu.org, Gleb Natapov , kvm@vger.kernel.org On Sun, Dec 14, 2008 at 01:15:42PM -0600, Anthony Liguori wrote: > Gleb Natapov wrote: > >On Sun, Dec 14, 2008 at 02:28:23PM +0200, Blue Swirl wrote: > > > >>On 12/14/08, Gleb Natapov wrote: > >> > >>>There is a need for communication channel between host and various > >>> agents that are running inside a VM guest. The channel will be used > >>> for statistic gathering, logging, cut & paste, host screen resolution > >>> changes notification, guest configuration etc. > >>> > >>Isn't this exactly what the firmware configuration device was supposed > >>to be used for? In the list of use cases you gave, I don't see > >>anything that could not be done with it. > >> > >> > >The requirement for firmware configuration interface was different. We > >wanted something simple that we can use as early as possible in cpu init > >code and performance was not considered at all. Obviously PCI device > >doesn't > >fit for this. We don't want to write PCI driver inside a BIOS and PCI > >initialization is too late in HW initialization sequence. > > > >The requirement for vmchannel was that it should allow a guest > >to communicate with external (to qemu) process and with reasonable > >performance too. > > This is not a requirement that I think is important. It's only a > requirement for you because you have closed code that you want to > implement the backend with. I would personally be more interested in > vmchannel backends in QEMU and I think there will be a lot of them. One non-QEMU backend I can see being implemented is a DBus daemon, providing a simple bus for RPC calls between guests & host. Or on a similar theme, perhaps a QPid message broker in the host OS. Yet another backend is a clustering service providing a virtual fence device to VMs. All of these would live outside QEMU, and as such exposing the backend using the character device infrastructure is a natural fit. Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://ovirt.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|