From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: Guest to Host communication Date: Thu, 31 Oct 2013 16:13:50 +0000 Message-ID: <527281BE.7080008@eu.citrix.com> References: <20131022075936.GB4223@google.com> <9AAE0902D5BC7E449B7C8E4E778ABCD013E890@AMSPEX01CL01.citrite.net> <20131022124857.GC4223@google.com> <9AAE0902D5BC7E449B7C8E4E778ABCD013ED63@AMSPEX01CL01.citrite.net> <20131022134220.GD4223@google.com> <20131031160835.GA30966@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1Vbusw-0002vw-Pl for xen-devel@lists.xenproject.org; Thu, 31 Oct 2013 16:14:15 +0000 In-Reply-To: <20131031160835.GA30966@google.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: "Jose A. Lopes" Cc: "xen-devel@lists.xenproject.org" , Paul Durrant List-Id: xen-devel@lists.xenproject.org On 31/10/13 16:08, Jose A. Lopes wrote: > On Thu, Oct 31, 2013 at 02:21:38PM +0000, George Dunlap wrote: >> On Tue, Oct 22, 2013 at 2:42 PM, Jose A. Lopes wrote: >>> On Tue, Oct 22, 2013 at 01:18:56PM +0000, Paul Durrant wrote: >>>>> -----Original Message----- >>>>> From: Jose A. Lopes [mailto:jabolopes@google.com] >>>>> Sent: 22 October 2013 13:49 >>>>> To: Paul Durrant >>>>> Cc: xen-devel@lists.xenproject.org >>>>> Subject: Re: [Xen-devel] Guest to Host communication >>>>> >>>>> Hi, >>>>> >>>>> If I understood correctly, Xenstore requires writing a driver and >>>>> loading it inside the VM. Is this correct? >>>>> >>>> Well, yes you'll need some code in the guest, but drivers already exist for linux and windows so you could just use them. >>>> >>>>> If so, then it seems this approach would require writing different >>>>> drivers for different OSes, such as, Linux and Windows. Currently, we >>>>> are just exploring different design options and we would like to aim >>>>> at a uniform approach across different OSes. Is there an option like that ? >>>>> >>>> What option do you expect that doesn't involve writing at least some code for each OS you want to use? >>> We were thinking of simply attaching a device. >>> For example, add a SSD disk in DomU which is backed in Dom0 by a file. >>> Is this possible? >> Of course you can attach as many disks as you want; or you could just >> have dom0 look for a file in the primary filesystem. But whether you >> use the primary filesystem or a secondary one, you still have the >> basic problem of introspection: if this is going to be a filesystem, >> then there may be a difference at any given time between what domU >> thinks the state of the filesystem is, and what dom0 can see on the >> disk (because there may be things in domU's buffer cache which haven't >> "hit the disk" yet). > We have changed our use case to the situation where the instance > writes a few bytes to this device. However, Ganeti only needs this > information once the instance has stopped. Therefore, while the > instance is running it can write and overwrite the information because > it is not important. > > I wonder if it is possible to change the caching policy of the device > in order to immediately flush the writes. This is not so important > because I imagine that by the time the instance has stopped (if it > didn't crash), the cache should have been flushed. > > We were however thinking about a usb serial device to make it easier > to do successive writes within the instance. Oh, right -- in that case, probably the easiest thing to do would be to just create a file in the guest filesystem and have your tools look inside to see if it's there. You could have a secondary disk just for that purpose, if that makes it easier to make it the same across instances. -George