WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-users

RE: [Xen-users] Can't use DVD Writer in DomU

To: "jim burns" <jim_burn@xxxxxxxxxxxxx>, <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-users] Can't use DVD Writer in DomU
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Mon, 18 Feb 2008 12:33:19 +1100
Delivery-date: Sun, 17 Feb 2008 17:33:52 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <200802171954.54567.jim_burn@xxxxxxxxxxxxx>
List-help: <mailto:xen-users-request@lists.xensource.com?subject=help>
List-id: Xen user discussion <xen-users.lists.xensource.com>
List-post: <mailto:xen-users@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-users>, <mailto:xen-users-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-users>, <mailto:xen-users-request@lists.xensource.com?subject=unsubscribe>
References: <200802141648.15568.paul@xxxxxxxxxxxxx><AEC6C66638C05B468B556EA548C1A77D0131AC90@trantor>(sfid-20080214_210955_381974_3232487E) <200802171954.54567.jim_burn@xxxxxxxxxxxxx>
Sender: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AchxyRwhf9BOZF+ATsmgpTcFTm466QABMhEA
Thread-topic: [Xen-users] Can't use DVD Writer in DomU
> On Thursday 14 February 2008 08:41:05 pm James Harper wrote:
> > The block interface provided by blkback and blkfront is pretty
basic,
> > supporting only read, write, and write+barrier. There is no
provision
> > for the sort of commands required for doing writing.
> 
> What is 'write+barrier'? Thanx.

The barrier is a signal to pass on to the disk that all writes sent to
the disk before the barrier should be completed before any writes sent
after the barrier. The disk (or disk array etc) may re-order writes for
efficiency reasons, especially if write caching is happening. This can
be disastrous if the operating system has made an assumption about the
atomicity of its write operation.

James


_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users