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-devel

Re: [Xen-devel] Re: [PATCH 12/13] Unplug emulated disks and nics

To: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH 12/13] Unplug emulated disks and nics
From: Don Dutile <ddutile@xxxxxxxxxx>
Date: Fri, 09 Jul 2010 09:42:27 -0400
Cc: "jeremy@xxxxxxxx" <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, "stefano@xxxxxxxxxxxxxx" <stefano@xxxxxxxxxxxxxx>, "sheng@xxxxxxxxxxxxxxx" <sheng@xxxxxxxxxxxxxxx>
Delivery-date: Fri, 09 Jul 2010 06:44:45 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <alpine.DEB.2.00.1007091150000.21432@kaball-desktop>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <alpine.DEB.2.00.1006211456360.18470@kaball-desktop> <1277136847-13266-12-git-send-email-stefano@xxxxxxxxxxxxxx> <4C2CEF56.4050008@xxxxxxxxxx> <alpine.DEB.2.00.1007051255310.29110@kaball-desktop> <4C34DD1B.3010601@xxxxxxxxxx> <alpine.DEB.2.00.1007081246440.21432@kaball-desktop> <4C362DC3.7000101@xxxxxxxxxx> <1278624583.12109.15.camel@xxxxxxxxxxxxxxxxxxxxx> <4C364A3F.8020900@xxxxxxxxxx> <1278662546.28432.602.camel@xxxxxxxxxxxxxxxxxxxxxx> <alpine.DEB.2.00.1007091150000.21432@kaball-desktop>
Reply-to: ddutile@xxxxxxxxxx
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Thunderbird 2.0.0.18 (X11/20081113)
Stefano Stabellini wrote:
> On Fri, 9 Jul 2010, Ian Campbell wrote:
>>>> Any guest which uses xvda in its configuration file today will be using
>>>> emulated devices but I think that with Stefano's patch and your proposed
>>>> change in default on a Xen system without support for unplug will start
>>>> using PV devices without unplugging the emulated ones first.
>>>>
>>> Well, Stefano requires the admin to add unplug switch to kernel cmd line,
>> In the case where the host platform does not support the unplug protocol
>> this is correct and requiring explicit admin action to allow the PV
>> frontends to activate is the only safe option WRT the users data.
>>
>> However if the host platform does support the unplug protocol then this
>> is incorrect. In that case the default (in the absence of the command
>> line option) is to automatically unplug any device for which a PV driver
>> is available and so no command line option will be required in the
>> common case. (see xen_unplug_emulated_devices() under the comment "Set
>> the default value of xen_emul_unplug depending on...")
>>
> 
> that's right: on host platforms supporting unplug no command line options
> are required; on the other hand if the host platform does not support
> unplug then xen_emul_unplug=ignore is required to use PV drivers anyway.
> 
> 
I see by looking at xen_unplug_emulated_devices() closer, that the default
unplugs emulated ide & emulated nic:
        if (xen_platform_pci_enabled && !xen_emul_unplug)

I had to work around the fact that xen_platform_pci_enabled would
not be set on rhel5-dom0 (no emul-unplug), so I hadn't looked at this default
so closely.


>>> so I don't see the harm in defaulting to unplug... 
>> As I described in my previous mail this is unsafe on host platforms
>> which do not support unplug. As I describe above it is unnecessary on
>> host platforms which do support unplug
>>
> 
> yep, keep in mind the copy and paste example.
> 
> 
> 
> If you are happy about the patch, I'll include it in my next version.
> 

Yes, the patch seems like a reasonable solution for running on older qemu-dm's.

Thanks for the clarification(s).

- Don

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