[Xen-devel] Re: [PATCH] Fix restore handling checks

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

On 06/22/2010 04:56 PM, Ian Jackson wrote:
> Michal Novotny writes ("Re: [Xen-devel] [PATCH] Fix restore handling checks"):
> > Right, there's the exception for CD-ROMs according to the spec. I should
> > implement this as well but read-only IDE disk devices are not supported
> > according to the IDE specs.
> I don't think this is a very good argument for not supporting them.
>
> The Xen administrator should be able to present a guest with an IDE
> disk and nevertheless prevent the guest from writing to it.
>
> If that means that the guest administrator needs to be told
> out-of-band that writes will not work, rather than having their kernel
> automatically discover the read-only nature, then that's fine.  And if
> the guest administrator doesn't do that and their kernel tries to
> write and gets IDE errors then that is the correct consequence.
We tried to get that to work, and we could not really find a device 
error that worked reliably in the guests.  We often got infinite loops 
on mount or little after that, on both Linux and Windows.
If you want to use read-only devices, you should really use SCSI or PV 
devices.
Paolo

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