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

To: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] Fix restore handling checks
From: Michal Novotny <minovotn@xxxxxxxxxx>
Date: Wed, 23 Jun 2010 14:37:07 +0200
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>, "'xen-devel@xxxxxxxxxxxxxxxxxxx'" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>
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On 06/23/2010 02:35 PM, Alan Cox wrote:
On Wed, 23 Jun 2010 13:29:56 +0200
Michal Novotny<minovotn@xxxxxxxxxx>  wrote:

On 06/23/2010 01:27 PM, Ian Jackson wrote:
Paolo Bonzini writes ("Re: [PATCH] Fix restore handling checks"):

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.

That's fine.  If the admins don't want that then they can use SCSI or
PV or simply not tell the guest to write to the device.

Disallowing the configuration entirely just because the error handling
is suboptimal (but safe!) is not correct.

Ian.

Why do you think so, Ian? This follows the IDE specifications to
disallow read-only IDE disks since the specs doesn't support IDE
read-only disks. The only read-only device being supported by IDE specs
is the CD-ROM device.
IDE (or more properly ATA) doesn't support CD-ROM either. ATAPI does, and
it also supports other ATAPI devices with write protect including magneto
optical and floppy.



Agreed Alan. This is right that ATAPI does. Nevertheless in IDE specs it's about ATA and ATAPI. The read-only file systems are supported for IDE drives only for floppy and tape media according to the linux kernel source codes. Also, CD-ROM devices can be read-only but no other IDE media, i.e. no IDE disks.

Michal

--
Michal Novotny<minovotn@xxxxxxxxxx>, RHCE
Virtualization Team (xen userspace), Red Hat


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