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Date: Wed, 06 Jan 2010 09:47:24 +0200
From: Naphtali Sprei <nsprei@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] Added 'access' option to -drive flag
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To: Jamie Lokier <jamie@shareable.org>
Cc: Markus Armbruster <armbru@redhat.com>, qemu-devel@nongnu.org

Jamie Lokier wrote:
> Anthony Liguori wrote:
>> On 12/24/2009 03:09 AM, Markus Armbruster wrote:
>>> Naphtali Sprei<nsprei@redhat.com>  writes:
>>>
>>>> Added 'access' option to -drive flag
>>>>
>>>> The new option is: access=[rw|ro|auto]
>>>> rw: open the drive's file with Read and Write permission, don't continue 
>>>> if failed
>>>> ro: open the file only with Read permission
>>>> auto: open the file with Read and Write permission, if failed, try only 
>>>> Read permision
>>>>
>>>> For compatibility reasons, the default is 'auto'. Should be changed later 
>>>> on.
>>>>
>>>> This option is to replace the 'readonly' options added lately.
>>> Can we take the readonly parameter away?  It's undocumented, for
>>> whatever that's worth...
>> readonly made 0.12.   Semantics, readonly makes it to the disk emulation 
>> whereas this effects how the file is opened.

I'm not sure I understand this semantic difference. The implementation of both versions (readonly and access) affects both
the disk emulation and the file access/open.
I did meant that 'access' to replace the 'readonly', and I do understand that I did it in bad timing.

> 
> With readonly in 0.12, if you _don't specify readonly, and the file is
> opened readonly because it applies qemu's fallback behaviour - does
> *that* read-only property make it to the disk emulation?  Or do guests
> still see unexplained I/O errors in that case?

The implementation of both 'readonly' and 'access' pass the information to the Guest, through the device API.
Indeed, only for supporting devices.
> 
> Btw, wasn't the access=[rw|ro|auto] option supposed to affect disk
> emulation too?
> 
> -- Jamie