Re: [Qemu-devel] [PATCH] Create the VMDK snapshot from the QEMUmonitor.

From: Anthony Liguori <aliguori@cs.utexas.edu>
To: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] Create the VMDK snapshot from the	QEMUmonitor.
Date: Tue, 09 Jan 2007 10:20:58 -0600	[thread overview]
Message-ID: <45A3C0EA.7030607@cs.utexas.edu> (raw)
In-Reply-To: <64F9B87B6B770947A9F8391472E0321609E93740@ehost011-8.exch011.intermedia.net>

Igor Lvovsky wrote:
> Hi Anthony,
>
> I wrote the patch before Fabrice introduced his solution and I didn't look at it before I sent my patch (my mistake). 
> But you are right; the new snapshot infrastructure can be useful.
> I'll modify my code for new approach and I hope Fabrice will accept it.
>   

Excellent.

> As for CID, I think that snapshot tag it's something else.
> The CID in VMDK is value updated on the first write every time the virtual disk is opened.
>   

I see.

> By the way, I have a question:
> I want to use the standard pread()/pwrite() functions instead of 
> pair:
> 	lseek()
> 	read() / write()
>   

Why do you want to use p{read,write}()?  If you are concerned about 
performance, you can simply cache the current file offset and only call 
lseek() conditionally.

> I know that this may do some problem for Windows implementation,
> but I can use some kind of define for Windows case.
> A question is if it's acceptable.
>   

Normally, guards for Windows specific stuff is okay but if there isn't a 
compelling reason to write non-portable code than I'd at least always be 
in favor of writing the portable version :-)

Regards,

Anthony Liguori

> 		Regards,
> 	Igor Lvovsky
>
>
>
>
> -----Original Message-----
> From: qemu-devel-bounces+igor.lvovsky=qumranet.com@nongnu.org [mailto:qemu-devel-bounces+igor.lvovsky=qumranet.com@nongnu.org] On Behalf Of Anthony Liguori
> Sent: Tuesday, December 26, 2006 7:25 PM
> To: qemu-devel@nongnu.org
> Subject: Re: [Qemu-devel] [PATCH] Create the VMDK snapshot from the QEMUmonitor.
>
> Hi Igor,
>
> Out of curiousity, why didn't you use the new snapshot infrastructure 
> that Fabrice introduced in CVS?  Shouldn't the CID just map directly to 
> a snapshot tag?
>
> Regards,
>
> Anthony Liguori
>
> Igor Lvovsky wrote:
>   
>>   Hi,
>>
>> This patch completes the previous one and allows the snapshot (VMDK 
>> style) creation from the QEMU monitor (Ctrl+Alt+2).
>>
>>  
>>
>> To clarify, the previous patch implements the snapshot capabilities 
>> according to the "Virtual Disk Format 1.0" document.
>>
>> http://lists.gnu.org/archive/html/qemu-devel/2006-12/msg00311.html
>>
>>  
>>
>> Implemented features:
>>
>>    1. Create snapshot.
>>    2. CID concept to prevent snapshots chain inconsistency.
>>    3. Snapshots read/write capabilities.
>>
>>  
>>
>> The whole chain (base image and snapshots) created by QEMU can be 
>> loaded from the VMware workstation and vice versa.
>>
>>  
>>
>> Igor Lvovsky.
>>
>> ------------------------------------------------------------------------
>>
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>>   
>>     
>
>
>
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