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From: Anthony Liguori <anthony@codemonkey.ws>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
	Anthony Liguori <aliguori@us.ibm.com>,
	qemu-devel@nongnu.org,
	Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>,
	Juan Quintela <quintela@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 2/3] block-nbd: fix use of protocols in backing files and nbd probing
Date: Sat, 11 Sep 2010 12:27:43 -0500	[thread overview]
Message-ID: <4C8BBC0F.2010309@codemonkey.ws> (raw)
In-Reply-To: <AANLkTi=AtFRQSUWA=Js1F_JH5agGw=UVYpd2SLZxpZf5@mail.gmail.com>

On 09/11/2010 11:53 AM, Stefan Hajnoczi wrote:
> On Sat, Sep 11, 2010 at 3:04 PM, Anthony Liguori<aliguori@us.ibm.com>  wrote:
>    
>> Additionally, there's a spurious read when using an nbd protocol that can be
>> quite destructive when using copy-on-read.  Potentially, this can lead to
>> probing an image file over top of NBD but this is completely wrong as NBD
>> devices are not growable.
>>      
> Can you describe the copy-on-read scenario where the 2 KB probe read
> is a problem?
>
> Accessing a fixed size image file over NBD is probably uncommon, but
> I'm not sure if there's a reason to forbid it.
>    

I think the better solution is to explicitly specific raw with nbd.  
IOW, I think -drive file=nbd:localhost:1026,format=raw should work the 
same way.  I still feel slightly weird about probing happening with 
nbd.  It seems like it could only result in badness.

The specific scenario is migration.  I'm using a copy-on-read file on 
the destination and I want to be sure that I don't read any blocks 
(since they're copied) until the source stops execution.

Regards,

Anthony Liguori

> Stefan
>
>    

  reply	other threads:[~2010-09-11 17:27 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-09-11 14:04 [Qemu-devel] [RFC][PATCH 0/3] Fix caching issues with live migration Anthony Liguori
2010-09-11 14:04 ` [Qemu-devel] [PATCH 1/3] block: allow migration to work with image files Anthony Liguori
2010-09-12 10:37   ` Avi Kivity
2010-09-12 13:06     ` Anthony Liguori
2010-09-12 13:28       ` Avi Kivity
2010-09-12 15:26         ` Anthony Liguori
2010-09-12 16:06           ` Avi Kivity
2010-09-12 17:10             ` Anthony Liguori
2010-09-12 17:51               ` Avi Kivity
2010-09-15 16:00                 ` [Qemu-devel] " Juan Quintela
2010-09-15 15:57         ` Juan Quintela
2010-09-13  8:21   ` Kevin Wolf
2010-09-13 13:27     ` Anthony Liguori
2010-09-15 16:03     ` Juan Quintela
2010-09-16  7:54       ` Kevin Wolf
2010-09-15 15:53   ` Juan Quintela
2010-09-11 14:04 ` [Qemu-devel] [PATCH 2/3] block-nbd: fix use of protocols in backing files and nbd probing Anthony Liguori
2010-09-11 16:53   ` Stefan Hajnoczi
2010-09-11 17:27     ` Anthony Liguori [this message]
2010-09-11 17:45       ` Anthony Liguori
2010-09-15 16:06   ` [Qemu-devel] " Juan Quintela
2010-09-16 15:40     ` Anthony Liguori
2010-09-17  8:53       ` Kevin Wolf
2010-09-16  8:08   ` Kevin Wolf
2010-09-16 13:00     ` Anthony Liguori
2010-09-16 14:08       ` Kevin Wolf
2010-09-11 14:04 ` [Qemu-devel] [PATCH 3/3] disk: don't read from disk until the guest starts Anthony Liguori
2010-09-11 17:24   ` Stefan Hajnoczi
2010-09-11 17:34     ` Anthony Liguori
2010-09-12 10:42   ` Avi Kivity
2010-09-12 13:08     ` Anthony Liguori
2010-09-12 13:26       ` Avi Kivity
2010-09-12 15:29         ` Anthony Liguori
2010-09-12 16:04           ` Avi Kivity
2010-09-15 16:10       ` [Qemu-devel] " Juan Quintela
2010-09-13  8:32   ` Kevin Wolf
2010-09-13 13:29     ` Anthony Liguori
2010-09-13 13:39       ` Kevin Wolf
2010-09-13 13:42         ` Anthony Liguori
2010-09-13 14:13           ` Kevin Wolf
2010-09-13 14:34             ` Anthony Liguori
2010-09-14  9:47               ` Avi Kivity
2010-09-14 12:51                 ` Anthony Liguori
2010-09-14 13:16                   ` Avi Kivity
2010-09-13 19:29             ` Stefan Hajnoczi
2010-09-13 20:03               ` Kevin Wolf
2010-09-13 20:09                 ` Anthony Liguori
2010-09-14  8:28                   ` Kevin Wolf
2010-09-15 16:16     ` Juan Quintela
2010-09-12 10:46 ` [Qemu-devel] [RFC][PATCH 0/3] Fix caching issues with live migration Avi Kivity
2010-09-12 13:12   ` Anthony Liguori

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