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Re: [Qemu-block] callout to *file in bdrv_co_get_block_status

From: Fam Zheng
Subject: Re: [Qemu-block] callout to *file in bdrv_co_get_block_status
Date: Fri, 17 Mar 2017 19:24:46 +0800
User-agent: Mutt/1.7.1 (2016-10-04)

On Fri, 03/17 12:16, Paolo Bonzini wrote:
> On 17/03/2017 12:11, Peter Lieven wrote:
> >>> like VMDK or QCOW2 shouldn't we trust the information from the l2 tables 
> >>> in the VMDK or QCOW2?
> >> It provides additional information, for example it works better with
> >> prealloc=metadata.
> > Okay, understood. Can you imagine of a away to conditionally avoid this 
> > second callout? In my case we have an additional
> > lseek for each cluster. For a 20GB file this are approx. 327k calls to 
> > lseek. And if the file has no preallocated metadata
> > it will likely not improve anything. And even if the metadata is prealloced 
> > what is the allocation status of the clusters?
> If the metadata is preallocated, cluster will (or should) show up as
> zero, speeding up the copy.

I think from qemu-img convert's perspective, it doesn't care about the *file
status if the metadata already speaks, because, like you said, the data shows up
as zeroes.

In other words I think this can be optimized.


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