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

From: Paolo Bonzini
Subject: Re: [Qemu-block] [Qemu-devel] callout to *file in bdrv_co_get_block_status
Date: Fri, 31 Mar 2017 12:20:10 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 31/03/2017 09:55, Peter Lieven wrote:
>>> Would it be an idea to introduce an inverse flag live BDRV_BLOCK_NOT_ZERO
>>> for cases where we know that there is really DATA and thus can avoid the
>>> second callout?
>> How would you know that a block is nonzero?
> I would trust the metadata. At least for VMDK and QCOW2v3.
> Bad idea?

The metadata only tells you that a block is zero, not that it's nonzero.
 What you are suggesting is really the same as removing the recursion.
However, I still haven't understood clearly if it's a QEMU or tmpfs bug;
if it's a tmpfs bug your suggestion would not fix tmpfs slowness on raw


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