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Re: [Qemu-block] [PATCH 4/8] block/backup: improve unallocated clusters

From: Max Reitz
Subject: Re: [Qemu-block] [PATCH 4/8] block/backup: improve unallocated clusters skipping
Date: Fri, 9 Aug 2019 14:25:43 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0

On 09.08.19 09:50, Vladimir Sementsov-Ogievskiy wrote:
> 07.08.2019 21:01, Max Reitz wrote:
>> On 07.08.19 10:07, Vladimir Sementsov-Ogievskiy wrote:
>>> Limit block_status querying to request bounds on write notifier to
>>> avoid extra seeking.
>> I don’t understand this reasoning.  Checking whether something is
>> allocated for qcow2 should just mean an L2 cache lookup.  Which we have
>> to do anyway when we try to copy data off the source.
> But for raw it's seeking.

(1) That’s a bug in block_status then, isn’t it?

file-posix cannot determine the allocation status, or rather, everything
is allocated.  bdrv_co_block_status() should probably pass @want_zero on
to the driver’s implementation, and file-posix should just
unconditionally return DATA if it’s false.

(2) Why would you even use sync=top for raw nodes?


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