Re: [Qemu-devel] [PATCH] qemu-img: return allocated size for block device with qcow2 format

[Max Reitz]

On 2018-05-03 15:06, 叶残风 wrote:
> 
> Thanks for your review, Eric.
> Yes, the wr_highest_offset can tell the end offset at runtime, and 
> write_threshold similar to it. But in my situation, I need to know 
> the allocated end without a vm running.

Oh, I've just seen that your patch doesn't even get the allocated size,
it actually determines the highest allocated offset.  Well, those are
two different things.  You should not return this value via
qcow2_get_allocated_file_size().  I'm not sure where it should go
(probably wr_highest_offset?) and how it should be presented in
qemu-img, though.

Also note that bdrv_get_allocated_file_size() is called by QMP's
query-named-block-nodes and query-block, both of which are online
synchronous functions.  It should not take a long time, specifically it
should not scan the whole qcow2 file.

Max

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