Re: [PATCH v2 0/5] fix & merge block_status_above and is_allocated_above

[Eric Blake <eblake@redhat.com>]

On 5/19/20 2:54 PM, Vladimir Sementsov-Ogievskiy wrote:

> This leads to the following effect:
> 
> ./qemu-img create -f qcow2 base.qcow2 2M
> ./qemu-io -c "write -P 0x1 0 2M" base.qcow2
> 
> ./qemu-img create -f qcow2 -b base.qcow2 mid.qcow2 1M
> ./qemu-img create -f qcow2 -b mid.qcow2 top.qcow2 2M
> 
> Region 1M..2M is shadowed by short middle image, so guest sees zeroes:
> ./qemu-io -c "read -P 0 1M 1M" top.qcow2
> read 1048576/1048576 bytes at offset 1048576
> 1 MiB, 1 ops; 00.00 sec (22.795 GiB/sec and 23341.5807 ops/sec)
> 
> But after commit guest visible state is changed, which seems wrong for me:
> ./qemu-img commit top.qcow2 -b mid.qcow2
> 
> ./qemu-io -c "read -P 0 1M 1M" mid.qcow2
> Pattern verification failed at offset 1048576, 1048576 bytes
> read 1048576/1048576 bytes at offset 1048576
> 1 MiB, 1 ops; 00.00 sec (4.981 GiB/sec and 5100.4794 ops/sec)

This no longer happens as of commit bf03dede47 and friends.  As such, 
how much of this series is still needed for other reasons?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org