Re: [Qemu-devel] [PATCH v3 3/3] iotests: test big qcow2 shrink

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

22.04.2019 16:59, Eric Blake wrote:
> On 4/19/19 9:05 AM, Vladimir Sementsov-Ogievskiy wrote:
>> This test checks bug in qcow2_process_discards, fixed by previous
>> commit.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> ---
> 
>> +# This test checks that qcow2_process_discards does not truncate a discard
>> +# request > 2G.
>> +# To reproduce bug we need to overflow int by one sequential discard, so we
>> +# need size > 2G, bigger cluster size (as with default 64k we may have maximum
>> +# of 512M sequential data, corresponding to one L1 entry), and we need some
>> +# data of the beginning of the disk mapped to the end of file to prevent
>> +# bdrv_co_truncate(bs->file) call in qcow2_co_truncate(), which may success
> 
> s/may success/might succeed/
> 
>> +# anyway.
>> +
>> +size=2100M
>> +IMGOPTS="cluster_size=1M,preallocation=metadata"
>> +
>> +_make_test_img $size
>> +$QEMU_IO -c 'discard 0 10M' -c 'discard 2090M 10M' \
>> +         -c 'write 2090M 10M' -c 'write 0 10M' "$TEST_IMG" | _filter_qemu_io
>> +
>> +# Check that our trick with swapping first and last 10M chunks succeeded.
>> +# Otherwise test will may pass even if bdrv_pdiscard() fails in
>> +# qcow2_process_discards()
>> +$QEMU_IMG map "$TEST_IMG" | _filter_testdir
>> +$QEMU_IMG info "$TEST_IMG" | grep size |  _filter_testdir
> 
> Nice - that's a lot faster than v1! And makes the test fit in the quick
> group after all.
> 
>> +
>> +$QEMU_IMG -T 'qcow2_process_discards_failed*' resize --shrink "$TEST_IMG" 5M
> 
> However, I'm quite certain that trace output is not reliable in iotests.
> Depending on configure options, traces might not be enabled at all, or
> might not go to stderr. Drop the -T '...'.  Even without the trace line,
> 
>> +
>> +$QEMU_IMG info "$TEST_IMG" | grep size | _filter_testdir
> 
> this second image info is sufficient to prove whether the resize had an
> effect (post-patch) or exposes the bug (without patch 2/3). That is,
> applying this patch but not 2/3, I see this (with my cleanups to
> qemu-img info in place, from Kevin's block-next branch):
> 
> +++ /home/eblake/qemu/tests/qemu-iotests/250.out.bad	2019-04-22
> 08:52:26.072968731 -0500
> @@ -14,8 +14,9 @@
>   virtual size: 2.05 GiB (2202009600 bytes)
>   disk size: 24 MiB
>   cluster_size: 1048576
> +18274@1555941145.999195:qcow2_process_discards_failed_region offset
> 0x500000 bytes 0x82a00000 ret -5
>   Image resized.
>   virtual size: 5 MiB (5242880 bytes)
> -disk size: 9.01 MiB
> +disk size: 19 MiB
> 
> where the trace did indeed show show that we had a bug, but where even
> without the trace, the difference in size between 19M with incomplete
> discards vs. 9M with patch 2/3 is enough to show that patch 2/3 fixes a bug.
> 
>> +virtual size: 2.1G (2202009600 bytes)
>> +disk size: 24M
>> +cluster_size: 1048576
>> +Image resized.
>> +virtual size: 5.0M (5242880 bytes)
>> +disk size: 9.0M
>> +cluster_size: 1048576
> 
> When Kevin's block-next branch is applied, you'll need this squashed in:
> 
> diff --git a/tests/qemu-iotests/250.out b/tests/qemu-iotests/250.out
> index 37e37f0c9e7..d1c1c7180b5 100644
> --- a/tests/qemu-iotests/250.out
> +++ b/tests/qemu-iotests/250.out
> @@ -11,11 +11,11 @@ wrote 10485760/10485760 bytes at offset 0
>   Offset          Length          Mapped to       File
>   0               0xa00000        0x82f00000      TEST_DIR/t.qcow2
>   0x82a00000      0xa00000        0x500000        TEST_DIR/t.qcow2
> -virtual size: 2.1G (2202009600 bytes)
> -disk size: 24M
> +virtual size: 2.05 GiB (2202009600 bytes)
> +disk size: 24 MiB
>   cluster_size: 1048576
>   Image resized.
> -virtual size: 5.0M (5242880 bytes)
> -disk size: 9.0M
> +virtual size: 5 MiB (5242880 bytes)
> +disk size: 9.01 MiB
>   cluster_size: 1048576
>   *** done
> 
> With the updated output to match changes to qemu-img output, the grammar
> fixes, and with the -T option removed,
> 
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Tested-by: Eric Blake <eblake@redhat.com>
> 

Thank you!

I'll resend soon.

-- 
Best regards,
Vladimir