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

[Eric Blake]

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 <address@hidden>
> ---

> +# 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
address@hidden: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 <address@hidden>
Tested-by: Eric Blake <address@hidden>

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

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