Re: [Qemu-devel] [PATCH 21/21] iotests: Add test for different refcount widths

[Eric Blake]

On 11/10/2014 06:45 AM, Max Reitz wrote:
> Add a test for conversion between different refcount widths and errors
> specific to certain widths (i.e. snapshots with refcount_width=1).
> 
> Signed-off-by: Max Reitz <address@hidden>
> ---
>  tests/qemu-iotests/112     | 225 
> +++++++++++++++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/112.out | 123 +++++++++++++++++++++++++
>  tests/qemu-iotests/group   |   1 +
>  3 files changed, 349 insertions(+)
>  create mode 100755 tests/qemu-iotests/112
>  create mode 100644 tests/qemu-iotests/112.out
> 

> +
> +# This tests qocw2-specific low-level functionality
> +_supported_fmt qcow2
> +_supported_proto file
> +_supported_os Linux

Might work on more than just Linux, but then again, it's probably worth
scrubbing the whole testsuite for situations like that, so don't worry
about it here.

> +# This test will set refcount_width on its own which would conflict with the
> +# manual setting; compat will be overridden as well
> +_unsupported_imgopts refcount_width 'compat=0.10'
> +
> +function print_refcount_width()
> +{
> +    $QEMU_IMG info "$TEST_IMG" | grep 'refcount width:' | sed -e 's/^ *//'

grep|sed is almost always a waste.  This is equivalent:

   $QEMU_IMG info "$TEST_IMG" | sed -n '/refcount width:/ s/^ *//p'

> +echo
> +echo '=== Snapshot limit on refcount_width=1 ==='
> +echo
> +
> +IMGOPTS="$IMGOPTS,refcount_width=1" _make_test_img 64M
> +print_refcount_width
> +
> +$QEMU_IO -c 'write 0 512' "$TEST_IMG" | _filter_qemu_io
> +
> +# Should fail
> +$QEMU_IMG snapshot -c foo "$TEST_IMG"
> +
> +# The new L1 table could/shoud be leaked

s/shoud/should/

> +_check_test_img
> +
> +echo
> +echo '=== Snapshot limit on refcount_width=2 ==='
> +echo
> +
> +IMGOPTS="$IMGOPTS,refcount_width=2" _make_test_img 64M
> +print_refcount_width
> +
> +$QEMU_IO -c 'write 0 512' "$TEST_IMG" | _filter_qemu_io
> +
> +# Should succeed
> +$QEMU_IMG snapshot -c foo "$TEST_IMG"
> +$QEMU_IMG snapshot -c bar "$TEST_IMG"
> +# Should fail (4th reference)
> +$QEMU_IMG snapshot -c baz "$TEST_IMG"
> +
> +# The new L1 table could/shoud be leaked

again

> +echo
> +echo '=== Amend with snapshot ==='
> +echo
> +
> +$QEMU_IMG snapshot -c foo "$TEST_IMG"
> +# Just to have different refcounts across the image
> +$QEMU_IO -c 'write 0 16M' "$TEST_IMG" | _filter_qemu_io
> +
> +# Should not work
> +$QEMU_IMG amend -o refcount_width=1 "$TEST_IMG"
> +_check_test_img
> +print_refcount_width

This matches your initial implementation. Someday, though, we may decide
to auto-COW any overflowed cluster, and thus allow the conversion to
succeed.  Worth a comment?

> +echo '=== Testing too many references for check ==='
> +echo
> +
> +IMGOPTS="$IMGOPTS,refcount_width=1" _make_test_img 64M
> +print_refcount_width
> +
> +# This cluster should be created at 0x50000
> +$QEMU_IO -c 'write 0 64k' "$TEST_IMG" | _filter_qemu_io
> +# Now make the second L2 entriy (the L2 table should be at 0x40000) point to

s/entriy/entry/


> +# success, all done
> +echo '*** done'
> +rm -f $seq.full
> +status=0

Overall a nice set of tests!


> +=== Snapshot limit on refcount_width=1 ===
> +
> +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864
> +refcount width: 1
> +wrote 512/512 bytes at offset 0
> +512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +qemu-img: Could not create snapshot 'foo': -22 (Invalid argument)
> +Leaked cluster 6 refcount=1 reference=0

Bummer that the error message did not state WHY (because a cluster would
overflow refcounts), but I'm not sure how hard it would be to make that
better, and at least we correctly errored out.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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