Re: [Qemu-devel] [PATCH 7/6] qemu-iotests: Test change-backing-file command

[Eric Blake <eblake@redhat.com>]

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On 09/15/2017 12:02 PM, Kevin Wolf wrote:
> This involves a temporary read-write reopen if the backing file link in
> the middle of a backing file chain should be changed and is therefore a
> good test for the latest bdrv_reopen() vs. op blockers fixes.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
> 
> I actually managed to find a simple case that reproduces the bug that
> is fixed in this series, but outside of my commit job improvements that
> originally led me to this work.
> 
>  tests/qemu-iotests/195     | 92 ++++++++++++++++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/195.out | 78 +++++++++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/group   |  1 +

The usual collision in test numbering ;)


> +_cleanup()
> +{
> +    _cleanup_test_img
> +    rm -f "$TEST_IMG.mid"
> +}
> +trap "_cleanup; exit \$status" 0 1 2 3 15

Semantic conflict with Jeff's work to add './check -s' to save
intermediate files in a per-test temp directory.

> +
> +echo
> +echo "Change backing file of mid (opened read-only)"
> +echo
> +
> +run_qemu -drive if=none,file="$TEST_IMG",backing.node-name=mid <<EOF
> +{"execute":"qmp_capabilities"}
> +{"execute":"change-backing-file", "arguments":{"device":"none0","image-node-name":"mid","backing-file":"/dev/null"}}

Since the images don't contain any content, I guess this works.  But
another possible change would be rewriting the backing file to alternate
between absolute and relative (or even between 'file' and './file') (so
that it's pointing to the same file at all times, just by different names)

> +{"execute":"quit"}
> +EOF
> +
> +TEST_IMG="$TEST_IMG.mid" _img_info
> +
> +echo
> +echo "Change backing file of top (opened writable)"
> +echo
> +
> +TEST_IMG="$TEST_IMG.mid" _make_test_img -b "$TEST_IMG.base"
> +
> +run_qemu -drive if=none,file="$TEST_IMG",node-name=top <<EOF
> +{"execute":"qmp_capabilities"}
> +{"execute":"change-backing-file", "arguments":{"device":"none0","image-node-name":"top","backing-file":"/dev/null"}}
> +{"execute":"quit"}

You've quit qemu between runs.  Would we get any further coverage by doing:

change mid
change active
change mid

all within a single run? (That is, make SURE that actions on one part of
the graph don't interfere with later actions elsewhere)

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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