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References: <20170915101008.16646-1-kwolf@redhat.com>
	<20170915170204.14023-1-kwolf@redhat.com>
From: Eric Blake <eblake@redhat.com>
Message-ID: <97519d8d-e00e-97f6-aa13-98ba06faca88@redhat.com>
Date: Fri, 15 Sep 2017 14:14:26 -0500
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Subject: Re: [Qemu-devel] [PATCH 7/6] qemu-iotests: Test change-backing-file
 command
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To: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org
Cc: famz@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com, Jeff Cody <jcody@redhat.com>

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From: Eric Blake <eblake@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org
Cc: famz@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com,
 Jeff Cody <jcody@redhat.com>
Message-ID: <97519d8d-e00e-97f6-aa13-98ba06faca88@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 7/6] qemu-iotests: Test change-backing-file
 command
References: <20170915101008.16646-1-kwolf@redhat.com>
 <20170915170204.14023-1-kwolf@redhat.com>
In-Reply-To: <20170915170204.14023-1-kwolf@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.
>=20
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>=20
> 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.
>=20
>  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=3Dnone,file=3D"$TEST_IMG",backing.node-name=3Dmid <=
<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=3D"$TEST_IMG.mid" _img_info
> +
> +echo
> +echo "Change backing file of top (opened writable)"
> +echo
> +
> +TEST_IMG=3D"$TEST_IMG.mid" _make_test_img -b "$TEST_IMG.base"
> +
> +run_qemu -drive if=3Dnone,file=3D"$TEST_IMG",node-name=3Dtop <<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 doin=
g:

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)

--=20
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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