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Date: Tue, 3 Dec 2013 14:45:23 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20131203134523.GC24604@stefanha-thinkpad.muc.redhat.com>
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Subject: Re: [Qemu-devel] [PATCH V6 3/6] qemu-iotests: add 058 internal
 snapshot export with qemu-nbd case
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To: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Cc: kwolf@redhat.com, pbonzini@redhat.com, jcody@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com

On Fri, Nov 22, 2013 at 12:27:09PM +0800, Wenchao Xia wrote:
> +nbd_snapshot_port=10850
> +nbd_snapshot_img="nbd:127.0.0.1:$nbd_snapshot_port"
> +
> +_export_nbd_snapshot()
> +{
> +    $QEMU_NBD -v -t -b 127.0.0.1 -p $nbd_snapshot_port "$TEST_IMG" -l $1 &

Please use a UNIX domain socket so that multiple qemu-iotests instances
can run on the same host in parallel.  The socket should be in the
scratch directory just like the temporary image files.

> +    NBD_SNAPSHOT_PID=$!
> +    sleep 1

qemu-nbd might not start within 1 second on a heavily loaded host.

To make this test case reliable please use a loop (e.g. wait for UNIX
domain socket to appear for up to 30 seconds).

If you feel qemu-nbd doesn't offer a good interface for reliable
startup, feel free to extend it.  Test cases must be reliable and
ideally shouldn't waste time sleeping.