Re: [Qemu-devel] [PATCH V6 3/6] qemu-iotests: add 058 internal snapshot export with qemu-nbd case

[Stefan Hajnoczi]

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.