Re: [Qemu-devel] [PATCH 3/3] iotests: Allow 147 to be run concurrently

[Eric Blake <eblake@redhat.com>]

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On 12/21/18 5:47 PM, Max Reitz wrote:
> To do this, we need to allow creating the NBD server on various ports
> instead of a single one (which may not even work if you run just one
> instance, because something entirely else might be using that port).

Can you instead reuse the ideas from nbd_server_set_tcp_port() from
qemu-iotests/common.nbd?

> 
> So we just pick a random port in [32768, 32768 + 1024) and try to create
> a server there.  If that fails, we just retry until something sticks.

That has the advantage of checking whether a port is actually in use
(using 'ss' - although it does limit the test to Linux-only; perhaps
using socat instead of ss could make the test portable to non-Linux?)

> 
> For the IPv6 test, we need a different range, though (just above that
> one).  This is because "localhost" resolves to both 127.0.0.1 and ::1.
> This means that if you bind to it, it will bind to both, if possible, or
> just one if the other is already in use.  Therefore, if the IPv6 test
> has already taken [::1]:some_port and we then try to take
> localhost:some_port, that will work -- only the second server will be
> bound to 127.0.0.1:some_port alone and not [::1]:some_port in addition.
> So we have two different servers on the same port, one for IPv4 and one
> for IPv6.
> 
> But when we then try to connect to the server through
> localhost:some_port, we will always end up at the IPv6 one (as long as
> it is up), and this may not be the one we want.
> 
> Thus, we must make sure not to create an IPv6-only NBD server on the
> same port as a normal "dual-stack" NBD server -- which is done by using
> distinct port ranges, as explained above.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  tests/qemu-iotests/147 | 98 +++++++++++++++++++++++++++++-------------
>  1 file changed, 68 insertions(+), 30 deletions(-)
> 

> @@ -88,17 +92,29 @@ class QemuNBD(NBDBlockdevAddBase):
>          except OSError:
>              pass
>  
> +    def _try_server_up(self, *args):
> +        status, msg = qemu_nbd_pipe('-f', imgfmt, test_img, *args)
> +        if status == 0:
> +            return True
> +        if 'Address already in use' in msg:
> +            return False
> +        self.fail(msg)

Do you actually need to attempt a qemu-nbd process, if you take my
suggestion of using ss to probe for an unused port?  And if not, do we
still need qemu_nbd_pipe() added earlier in the series?


> -        address = { 'type': 'inet',
> -                    'data': {
> -                        'host': 'localhost',
> -                        'port': str(NBD_PORT)
> -                    } }
> -        self._server_up(address, export_name)
> +        while True:
> +            nbd_port = random.randrange(NBD_PORT_START, NBD_PORT_END)

common.nbd just iterates, instead of trying random ports.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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