linux-kernel - Re: [PATCH net-next 3/3] hv_sock: implements Hyper-V transport for Virtual Sockets (AF

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Date:   Thu, 17 Aug 2017 15:55:51 +0100
From:   Stefan Hajnoczi <stefanha@...hat.com>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        George Zhang <georgezhang@...are.com>,
        Jorgen Hansen <jhansen@...are.com>,
        Michal Kubecek <mkubecek@...e.cz>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Cathy Avery <cavery@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        Rolf Neugebauer <rolf.neugebauer@...ker.com>,
        Dave Scott <dave.scott@...ker.com>,
        Marcelo Cerri <marcelo.cerri@...onical.com>,
        "apw@...onical.com" <apw@...onical.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "joe@...ches.com" <joe@...ches.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH net-next 3/3] hv_sock: implements Hyper-V transport for
 Virtual Sockets (AF_VSOCK)

On Tue, Aug 15, 2017 at 10:18:41PM +0000, Dexuan Cui wrote:
> +static u32 hvs_get_local_cid(void)
> +{
> +	return VMADDR_CID_ANY;
> +}

Interesting concept: the guest never knows its CID.  This is nice from a
live migration perspective.  Currently VMCI and virtio adjust listen
socket local CIDs after migration.

> +static bool hvs_stream_allow(u32 cid, u32 port)
> +{
> +	static const u32 valid_cids[] = {
> +		VMADDR_CID_ANY,

Is this for loopback?

> +		VMADDR_CID_HOST,
> +	};
> +	int i;
> +
> +	/* The host's port range [MIN_HOST_EPHEMERAL_PORT, 0xFFFFFFFF) is
> +	 * reserved as ephemeral ports, which are used as the host's ports
> +	 * when the host initiates connections.
> +	 */
> +	if (port > MAX_HOST_LISTEN_PORT)
> +		return false;

Without this if statement the guest will attempt to connect.  I guess
there will be no listen sockets above MAX_HOST_LISTEN_PORT, so the
connection attempt will fail.

...but hardcode this knowledge into the guest driver?

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