netdev - Re: [PATCH 0/7] introduce Hyper-V VM Sockets(hvsock)

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Date:	Thu, 16 Jul 2015 16:58:59 +0100
From:	Stefan Hajnoczi <stefanha@...hat.com>
To:	Dexuan Cui <decui@...rosoft.com>
Cc:	gregkh@...uxfoundation.org, davem@...emloft.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	driverdev-devel@...uxdriverproject.org, olaf@...fle.de,
	apw@...onical.com, jasowang@...hat.com, kys@...rosoft.com,
	haiyangz@...rosoft.com
Subject: Re: [PATCH 0/7] introduce Hyper-V VM Sockets(hvsock)

On Mon, Jul 06, 2015 at 07:39:35AM -0700, Dexuan Cui wrote:
> Hyper-V VM Sockets (hvsock) is a byte-stream based communication mechanism
> between Windowsd 10 (or later) host and a guest. It's kind of TCP over
> VMBus, but the transportation layer (VMBus) is much simpler than IP.
> With Hyper-V VM Sockets, applications between the host and a guest can
> talk with each other directly by the traditional BSD-style socket APIs.
> 
> The patchset implements the necessary support in the guest side by adding
> the necessary new APIs in the vmbus driver, and introducing a new driver
> hv_sock.ko, which implements_a new socket address family AF_HYPERV.
> 
> 
> I know the kernel has already had a VM Sockets driver (AF_VSOCK) based
> on VMware's VMCI (net/vmw_vsock/, drivers/misc/vmw_vmci), and KVM is
> proposing AF_VSOCK of virtio version:
> http://thread.gmane.org/gmane.linux.network/365205.
> 
> However, though Hyper-V VM Sockets may seem conceptually similar to
> AF_VOSCK, there are differences in the transportation layer, and IMO these
> make the direct code reusing impractical:
> 
> 1. In AF_VSOCK, the endpoint type is: <u32 ContextID, u32 Port>, but in
> AF_HYPERV, the endpoint type is: <GUID VM_ID, GUID ServiceID>. Here GUID
> is 128-bit.
> 
> 2. AF_VSOCK supports SOCK_DGRAM, while AF_HYPERV doesn't.
> 
> 3. AF_VSOCK supports some special sock opts, like SO_VM_SOCKETS_BUFFER_SIZE,
> SO_VM_SOCKETS_BUFFER_MIN/MAX_SIZE and SO_VM_SOCKETS_CONNECT_TIMEOUT.
> These are meaningless to AF_HYPERV.
> 
> 4. Some AF_VSOCK's VMCI transportation ops are meanless to AF_HYPERV/VMBus,
> like    .notify_recv_init
>         .notify_recv_pre_block
>         .notify_recv_pre_dequeue
>         .notify_recv_post_dequeue
>         .notify_send_init
>         .notify_send_pre_block
>         .notify_send_pre_enqueue
>         .notify_send_post_enqueue
> etc.
> 
> So I think we'd better introduce a new address family: AF_HYPERV.

Points 2-4 are not critical.  I think there are solutions to them.

Point 1 is the main issue: hvsock has <GUID, GUID> addresses instead of
vsock's <u32, u32> addresses.  Perhaps a mapping could be used but that
is pretty ugly.  One idea is something like a userspace <GUID, GUID> <->
<u32, u32> lookup function that applications can use if they want to
accept GUIDs.

I don't have a workable alternative to propose, so I agree that a new
address family is justified.

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