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Date: Wed, 13 Jul 2016 09:30:49 +0200
From: Michal Kubecek <mkubecek@suse.cz>
To: Dexuan Cui <decui@microsoft.com>
Cc: "davem@davemloft.net" <davem@davemloft.net>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
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        Rolf Neugebauer <rolf.neugebauer@docker.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Dave Scott <dave.scott@docker.com>
Subject: Re: [PATCH v16 net-next 0/1] introduce Hyper-V VM Sockets(hv_sock)
Message-ID: <20160713073048.GD27436@unicorn.suse.cz>
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On Mon, Jul 11, 2016 at 02:54:59PM +0000, Dexuan Cui wrote:
> 
> I know the kernel has already had a VM Sockets driver (AF_VSOCK) based
> on VMware VMCI (net/vmw_vsock/, drivers/misc/vmw_vmci), and KVM is
> proposing AF_VSOCK of virtio version:
> http://marc.info/?l=linux-netdev&m=145952064004765&w=2
> 
> However, though Hyper-V 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.

OK, this could be a problem.

> 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.

I don't quite understand the logic here. All these sound like "AF_VSOCK
has this feature we don't need so (rather than not using the feature) we
are not going to use AF_VSOCK". I would understand if you pointed out
features important for you that are missing in AF_VSOCK but this kind of
reasoning sounds strange to me.

Michal Kubecek