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Date:   Thu, 3 Dec 2020 16:04:44 +0200
From:   "Paraschiv, Andra-Irina" <andraprs@...zon.com>
To:     Stefano Garzarella <sgarzare@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>
CC:     netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        David Duncan <davdunc@...zon.com>,
        Dexuan Cui <decui@...rosoft.com>,
        Alexander Graf <graf@...zon.de>,
        Jorgen Hansen <jhansen@...are.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH net-next v1 1/3] vm_sockets: Include flag field in the
 vsock address data structure



On 03/12/2020 15:38, Stefano Garzarella wrote:
>
> On Thu, Dec 03, 2020 at 12:32:08PM +0200, Paraschiv, Andra-Irina wrote:
>>
>>
>> On 03/12/2020 11:21, Stefan Hajnoczi wrote:
>>> On Tue, Dec 01, 2020 at 05:25:03PM +0200, Andra Paraschiv wrote:
>>>> vsock enables communication between virtual machines and the host they
>>>> are running on. With the multi transport support (guest->host and
>>>> host->guest), nested VMs can also use vsock channels for 
>>>> communication.
>>>>
>>>> In addition to this, by default, all the vsock packets are 
>>>> forwarded to
>>>> the host, if no host->guest transport is loaded. This behavior can be
>>>> implicitly used for enabling vsock communication between sibling VMs.
>>>>
>>>> Add a flag field in the vsock address data structure that can be 
>>>> used to
>>>> explicitly mark the vsock connection as being targeted for a certain
>>>> type of communication. This way, can distinguish between nested VMs 
>>>> and
>>>> sibling VMs use cases and can also setup them at the same time. Till
>>>> now, could either have nested VMs or sibling VMs at a time using the
>>>> vsock communication stack.
>>>>
>>>> Use the already available "svm_reserved1" field and mark it as a flag
>>>> field instead. This flag can be set when initializing the vsock 
>>>> address
>>>> variable used for the connect() call.
>>>>
>>>> Signed-off-by: Andra Paraschiv <andraprs@...zon.com>
>>>> ---
>>>>  include/uapi/linux/vm_sockets.h | 18 +++++++++++++++++-
>>>>  1 file changed, 17 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/include/uapi/linux/vm_sockets.h 
>>>> b/include/uapi/linux/vm_sockets.h
>>>> index fd0ed7221645d..58da5a91413ac 100644
>>>> --- a/include/uapi/linux/vm_sockets.h
>>>> +++ b/include/uapi/linux/vm_sockets.h
>>>> @@ -114,6 +114,22 @@
>>>>  #define VMADDR_CID_HOST 2
>>>> +/* This sockaddr_vm flag value covers the current default use case:
>>>> + * local vsock communication between guest and host and nested VMs 
>>>> setup.
>>>> + * In addition to this, implicitly, the vsock packets are 
>>>> forwarded to the host
>>>> + * if no host->guest vsock transport is set.
>>>> + */
>>>> +#define VMADDR_FLAG_DEFAULT_COMMUNICATION   0x0000
>>>> +
>>>> +/* Set this flag value in the sockaddr_vm corresponding field if 
>>>> the vsock
>>>> + * channel needs to be setup between two sibling VMs running on 
>>>> the same host.
>>>> + * This way can explicitly distinguish between vsock channels 
>>>> created for nested
>>>> + * VMs (or local communication between guest and host) and the 
>>>> ones created for
>>>> + * sibling VMs. And vsock channels for multiple use cases (nested 
>>>> / sibling VMs)
>>>> + * can be setup at the same time.
>>>> + */
>>>> +#define VMADDR_FLAG_SIBLING_VMS_COMMUNICATION       0x0001
>>> vsock has the h2g and g2h concept. It would be more general to call 
>>> this
>>> flag VMADDR_FLAG_G2H or less cryptically VMADDR_FLAG_TO_HOST.
>
> I agree, VMADDR_FLAG_TO_HOST is more general and it's clearer that is up
> to the host where to forward the packet (sibling if supported, or
> whatever).

Ok, then VMADDR_FLAG_TO_HOST it is. :) I also updated the commit 
messages / comments to reflect this more general angle, with one of the 
current use cases being guest to guest communication.

Thanks,
Andra

>
>>
>> Thanks for the feedback, Stefan.
>>
>> I can update the naming to be more general, such as "_TO_HOST", and
>> keep the use cases (e.g. guest <-> host / nested / sibling VMs
>> communication) mention in the comments so that would relate more to
>> the motivation behind it.
>>
>> Andra
>>
>>>
>>> That way it just tells the driver in which direction to send packets
>>> without implying that sibling communication is possible (it's not
>>> allowed by default on any transport).
>>>
>>> I don't have a strong opinion on this but wanted to suggest the idea.
>>>
>>> Stefan
>>
>>
>>
>>
>> Amazon Development Center (Romania) S.R.L. registered office: 27A Sf. 
>> Lazar Street, UBC5, floor 2, Iasi, Iasi County, 700045, Romania. 
>> Registered in Romania. Registration number J22/2621/2005.
>>
>




Amazon Development Center (Romania) S.R.L. registered office: 27A Sf. Lazar Street, UBC5, floor 2, Iasi, Iasi County, 700045, Romania. Registered in Romania. Registration number J22/2621/2005.

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