netdev - Re: [PATCH net-next v1 1/3] vm_sockets: Include flag field in the vsock address data structure

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Date:   Wed, 2 Dec 2020 09:32:09 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     "Paraschiv, Andra-Irina" <andraprs@...zon.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>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        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 Tue, Dec 01, 2020 at 08:15:04PM +0200, Paraschiv, Andra-Irina wrote:
>
>
>On 01/12/2020 18:09, Stefano Garzarella 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.
>>
>>Maybe we can split this patch in 2 patches, one to rename the svm_flag
>>and one to add the new flags.
>
>Sure, I can split this in 2 patches, to have a bit more separation of 
>duties.
>
>>
>>>
>>>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
>>
>>I think we don't need this macro, since the next one can be used to
>>check if it a sibling communication (flag 0x1 set) or not (flag 0x1
>>not set).
>
>Right, that's not particularly the use of the flag value, as by 
>default comes as 0. It was more for sharing the cases this covers. But 
>I can remove the define and keep this kind of info, with regard to the 
>default case, in the commit message / comments.
>

Agree, you can add few lines in the comment block of VMADDR_FLAG_SIBLING 
describing the default case when it is not set.

>>
>>>+
>>>+/* 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
>>
>>What do you think if we shorten in VMADDR_FLAG_SIBLING?
>>
>
>Yup, this seems ok as well for me. I'll update the naming.
>

Thanks,
Stefano