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

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Date:   Tue, 1 Dec 2020 17:09:37 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Andra Paraschiv <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 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.

>
>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).

>+
>+/* 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?

Thanks,
Stefano

>+
> /* Invalid vSockets version. */
>
> #define VM_SOCKETS_INVALID_VERSION -1U
>@@ -145,7 +161,7 @@
>
> struct sockaddr_vm {
> 	__kernel_sa_family_t svm_family;
>-	unsigned short svm_reserved1;
>+	unsigned short svm_flag;
> 	unsigned int svm_port;
> 	unsigned int svm_cid;
> 	unsigned char svm_zero[sizeof(struct sockaddr) -
>-- 
>2.20.1 (Apple Git-117)
>
>
>
>
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