linux-kernel - Re: [RFC PATCH 5/5] vsock: Add an ioctl request to get all CIDs

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Date: Thu, 23 May 2024 12:45:48 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Xuewei Niu <niuxuewei97@...il.com>
Cc: stefanha@...hat.com, mst@...hat.com, davem@...emloft.net, 
	kvm@...r.kernel.org, virtualization@...ts.linux.dev, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Xuewei Niu <niuxuewei.nxw@...group.com>
Subject: Re: [RFC PATCH 5/5] vsock: Add an ioctl request to get all CIDs

On Fri, May 17, 2024 at 10:46:07PM GMT, Xuewei Niu wrote:
>The new request is called `IOCTL_VM_SOCKETS_GET_LOCAL_CIDS`. And the old
>one, `IOCTL_VM_SOCKETS_GET_LOCAL_CID` is retained.
>
>For the transport that supports multi-devices:
>
>* `IOCTL_VM_SOCKETS_GET_LOCAL_CID` returns "-1";

What about returning the default CID (lower prio)?

>* `IOCTL_VM_SOCKETS_GET_LOCAL_CIDS` returns a vector of CIDS. The usage 
>is
>shown as following.
>
>```
>struct vsock_local_cids local_cids;
>if ((ret = ioctl(fd, IOCTL_VM_SOCKETS_GET_LOCAL_CIDS, &local_cids))) {
>    perror("failed to get cids");
>    exit(1);
>}
>for (i = 0; i<local_cids.nr; i++) {
>    if (i == (local_cids.nr - 1))
>        printf("%u", local_cids.data[i]);
>    else
>        printf("%u,", local_cids.data[i]);
>}
>```
>
>Signed-off-by: Xuewei Niu <niuxuewei.nxw@...group.com>
>---
> include/net/af_vsock.h          |  7 +++++++
> include/uapi/linux/vm_sockets.h |  8 ++++++++
> net/vmw_vsock/af_vsock.c        | 19 +++++++++++++++++++
> 3 files changed, 34 insertions(+)
>
>diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>index 25f7dc3d602d..2febc816e388 100644
>--- a/include/net/af_vsock.h
>+++ b/include/net/af_vsock.h
>@@ -264,4 +264,11 @@ static inline bool vsock_msgzerocopy_allow(const struct vsock_transport *t)
> {
> 	return t->msgzerocopy_allow && t->msgzerocopy_allow();
> }
>+
>+/**** IOCTL ****/
>+/* Type of return value of IOCTL_VM_SOCKETS_GET_LOCAL_CIDS. */
>+struct vsock_local_cids {
>+	int nr;
>+	unsigned int data[MAX_VSOCK_NUM];
>+};
> #endif /* __AF_VSOCK_H__ */
>diff --git a/include/uapi/linux/vm_sockets.h b/include/uapi/linux/vm_sockets.h
>index 36ca5023293a..01f73fb7af5a 100644
>--- a/include/uapi/linux/vm_sockets.h
>+++ b/include/uapi/linux/vm_sockets.h
>@@ -195,8 +195,16 @@ struct sockaddr_vm {
>
> #define MAX_VSOCK_NUM 16

Okay, now I see why you need this in the UAPI, but pleace try to follow
other defines.

What about VM_SOCKETS_MAX_DEVS ?

>
>+/* Return actual context id if the transport not support vsock
>+ * multi-devices. Otherwise, return `-1U`.
>+ */
>+
> #define IOCTL_VM_SOCKETS_GET_LOCAL_CID		_IO(7, 0xb9)
>
>+/* Only available in transports that support multiple devices. */
>+
>+#define IOCTL_VM_SOCKETS_GET_LOCAL_CIDS     _IOR(7, 0xba, struct vsock_local_cids)
>+
> /* MSG_ZEROCOPY notifications are encoded in the standard error format,
>  * sock_extended_err. See Documentation/networking/msg_zerocopy.rst in
>  * kernel source tree for more details.
>diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>index 3b34be802bf2..2ea2ff52f15b 100644
>--- a/net/vmw_vsock/af_vsock.c
>+++ b/net/vmw_vsock/af_vsock.c
>@@ -2454,6 +2454,7 @@ static long vsock_dev_do_ioctl(struct file *filp,
> 	u32 __user *p = ptr;
> 	u32 cid = VMADDR_CID_ANY;
> 	int retval = 0;
>+	struct vsock_local_cids local_cids;
>
> 	switch (cmd) {
> 	case IOCTL_VM_SOCKETS_GET_LOCAL_CID:
>@@ -2469,6 +2470,24 @@ static long vsock_dev_do_ioctl(struct file *filp,
> 			retval = -EFAULT;
> 		break;
>
>+	case IOCTL_VM_SOCKETS_GET_LOCAL_CIDS:
>+		if (!transport_g2h || !transport_g2h->get_local_cids)
>+			goto fault;
>+
>+		rcu_read_lock();
>+		local_cids.nr = transport_g2h->get_local_cids(local_cids.data);
>+		rcu_read_unlock();
>+
>+		if (local_cids.nr < 0 ||
>+		    copy_to_user(p, &local_cids, sizeof(local_cids)))
>+			goto fault;
>+
>+		break;
>+
>+fault:
>+		retval = -EFAULT;
>+		break;
>+
> 	default:
> 		retval = -ENOIOCTLCMD;
> 	}
>-- 
>2.34.1
>