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

[Xuewei Niu]

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";
* `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@xxxxxxxxxxxx>
---
 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
 
+/* 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