[PATCH v8 net-next 1/1] hv_sock: introduce Hyper-V Sockets

[Dexuan Cui]

Hyper-V Sockets (hv_sock) supplies a byte-stream based communication
mechanism between the host and the guest. It's somewhat like TCP over
VMBus, but the transportation layer (VMBus) is much simpler than IP.

With Hyper-V Sockets, applications between the host and the guest can talk
to each other directly by the traditional BSD-style socket APIs.

Hyper-V Sockets is only available on new Windows hosts, like Windows Server
2016. More info is in this article "Make your own integration services":
https://msdn.microsoft.com/en-us/virtualization/hyperv_on_windows/develop/make_mgmt_service

The patch implements the necessary support in the guest side by introducing
a new socket address family AF_HYPERV.

Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
 MAINTAINERS                 |    2 +
 include/linux/hyperv.h      |   16 +
 include/linux/socket.h      |    5 +-
 include/net/af_hvsock.h     |   51 ++
 include/uapi/linux/hyperv.h |   25 +
 net/Kconfig                 |    1 +
 net/Makefile                |    1 +
 net/hv_sock/Kconfig         |   10 +
 net/hv_sock/Makefile        |    3 +
 net/hv_sock/af_hvsock.c     | 1483 +++++++++++++++++++++++++++++++++++++++++++
 10 files changed, 1595 insertions(+), 2 deletions(-)
 create mode 100644 include/net/af_hvsock.h
 create mode 100644 net/hv_sock/Kconfig
 create mode 100644 net/hv_sock/Makefile
 create mode 100644 net/hv_sock/af_hvsock.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 67d99dd..7b6f203 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5267,7 +5267,9 @@ F:	drivers/pci/host/pci-hyperv.c
 F:	drivers/net/hyperv/
 F:	drivers/scsi/storvsc_drv.c
 F:	drivers/video/fbdev/hyperv_fb.c
+F:	net/hv_sock/
 F:	include/linux/hyperv.h
+F:	include/net/af_hvsock.h
 F:	tools/hv/
 F:	Documentation/ABI/stable/sysfs-bus-vmbus
 
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index aa0fadc..b92439d 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1338,4 +1338,20 @@ extern __u32 vmbus_proto_version;
 
 int vmbus_send_tl_connect_request(const uuid_le *shv_guest_servie_id,
 				  const uuid_le *shv_host_servie_id);
+struct vmpipe_proto_header {
+	u32 pkt_type;
+	u32 data_size;
+} __packed;
+
+#define HVSOCK_HEADER_LEN	(sizeof(struct vmpacket_descriptor) + \
+				 sizeof(struct vmpipe_proto_header))
+
+/* See 'prev_indices' in hv_ringbuffer_read(), hv_ringbuffer_write() */
+#define PREV_INDICES_LEN	(sizeof(u64))
+
+#define HVSOCK_PKT_LEN(payload_len)	(HVSOCK_HEADER_LEN + \
+					ALIGN((payload_len), 8) + \
+					PREV_INDICES_LEN)
+#define HVSOCK_MIN_PKT_LEN	HVSOCK_PKT_LEN(1)
+
 #endif /* _HYPERV_H */
diff --git a/include/linux/socket.h b/include/linux/socket.h
index 73bf6c6..88b1ccd 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -201,8 +201,8 @@ struct ucred {
 #define AF_NFC		39	/* NFC sockets			*/
 #define AF_VSOCK	40	/* vSockets			*/
 #define AF_KCM		41	/* Kernel Connection Multiplexor*/
-
-#define AF_MAX		42	/* For now.. */
+#define AF_HYPERV	42	/* Hyper-V Sockets		*/
+#define AF_MAX		43	/* For now.. */
 
 /* Protocol families, same as address families. */
 #define PF_UNSPEC	AF_UNSPEC
@@ -249,6 +249,7 @@ struct ucred {
 #define PF_NFC		AF_NFC
 #define PF_VSOCK	AF_VSOCK
 #define PF_KCM		AF_KCM
+#define PF_HYPERV	AF_HYPERV
 #define PF_MAX		AF_MAX
 
 /* Maximum queue length specifiable by listen.  */
diff --git a/include/net/af_hvsock.h b/include/net/af_hvsock.h
new file mode 100644
index 0000000..a5aa28d
--- /dev/null
+++ b/include/net/af_hvsock.h
@@ -0,0 +1,51 @@
+#ifndef __AF_HVSOCK_H__
+#define __AF_HVSOCK_H__
+
+#include <linux/kernel.h>
+#include <linux/hyperv.h>
+#include <net/sock.h>
+
+#define VMBUS_RINGBUFFER_SIZE_HVSOCK_RECV (5 * PAGE_SIZE)
+#define VMBUS_RINGBUFFER_SIZE_HVSOCK_SEND (5 * PAGE_SIZE)
+
+#define HVSOCK_RCV_BUF_SZ	VMBUS_RINGBUFFER_SIZE_HVSOCK_RECV
+#define HVSOCK_SND_BUF_SZ	PAGE_SIZE
+
+#define sk_to_hvsock(__sk)    ((struct hvsock_sock *)(__sk))
+#define hvsock_to_sk(__hvsk)   ((struct sock *)(__hvsk))
+
+struct hvsock_sock {
+	/* sk must be the first member. */
+	struct sock sk;
+
+	struct sockaddr_hv local_addr;
+	struct sockaddr_hv remote_addr;
+
+	/* protected by the global hvsock_mutex */
+	struct list_head bound_list;
+	struct list_head connected_list;
+
+	struct list_head accept_queue;
+	/* used by enqueue and dequeue */
+	struct mutex accept_queue_mutex;
+
+	struct delayed_work dwork;
+
+	u32 peer_shutdown;
+
+	struct vmbus_channel *channel;
+
+	struct {
+		struct vmpipe_proto_header hdr;
+		char buf[HVSOCK_SND_BUF_SZ];
+	} __packed send;
+
+	struct {
+		struct vmpipe_proto_header hdr;
+		char buf[HVSOCK_RCV_BUF_SZ];
+		unsigned int data_len;
+		unsigned int data_offset;
+	} __packed recv;
+};
+
+#endif /* __AF_HVSOCK_H__ */
diff --git a/include/uapi/linux/hyperv.h b/include/uapi/linux/hyperv.h
index e347b24..f1d0bca 100644
--- a/include/uapi/linux/hyperv.h
+++ b/include/uapi/linux/hyperv.h
@@ -26,6 +26,7 @@
 #define _UAPI_HYPERV_H
 
 #include <linux/uuid.h>
+#include <linux/socket.h>
 
 /*
  * Framework version for util services.
@@ -396,4 +397,28 @@ struct hv_kvp_ip_msg {
 	struct hv_kvp_ipaddr_value      kvp_ip_val;
 } __attribute__((packed));
 
+/*
+ * This is the address fromat of Hyper-V Sockets.
+ * Note: here we just borrow the kernel's built-in type uuid_le. When
+ * an application calls bind() or connect(), the 2 members of struct
+ * sockaddr_hv must be of GUID.
+ * The GUID format differs from the UUID format only in the byte order of
+ * the first 3 fields. Refer to:
+ * https://en.wikipedia.org/wiki/Globally_unique_identifier
+ */
+#define guid_t uuid_le
+struct sockaddr_hv {
+	__kernel_sa_family_t	shv_family;  /* Address family		*/
+	__le16		reserved;	     /* Must be Zero		*/
+	guid_t		shv_vm_id;	     /* Not used. Must be Zero. */
+	guid_t		shv_service_id;	     /* Service ID		*/
+};
+
+#define SHV_VMID_GUEST	NULL_UUID_LE
+#define SHV_VMID_HOST	NULL_UUID_LE
+
+#define SHV_SERVICE_ID_ANY	NULL_UUID_LE
+
+#define SHV_PROTO_RAW		1
+
 #endif /* _UAPI_HYPERV_H */
diff --git a/net/Kconfig b/net/Kconfig
index a8934d8..68d13d7 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -231,6 +231,7 @@ source "net/dns_resolver/Kconfig"
 source "net/batman-adv/Kconfig"
 source "net/openvswitch/Kconfig"
 source "net/vmw_vsock/Kconfig"
+source "net/hv_sock/Kconfig"
 source "net/netlink/Kconfig"
 source "net/mpls/Kconfig"
 source "net/hsr/Kconfig"
diff --git a/net/Makefile b/net/Makefile
index 81d1411..d115c31 100644
--- a/net/Makefile
+++ b/net/Makefile
@@ -70,6 +70,7 @@ obj-$(CONFIG_BATMAN_ADV)	+= batman-adv/
 obj-$(CONFIG_NFC)		+= nfc/
 obj-$(CONFIG_OPENVSWITCH)	+= openvswitch/
 obj-$(CONFIG_VSOCKETS)	+= vmw_vsock/
+obj-$(CONFIG_HYPERV_SOCK)	+= hv_sock/
 obj-$(CONFIG_MPLS)		+= mpls/
 obj-$(CONFIG_HSR)		+= hsr/
 ifneq ($(CONFIG_NET_SWITCHDEV),)
diff --git a/net/hv_sock/Kconfig b/net/hv_sock/Kconfig
new file mode 100644
index 0000000..1f41848
--- /dev/null
+++ b/net/hv_sock/Kconfig
@@ -0,0 +1,10 @@
+config HYPERV_SOCK
+	tristate "Hyper-V Sockets"
+	depends on HYPERV
+	default m if HYPERV
+	help
+	  Hyper-V Sockets is somewhat like TCP over VMBus, allowing
+	  communication between Linux guest and Hyper-V host without TCP/IP.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called hv_sock.
diff --git a/net/hv_sock/Makefile b/net/hv_sock/Makefile
new file mode 100644
index 0000000..716c012
--- /dev/null
+++ b/net/hv_sock/Makefile
@@ -0,0 +1,3 @@
+obj-$(CONFIG_HYPERV_SOCK) += hv_sock.o
+
+hv_sock-y += af_hvsock.o
diff --git a/net/hv_sock/af_hvsock.c b/net/hv_sock/af_hvsock.c
new file mode 100644
index 0000000..185a382
--- /dev/null
+++ b/net/hv_sock/af_hvsock.c
@@ -0,0 +1,1483 @@
+/*
+ * Hyper-V Sockets -- a socket-based communication channel between the
+ * Hyper-V host and the virtual machines running on it.
+ *
+ * Copyright(c) 2016, Microsoft Corporation. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote
+ *    products derived from this software without specific prior written
+ *    permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+ * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <net/af_hvsock.h>
+
+static struct proto hvsock_proto = {
+	.name = "HV_SOCK",
+	.owner = THIS_MODULE,
+	.obj_size = sizeof(struct hvsock_sock),
+};
+
+#define SS_LISTEN 255
+
+static LIST_HEAD(hvsock_bound_list);
+static LIST_HEAD(hvsock_connected_list);
+static DEFINE_MUTEX(hvsock_mutex);
+
+static bool uuid_equals(uuid_le u1, uuid_le u2)
+{
+	return !uuid_le_cmp(u1, u2);
+}
+
+/* NOTE: hvsock_mutex must be held when the below helper functions, whose
+ * names begin with __ hvsock, are invoked.
+ */
+static void __hvsock_insert_bound(struct list_head *list,
+				  struct hvsock_sock *hvsk)
+{
+	sock_hold(&hvsk->sk);
+	list_add(&hvsk->bound_list, list);
+}
+
+static void __hvsock_insert_connected(struct list_head *list,
+				      struct hvsock_sock *hvsk)
+{
+	sock_hold(&hvsk->sk);
+	list_add(&hvsk->connected_list, list);
+}
+
+static void __hvsock_remove_bound(struct hvsock_sock *hvsk)
+{
+	list_del_init(&hvsk->bound_list);
+	sock_put(&hvsk->sk);
+}
+
+static void __hvsock_remove_connected(struct hvsock_sock *hvsk)
+{
+	list_del_init(&hvsk->connected_list);
+	sock_put(&hvsk->sk);
+}
+
+static struct sock *__hvsock_find_bound_socket(const struct sockaddr_hv *addr)
+{
+	struct hvsock_sock *hvsk;
+
+	list_for_each_entry(hvsk, &hvsock_bound_list, bound_list) {
+		if (uuid_equals(addr->shv_service_id,
+				hvsk->local_addr.shv_service_id))
+			return hvsock_to_sk(hvsk);
+	}
+	return NULL;
+}
+
+static struct sock *__hvsock_find_connected_socket_by_channel(
+	const struct vmbus_channel *channel)
+{
+	struct hvsock_sock *hvsk;
+
+	list_for_each_entry(hvsk, &hvsock_connected_list, connected_list) {
+		if (hvsk->channel == channel)
+			return hvsock_to_sk(hvsk);
+	}
+	return NULL;
+}
+
+static bool __hvsock_in_bound_list(struct hvsock_sock *hvsk)
+{
+	return !list_empty(&hvsk->bound_list);
+}
+
+static bool __hvsock_in_connected_list(struct hvsock_sock *hvsk)
+{
+	return !list_empty(&hvsk->connected_list);
+}
+
+static void hvsock_insert_connected(struct hvsock_sock *hvsk)
+{
+	__hvsock_insert_connected(&hvsock_connected_list, hvsk);
+}
+
+static
+void hvsock_enqueue_accept(struct sock *listener, struct sock *connected)
+{
+	struct hvsock_sock *hvlistener;
+	struct hvsock_sock *hvconnected;
+
+	hvlistener = sk_to_hvsock(listener);
+	hvconnected = sk_to_hvsock(connected);
+
+	sock_hold(connected);
+	sock_hold(listener);
+
+	mutex_lock(&hvlistener->accept_queue_mutex);
+	list_add_tail(&hvconnected->accept_queue, &hvlistener->accept_queue);
+	listener->sk_ack_backlog++;
+	mutex_unlock(&hvlistener->accept_queue_mutex);
+}
+
+static struct sock *hvsock_dequeue_accept(struct sock *listener)
+{
+	struct hvsock_sock *hvlistener;
+	struct hvsock_sock *hvconnected;
+
+	hvlistener = sk_to_hvsock(listener);
+
+	mutex_lock(&hvlistener->accept_queue_mutex);
+
+	if (list_empty(&hvlistener->accept_queue)) {
+		mutex_unlock(&hvlistener->accept_queue_mutex);
+		return NULL;
+	}
+
+	hvconnected = list_entry(hvlistener->accept_queue.next,
+				 struct hvsock_sock, accept_queue);
+
+	list_del_init(&hvconnected->accept_queue);
+	listener->sk_ack_backlog--;
+
+	mutex_unlock(&hvlistener->accept_queue_mutex);
+
+	sock_put(listener);
+	/* The caller will need a reference on the connected socket so we let
+	 * it call sock_put().
+	 */
+
+	return hvsock_to_sk(hvconnected);
+}
+
+static bool hvsock_is_accept_queue_empty(struct sock *sk)
+{
+	struct hvsock_sock *hvsk = sk_to_hvsock(sk);
+	int ret;
+
+	mutex_lock(&hvsk->accept_queue_mutex);
+	ret = list_empty(&hvsk->accept_queue);
+	mutex_unlock(&hvsk->accept_queue_mutex);
+
+	return ret;
+}
+
+static void hvsock_addr_init(struct sockaddr_hv *addr, uuid_le service_id)
+{
+	memset(addr, 0, sizeof(*addr));
+	addr->shv_family = AF_HYPERV;
+	addr->shv_service_id = service_id;
+}
+
+static int hvsock_addr_validate(const struct sockaddr_hv *addr)
+{
+	if (!addr)
+		return -EFAULT;
+
+	if (addr->shv_family != AF_HYPERV)
+		return -EAFNOSUPPORT;
+
+	if (addr->reserved != 0)
+		return -EINVAL;
+
+	if (!uuid_equals(addr->shv_vm_id, NULL_UUID_LE))
+		return -EINVAL;
+
+	return 0;
+}
+
+static bool hvsock_addr_bound(const struct sockaddr_hv *addr)
+{
+	return !uuid_equals(addr->shv_service_id, SHV_SERVICE_ID_ANY);
+}
+
+static int hvsock_addr_cast(const struct sockaddr *addr, size_t len,
+			    struct sockaddr_hv **out_addr)
+{
+	if (len < sizeof(**out_addr))
+		return -EFAULT;
+
+	*out_addr = (struct sockaddr_hv *)addr;
+	return hvsock_addr_validate(*out_addr);
+}
+
+static int __hvsock_do_bind(struct hvsock_sock *hvsk,
+			    struct sockaddr_hv *addr)
+{
+	struct sockaddr_hv hv_addr;
+	int ret = 0;
+
+	hvsock_addr_init(&hv_addr, addr->shv_service_id);
+
+	mutex_lock(&hvsock_mutex);
+
+	if (uuid_equals(addr->shv_service_id, SHV_SERVICE_ID_ANY)) {
+		do {
+			uuid_le_gen(&hv_addr.shv_service_id);
+		} while (__hvsock_find_bound_socket(&hv_addr));
+	} else {
+		if (__hvsock_find_bound_socket(&hv_addr)) {
+			ret = -EADDRINUSE;
+			goto out;
+		}
+	}
+
+	hvsock_addr_init(&hvsk->local_addr, hv_addr.shv_service_id);
+	__hvsock_insert_bound(&hvsock_bound_list, hvsk);
+
+out:
+	mutex_unlock(&hvsock_mutex);
+
+	return ret;
+}
+
+static int __hvsock_bind(struct sock *sk, struct sockaddr_hv *addr)
+{
+	struct hvsock_sock *hvsk = sk_to_hvsock(sk);
+	int ret;
+
+	if (hvsock_addr_bound(&hvsk->local_addr))
+		return -EINVAL;
+
+	switch (sk->sk_socket->type) {
+	case SOCK_STREAM:
+		ret = __hvsock_do_bind(hvsk, addr);
+		break;
+
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	return ret;
+}
+
+/* Autobind this socket to the local address if necessary. */
+static int hvsock_auto_bind(struct hvsock_sock *hvsk)
+{
+	struct sock *sk = hvsock_to_sk(hvsk);
+	struct sockaddr_hv local_addr;
+
+	if (hvsock_addr_bound(&hvsk->local_addr))
+		return 0;
+	hvsock_addr_init(&local_addr, SHV_SERVICE_ID_ANY);
+	return __hvsock_bind(sk, &local_addr);
+}
+
+static void hvsock_sk_destruct(struct sock *sk)
+{
+	struct hvsock_sock *hvsk = sk_to_hvsock(sk);
+	struct vmbus_channel *channel = hvsk->channel;
+
+	if (!channel)
+		return;
+
+	vmbus_hvsock_device_unregister(channel);
+}
+
+static void __hvsock_release(struct sock *sk)
+{
+	struct hvsock_sock *hvsk;
+	struct sock *pending;
+
+	hvsk = sk_to_hvsock(sk);
+
+	mutex_lock(&hvsock_mutex);
+	if (__hvsock_in_bound_list(hvsk))
+		__hvsock_remove_bound(hvsk);
+
+	if (__hvsock_in_connected_list(hvsk))
+		__hvsock_remove_connected(hvsk);
+	mutex_unlock(&hvsock_mutex);
+
+	lock_sock(sk);
+	sock_orphan(sk);
+	sk->sk_shutdown = SHUTDOWN_MASK;
+
+	/* Clean up any sockets that never were accepted. */
+	while ((pending = hvsock_dequeue_accept(sk)) != NULL) {
+		__hvsock_release(pending);
+		sock_put(pending);
+	}
+
+	release_sock(sk);
+	sock_put(sk);
+}
+
+static int hvsock_release(struct socket *sock)
+{
+	/* If accept() is interrupted by a signal, the temporary socket
+	 * struct's sock->sk is NULL.
+	 */
+	if (sock->sk) {
+		__hvsock_release(sock->sk);
+		sock->sk = NULL;
+	}
+
+	sock->state = SS_FREE;
+	return 0;
+}
+
+static struct sock *__hvsock_create(struct net *net, struct socket *sock,
+				    gfp_t priority, unsigned short type)
+{
+	struct hvsock_sock *hvsk;
+	struct sock *sk;
+
+	sk = sk_alloc(net, AF_HYPERV, priority, &hvsock_proto, 0);
+	if (!sk)
+		return NULL;
+
+	sock_init_data(sock, sk);
+
+	/* sk->sk_type is normally set in sock_init_data, but only if sock is
+	 * non-NULL. We make sure that our sockets always have a type by
+	 * setting it here if needed.
+	 */
+	if (!sock)
+		sk->sk_type = type;
+
+	hvsk = sk_to_hvsock(sk);
+	hvsock_addr_init(&hvsk->local_addr, SHV_SERVICE_ID_ANY);
+	hvsock_addr_init(&hvsk->remote_addr, SHV_SERVICE_ID_ANY);
+
+	sk->sk_destruct = hvsock_sk_destruct;
+
+	/* Looks stream-based socket doesn't need this. */
+	sk->sk_backlog_rcv = NULL;
+
+	sk->sk_state = 0;
+	sock_reset_flag(sk, SOCK_DONE);
+
+	INIT_LIST_HEAD(&hvsk->bound_list);
+	INIT_LIST_HEAD(&hvsk->connected_list);
+
+	INIT_LIST_HEAD(&hvsk->accept_queue);
+	mutex_init(&hvsk->accept_queue_mutex);
+
+	hvsk->peer_shutdown = 0;
+
+	hvsk->recv.data_len = 0;
+	hvsk->recv.data_offset = 0;
+
+	return sk;
+}
+
+static int hvsock_bind(struct socket *sock, struct sockaddr *addr,
+		       int addr_len)
+{
+	struct sockaddr_hv *hv_addr;
+	struct sock *sk;
+	int ret;
+
+	sk = sock->sk;
+
+	if (hvsock_addr_cast(addr, addr_len, &hv_addr) != 0)
+		return -EINVAL;
+
+	lock_sock(sk);
+	ret = __hvsock_bind(sk, hv_addr);
+	release_sock(sk);
+
+	return ret;
+}
+
+static int hvsock_getname(struct socket *sock,
+			  struct sockaddr *addr, int *addr_len, int peer)
+{
+	struct sockaddr_hv *hv_addr;
+	struct hvsock_sock *hvsk;
+	struct sock *sk;
+	int ret;
+
+	sk = sock->sk;
+	hvsk = sk_to_hvsock(sk);
+	ret = 0;
+
+	lock_sock(sk);
+
+	if (peer) {
+		if (sock->state != SS_CONNECTED) {
+			ret = -ENOTCONN;
+			goto out;
+		}
+		hv_addr = &hvsk->remote_addr;
+	} else {
+		hv_addr = &hvsk->local_addr;
+	}
+
+	__sockaddr_check_size(sizeof(*hv_addr));
+
+	memcpy(addr, hv_addr, sizeof(*hv_addr));
+	*addr_len = sizeof(*hv_addr);
+
+out:
+	release_sock(sk);
+	return ret;
+}
+
+static int hvsock_shutdown(struct socket *sock, int mode)
+{
+	struct sock *sk;
+
+	if (mode < SHUT_RD || mode > SHUT_RDWR)
+		return -EINVAL;
+	/* This maps:
+	 * SHUT_RD   (0) -> RCV_SHUTDOWN  (1)
+	 * SHUT_WR   (1) -> SEND_SHUTDOWN (2)
+	 * SHUT_RDWR (2) -> SHUTDOWN_MASK (3)
+	 */
+	++mode;
+
+	if (sock->state == SS_UNCONNECTED)
+		return -ENOTCONN;
+
+	sock->state = SS_DISCONNECTING;
+
+	sk = sock->sk;
+
+	lock_sock(sk);
+
+	sk->sk_shutdown |= mode;
+	sk->sk_state_change(sk);
+
+	/* TODO: how to send a FIN if we haven't done that? */
+	if (mode & SEND_SHUTDOWN)
+		;
+
+	release_sock(sk);
+
+	return 0;
+}
+
+static void get_ringbuffer_rw_status(struct vmbus_channel *channel,
+				     bool *can_read, bool *can_write)
+{
+	u32 avl_read_bytes, avl_write_bytes, dummy;
+
+	if (can_read) {
+		hv_get_ringbuffer_availbytes(&channel->inbound,
+					     &avl_read_bytes,
+					     &dummy);
+		*can_read = avl_read_bytes >= HVSOCK_MIN_PKT_LEN;
+	}
+
+	/* We write into the ringbuffer only when we're able to write a
+	 * a payload of 4096 bytes (the actual written payload's length may be
+	 * less than 4096).
+	 */
+	if (can_write) {
+		hv_get_ringbuffer_availbytes(&channel->outbound,
+					     &dummy,
+					     &avl_write_bytes);
+		*can_write = avl_write_bytes > HVSOCK_PKT_LEN(PAGE_SIZE);
+	}
+}
+
+static unsigned int hvsock_poll(struct file *file, struct socket *sock,
+				poll_table *wait)
+{
+	struct vmbus_channel *channel;
+	bool can_read, can_write;
+	struct hvsock_sock *hvsk;
+	struct sock *sk;
+	unsigned int mask;
+
+	sk = sock->sk;
+	hvsk = sk_to_hvsock(sk);
+
+	poll_wait(file, sk_sleep(sk), wait);
+	mask = 0;
+
+	if (sk->sk_err)
+		/* Signify that there has been an error on this socket. */
+		mask |= POLLERR;
+
+	/* INET sockets treat local write shutdown and peer write shutdown as a
+	 * case of POLLHUP set.
+	 */
+	if ((sk->sk_shutdown == SHUTDOWN_MASK) ||
+	    ((sk->sk_shutdown & SEND_SHUTDOWN) &&
+	     (hvsk->peer_shutdown & SEND_SHUTDOWN))) {
+		mask |= POLLHUP;
+	}
+
+	if (sk->sk_shutdown & RCV_SHUTDOWN ||
+	    hvsk->peer_shutdown & SEND_SHUTDOWN) {
+		mask |= POLLRDHUP;
+	}
+
+	lock_sock(sk);
+
+	/* Listening sockets that have connections in their accept
+	 * queue can be read.
+	 */
+	if (sk->sk_state == SS_LISTEN && !hvsock_is_accept_queue_empty(sk))
+		mask |= POLLIN | POLLRDNORM;
+
+	/* The mutex is to against hvsock_open_connection() */
+	mutex_lock(&hvsock_mutex);
+
+	channel = hvsk->channel;
+	if (channel) {
+		/* If there is something in the queue then we can read */
+		get_ringbuffer_rw_status(channel, &can_read, &can_write);
+
+		if (!can_read && hvsk->recv.data_len > 0)
+			can_read = true;
+
+		if (!(sk->sk_shutdown & RCV_SHUTDOWN) && can_read)
+			mask |= POLLIN | POLLRDNORM;
+	} else {
+		can_read = false;
+		can_write = false;
+	}
+
+	mutex_unlock(&hvsock_mutex);
+
+	/* Sockets whose connections have been closed terminated should
+	 * also be considered read, and we check the shutdown flag for that.
+	 */
+	if (sk->sk_shutdown & RCV_SHUTDOWN ||
+	    hvsk->peer_shutdown & SEND_SHUTDOWN) {
+		mask |= POLLIN | POLLRDNORM;
+	}
+
+	/* Connected sockets that can produce data can be written. */
+	if (sk->sk_state == SS_CONNECTED && can_write &&
+	    !(sk->sk_shutdown & SEND_SHUTDOWN)) {
+		/* Remove POLLWRBAND since INET sockets are not setting it.
+		 */
+		mask |= POLLOUT | POLLWRNORM;
+	}
+
+	/* Simulate INET socket poll behaviors, which sets
+	 * POLLOUT|POLLWRNORM when peer is closed and nothing to read,
+	 * but local send is not shutdown.
+	 */
+	if (sk->sk_state == SS_UNCONNECTED &&
+	    !(sk->sk_shutdown & SEND_SHUTDOWN))
+		mask |= POLLOUT | POLLWRNORM;
+
+	release_sock(sk);
+
+	return mask;
+}
+
+/* This function runs in the tasklet context of process_chn_event() */
+static void hvsock_on_channel_cb(void *ctx)
+{
+	struct sock *sk = (struct sock *)ctx;
+	struct hvsock_sock *hvsk = sk_to_hvsock(sk);
+	struct vmbus_channel *channel = hvsk->channel;
+	bool can_read, can_write;
+
+	if (!channel) {
+		WARN_ONCE(1, "NULL channel! There is a programming bug.\n");
+		return;
+	}
+
+	get_ringbuffer_rw_status(channel, &can_read, &can_write);
+
+	if (can_read)
+		sk->sk_data_ready(sk);
+
+	if (can_write)
+		sk->sk_write_space(sk);
+}
+
+static void hvsock_close_connection(struct vmbus_channel *channel)
+{
+	struct hvsock_sock *hvsk;
+	struct sock *sk;
+
+	mutex_lock(&hvsock_mutex);
+
+	sk = __hvsock_find_connected_socket_by_channel(channel);
+
+	/* The guest has already closed the connection? */
+	if (!sk)
+		goto out;
+
+	sk->sk_socket->state = SS_UNCONNECTED;
+	sk->sk_state = SS_UNCONNECTED;
+	sock_set_flag(sk, SOCK_DONE);
+
+	hvsk = sk_to_hvsock(sk);
+	hvsk->peer_shutdown |= SEND_SHUTDOWN | RCV_SHUTDOWN;
+
+	sk->sk_state_change(sk);
+out:
+	mutex_unlock(&hvsock_mutex);
+}
+
+static int hvsock_open_connection(struct vmbus_channel *channel)
+{
+	struct hvsock_sock *hvsk, *new_hvsk;
+	struct sockaddr_hv hv_addr;
+	struct sock *sk, *new_sk;
+
+	uuid_le *instance, *service_id;
+	int ret;
+
+	instance = &channel->offermsg.offer.if_instance;
+	service_id = &channel->offermsg.offer.if_type;
+
+	hvsock_addr_init(&hv_addr, *instance);
+
+	mutex_lock(&hvsock_mutex);
+
+	sk = __hvsock_find_bound_socket(&hv_addr);
+
+	if (sk) {
+		/* It is from the guest client's connect() */
+		if (sk->sk_state != SS_CONNECTING) {
+			ret = -ENXIO;
+			goto out;
+		}
+
+		hvsk = sk_to_hvsock(sk);
+		hvsk->channel = channel;
+		set_channel_read_state(channel, false);
+		vmbus_set_chn_rescind_callback(channel,
+					       hvsock_close_connection);
+		ret = vmbus_open(channel, VMBUS_RINGBUFFER_SIZE_HVSOCK_SEND,
+				 VMBUS_RINGBUFFER_SIZE_HVSOCK_RECV, NULL, 0,
+				 hvsock_on_channel_cb, sk);
+		if (ret != 0) {
+			hvsk->channel = NULL;
+			goto out;
+		}
+
+		set_channel_pending_send_size(channel,
+					      HVSOCK_PKT_LEN(PAGE_SIZE));
+		sk->sk_state = SS_CONNECTED;
+		sk->sk_socket->state = SS_CONNECTED;
+		hvsock_insert_connected(hvsk);
+		sk->sk_state_change(sk);
+		goto out;
+	}
+
+	/* Now we suppose it is from a host client's connect() */
+	hvsock_addr_init(&hv_addr, *service_id);
+	sk = __hvsock_find_bound_socket(&hv_addr);
+
+	/* No guest server listening? Well, let's ignore the offer */
+	if (!sk || sk->sk_state != SS_LISTEN) {
+		ret = -ENXIO;
+		goto out;
+	}
+
+	if (sk->sk_ack_backlog >= sk->sk_max_ack_backlog) {
+		ret = -EMFILE;
+		goto out;
+	}
+
+	new_sk = __hvsock_create(sock_net(sk), NULL, GFP_KERNEL, sk->sk_type);
+	if (!new_sk) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	new_hvsk = sk_to_hvsock(new_sk);
+	new_sk->sk_state = SS_CONNECTING;
+	hvsock_addr_init(&new_hvsk->local_addr, *service_id);
+	hvsock_addr_init(&new_hvsk->remote_addr, *instance);
+
+	set_channel_read_state(channel, false);
+	new_hvsk->channel = channel;
+	vmbus_set_chn_rescind_callback(channel, hvsock_close_connection);
+	ret = vmbus_open(channel, VMBUS_RINGBUFFER_SIZE_HVSOCK_SEND,
+			 VMBUS_RINGBUFFER_SIZE_HVSOCK_RECV, NULL, 0,
+			 hvsock_on_channel_cb, new_sk);
+	if (ret != 0) {
+		new_hvsk->channel = NULL;
+		sock_put(new_sk);
+		goto out;
+	}
+	set_channel_pending_send_size(channel, HVSOCK_PKT_LEN(PAGE_SIZE));
+
+	new_sk->sk_state = SS_CONNECTED;
+	hvsock_insert_connected(new_hvsk);
+	hvsock_enqueue_accept(sk, new_sk);
+	sk->sk_state_change(sk);
+out:
+	mutex_unlock(&hvsock_mutex);
+	return ret;
+}
+
+static void hvsock_connect_timeout(struct work_struct *work)
+{
+	struct hvsock_sock *hvsk;
+	struct sock *sk;
+
+	hvsk = container_of(work, struct hvsock_sock, dwork.work);
+	sk = hvsock_to_sk(hvsk);
+
+	lock_sock(sk);
+	if ((sk->sk_state == SS_CONNECTING) &&
+	    (sk->sk_shutdown != SHUTDOWN_MASK)) {
+		sk->sk_state = SS_UNCONNECTED;
+		sk->sk_err = ETIMEDOUT;
+		sk->sk_error_report(sk);
+	}
+	release_sock(sk);
+
+	sock_put(sk);
+}
+
+static int hvsock_connect(struct socket *sock, struct sockaddr *addr,
+			  int addr_len, int flags)
+{
+	struct sockaddr_hv *remote_addr;
+	struct hvsock_sock *hvsk;
+	struct sock *sk;
+
+	DEFINE_WAIT(wait);
+	long timeout;
+
+	int ret = 0;
+
+	sk = sock->sk;
+	hvsk = sk_to_hvsock(sk);
+
+	lock_sock(sk);
+
+	switch (sock->state) {
+	case SS_CONNECTED:
+		ret = -EISCONN;
+		goto out;
+	case SS_DISCONNECTING:
+		ret = -EINVAL;
+		goto out;
+	case SS_CONNECTING:
+		/* This continues on so we can move sock into the SS_CONNECTED
+		 * state once the connection has completed (at which point err
+		 * will be set to zero also).  Otherwise, we will either wait
+		 * for the connection or return -EALREADY should this be a
+		 * non-blocking call.
+		 */
+		ret = -EALREADY;
+		break;
+	default:
+		if ((sk->sk_state == SS_LISTEN) ||
+		    hvsock_addr_cast(addr, addr_len, &remote_addr) != 0) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		/* Set the remote address that we are connecting to. */
+		memcpy(&hvsk->remote_addr, remote_addr,
+		       sizeof(hvsk->remote_addr));
+
+		ret = hvsock_auto_bind(hvsk);
+		if (ret)
+			goto out;
+
+		sk->sk_state = SS_CONNECTING;
+
+		ret = vmbus_send_tl_connect_request(
+					&hvsk->local_addr.shv_service_id,
+					&hvsk->remote_addr.shv_service_id);
+		if (ret < 0)
+			goto out;
+
+		/* Mark sock as connecting and set the error code to in
+		 * progress in case this is a non-blocking connect.
+		 */
+		sock->state = SS_CONNECTING;
+		ret = -EINPROGRESS;
+	}
+
+	/* The receive path will handle all communication until we are able to
+	 * enter the connected state.  Here we wait for the connection to be
+	 * completed or a notification of an error.
+	 */
+	timeout = 30 * HZ;
+	prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
+
+	while (sk->sk_state != SS_CONNECTED && sk->sk_err == 0) {
+		if (flags & O_NONBLOCK) {
+			/* If we're not going to block, we schedule a timeout
+			 * function to generate a timeout on the connection
+			 * attempt, in case the peer doesn't respond in a
+			 * timely manner. We hold on to the socket until the
+			 * timeout fires.
+			 */
+			sock_hold(sk);
+			INIT_DELAYED_WORK(&hvsk->dwork,
+					  hvsock_connect_timeout);
+			schedule_delayed_work(&hvsk->dwork, timeout);
+
+			/* Skip ahead to preserve error code set above. */
+			goto out_wait;
+		}
+
+		release_sock(sk);
+		timeout = schedule_timeout(timeout);
+		lock_sock(sk);
+
+		if (signal_pending(current)) {
+			ret = sock_intr_errno(timeout);
+			goto out_wait_error;
+		} else if (timeout == 0) {
+			ret = -ETIMEDOUT;
+			goto out_wait_error;
+		}
+
+		prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
+	}
+
+	ret = sk->sk_err ? -sk->sk_err : 0;
+
+out_wait_error:
+	if (ret < 0) {
+		sk->sk_state = SS_UNCONNECTED;
+		sock->state = SS_UNCONNECTED;
+	}
+out_wait:
+	finish_wait(sk_sleep(sk), &wait);
+out:
+	release_sock(sk);
+	return ret;
+}
+
+static
+int hvsock_accept(struct socket *sock, struct socket *newsock, int flags)
+{
+	struct hvsock_sock *hvconnected;
+	struct sock *connected;
+	struct sock *listener;
+
+	DEFINE_WAIT(wait);
+	long timeout;
+
+	int ret = 0;
+
+	listener = sock->sk;
+
+	lock_sock(listener);
+
+	if (sock->type != SOCK_STREAM) {
+		ret = -EOPNOTSUPP;
+		goto out;
+	}
+
+	if (listener->sk_state != SS_LISTEN) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/* Wait for children sockets to appear; these are the new sockets
+	 * created upon connection establishment.
+	 */
+	timeout = sock_sndtimeo(listener, flags & O_NONBLOCK);
+	prepare_to_wait(sk_sleep(listener), &wait, TASK_INTERRUPTIBLE);
+
+	while ((connected = hvsock_dequeue_accept(listener)) == NULL &&
+	       listener->sk_err == 0) {
+		release_sock(listener);
+		timeout = schedule_timeout(timeout);
+		lock_sock(listener);
+
+		if (signal_pending(current)) {
+			ret = sock_intr_errno(timeout);
+			goto out_wait;
+		} else if (timeout == 0) {
+			ret = -EAGAIN;
+			goto out_wait;
+		}
+
+		prepare_to_wait(sk_sleep(listener), &wait, TASK_INTERRUPTIBLE);
+	}
+
+	if (listener->sk_err)
+		ret = -listener->sk_err;
+
+	if (connected) {
+		lock_sock(connected);
+		hvconnected = sk_to_hvsock(connected);
+
+		/* If the listener socket has received an error, then we should
+		 * reject this socket and return.  Note that we simply mark the
+		 * socket rejected, drop our reference, and let the cleanup
+		 * function handle the cleanup; the fact that we found it in
+		 * the listener's accept queue guarantees that the cleanup
+		 * function hasn't run yet.
+		 */
+		if (ret) {
+			release_sock(connected);
+			sock_put(connected);
+			goto out_wait;
+		}
+
+		newsock->state = SS_CONNECTED;
+		sock_graft(connected, newsock);
+		release_sock(connected);
+		sock_put(connected);
+	}
+
+out_wait:
+	finish_wait(sk_sleep(listener), &wait);
+out:
+	release_sock(listener);
+	return ret;
+}
+
+static int hvsock_listen(struct socket *sock, int backlog)
+{
+	struct hvsock_sock *hvsk;
+	struct sock *sk;
+	int ret = 0;
+
+	sk = sock->sk;
+	lock_sock(sk);
+
+	if (sock->type != SOCK_STREAM) {
+		ret = -EOPNOTSUPP;
+		goto out;
+	}
+
+	if (sock->state != SS_UNCONNECTED) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	if (backlog <= 0) {
+		ret = -EINVAL;
+		goto out;
+	}
+	/* This is an artificial limit */
+	if (backlog > 128)
+		backlog = 128;
+
+	hvsk = sk_to_hvsock(sk);
+	if (!hvsock_addr_bound(&hvsk->local_addr)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	sk->sk_ack_backlog = 0;
+	sk->sk_max_ack_backlog = backlog;
+	sk->sk_state = SS_LISTEN;
+out:
+	release_sock(sk);
+	return ret;
+}
+
+static int hvsock_setsockopt(struct socket *sock,
+			     int level,
+			     int optname,
+			     char __user *optval, unsigned int optlen)
+{
+	return -ENOPROTOOPT;
+}
+
+static int hvsock_getsockopt(struct socket *sock,
+			     int level,
+			     int optname,
+			     char __user *optval, int __user *optlen)
+{
+	return -ENOPROTOOPT;
+}
+
+static int hvsock_send_data(struct vmbus_channel *channel,
+			    struct hvsock_sock *hvsk,
+			    size_t to_write)
+{
+	hvsk->send.hdr.pkt_type = 1;
+	hvsk->send.hdr.data_size = to_write;
+	return vmbus_sendpacket(channel, &hvsk->send.hdr,
+				sizeof(hvsk->send.hdr) + to_write,
+				0, VM_PKT_DATA_INBAND, 0);
+}
+
+static int hvsock_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
+{
+	struct vmbus_channel *channel;
+	struct hvsock_sock *hvsk;
+	struct sock *sk;
+
+	size_t total_to_write = len;
+	size_t total_written = 0;
+
+	bool can_write;
+	long timeout;
+	int ret = 0;
+
+	DEFINE_WAIT(wait);
+
+	if (len == 0)
+		return -EINVAL;
+
+	if (msg->msg_flags & ~MSG_DONTWAIT) {
+		pr_err("%s: unsupported flags=0x%x\n", __func__,
+		       msg->msg_flags);
+		return -EOPNOTSUPP;
+	}
+
+	sk = sock->sk;
+	hvsk = sk_to_hvsock(sk);
+	channel = hvsk->channel;
+
+	lock_sock(sk);
+
+	/* Callers should not provide a destination with stream sockets. */
+	if (msg->msg_namelen) {
+		ret = -EOPNOTSUPP;
+		goto out;
+	}
+
+	/* Send data only if both sides are not shutdown in the direction. */
+	if (sk->sk_shutdown & SEND_SHUTDOWN ||
+	    hvsk->peer_shutdown & RCV_SHUTDOWN) {
+		ret = -EPIPE;
+		goto out;
+	}
+
+	if (sk->sk_state != SS_CONNECTED ||
+	    !hvsock_addr_bound(&hvsk->local_addr)) {
+		ret = -ENOTCONN;
+		goto out;
+	}
+
+	if (!hvsock_addr_bound(&hvsk->remote_addr)) {
+		ret = -EDESTADDRREQ;
+		goto out;
+	}
+
+	timeout = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
+
+	prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
+
+	while (total_to_write > 0) {
+		size_t to_write;
+
+		while (1) {
+			get_ringbuffer_rw_status(channel, NULL, &can_write);
+
+			if (can_write || sk->sk_err != 0 ||
+			    (sk->sk_shutdown & SEND_SHUTDOWN) ||
+			    (hvsk->peer_shutdown & RCV_SHUTDOWN))
+				break;
+
+			/* Don't wait for non-blocking sockets. */
+			if (timeout == 0) {
+				ret = -EAGAIN;
+				goto out_wait;
+			}
+
+			release_sock(sk);
+
+			timeout = schedule_timeout(timeout);
+
+			lock_sock(sk);
+			if (signal_pending(current)) {
+				ret = sock_intr_errno(timeout);
+				goto out_wait;
+			} else if (timeout == 0) {
+				ret = -EAGAIN;
+				goto out_wait;
+			}
+
+			prepare_to_wait(sk_sleep(sk), &wait,
+					TASK_INTERRUPTIBLE);
+		}
+
+		/* These checks occur both as part of and after the loop
+		 * conditional since we need to check before and after
+		 * sleeping.
+		 */
+		if (sk->sk_err) {
+			ret = -sk->sk_err;
+			goto out_wait;
+		} else if ((sk->sk_shutdown & SEND_SHUTDOWN) ||
+			   (hvsk->peer_shutdown & RCV_SHUTDOWN)) {
+			ret = -EPIPE;
+			goto out_wait;
+		}
+
+		/* Note: that write will only write as many bytes as possible
+		 * in the ringbuffer. It is the caller's responsibility to
+		 * check how many bytes we actually wrote.
+		 */
+		do {
+			to_write = min_t(size_t, HVSOCK_SND_BUF_SZ,
+					 total_to_write);
+			ret = memcpy_from_msg(hvsk->send.buf, msg, to_write);
+			if (ret != 0)
+				goto out_wait;
+
+			ret = hvsock_send_data(channel, hvsk, to_write);
+			if (ret != 0)
+				goto out_wait;
+
+			total_written += to_write;
+			total_to_write -= to_write;
+		} while (total_to_write > 0);
+	}
+out_wait:
+	if (total_written > 0)
+		ret = total_written;
+
+	finish_wait(sk_sleep(sk), &wait);
+out:
+	release_sock(sk);
+
+	/* ret is a bigger-than-0 total_written or a negative err code. */
+	if (ret == 0) {
+		WARN(1, "unexpected return value of 0\n");
+		ret = -EIO;
+	}
+
+	return ret;
+}
+
+static int hvsock_recv_data(struct vmbus_channel *channel,
+			    struct hvsock_sock *hvsk,
+			    size_t *payload_len)
+{
+	u32 buffer_actual_len;
+	u64 dummy_req_id;
+	int ret;
+
+	ret = vmbus_recvpacket(channel, &hvsk->recv.hdr,
+			       sizeof(hvsk->recv.hdr) + sizeof(hvsk->recv.buf),
+			       &buffer_actual_len, &dummy_req_id);
+	if (ret != 0 || buffer_actual_len <= sizeof(hvsk->recv.hdr))
+		*payload_len = 0;
+	else
+		*payload_len = hvsk->recv.hdr.data_size;
+
+	return ret;
+}
+
+static int hvsock_recvmsg(struct socket *sock, struct msghdr *msg,
+			  size_t len, int flags)
+{
+	struct vmbus_channel *channel;
+	struct hvsock_sock *hvsk;
+	struct sock *sk;
+
+	size_t total_to_read = len;
+	size_t copied;
+
+	bool can_read;
+	long timeout;
+
+	int ret = 0;
+
+	DEFINE_WAIT(wait);
+
+	sk = sock->sk;
+	hvsk = sk_to_hvsock(sk);
+	channel = hvsk->channel;
+
+	lock_sock(sk);
+
+	if (sk->sk_state != SS_CONNECTED) {
+		/* Recvmsg is supposed to return 0 if a peer performs an
+		 * orderly shutdown. Differentiate between that case and when a
+		 * peer has not connected or a local shutdown occurred with the
+		 * SOCK_DONE flag.
+		 */
+		if (sock_flag(sk, SOCK_DONE))
+			ret = 0;
+		else
+			ret = -ENOTCONN;
+
+		goto out;
+	}
+
+	/* We ignore msg->addr_name/len. */
+	if (flags & ~MSG_DONTWAIT) {
+		pr_err("%s: unsupported flags=0x%x\n", __func__, flags);
+		ret = -EOPNOTSUPP;
+		goto out;
+	}
+
+	/* We don't check peer_shutdown flag here since peer may actually shut
+	 * down, but there can be data in the queue that a local socket can
+	 * receive.
+	 */
+	if (sk->sk_shutdown & RCV_SHUTDOWN) {
+		ret = 0;
+		goto out;
+	}
+
+	/* It is valid on Linux to pass in a zero-length receive buffer.  This
+	 * is not an error.  We may as well bail out now.
+	 */
+	if (!len) {
+		ret = 0;
+		goto out;
+	}
+
+	timeout = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
+	copied = 0;
+
+	prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
+
+	while (1) {
+		bool need_refill = hvsk->recv.data_len == 0;
+
+		if (need_refill)
+			get_ringbuffer_rw_status(channel, &can_read, NULL);
+		else
+			can_read = true;
+
+		if (can_read) {
+			size_t payload_len;
+
+			if (need_refill) {
+				ret = hvsock_recv_data(channel, hvsk,
+						       &payload_len);
+				if (ret != 0 || payload_len == 0 ||
+				    payload_len > HVSOCK_RCV_BUF_SZ) {
+					ret = -EIO;
+					goto out_wait;
+				}
+
+				hvsk->recv.data_len = payload_len;
+				hvsk->recv.data_offset = 0;
+			}
+
+			if (hvsk->recv.data_len <= total_to_read) {
+				ret = memcpy_to_msg(msg, hvsk->recv.buf +
+						    hvsk->recv.data_offset,
+						    hvsk->recv.data_len);
+				if (ret != 0)
+					break;
+
+				copied += hvsk->recv.data_len;
+				total_to_read -= hvsk->recv.data_len;
+				hvsk->recv.data_len = 0;
+				hvsk->recv.data_offset = 0;
+
+				if (total_to_read == 0)
+					break;
+			} else {
+				ret = memcpy_to_msg(msg, hvsk->recv.buf +
+						    hvsk->recv.data_offset,
+						    total_to_read);
+				if (ret != 0)
+					break;
+
+				copied += total_to_read;
+				hvsk->recv.data_len -= total_to_read;
+				hvsk->recv.data_offset += total_to_read;
+				total_to_read = 0;
+				break;
+			}
+		} else {
+			if (sk->sk_err || (sk->sk_shutdown & RCV_SHUTDOWN) ||
+			    (hvsk->peer_shutdown & SEND_SHUTDOWN))
+				break;
+
+			/* Don't wait for non-blocking sockets. */
+			if (timeout == 0) {
+				ret = -EAGAIN;
+				break;
+			}
+
+			if (copied > 0)
+				break;
+
+			release_sock(sk);
+			timeout = schedule_timeout(timeout);
+			lock_sock(sk);
+
+			if (signal_pending(current)) {
+				ret = sock_intr_errno(timeout);
+				break;
+			} else if (timeout == 0) {
+				ret = -EAGAIN;
+				break;
+			}
+
+			prepare_to_wait(sk_sleep(sk), &wait,
+					TASK_INTERRUPTIBLE);
+		}
+	}
+
+	if (sk->sk_err)
+		ret = -sk->sk_err;
+	else if (sk->sk_shutdown & RCV_SHUTDOWN)
+		ret = 0;
+
+	if (copied > 0) {
+		ret = copied;
+
+		/* If the other side has shutdown for sending and there
+		 * is nothing more to read, then we modify the socket
+		 * state.
+		 */
+		if ((hvsk->peer_shutdown & SEND_SHUTDOWN) &&
+		    hvsk->recv.data_len == 0) {
+			get_ringbuffer_rw_status(channel, &can_read, NULL);
+			if (!can_read) {
+				sk->sk_state = SS_UNCONNECTED;
+				sock_set_flag(sk, SOCK_DONE);
+				sk->sk_state_change(sk);
+			}
+		}
+	}
+out_wait:
+	finish_wait(sk_sleep(sk), &wait);
+out:
+	release_sock(sk);
+	return ret;
+}
+
+static const struct proto_ops hvsock_ops = {
+	.family = PF_HYPERV,
+	.owner = THIS_MODULE,
+	.release = hvsock_release,
+	.bind = hvsock_bind,
+	.connect = hvsock_connect,
+	.socketpair = sock_no_socketpair,
+	.accept = hvsock_accept,
+	.getname = hvsock_getname,
+	.poll = hvsock_poll,
+	.ioctl = sock_no_ioctl,
+	.listen = hvsock_listen,
+	.shutdown = hvsock_shutdown,
+	.setsockopt = hvsock_setsockopt,
+	.getsockopt = hvsock_getsockopt,
+	.sendmsg = hvsock_sendmsg,
+	.recvmsg = hvsock_recvmsg,
+	.mmap = sock_no_mmap,
+	.sendpage = sock_no_sendpage,
+};
+
+static int hvsock_create(struct net *net, struct socket *sock,
+			 int protocol, int kern)
+{
+	if (!capable(CAP_SYS_ADMIN) && !capable(CAP_NET_ADMIN))
+		return -EPERM;
+
+	if (protocol != 0 && protocol != SHV_PROTO_RAW)
+		return -EPROTONOSUPPORT;
+
+	switch (sock->type) {
+	case SOCK_STREAM:
+		sock->ops = &hvsock_ops;
+		break;
+	default:
+		return -ESOCKTNOSUPPORT;
+	}
+
+	sock->state = SS_UNCONNECTED;
+
+	return __hvsock_create(net, sock, GFP_KERNEL, 0) ? 0 : -ENOMEM;
+}
+
+static const struct net_proto_family hvsock_family_ops = {
+	.family = AF_HYPERV,
+	.create = hvsock_create,
+	.owner = THIS_MODULE,
+};
+
+static int hvsock_probe(struct hv_device *hdev,
+			const struct hv_vmbus_device_id *dev_id)
+{
+	struct vmbus_channel *channel = hdev->channel;
+
+	/* We ignore the error return code to suppress the unnecessary
+	 * error message in vmbus_probe(): on error the host will rescind
+	 * the offer in 30 seconds and we can do cleanup at that time.
+	 */
+	(void)hvsock_open_connection(channel);
+
+	return 0;
+}
+
+static int hvsock_remove(struct hv_device *hdev)
+{
+	struct vmbus_channel *channel = hdev->channel;
+
+	vmbus_close(channel);
+
+	return 0;
+}
+
+/* It's not really used. See vmbus_match() and vmbus_probe(). */
+static const struct hv_vmbus_device_id id_table[] = {
+	{},
+};
+
+static struct hv_driver hvsock_drv = {
+	.name		= "hv_sock",
+	.hvsock		= true,
+	.id_table	= id_table,
+	.probe		= hvsock_probe,
+	.remove		= hvsock_remove,
+};
+
+static int __init hvsock_init(void)
+{
+	int ret;
+
+	/* Hyper-V Sockets requires at least VMBus 4.0 */
+	if ((vmbus_proto_version >> 16) < 4) {
+		pr_err("failed to load: VMBus 4 or later is required\n");
+		return -ENODEV;
+	}
+
+	ret = vmbus_driver_register(&hvsock_drv);
+	if (ret) {
+		pr_err("failed to register hv_sock driver\n");
+		return ret;
+	}
+
+	ret = proto_register(&hvsock_proto, 0);
+	if (ret) {
+		pr_err("failed to register protocol\n");
+		goto unreg_hvsock_drv;
+	}
+
+	ret = sock_register(&hvsock_family_ops);
+	if (ret) {
+		pr_err("failed to register address family\n");
+		goto unreg_proto;
+	}
+
+	return 0;
+
+unreg_proto:
+	proto_unregister(&hvsock_proto);
+unreg_hvsock_drv:
+	vmbus_driver_unregister(&hvsock_drv);
+	return ret;
+}
+
+static void __exit hvsock_exit(void)
+{
+	sock_unregister(AF_HYPERV);
+	proto_unregister(&hvsock_proto);
+	vmbus_driver_unregister(&hvsock_drv);
+}
+
+module_init(hvsock_init);
+module_exit(hvsock_exit);
+
+MODULE_DESCRIPTION("Hyper-V Sockets");
+MODULE_LICENSE("Dual BSD/GPL");
-- 
2.1.0