drivers/hv/hv_snapshot.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * An implementation of host initiated guest snapshot.
  *
  * Copyright (C) 2013, Microsoft, Inc.
  * Author : K. Y. Srinivasan <kys@microsoft.com>
  */
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

 #include <linux/net.h>
 #include <linux/nls.h>
 #include <linux/connector.h>
 #include <linux/workqueue.h>
 #include <linux/hyperv.h>
 #include <asm/hyperv-tlfs.h>

 #include "hyperv_vmbus.h"
 #include "hv_utils_transport.h"

 #define VSS_MAJOR  5
 #define VSS_MINOR  0
 #define VSS_VERSION    (VSS_MAJOR << 16 | VSS_MINOR)

 #define VSS_VER_COUNT 1
 static const int vss_versions[] = {
 	VSS_VERSION
 };

 #define FW_VER_COUNT 1
 static const int fw_versions[] = {
 	UTIL_FW_VERSION
 };

 /* See comment with struct hv_vss_msg regarding the max VMbus packet size */
 #define VSS_MAX_PKT_SIZE (HV_HYP_PAGE_SIZE * 2)

 /*
  * Timeout values are based on expecations from host
  */
 #define VSS_FREEZE_TIMEOUT (15 * 60)

 /*
  * Global state maintained for transaction that is being processed. For a class
  * of integration services, including the "VSS service", the specified protocol
  * is a "request/response" protocol which means that there can only be single
  * outstanding transaction from the host at any given point in time. We use
  * this to simplify memory management in this driver - we cache and process
  * only one message at a time.
  *
  * While the request/response protocol is guaranteed by the host, we further
  * ensure this by serializing packet processing in this driver - we do not
  * read additional packets from the VMBUs until the current packet is fully
  * handled.
  */

 static struct {
 	int state;   /* hvutil_device_state */
 	int recv_len; /* number of bytes received. */
 	struct vmbus_channel *recv_channel; /* chn we got the request */
 	u64 recv_req_id; /* request ID. */
 	struct hv_vss_msg  *msg; /* current message */
 } vss_transaction;


 static void vss_respond_to_host(int error);

 /*
  * This state maintains the version number registered by the daemon.
  */
 static int dm_reg_value;

 static const char vss_devname[] = "vmbus/hv_vss";
 static __u8 *recv_buffer;
 static struct hvutil_transport *hvt;

 static void vss_timeout_func(struct work_struct *dummy);
 static void vss_handle_request(struct work_struct *dummy);

 static DECLARE_DELAYED_WORK(vss_timeout_work, vss_timeout_func);
 static DECLARE_WORK(vss_handle_request_work, vss_handle_request);

 static void vss_poll_wrapper(void *channel)
 {
 	/* Transaction is finished, reset the state here to avoid races. */
 	vss_transaction.state = HVUTIL_READY;
 	tasklet_schedule(&((struct vmbus_channel *)channel)->callback_event);
 }

 /*
  * Callback when data is received from user mode.
  */

 static void vss_timeout_func(struct work_struct *dummy)
 {
 	/*
 	 * Timeout waiting for userspace component to reply happened.
 	 */
 	pr_warn("VSS: timeout waiting for daemon to reply\n");
 	vss_respond_to_host(HV_E_FAIL);

 	hv_poll_channel(vss_transaction.recv_channel, vss_poll_wrapper);
 }

 static void vss_register_done(void)
 {
 	hv_poll_channel(vss_transaction.recv_channel, vss_poll_wrapper);
 	pr_debug("VSS: userspace daemon registered\n");
 }

 static int vss_handle_handshake(struct hv_vss_msg *vss_msg)
 {
 	u32 our_ver = VSS_OP_REGISTER1;

 	switch (vss_msg->vss_hdr.operation) {
 	case VSS_OP_REGISTER:
 		/* Daemon doesn't expect us to reply */
 		dm_reg_value = VSS_OP_REGISTER;
 		break;
 	case VSS_OP_REGISTER1:
 		/* Daemon expects us to reply with our own version */
 		if (hvutil_transport_send(hvt, &our_ver, sizeof(our_ver),
 					  vss_register_done))
 			return -EFAULT;
 		dm_reg_value = VSS_OP_REGISTER1;
 		break;
 	default:
 		return -EINVAL;
 	}
 	pr_info("VSS: userspace daemon ver. %d connected\n", dm_reg_value);
 	return 0;
 }

 static int vss_on_msg(void *msg, int len)
 {
 	struct hv_vss_msg *vss_msg = (struct hv_vss_msg *)msg;

 	if (len != sizeof(*vss_msg)) {
 		pr_debug("VSS: Message size does not match length\n");
 		return -EINVAL;
 	}

 	if (vss_msg->vss_hdr.operation == VSS_OP_REGISTER ||
 	    vss_msg->vss_hdr.operation == VSS_OP_REGISTER1) {
 		/*
 		 * Don't process registration messages if we're in the middle
 		 * of a transaction processing.
 		 */
 		if (vss_transaction.state > HVUTIL_READY) {
 			pr_debug("VSS: Got unexpected registration request\n");
 			return -EINVAL;
 		}

 		return vss_handle_handshake(vss_msg);
 	} else if (vss_transaction.state == HVUTIL_USERSPACE_REQ) {
 		vss_transaction.state = HVUTIL_USERSPACE_RECV;

 		if (vss_msg->vss_hdr.operation == VSS_OP_HOT_BACKUP)
 			vss_transaction.msg->vss_cf.flags =
 				VSS_HBU_NO_AUTO_RECOVERY;

 		if (cancel_delayed_work_sync(&vss_timeout_work)) {
 			vss_respond_to_host(vss_msg->error);
 			/* Transaction is finished, reset the state. */
 			hv_poll_channel(vss_transaction.recv_channel,
 					vss_poll_wrapper);
 		}
 	} else {
 		/* This is a spurious call! */
 		pr_debug("VSS: Transaction not active\n");
 		return -EINVAL;
 	}
 	return 0;
 }

 static void vss_send_op(void)
 {
 	int op = vss_transaction.msg->vss_hdr.operation;
 	int rc;
 	struct hv_vss_msg *vss_msg;

 	/* The transaction state is wrong. */
 	if (vss_transaction.state != HVUTIL_HOSTMSG_RECEIVED) {
 		pr_debug("VSS: Unexpected attempt to send to daemon\n");
 		return;
 	}

 	vss_msg = kzalloc(sizeof(*vss_msg), GFP_KERNEL);
 	if (!vss_msg)
 		return;

 	vss_msg->vss_hdr.operation = op;

 	vss_transaction.state = HVUTIL_USERSPACE_REQ;

 	schedule_delayed_work(&vss_timeout_work, op == VSS_OP_FREEZE ?
 			VSS_FREEZE_TIMEOUT * HZ : HV_UTIL_TIMEOUT * HZ);

 	rc = hvutil_transport_send(hvt, vss_msg, sizeof(*vss_msg), NULL);
 	if (rc) {
 		pr_warn("VSS: failed to communicate to the daemon: %d\n", rc);
 		if (cancel_delayed_work_sync(&vss_timeout_work)) {
 			vss_respond_to_host(HV_E_FAIL);
 			vss_transaction.state = HVUTIL_READY;
 		}
 	}

 	kfree(vss_msg);
 }

 static void vss_handle_request(struct work_struct *dummy)
 {
 	switch (vss_transaction.msg->vss_hdr.operation) {
 	/*
 	 * Initiate a "freeze/thaw" operation in the guest.
 	 * We respond to the host once the operation is complete.
 	 *
 	 * We send the message to the user space daemon and the operation is
 	 * performed in the daemon.
 	 */
 	case VSS_OP_THAW:
 	case VSS_OP_FREEZE:
 	case VSS_OP_HOT_BACKUP:
 		if (vss_transaction.state < HVUTIL_READY) {
 			/* Userspace is not registered yet */
 			pr_debug("VSS: Not ready for request.\n");
 			vss_respond_to_host(HV_E_FAIL);
 			return;
 		}

 		pr_debug("VSS: Received request for op code: %d\n",
 			vss_transaction.msg->vss_hdr.operation);
 		vss_transaction.state = HVUTIL_HOSTMSG_RECEIVED;
 		vss_send_op();
 		return;
 	case VSS_OP_GET_DM_INFO:
 		vss_transaction.msg->dm_info.flags = 0;
 		break;
 	default:
 		break;
 	}

 	vss_respond_to_host(0);
 	hv_poll_channel(vss_transaction.recv_channel, vss_poll_wrapper);
 }

 /*
  * Send a response back to the host.
  */

 static void
 vss_respond_to_host(int error)
 {
 	struct icmsg_hdr *icmsghdrp;
 	u32	buf_len;
 	struct vmbus_channel *channel;
 	u64	req_id;

 	/*
 	 * Copy the global state for completing the transaction. Note that
 	 * only one transaction can be active at a time.
 	 */

 	buf_len = vss_transaction.recv_len;
 	channel = vss_transaction.recv_channel;
 	req_id = vss_transaction.recv_req_id;

 	icmsghdrp = (struct icmsg_hdr *)
 			&recv_buffer[sizeof(struct vmbuspipe_hdr)];

 	if (channel->onchannel_callback == NULL)
 		/*
 		 * We have raced with util driver being unloaded;
 		 * silently return.
 		 */
 		return;

 	icmsghdrp->status = error;

 	icmsghdrp->icflags = ICMSGHDRFLAG_TRANSACTION | ICMSGHDRFLAG_RESPONSE;

 	vmbus_sendpacket(channel, recv_buffer, buf_len, req_id,
 				VM_PKT_DATA_INBAND, 0);

 }

 /*
  * This callback is invoked when we get a VSS message from the host.
  * The host ensures that only one VSS transaction can be active at a time.
  */

 void hv_vss_onchannelcallback(void *context)
 {
 	struct vmbus_channel *channel = context;
 	u32 recvlen;
 	u64 requestid;
 	struct hv_vss_msg *vss_msg;
 	int vss_srv_version;

 	struct icmsg_hdr *icmsghdrp;

 	if (vss_transaction.state > HVUTIL_READY)
 		return;

 	if (vmbus_recvpacket(channel, recv_buffer, VSS_MAX_PKT_SIZE, &recvlen, &requestid)) {
 		pr_err_ratelimited("VSS request received. Could not read into recv buf\n");
 		return;
 	}

 	if (!recvlen)
 		return;

 	/* Ensure recvlen is big enough to read header data */
 	if (recvlen < ICMSG_HDR) {
 		pr_err_ratelimited("VSS request received. Packet length too small: %d\n",
 				   recvlen);
 		return;
 	}

 	icmsghdrp = (struct icmsg_hdr *)&recv_buffer[sizeof(struct vmbuspipe_hdr)];

 	if (icmsghdrp->icmsgtype == ICMSGTYPE_NEGOTIATE) {
 		if (vmbus_prep_negotiate_resp(icmsghdrp,
 				recv_buffer, recvlen,
 				fw_versions, FW_VER_COUNT,
 				vss_versions, VSS_VER_COUNT,
 				NULL, &vss_srv_version)) {

 			pr_info("VSS IC version %d.%d\n",
 				vss_srv_version >> 16,
 				vss_srv_version & 0xFFFF);
 		}
 	} else if (icmsghdrp->icmsgtype == ICMSGTYPE_VSS) {
 		/* Ensure recvlen is big enough to contain hv_vss_msg */
 		if (recvlen < ICMSG_HDR + sizeof(struct hv_vss_msg)) {
 			pr_err_ratelimited("Invalid VSS msg. Packet length too small: %u\n",
 					   recvlen);
 			return;
 		}
 		vss_msg = (struct hv_vss_msg *)&recv_buffer[ICMSG_HDR];

 		/*
 		 * Stash away this global state for completing the
 		 * transaction; note transactions are serialized.
 		 */

 		vss_transaction.recv_len = recvlen;
 		vss_transaction.recv_req_id = requestid;
 		vss_transaction.msg = (struct hv_vss_msg *)vss_msg;

 		schedule_work(&vss_handle_request_work);
 		return;
 	} else {
 		pr_err_ratelimited("VSS request received. Invalid msg type: %d\n",
 				   icmsghdrp->icmsgtype);
 		return;
 	}

 	icmsghdrp->icflags = ICMSGHDRFLAG_TRANSACTION |
 		ICMSGHDRFLAG_RESPONSE;
 	vmbus_sendpacket(channel, recv_buffer, recvlen, requestid,
 			 VM_PKT_DATA_INBAND, 0);
 }

 static void vss_on_reset(void)
 {
 	if (cancel_delayed_work_sync(&vss_timeout_work))
 		vss_respond_to_host(HV_E_FAIL);
 	vss_transaction.state = HVUTIL_DEVICE_INIT;
 }

 int
 hv_vss_init(struct hv_util_service *srv)
 {
 	if (vmbus_proto_version < VERSION_WIN8_1) {
 		pr_warn("Integration service 'Backup (volume snapshot)'"
 			" not supported on this host version.\n");
 		return -ENOTSUPP;
 	}
 	recv_buffer = srv->recv_buffer;
 	vss_transaction.recv_channel = srv->channel;
 	vss_transaction.recv_channel->max_pkt_size = VSS_MAX_PKT_SIZE;

 	/*
 	 * When this driver loads, the user level daemon that
 	 * processes the host requests may not yet be running.
 	 * Defer processing channel callbacks until the daemon
 	 * has registered.
 	 */
 	vss_transaction.state = HVUTIL_DEVICE_INIT;

 	hvt = hvutil_transport_init(vss_devname, CN_VSS_IDX, CN_VSS_VAL,
 				    vss_on_msg, vss_on_reset);
 	if (!hvt) {
 		pr_warn("VSS: Failed to initialize transport\n");
 		return -EFAULT;
 	}

 	return 0;
 }

 static void hv_vss_cancel_work(void)
 {
 	cancel_delayed_work_sync(&vss_timeout_work);
 	cancel_work_sync(&vss_handle_request_work);
 }

 int hv_vss_pre_suspend(void)
 {
 	struct vmbus_channel *channel = vss_transaction.recv_channel;
 	struct hv_vss_msg *vss_msg;

 	/*
 	 * Fake a THAW message for the user space daemon in case the daemon
 	 * has frozen the file systems. It doesn't matter if there is already
 	 * a message pending to be delivered to the user space since we force
 	 * vss_transaction.state to be HVUTIL_READY, so the user space daemon's
 	 * write() will fail with EINVAL (see vss_on_msg()), and the daemon
 	 * will reset the device by closing and re-opening it.
 	 */
 	vss_msg = kzalloc(sizeof(*vss_msg), GFP_KERNEL);
 	if (!vss_msg)
 		return -ENOMEM;

 	tasklet_disable(&channel->callback_event);

 	vss_msg->vss_hdr.operation = VSS_OP_THAW;

 	/* Cancel any possible pending work. */
 	hv_vss_cancel_work();

 	/* We don't care about the return value. */
 	hvutil_transport_send(hvt, vss_msg, sizeof(*vss_msg), NULL);

 	kfree(vss_msg);

 	vss_transaction.state = HVUTIL_READY;

 	/* tasklet_enable() will be called in hv_vss_pre_resume(). */
 	return 0;
 }

 int hv_vss_pre_resume(void)
 {
 	struct vmbus_channel *channel = vss_transaction.recv_channel;

 	tasklet_enable(&channel->callback_event);

 	return 0;
 }

 void hv_vss_deinit(void)
 {
 	vss_transaction.state = HVUTIL_DEVICE_DYING;

 	hv_vss_cancel_work();

 	hvutil_transport_destroy(hvt);
 }
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* An implementation of host initiated guest snapshot.
	*
	* Copyright (C) 2013, Microsoft, Inc.
	* Author : K. Y. Srinivasan <kys@microsoft.com>
	*/
	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

	#include <linux/net.h>
	#include <linux/nls.h>
	#include <linux/connector.h>
	#include <linux/workqueue.h>
	#include <linux/hyperv.h>
	#include <asm/hyperv-tlfs.h>

	#include "hyperv_vmbus.h"
	#include "hv_utils_transport.h"

	#define VSS_MAJOR 5
	#define VSS_MINOR 0
	#define VSS_VERSION (VSS_MAJOR << 16 \| VSS_MINOR)

	#define VSS_VER_COUNT 1
	static const int vss_versions[] = {
	VSS_VERSION
	};

	#define FW_VER_COUNT 1
	static const int fw_versions[] = {
	UTIL_FW_VERSION
	};

	/* See comment with struct hv_vss_msg regarding the max VMbus packet size */
	#define VSS_MAX_PKT_SIZE (HV_HYP_PAGE_SIZE * 2)

	/*
	* Timeout values are based on expecations from host
	*/
	#define VSS_FREEZE_TIMEOUT (15 * 60)

	/*
	* Global state maintained for transaction that is being processed. For a class
	* of integration services, including the "VSS service", the specified protocol
	* is a "request/response" protocol which means that there can only be single
	* outstanding transaction from the host at any given point in time. We use
	* this to simplify memory management in this driver - we cache and process
	* only one message at a time.
	*
	* While the request/response protocol is guaranteed by the host, we further
	* ensure this by serializing packet processing in this driver - we do not
	* read additional packets from the VMBUs until the current packet is fully
	* handled.
	*/

	static struct {
	int state; /* hvutil_device_state */
	int recv_len; /* number of bytes received. */
	struct vmbus_channel recv_channel; / chn we got the request */
	u64 recv_req_id; /* request ID. */
	struct hv_vss_msg msg; / current message */
	} vss_transaction;


	static void vss_respond_to_host(int error);

	/*
	* This state maintains the version number registered by the daemon.
	*/
	static int dm_reg_value;

	static const char vss_devname[] = "vmbus/hv_vss";
	static __u8 *recv_buffer;
	static struct hvutil_transport *hvt;

	static void vss_timeout_func(struct work_struct *dummy);
	static void vss_handle_request(struct work_struct *dummy);

	static DECLARE_DELAYED_WORK(vss_timeout_work, vss_timeout_func);
	static DECLARE_WORK(vss_handle_request_work, vss_handle_request);

	static void vss_poll_wrapper(void *channel)
	{
	/* Transaction is finished, reset the state here to avoid races. */
	vss_transaction.state = HVUTIL_READY;
	tasklet_schedule(&((struct vmbus_channel *)channel)->callback_event);
	}

	/*
	* Callback when data is received from user mode.
	*/

	static void vss_timeout_func(struct work_struct *dummy)
	{
	/*
	* Timeout waiting for userspace component to reply happened.
	*/
	pr_warn("VSS: timeout waiting for daemon to reply\n");
	vss_respond_to_host(HV_E_FAIL);

	hv_poll_channel(vss_transaction.recv_channel, vss_poll_wrapper);
	}

	static void vss_register_done(void)
	{
	hv_poll_channel(vss_transaction.recv_channel, vss_poll_wrapper);
	pr_debug("VSS: userspace daemon registered\n");
	}

	static int vss_handle_handshake(struct hv_vss_msg *vss_msg)
	{
	u32 our_ver = VSS_OP_REGISTER1;

	switch (vss_msg->vss_hdr.operation) {
	case VSS_OP_REGISTER:
	/* Daemon doesn't expect us to reply */
	dm_reg_value = VSS_OP_REGISTER;
	break;
	case VSS_OP_REGISTER1:
	/* Daemon expects us to reply with our own version */
	if (hvutil_transport_send(hvt, &our_ver, sizeof(our_ver),
	vss_register_done))
	return -EFAULT;
	dm_reg_value = VSS_OP_REGISTER1;
	break;
	default:
	return -EINVAL;
	}
	pr_info("VSS: userspace daemon ver. %d connected\n", dm_reg_value);
	return 0;
	}

	static int vss_on_msg(void *msg, int len)
	{
	struct hv_vss_msg vss_msg = (struct hv_vss_msg )msg;

	if (len != sizeof(*vss_msg)) {
	pr_debug("VSS: Message size does not match length\n");
	return -EINVAL;
	}

	if (vss_msg->vss_hdr.operation == VSS_OP_REGISTER \|\|
	vss_msg->vss_hdr.operation == VSS_OP_REGISTER1) {
	/*
	* Don't process registration messages if we're in the middle
	* of a transaction processing.
	*/
	if (vss_transaction.state > HVUTIL_READY) {
	pr_debug("VSS: Got unexpected registration request\n");
	return -EINVAL;
	}

	return vss_handle_handshake(vss_msg);
	} else if (vss_transaction.state == HVUTIL_USERSPACE_REQ) {
	vss_transaction.state = HVUTIL_USERSPACE_RECV;

	if (vss_msg->vss_hdr.operation == VSS_OP_HOT_BACKUP)
	vss_transaction.msg->vss_cf.flags =
	VSS_HBU_NO_AUTO_RECOVERY;

	if (cancel_delayed_work_sync(&vss_timeout_work)) {
	vss_respond_to_host(vss_msg->error);
	/* Transaction is finished, reset the state. */
	hv_poll_channel(vss_transaction.recv_channel,
	vss_poll_wrapper);
	}
	} else {
	/* This is a spurious call! */
	pr_debug("VSS: Transaction not active\n");
	return -EINVAL;
	}
	return 0;
	}

	static void vss_send_op(void)
	{
	int op = vss_transaction.msg->vss_hdr.operation;
	int rc;
	struct hv_vss_msg *vss_msg;

	/* The transaction state is wrong. */
	if (vss_transaction.state != HVUTIL_HOSTMSG_RECEIVED) {
	pr_debug("VSS: Unexpected attempt to send to daemon\n");
	return;
	}

	vss_msg = kzalloc(sizeof(*vss_msg), GFP_KERNEL);
	if (!vss_msg)
	return;

	vss_msg->vss_hdr.operation = op;

	vss_transaction.state = HVUTIL_USERSPACE_REQ;

	schedule_delayed_work(&vss_timeout_work, op == VSS_OP_FREEZE ?
	VSS_FREEZE_TIMEOUT * HZ : HV_UTIL_TIMEOUT * HZ);

	rc = hvutil_transport_send(hvt, vss_msg, sizeof(*vss_msg), NULL);
	if (rc) {
	pr_warn("VSS: failed to communicate to the daemon: %d\n", rc);
	if (cancel_delayed_work_sync(&vss_timeout_work)) {
	vss_respond_to_host(HV_E_FAIL);
	vss_transaction.state = HVUTIL_READY;
	}
	}

	kfree(vss_msg);
	}

	static void vss_handle_request(struct work_struct *dummy)
	{
	switch (vss_transaction.msg->vss_hdr.operation) {
	/*
	* Initiate a "freeze/thaw" operation in the guest.
	* We respond to the host once the operation is complete.
	*
	* We send the message to the user space daemon and the operation is
	* performed in the daemon.
	*/
	case VSS_OP_THAW:
	case VSS_OP_FREEZE:
	case VSS_OP_HOT_BACKUP:
	if (vss_transaction.state < HVUTIL_READY) {
	/* Userspace is not registered yet */
	pr_debug("VSS: Not ready for request.\n");
	vss_respond_to_host(HV_E_FAIL);
	return;
	}

	pr_debug("VSS: Received request for op code: %d\n",
	vss_transaction.msg->vss_hdr.operation);
	vss_transaction.state = HVUTIL_HOSTMSG_RECEIVED;
	vss_send_op();
	return;
	case VSS_OP_GET_DM_INFO:
	vss_transaction.msg->dm_info.flags = 0;
	break;
	default:
	break;
	}

	vss_respond_to_host(0);
	hv_poll_channel(vss_transaction.recv_channel, vss_poll_wrapper);
	}

	/*
	* Send a response back to the host.
	*/

	static void
	vss_respond_to_host(int error)
	{
	struct icmsg_hdr *icmsghdrp;
	u32 buf_len;
	struct vmbus_channel *channel;
	u64 req_id;

	/*
	* Copy the global state for completing the transaction. Note that
	* only one transaction can be active at a time.
	*/

	buf_len = vss_transaction.recv_len;
	channel = vss_transaction.recv_channel;
	req_id = vss_transaction.recv_req_id;

	icmsghdrp = (struct icmsg_hdr *)
	&recv_buffer[sizeof(struct vmbuspipe_hdr)];

	if (channel->onchannel_callback == NULL)
	/*
	* We have raced with util driver being unloaded;
	* silently return.
	*/
	return;

	icmsghdrp->status = error;

	icmsghdrp->icflags = ICMSGHDRFLAG_TRANSACTION \| ICMSGHDRFLAG_RESPONSE;

	vmbus_sendpacket(channel, recv_buffer, buf_len, req_id,
	VM_PKT_DATA_INBAND, 0);

	}

	/*
	* This callback is invoked when we get a VSS message from the host.
	* The host ensures that only one VSS transaction can be active at a time.
	*/

	void hv_vss_onchannelcallback(void *context)
	{
	struct vmbus_channel *channel = context;
	u32 recvlen;
	u64 requestid;
	struct hv_vss_msg *vss_msg;
	int vss_srv_version;

	struct icmsg_hdr *icmsghdrp;

	if (vss_transaction.state > HVUTIL_READY)
	return;

	if (vmbus_recvpacket(channel, recv_buffer, VSS_MAX_PKT_SIZE, &recvlen, &requestid)) {
	pr_err_ratelimited("VSS request received. Could not read into recv buf\n");
	return;
	}

	if (!recvlen)
	return;

	/* Ensure recvlen is big enough to read header data */
	if (recvlen < ICMSG_HDR) {
	pr_err_ratelimited("VSS request received. Packet length too small: %d\n",
	recvlen);
	return;
	}

	icmsghdrp = (struct icmsg_hdr *)&recv_buffer[sizeof(struct vmbuspipe_hdr)];

	if (icmsghdrp->icmsgtype == ICMSGTYPE_NEGOTIATE) {
	if (vmbus_prep_negotiate_resp(icmsghdrp,
	recv_buffer, recvlen,
	fw_versions, FW_VER_COUNT,
	vss_versions, VSS_VER_COUNT,
	NULL, &vss_srv_version)) {

	pr_info("VSS IC version %d.%d\n",
	vss_srv_version >> 16,
	vss_srv_version & 0xFFFF);
	}
	} else if (icmsghdrp->icmsgtype == ICMSGTYPE_VSS) {
	/* Ensure recvlen is big enough to contain hv_vss_msg */
	if (recvlen < ICMSG_HDR + sizeof(struct hv_vss_msg)) {
	pr_err_ratelimited("Invalid VSS msg. Packet length too small: %u\n",
	recvlen);
	return;
	}
	vss_msg = (struct hv_vss_msg *)&recv_buffer[ICMSG_HDR];

	/*
	* Stash away this global state for completing the
	* transaction; note transactions are serialized.
	*/

	vss_transaction.recv_len = recvlen;
	vss_transaction.recv_req_id = requestid;
	vss_transaction.msg = (struct hv_vss_msg *)vss_msg;

	schedule_work(&vss_handle_request_work);
	return;
	} else {
	pr_err_ratelimited("VSS request received. Invalid msg type: %d\n",
	icmsghdrp->icmsgtype);
	return;
	}

	icmsghdrp->icflags = ICMSGHDRFLAG_TRANSACTION \|
	ICMSGHDRFLAG_RESPONSE;
	vmbus_sendpacket(channel, recv_buffer, recvlen, requestid,
	VM_PKT_DATA_INBAND, 0);
	}

	static void vss_on_reset(void)
	{
	if (cancel_delayed_work_sync(&vss_timeout_work))
	vss_respond_to_host(HV_E_FAIL);
	vss_transaction.state = HVUTIL_DEVICE_INIT;
	}

	int
	hv_vss_init(struct hv_util_service *srv)
	{
	if (vmbus_proto_version < VERSION_WIN8_1) {
	pr_warn("Integration service 'Backup (volume snapshot)'"
	" not supported on this host version.\n");
	return -ENOTSUPP;
	}
	recv_buffer = srv->recv_buffer;
	vss_transaction.recv_channel = srv->channel;
	vss_transaction.recv_channel->max_pkt_size = VSS_MAX_PKT_SIZE;

	/*
	* When this driver loads, the user level daemon that
	* processes the host requests may not yet be running.
	* Defer processing channel callbacks until the daemon
	* has registered.
	*/
	vss_transaction.state = HVUTIL_DEVICE_INIT;

	hvt = hvutil_transport_init(vss_devname, CN_VSS_IDX, CN_VSS_VAL,
	vss_on_msg, vss_on_reset);
	if (!hvt) {
	pr_warn("VSS: Failed to initialize transport\n");
	return -EFAULT;
	}

	return 0;
	}

	static void hv_vss_cancel_work(void)
	{
	cancel_delayed_work_sync(&vss_timeout_work);
	cancel_work_sync(&vss_handle_request_work);
	}

	int hv_vss_pre_suspend(void)
	{
	struct vmbus_channel *channel = vss_transaction.recv_channel;
	struct hv_vss_msg *vss_msg;

	/*
	* Fake a THAW message for the user space daemon in case the daemon
	* has frozen the file systems. It doesn't matter if there is already
	* a message pending to be delivered to the user space since we force
	* vss_transaction.state to be HVUTIL_READY, so the user space daemon's
	* write() will fail with EINVAL (see vss_on_msg()), and the daemon
	* will reset the device by closing and re-opening it.
	*/
	vss_msg = kzalloc(sizeof(*vss_msg), GFP_KERNEL);
	if (!vss_msg)
	return -ENOMEM;

	tasklet_disable(&channel->callback_event);

	vss_msg->vss_hdr.operation = VSS_OP_THAW;

	/* Cancel any possible pending work. */
	hv_vss_cancel_work();

	/* We don't care about the return value. */
	hvutil_transport_send(hvt, vss_msg, sizeof(*vss_msg), NULL);

	kfree(vss_msg);

	vss_transaction.state = HVUTIL_READY;

	/* tasklet_enable() will be called in hv_vss_pre_resume(). */
	return 0;
	}

	int hv_vss_pre_resume(void)
	{
	struct vmbus_channel *channel = vss_transaction.recv_channel;

	tasklet_enable(&channel->callback_event);

	return 0;
	}

	void hv_vss_deinit(void)
	{
	vss_transaction.state = HVUTIL_DEVICE_DYING;

	hv_vss_cancel_work();

	hvutil_transport_destroy(hvt);
	}