drivers/hv/hv_kvp.c - kernel/msm-4.9 - Gitiles

 /*
  * An implementation of key value pair (KVP) functionality for Linux.
  *
  *
  * Copyright (C) 2010, Novell, Inc.
  * Author : K. Y. Srinivasan <ksrinivasan@novell.com>
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 as published
  * by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful, but
  * WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  * NON INFRINGEMENT.  See the GNU General Public License for more
  * details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  */
 #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>


 /*
  * Global state maintained for transaction that is being processed.
  * Note that only one transaction can be active at any point in time.
  *
  * This state is set when we receive a request from the host; we
  * cleanup this state when the transaction is completed - when we respond
  * to the host with the key value.
  */

 static struct {
 	bool active; /* transaction status - active or not */
 	int recv_len; /* number of bytes received. */
 	struct hv_kvp_msg  *kvp_msg; /* current message */
 	struct vmbus_channel *recv_channel; /* chn we got the request */
 	u64 recv_req_id; /* request ID. */
 	void *kvp_context; /* for the channel callback */
 } kvp_transaction;

 static void kvp_send_key(struct work_struct *dummy);

 #define TIMEOUT_FIRED 1

 static void kvp_respond_to_host(char *key, char *value, int error);
 static void kvp_work_func(struct work_struct *dummy);
 static void kvp_register(void);

 static DECLARE_DELAYED_WORK(kvp_work, kvp_work_func);
 static DECLARE_WORK(kvp_sendkey_work, kvp_send_key);

 static struct cb_id kvp_id = { CN_KVP_IDX, CN_KVP_VAL };
 static const char kvp_name[] = "kvp_kernel_module";
 static u8 *recv_buffer;
 /*
  * Register the kernel component with the user-level daemon.
  * As part of this registration, pass the LIC version number.
  */

 static void
 kvp_register(void)
 {

 	struct cn_msg *msg;
 	struct hv_kvp_msg *kvp_msg;
 	char *version;

 	msg = kzalloc(sizeof(*msg) + sizeof(struct hv_kvp_msg), GFP_ATOMIC);

 	if (msg) {
 		kvp_msg = (struct hv_kvp_msg *)msg->data;
 		version = kvp_msg->body.kvp_register.version;
 		msg->id.idx =  CN_KVP_IDX;
 		msg->id.val = CN_KVP_VAL;

 		kvp_msg->kvp_hdr.operation = KVP_OP_REGISTER;
 		strcpy(version, HV_DRV_VERSION);
 		msg->len = sizeof(struct hv_kvp_msg);
 		cn_netlink_send(msg, 0, GFP_ATOMIC);
 		kfree(msg);
 	}
 }
 static void
 kvp_work_func(struct work_struct *dummy)
 {
 	/*
 	 * If the timer fires, the user-mode component has not responded;
 	 * process the pending transaction.
 	 */
 	kvp_respond_to_host("Unknown key", "Guest timed out", TIMEOUT_FIRED);
 }

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

 static void
 kvp_cn_callback(struct cn_msg *msg, struct netlink_skb_parms *nsp)
 {
 	struct hv_kvp_msg *message;
 	struct hv_kvp_msg_enumerate *data;

 	message = (struct hv_kvp_msg *)msg->data;
 	switch (message->kvp_hdr.operation) {
 	case KVP_OP_REGISTER:
 		pr_info("KVP: user-mode registering done.\n");
 		kvp_register();
 		kvp_transaction.active = false;
 		hv_kvp_onchannelcallback(kvp_transaction.kvp_context);
 		break;

 	default:
 		data = &message->body.kvp_enum_data;
 		/*
 		 * Complete the transaction by forwarding the key value
 		 * to the host. But first, cancel the timeout.
 		 */
 		if (cancel_delayed_work_sync(&kvp_work))
 			kvp_respond_to_host(data->data.key,
 					 data->data.value,
 					!strlen(data->data.key));
 	}
 }

 static void
 kvp_send_key(struct work_struct *dummy)
 {
 	struct cn_msg *msg;
 	struct hv_kvp_msg *message;
 	struct hv_kvp_msg *in_msg;
 	__u8 operation = kvp_transaction.kvp_msg->kvp_hdr.operation;
 	__u8 pool = kvp_transaction.kvp_msg->kvp_hdr.pool;
 	__u32 val32;
 	__u64 val64;

 	msg = kzalloc(sizeof(*msg) + sizeof(struct hv_kvp_msg) , GFP_ATOMIC);
 	if (!msg)
 		return;

 	msg->id.idx =  CN_KVP_IDX;
 	msg->id.val = CN_KVP_VAL;

 	message = (struct hv_kvp_msg *)msg->data;
 	message->kvp_hdr.operation = operation;
 	message->kvp_hdr.pool = pool;
 	in_msg = kvp_transaction.kvp_msg;

 	/*
 	 * The key/value strings sent from the host are encoded in
 	 * in utf16; convert it to utf8 strings.
 	 * The host assures us that the utf16 strings will not exceed
 	 * the max lengths specified. We will however, reserve room
 	 * for the string terminating character - in the utf16s_utf8s()
 	 * function we limit the size of the buffer where the converted
 	 * string is placed to HV_KVP_EXCHANGE_MAX_*_SIZE -1 to gaurantee
 	 * that the strings can be properly terminated!
 	 */

 	switch (message->kvp_hdr.operation) {
 	case KVP_OP_SET:
 		switch (in_msg->body.kvp_set.data.value_type) {
 		case REG_SZ:
 			/*
 			 * The value is a string - utf16 encoding.
 			 */
 			message->body.kvp_set.data.value_size =
 				utf16s_to_utf8s(
 				(wchar_t *)in_msg->body.kvp_set.data.value,
 				in_msg->body.kvp_set.data.value_size,
 				UTF16_LITTLE_ENDIAN,
 				message->body.kvp_set.data.value,
 				HV_KVP_EXCHANGE_MAX_VALUE_SIZE - 1) + 1;
 				break;

 		case REG_U32:
 			/*
 			 * The value is a 32 bit scalar.
 			 * We save this as a utf8 string.
 			 */
 			val32 = in_msg->body.kvp_set.data.value_u32;
 			message->body.kvp_set.data.value_size =
 				sprintf(message->body.kvp_set.data.value,
 					"%d", val32) + 1;
 			break;

 		case REG_U64:
 			/*
 			 * The value is a 64 bit scalar.
 			 * We save this as a utf8 string.
 			 */
 			val64 = in_msg->body.kvp_set.data.value_u64;
 			message->body.kvp_set.data.value_size =
 				sprintf(message->body.kvp_set.data.value,
 					"%llu", val64) + 1;
 			break;

 		}
 	case KVP_OP_GET:
 		message->body.kvp_set.data.key_size =
 			utf16s_to_utf8s(
 			(wchar_t *)in_msg->body.kvp_set.data.key,
 			in_msg->body.kvp_set.data.key_size,
 			UTF16_LITTLE_ENDIAN,
 			message->body.kvp_set.data.key,
 			HV_KVP_EXCHANGE_MAX_KEY_SIZE - 1) + 1;
 			break;

 	case KVP_OP_DELETE:
 		message->body.kvp_delete.key_size =
 			utf16s_to_utf8s(
 			(wchar_t *)in_msg->body.kvp_delete.key,
 			in_msg->body.kvp_delete.key_size,
 			UTF16_LITTLE_ENDIAN,
 			message->body.kvp_delete.key,
 			HV_KVP_EXCHANGE_MAX_KEY_SIZE - 1) + 1;
 			break;

 	case KVP_OP_ENUMERATE:
 		message->body.kvp_enum_data.index =
 			in_msg->body.kvp_enum_data.index;
 			break;
 	}

 	msg->len = sizeof(struct hv_kvp_msg);
 	cn_netlink_send(msg, 0, GFP_ATOMIC);
 	kfree(msg);

 	return;
 }

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

 static void
 kvp_respond_to_host(char *key, char *value, int error)
 {
 	struct hv_kvp_msg  *kvp_msg;
 	struct hv_kvp_exchg_msg_value  *kvp_data;
 	char	*key_name;
 	struct icmsg_hdr *icmsghdrp;
 	int	keylen = 0;
 	int	valuelen = 0;
 	u32	buf_len;
 	struct vmbus_channel *channel;
 	u64	req_id;

 	/*
 	 * If a transaction is not active; log and return.
 	 */

 	if (!kvp_transaction.active) {
 		/*
 		 * This is a spurious call!
 		 */
 		pr_warn("KVP: Transaction not active\n");
 		return;
 	}
 	/*
 	 * Copy the global state for completing the transaction. Note that
 	 * only one transaction can be active at a time.
 	 */

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

 	kvp_transaction.active = false;

 	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;


 	/*
 	 * If the error parameter is set, terminate the host's enumeration
 	 * on this pool.
 	 */
 	if (error) {
 		/*
 		 * Something failed or the we have timedout;
 		 * terminate the current  host-side iteration.
 		 */
 		icmsghdrp->status = HV_S_CONT;
 		goto response_done;
 	}

 	icmsghdrp->status = HV_S_OK;

 	kvp_msg = (struct hv_kvp_msg *)
 			&recv_buffer[sizeof(struct vmbuspipe_hdr) +
 			sizeof(struct icmsg_hdr)];

 	switch (kvp_transaction.kvp_msg->kvp_hdr.operation) {
 	case KVP_OP_GET:
 		kvp_data = &kvp_msg->body.kvp_get.data;
 		goto copy_value;

 	case KVP_OP_SET:
 	case KVP_OP_DELETE:
 		goto response_done;

 	default:
 		break;
 	}

 	kvp_data = &kvp_msg->body.kvp_enum_data.data;
 	key_name = key;

 	/*
 	 * The windows host expects the key/value pair to be encoded
 	 * in utf16. Ensure that the key/value size reported to the host
 	 * will be less than or equal to the MAX size (including the
 	 * terminating character).
 	 */
 	keylen = utf8s_to_utf16s(key_name, strlen(key_name), UTF16_HOST_ENDIAN,
 				(wchar_t *) kvp_data->key,
 				(HV_KVP_EXCHANGE_MAX_KEY_SIZE / 2) - 2);
 	kvp_data->key_size = 2*(keylen + 1); /* utf16 encoding */

 copy_value:
 	valuelen = utf8s_to_utf16s(value, strlen(value), UTF16_HOST_ENDIAN,
 				(wchar_t *) kvp_data->value,
 				(HV_KVP_EXCHANGE_MAX_VALUE_SIZE / 2) - 2);
 	kvp_data->value_size = 2*(valuelen + 1); /* utf16 encoding */

 	/*
 	 * If the utf8s to utf16s conversion failed; notify host
 	 * of the error.
 	 */
 	if ((keylen < 0) || (valuelen < 0))
 		icmsghdrp->status = HV_E_FAIL;

 	kvp_data->value_type = REG_SZ; /* all our values are strings */

 response_done:
 	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 KVP message from the host.
  * The host ensures that only one KVP transaction can be active at a time.
  * KVP implementation in Linux needs to forward the key to a user-mde
  * component to retrive the corresponding value. Consequently, we cannot
  * respond to the host in the conext of this callback. Since the host
  * guarantees that at most only one transaction can be active at a time,
  * we stash away the transaction state in a set of global variables.
  */

 void hv_kvp_onchannelcallback(void *context)
 {
 	struct vmbus_channel *channel = context;
 	u32 recvlen;
 	u64 requestid;

 	struct hv_kvp_msg *kvp_msg;

 	struct icmsg_hdr *icmsghdrp;
 	struct icmsg_negotiate *negop = NULL;

 	if (kvp_transaction.active) {
 		/*
 		 * We will defer processing this callback once
 		 * the current transaction is complete.
 		 */
 		kvp_transaction.kvp_context = context;
 		return;
 	}

 	vmbus_recvpacket(channel, recv_buffer, PAGE_SIZE, &recvlen, &requestid);

 	if (recvlen > 0) {
 		icmsghdrp = (struct icmsg_hdr *)&recv_buffer[
 			sizeof(struct vmbuspipe_hdr)];

 		if (icmsghdrp->icmsgtype == ICMSGTYPE_NEGOTIATE) {
 			vmbus_prep_negotiate_resp(icmsghdrp, negop,
 				 recv_buffer, MAX_SRV_VER, MAX_SRV_VER);
 		} else {
 			kvp_msg = (struct hv_kvp_msg *)&recv_buffer[
 				sizeof(struct vmbuspipe_hdr) +
 				sizeof(struct icmsg_hdr)];

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

 			kvp_transaction.recv_len = recvlen;
 			kvp_transaction.recv_channel = channel;
 			kvp_transaction.recv_req_id = requestid;
 			kvp_transaction.active = true;
 			kvp_transaction.kvp_msg = kvp_msg;

 			/*
 			 * Get the information from the
 			 * user-mode component.
 			 * component. This transaction will be
 			 * completed when we get the value from
 			 * the user-mode component.
 			 * Set a timeout to deal with
 			 * user-mode not responding.
 			 */
 			schedule_work(&kvp_sendkey_work);
 			schedule_delayed_work(&kvp_work, 5*HZ);

 			return;

 		}

 		icmsghdrp->icflags = ICMSGHDRFLAG_TRANSACTION
 			| ICMSGHDRFLAG_RESPONSE;

 		vmbus_sendpacket(channel, recv_buffer,
 				       recvlen, requestid,
 				       VM_PKT_DATA_INBAND, 0);
 	}

 }

 int
 hv_kvp_init(struct hv_util_service *srv)
 {
 	int err;

 	err = cn_add_callback(&kvp_id, kvp_name, kvp_cn_callback);
 	if (err)
 		return err;
 	recv_buffer = srv->recv_buffer;

 	/*
 	 * 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.
 	 */
 	kvp_transaction.active = true;

 	return 0;
 }

 void hv_kvp_deinit(void)
 {
 	cn_del_callback(&kvp_id);
 	cancel_delayed_work_sync(&kvp_work);
 	cancel_work_sync(&kvp_sendkey_work);
 }
	/*
	* An implementation of key value pair (KVP) functionality for Linux.
	*
	*
	* Copyright (C) 2010, Novell, Inc.
	* Author : K. Y. Srinivasan <ksrinivasan@novell.com>
	*
	* This program is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 as published
	* by the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful, but
	* WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
	* NON INFRINGEMENT. See the GNU General Public License for more
	* details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	*/
	#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>



	/*
	* Global state maintained for transaction that is being processed.
	* Note that only one transaction can be active at any point in time.
	*
	* This state is set when we receive a request from the host; we
	* cleanup this state when the transaction is completed - when we respond
	* to the host with the key value.
	*/

	static struct {
	bool active; /* transaction status - active or not */
	int recv_len; /* number of bytes received. */
	struct hv_kvp_msg kvp_msg; / current message */
	struct vmbus_channel recv_channel; / chn we got the request */
	u64 recv_req_id; /* request ID. */
	void kvp_context; / for the channel callback */
	} kvp_transaction;

	static void kvp_send_key(struct work_struct *dummy);

	#define TIMEOUT_FIRED 1

	static void kvp_respond_to_host(char key, char value, int error);
	static void kvp_work_func(struct work_struct *dummy);
	static void kvp_register(void);

	static DECLARE_DELAYED_WORK(kvp_work, kvp_work_func);
	static DECLARE_WORK(kvp_sendkey_work, kvp_send_key);

	static struct cb_id kvp_id = { CN_KVP_IDX, CN_KVP_VAL };
	static const char kvp_name[] = "kvp_kernel_module";
	static u8 *recv_buffer;
	/*
	* Register the kernel component with the user-level daemon.
	* As part of this registration, pass the LIC version number.
	*/

	static void
	kvp_register(void)
	{

	struct cn_msg *msg;
	struct hv_kvp_msg *kvp_msg;
	char *version;

	msg = kzalloc(sizeof(*msg) + sizeof(struct hv_kvp_msg), GFP_ATOMIC);

	if (msg) {
	kvp_msg = (struct hv_kvp_msg *)msg->data;
	version = kvp_msg->body.kvp_register.version;
	msg->id.idx = CN_KVP_IDX;
	msg->id.val = CN_KVP_VAL;

	kvp_msg->kvp_hdr.operation = KVP_OP_REGISTER;
	strcpy(version, HV_DRV_VERSION);
	msg->len = sizeof(struct hv_kvp_msg);
	cn_netlink_send(msg, 0, GFP_ATOMIC);
	kfree(msg);
	}
	}
	static void
	kvp_work_func(struct work_struct *dummy)
	{
	/*
	* If the timer fires, the user-mode component has not responded;
	* process the pending transaction.
	*/
	kvp_respond_to_host("Unknown key", "Guest timed out", TIMEOUT_FIRED);
	}

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

	static void
	kvp_cn_callback(struct cn_msg msg, struct netlink_skb_parms nsp)
	{
	struct hv_kvp_msg *message;
	struct hv_kvp_msg_enumerate *data;

	message = (struct hv_kvp_msg *)msg->data;
	switch (message->kvp_hdr.operation) {
	case KVP_OP_REGISTER:
	pr_info("KVP: user-mode registering done.\n");
	kvp_register();
	kvp_transaction.active = false;
	hv_kvp_onchannelcallback(kvp_transaction.kvp_context);
	break;

	default:
	data = &message->body.kvp_enum_data;
	/*
	* Complete the transaction by forwarding the key value
	* to the host. But first, cancel the timeout.
	*/
	if (cancel_delayed_work_sync(&kvp_work))
	kvp_respond_to_host(data->data.key,
	data->data.value,
	!strlen(data->data.key));
	}
	}

	static void
	kvp_send_key(struct work_struct *dummy)
	{
	struct cn_msg *msg;
	struct hv_kvp_msg *message;
	struct hv_kvp_msg *in_msg;
	__u8 operation = kvp_transaction.kvp_msg->kvp_hdr.operation;
	__u8 pool = kvp_transaction.kvp_msg->kvp_hdr.pool;
	__u32 val32;
	__u64 val64;

	msg = kzalloc(sizeof(*msg) + sizeof(struct hv_kvp_msg) , GFP_ATOMIC);
	if (!msg)
	return;

	msg->id.idx = CN_KVP_IDX;
	msg->id.val = CN_KVP_VAL;

	message = (struct hv_kvp_msg *)msg->data;
	message->kvp_hdr.operation = operation;
	message->kvp_hdr.pool = pool;
	in_msg = kvp_transaction.kvp_msg;

	/*
	* The key/value strings sent from the host are encoded in
	* in utf16; convert it to utf8 strings.
	* The host assures us that the utf16 strings will not exceed
	* the max lengths specified. We will however, reserve room
	* for the string terminating character - in the utf16s_utf8s()
	* function we limit the size of the buffer where the converted
	* string is placed to HV_KVP_EXCHANGE_MAX_*_SIZE -1 to gaurantee
	* that the strings can be properly terminated!
	*/

	switch (message->kvp_hdr.operation) {
	case KVP_OP_SET:
	switch (in_msg->body.kvp_set.data.value_type) {
	case REG_SZ:
	/*
	* The value is a string - utf16 encoding.
	*/
	message->body.kvp_set.data.value_size =
	utf16s_to_utf8s(
	(wchar_t *)in_msg->body.kvp_set.data.value,
	in_msg->body.kvp_set.data.value_size,
	UTF16_LITTLE_ENDIAN,
	message->body.kvp_set.data.value,
	HV_KVP_EXCHANGE_MAX_VALUE_SIZE - 1) + 1;
	break;

	case REG_U32:
	/*
	* The value is a 32 bit scalar.
	* We save this as a utf8 string.
	*/
	val32 = in_msg->body.kvp_set.data.value_u32;
	message->body.kvp_set.data.value_size =
	sprintf(message->body.kvp_set.data.value,
	"%d", val32) + 1;
	break;

	case REG_U64:
	/*
	* The value is a 64 bit scalar.
	* We save this as a utf8 string.
	*/
	val64 = in_msg->body.kvp_set.data.value_u64;
	message->body.kvp_set.data.value_size =
	sprintf(message->body.kvp_set.data.value,
	"%llu", val64) + 1;
	break;

	}
	case KVP_OP_GET:
	message->body.kvp_set.data.key_size =
	utf16s_to_utf8s(
	(wchar_t *)in_msg->body.kvp_set.data.key,
	in_msg->body.kvp_set.data.key_size,
	UTF16_LITTLE_ENDIAN,
	message->body.kvp_set.data.key,
	HV_KVP_EXCHANGE_MAX_KEY_SIZE - 1) + 1;
	break;

	case KVP_OP_DELETE:
	message->body.kvp_delete.key_size =
	utf16s_to_utf8s(
	(wchar_t *)in_msg->body.kvp_delete.key,
	in_msg->body.kvp_delete.key_size,
	UTF16_LITTLE_ENDIAN,
	message->body.kvp_delete.key,
	HV_KVP_EXCHANGE_MAX_KEY_SIZE - 1) + 1;
	break;

	case KVP_OP_ENUMERATE:
	message->body.kvp_enum_data.index =
	in_msg->body.kvp_enum_data.index;
	break;
	}

	msg->len = sizeof(struct hv_kvp_msg);
	cn_netlink_send(msg, 0, GFP_ATOMIC);
	kfree(msg);

	return;
	}

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

	static void
	kvp_respond_to_host(char key, char value, int error)
	{
	struct hv_kvp_msg *kvp_msg;
	struct hv_kvp_exchg_msg_value *kvp_data;
	char *key_name;
	struct icmsg_hdr *icmsghdrp;
	int keylen = 0;
	int valuelen = 0;
	u32 buf_len;
	struct vmbus_channel *channel;
	u64 req_id;

	/*
	* If a transaction is not active; log and return.
	*/

	if (!kvp_transaction.active) {
	/*
	* This is a spurious call!
	*/
	pr_warn("KVP: Transaction not active\n");
	return;
	}
	/*
	* Copy the global state for completing the transaction. Note that
	* only one transaction can be active at a time.
	*/

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

	kvp_transaction.active = false;

	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;


	/*
	* If the error parameter is set, terminate the host's enumeration
	* on this pool.
	*/
	if (error) {
	/*
	* Something failed or the we have timedout;
	* terminate the current host-side iteration.
	*/
	icmsghdrp->status = HV_S_CONT;
	goto response_done;
	}

	icmsghdrp->status = HV_S_OK;

	kvp_msg = (struct hv_kvp_msg *)
	&recv_buffer[sizeof(struct vmbuspipe_hdr) +
	sizeof(struct icmsg_hdr)];

	switch (kvp_transaction.kvp_msg->kvp_hdr.operation) {
	case KVP_OP_GET:
	kvp_data = &kvp_msg->body.kvp_get.data;
	goto copy_value;

	case KVP_OP_SET:
	case KVP_OP_DELETE:
	goto response_done;

	default:
	break;
	}

	kvp_data = &kvp_msg->body.kvp_enum_data.data;
	key_name = key;

	/*
	* The windows host expects the key/value pair to be encoded
	* in utf16. Ensure that the key/value size reported to the host
	* will be less than or equal to the MAX size (including the
	* terminating character).
	*/
	keylen = utf8s_to_utf16s(key_name, strlen(key_name), UTF16_HOST_ENDIAN,
	(wchar_t *) kvp_data->key,
	(HV_KVP_EXCHANGE_MAX_KEY_SIZE / 2) - 2);
	kvp_data->key_size = 2(keylen + 1); / utf16 encoding */

	copy_value:
	valuelen = utf8s_to_utf16s(value, strlen(value), UTF16_HOST_ENDIAN,
	(wchar_t *) kvp_data->value,
	(HV_KVP_EXCHANGE_MAX_VALUE_SIZE / 2) - 2);
	kvp_data->value_size = 2(valuelen + 1); / utf16 encoding */

	/*
	* If the utf8s to utf16s conversion failed; notify host
	* of the error.
	*/
	if ((keylen < 0) \|\| (valuelen < 0))
	icmsghdrp->status = HV_E_FAIL;

	kvp_data->value_type = REG_SZ; /* all our values are strings */

	response_done:
	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 KVP message from the host.
	* The host ensures that only one KVP transaction can be active at a time.
	* KVP implementation in Linux needs to forward the key to a user-mde
	* component to retrive the corresponding value. Consequently, we cannot
	* respond to the host in the conext of this callback. Since the host
	* guarantees that at most only one transaction can be active at a time,
	* we stash away the transaction state in a set of global variables.
	*/

	void hv_kvp_onchannelcallback(void *context)
	{
	struct vmbus_channel *channel = context;
	u32 recvlen;
	u64 requestid;

	struct hv_kvp_msg *kvp_msg;

	struct icmsg_hdr *icmsghdrp;
	struct icmsg_negotiate *negop = NULL;

	if (kvp_transaction.active) {
	/*
	* We will defer processing this callback once
	* the current transaction is complete.
	*/
	kvp_transaction.kvp_context = context;
	return;
	}

	vmbus_recvpacket(channel, recv_buffer, PAGE_SIZE, &recvlen, &requestid);

	if (recvlen > 0) {
	icmsghdrp = (struct icmsg_hdr *)&recv_buffer[
	sizeof(struct vmbuspipe_hdr)];

	if (icmsghdrp->icmsgtype == ICMSGTYPE_NEGOTIATE) {
	vmbus_prep_negotiate_resp(icmsghdrp, negop,
	recv_buffer, MAX_SRV_VER, MAX_SRV_VER);
	} else {
	kvp_msg = (struct hv_kvp_msg *)&recv_buffer[
	sizeof(struct vmbuspipe_hdr) +
	sizeof(struct icmsg_hdr)];

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

	kvp_transaction.recv_len = recvlen;
	kvp_transaction.recv_channel = channel;
	kvp_transaction.recv_req_id = requestid;
	kvp_transaction.active = true;
	kvp_transaction.kvp_msg = kvp_msg;

	/*
	* Get the information from the
	* user-mode component.
	* component. This transaction will be
	* completed when we get the value from
	* the user-mode component.
	* Set a timeout to deal with
	* user-mode not responding.
	*/
	schedule_work(&kvp_sendkey_work);
	schedule_delayed_work(&kvp_work, 5*HZ);

	return;

	}

	icmsghdrp->icflags = ICMSGHDRFLAG_TRANSACTION
	\| ICMSGHDRFLAG_RESPONSE;

	vmbus_sendpacket(channel, recv_buffer,
	recvlen, requestid,
	VM_PKT_DATA_INBAND, 0);
	}

	}

	int
	hv_kvp_init(struct hv_util_service *srv)
	{
	int err;

	err = cn_add_callback(&kvp_id, kvp_name, kvp_cn_callback);
	if (err)
	return err;
	recv_buffer = srv->recv_buffer;

	/*
	* 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.
	*/
	kvp_transaction.active = true;

	return 0;
	}

	void hv_kvp_deinit(void)
	{
	cn_del_callback(&kvp_id);
	cancel_delayed_work_sync(&kvp_work);
	cancel_work_sync(&kvp_sendkey_work);
	}