/*
 * An implementation of host initiated guest snapshot.
 *
 *
 * Copyright (C) 2013, Microsoft, Inc.
 * Author : K. Y. Srinivasan <kys@microsoft.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.
 *
 */
#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 "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
};

/*
 * 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;
        hv_vss_onchannelcallback(channel);
}

/*
 * 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;

        vmbus_recvpacket(channel, recv_buffer, PAGE_SIZE * 2, &recvlen,
                         &requestid);

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

                if (icmsghdrp->icmsgtype == ICMSGTYPE_NEGOTIATE) {
                        if (vmbus_prep_negotiate_resp(icmsghdrp,
                                 recv_buffer, 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 {
                        vss_msg = (struct hv_vss_msg *)&recv_buffer[
                                sizeof(struct vmbuspipe_hdr) +
                                sizeof(struct 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;
                }

                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;

        /*
         * 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;
}

void hv_vss_deinit(void)
{
        vss_transaction.state = HVUTIL_DEVICE_DYING;
        cancel_delayed_work_sync(&vss_timeout_work);
        cancel_work_sync(&vss_handle_request_work);
        hvutil_transport_destroy(hvt);
}