/*
 * Kernel/userspace transport abstraction for Hyper-V util driver.
 *
 * Copyright (C) 2015, Vitaly Kuznetsov <vkuznets@redhat.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.
 *
 */

#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/poll.h>

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

static DEFINE_SPINLOCK(hvt_list_lock);
static struct list_head hvt_list = LIST_HEAD_INIT(hvt_list);

static void hvt_reset(struct hvutil_transport *hvt)
{
	kfree(hvt->outmsg);
	hvt->outmsg = NULL;
	hvt->outmsg_len = 0;
	if (hvt->on_reset)
		hvt->on_reset();
}

static ssize_t hvt_op_read(struct file *file, char __user *buf,
			   size_t count, loff_t *ppos)
{
	struct hvutil_transport *hvt;
	int ret;

	hvt = container_of(file->f_op, struct hvutil_transport, fops);

	if (wait_event_interruptible(hvt->outmsg_q, hvt->outmsg_len > 0 ||
				     hvt->mode != HVUTIL_TRANSPORT_CHARDEV))
		return -EINTR;

	mutex_lock(&hvt->lock);

	if (hvt->mode == HVUTIL_TRANSPORT_DESTROY) {
		ret = -EBADF;
		goto out_unlock;
	}

	if (!hvt->outmsg) {
		ret = -EAGAIN;
		goto out_unlock;
	}

	if (count < hvt->outmsg_len) {
		ret = -EINVAL;
		goto out_unlock;
	}

	if (!copy_to_user(buf, hvt->outmsg, hvt->outmsg_len))
		ret = hvt->outmsg_len;
	else
		ret = -EFAULT;

	kfree(hvt->outmsg);
	hvt->outmsg = NULL;
	hvt->outmsg_len = 0;

	if (hvt->on_read)
		hvt->on_read();
	hvt->on_read = NULL;

out_unlock:
	mutex_unlock(&hvt->lock);
	return ret;
}

static ssize_t hvt_op_write(struct file *file, const char __user *buf,
			    size_t count, loff_t *ppos)
{
	struct hvutil_transport *hvt;
	u8 *inmsg;
	int ret;

	hvt = container_of(file->f_op, struct hvutil_transport, fops);

	inmsg = memdup_user(buf, count);
	if (IS_ERR(inmsg))
		return PTR_ERR(inmsg);

	if (hvt->mode == HVUTIL_TRANSPORT_DESTROY)
		ret = -EBADF;
	else
		ret = hvt->on_msg(inmsg, count);

	kfree(inmsg);

	return ret ? ret : count;
}

static __poll_t hvt_op_poll(struct file *file, poll_table *wait)
{
	struct hvutil_transport *hvt;

	hvt = container_of(file->f_op, struct hvutil_transport, fops);

	poll_wait(file, &hvt->outmsg_q, wait);

	if (hvt->mode == HVUTIL_TRANSPORT_DESTROY)
		return EPOLLERR | EPOLLHUP;

	if (hvt->outmsg_len > 0)
		return EPOLLIN | EPOLLRDNORM;

	return 0;
}

static int hvt_op_open(struct inode *inode, struct file *file)
{
	struct hvutil_transport *hvt;
	int ret = 0;
	bool issue_reset = false;

	hvt = container_of(file->f_op, struct hvutil_transport, fops);

	mutex_lock(&hvt->lock);

	if (hvt->mode == HVUTIL_TRANSPORT_DESTROY) {
		ret = -EBADF;
	} else if (hvt->mode == HVUTIL_TRANSPORT_INIT) {
		/*
		 * Switching to CHARDEV mode. We switch bach to INIT when
		 * device gets released.
		 */
		hvt->mode = HVUTIL_TRANSPORT_CHARDEV;
	}
	else if (hvt->mode == HVUTIL_TRANSPORT_NETLINK) {
		/*
		 * We're switching from netlink communication to using char
		 * device. Issue the reset first.
		 */
		issue_reset = true;
		hvt->mode = HVUTIL_TRANSPORT_CHARDEV;
	} else {
		ret = -EBUSY;
	}

	if (issue_reset)
		hvt_reset(hvt);

	mutex_unlock(&hvt->lock);

	return ret;
}

static void hvt_transport_free(struct hvutil_transport *hvt)
{
	misc_deregister(&hvt->mdev);
	kfree(hvt->outmsg);
	kfree(hvt);
}

static int hvt_op_release(struct inode *inode, struct file *file)
{
	struct hvutil_transport *hvt;
	int mode_old;

	hvt = container_of(file->f_op, struct hvutil_transport, fops);

	mutex_lock(&hvt->lock);
	mode_old = hvt->mode;
	if (hvt->mode != HVUTIL_TRANSPORT_DESTROY)
		hvt->mode = HVUTIL_TRANSPORT_INIT;
	/*
	 * Cleanup message buffers to avoid spurious messages when the daemon
	 * connects back.
	 */
	hvt_reset(hvt);

	if (mode_old == HVUTIL_TRANSPORT_DESTROY)
		complete(&hvt->release);

	mutex_unlock(&hvt->lock);

	return 0;
}

static void hvt_cn_callback(struct cn_msg *msg, struct netlink_skb_parms *nsp)
{
	struct hvutil_transport *hvt, *hvt_found = NULL;

	spin_lock(&hvt_list_lock);
	list_for_each_entry(hvt, &hvt_list, list) {
		if (hvt->cn_id.idx == msg->id.idx &&
		    hvt->cn_id.val == msg->id.val) {
			hvt_found = hvt;
			break;
		}
	}
	spin_unlock(&hvt_list_lock);
	if (!hvt_found) {
		pr_warn("hvt_cn_callback: spurious message received!\n");
		return;
	}

	/*
	 * Switching to NETLINK mode. Switching to CHARDEV happens when someone
	 * opens the device.
	 */
	mutex_lock(&hvt->lock);
	if (hvt->mode == HVUTIL_TRANSPORT_INIT)
		hvt->mode = HVUTIL_TRANSPORT_NETLINK;

	if (hvt->mode == HVUTIL_TRANSPORT_NETLINK)
		hvt_found->on_msg(msg->data, msg->len);
	else
		pr_warn("hvt_cn_callback: unexpected netlink message!\n");
	mutex_unlock(&hvt->lock);
}

int hvutil_transport_send(struct hvutil_transport *hvt, void *msg, int len,
			  void (*on_read_cb)(void))
{
	struct cn_msg *cn_msg;
	int ret = 0;

	if (hvt->mode == HVUTIL_TRANSPORT_INIT ||
	    hvt->mode == HVUTIL_TRANSPORT_DESTROY) {
		return -EINVAL;
	} else if (hvt->mode == HVUTIL_TRANSPORT_NETLINK) {
		cn_msg = kzalloc(sizeof(*cn_msg) + len, GFP_ATOMIC);
		if (!cn_msg)
			return -ENOMEM;
		cn_msg->id.idx = hvt->cn_id.idx;
		cn_msg->id.val = hvt->cn_id.val;
		cn_msg->len = len;
		memcpy(cn_msg->data, msg, len);
		ret = cn_netlink_send(cn_msg, 0, 0, GFP_ATOMIC);
		kfree(cn_msg);
		/*
		 * We don't know when netlink messages are delivered but unlike
		 * in CHARDEV mode we're not blocked and we can send next
		 * messages right away.
		 */
		if (on_read_cb)
			on_read_cb();
		return ret;
	}
	/* HVUTIL_TRANSPORT_CHARDEV */
	mutex_lock(&hvt->lock);
	if (hvt->mode != HVUTIL_TRANSPORT_CHARDEV) {
		ret = -EINVAL;
		goto out_unlock;
	}

	if (hvt->outmsg) {
		/* Previous message wasn't received */
		ret = -EFAULT;
		goto out_unlock;
	}
	hvt->outmsg = kzalloc(len, GFP_KERNEL);
	if (hvt->outmsg) {
		memcpy(hvt->outmsg, msg, len);
		hvt->outmsg_len = len;
		hvt->on_read = on_read_cb;
		wake_up_interruptible(&hvt->outmsg_q);
	} else
		ret = -ENOMEM;
out_unlock:
	mutex_unlock(&hvt->lock);
	return ret;
}

struct hvutil_transport *hvutil_transport_init(const char *name,
					       u32 cn_idx, u32 cn_val,
					       int (*on_msg)(void *, int),
					       void (*on_reset)(void))
{
	struct hvutil_transport *hvt;

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

	hvt->cn_id.idx = cn_idx;
	hvt->cn_id.val = cn_val;

	hvt->mdev.minor = MISC_DYNAMIC_MINOR;
	hvt->mdev.name = name;

	hvt->fops.owner = THIS_MODULE;
	hvt->fops.read = hvt_op_read;
	hvt->fops.write = hvt_op_write;
	hvt->fops.poll = hvt_op_poll;
	hvt->fops.open = hvt_op_open;
	hvt->fops.release = hvt_op_release;

	hvt->mdev.fops = &hvt->fops;

	init_waitqueue_head(&hvt->outmsg_q);
	mutex_init(&hvt->lock);
	init_completion(&hvt->release);

	spin_lock(&hvt_list_lock);
	list_add(&hvt->list, &hvt_list);
	spin_unlock(&hvt_list_lock);

	hvt->on_msg = on_msg;
	hvt->on_reset = on_reset;

	if (misc_register(&hvt->mdev))
		goto err_free_hvt;

	/* Use cn_id.idx/cn_id.val to determine if we need to setup netlink */
	if (hvt->cn_id.idx > 0 && hvt->cn_id.val > 0 &&
	    cn_add_callback(&hvt->cn_id, name, hvt_cn_callback))
		goto err_free_hvt;

	return hvt;

err_free_hvt:
	spin_lock(&hvt_list_lock);
	list_del(&hvt->list);
	spin_unlock(&hvt_list_lock);
	kfree(hvt);
	return NULL;
}

void hvutil_transport_destroy(struct hvutil_transport *hvt)
{
	int mode_old;

	mutex_lock(&hvt->lock);
	mode_old = hvt->mode;
	hvt->mode = HVUTIL_TRANSPORT_DESTROY;
	wake_up_interruptible(&hvt->outmsg_q);
	mutex_unlock(&hvt->lock);

	/*
	 * In case we were in 'chardev' mode we still have an open fd so we
	 * have to defer freeing the device. Netlink interface can be freed
	 * now.
	 */
	spin_lock(&hvt_list_lock);
	list_del(&hvt->list);
	spin_unlock(&hvt_list_lock);
	if (hvt->cn_id.idx > 0 && hvt->cn_id.val > 0)
		cn_del_callback(&hvt->cn_id);

	if (mode_old == HVUTIL_TRANSPORT_CHARDEV)
		wait_for_completion(&hvt->release);

	hvt_transport_free(hvt);
}