// SPDX-License-Identifier: GPL-2.0-only
/*
 * Kernel/userspace transport abstraction for Hyper-V util driver.
 *
 * Copyright (C) 2015, Vitaly Kuznetsov <vkuznets@redhat.com>
 */

#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 LIST_HEAD(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("%s: spurious message received!\n", __func__);
                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("%s: unexpected netlink message!\n", __func__);
        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_obj(*hvt);
        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);
}