/******************************************************************************
 * xenbus_comms.c
 *
 * Low level code to talks to Xen Store: ringbuffer and event channel.
 *
 * Copyright (C) 2005 Rusty Russell, IBM Corporation
 *
 * 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; or, when distributed
 * separately from the Linux kernel or incorporated into other
 * software packages, subject to the following license:
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this source file (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include <linux/wait.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/err.h>
#include <xen/xenbus.h>
#include <asm/xen/hypervisor.h>
#include <xen/events.h>
#include <xen/page.h>
#include "xenbus_comms.h"

static int xenbus_irq;

static DECLARE_WORK(probe_work, xenbus_probe);

static DECLARE_WAIT_QUEUE_HEAD(xb_waitq);

static irqreturn_t wake_waiting(int irq, void *unused)
{
        if (unlikely(xenstored_ready == 0)) {
                xenstored_ready = 1;
                schedule_work(&probe_work);
        }

        wake_up(&xb_waitq);
        return IRQ_HANDLED;
}

static int check_indexes(XENSTORE_RING_IDX cons, XENSTORE_RING_IDX prod)
{
        return ((prod - cons) <= XENSTORE_RING_SIZE);
}

static void *get_output_chunk(XENSTORE_RING_IDX cons,
                              XENSTORE_RING_IDX prod,
                              char *buf, uint32_t *len)
{
        *len = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(prod);
        if ((XENSTORE_RING_SIZE - (prod - cons)) < *len)
                *len = XENSTORE_RING_SIZE - (prod - cons);
        return buf + MASK_XENSTORE_IDX(prod);
}

static const void *get_input_chunk(XENSTORE_RING_IDX cons,
                                   XENSTORE_RING_IDX prod,
                                   const char *buf, uint32_t *len)
{
        *len = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(cons);
        if ((prod - cons) < *len)
                *len = prod - cons;
        return buf + MASK_XENSTORE_IDX(cons);
}

/**
 * xb_write - low level write
 * @data: buffer to send
 * @len: length of buffer
 *
 * Returns 0 on success, error otherwise.
 */
int xb_write(const void *data, unsigned len)
{
        struct xenstore_domain_interface *intf = xen_store_interface;
        XENSTORE_RING_IDX cons, prod;
        int rc;

        while (len != 0) {
                void *dst;
                unsigned int avail;

                rc = wait_event_interruptible(
                        xb_waitq,
                        (intf->req_prod - intf->req_cons) !=
                        XENSTORE_RING_SIZE);
                if (rc < 0)
                        return rc;

                /* Read indexes, then verify. */
                cons = intf->req_cons;
                prod = intf->req_prod;
                if (!check_indexes(cons, prod)) {
                        intf->req_cons = intf->req_prod = 0;
                        return -EIO;
                }

                dst = get_output_chunk(cons, prod, intf->req, &avail);
                if (avail == 0)
                        continue;
                if (avail > len)
                        avail = len;

                /* Must write data /after/ reading the consumer index. */
                mb();

                memcpy(dst, data, avail);
                data += avail;
                len -= avail;

                /* Other side must not see new producer until data is there. */
                wmb();
                intf->req_prod += avail;

                /* Implies mb(): other side will see the updated producer. */
                notify_remote_via_evtchn(xen_store_evtchn);
        }

        return 0;
}

int xb_data_to_read(void)
{
        struct xenstore_domain_interface *intf = xen_store_interface;
        return (intf->rsp_cons != intf->rsp_prod);
}

int xb_wait_for_data_to_read(void)
{
        return wait_event_interruptible(xb_waitq, xb_data_to_read());
}

int xb_read(void *data, unsigned len)
{
        struct xenstore_domain_interface *intf = xen_store_interface;
        XENSTORE_RING_IDX cons, prod;
        int rc;

        while (len != 0) {
                unsigned int avail;
                const char *src;

                rc = xb_wait_for_data_to_read();
                if (rc < 0)
                        return rc;

                /* Read indexes, then verify. */
                cons = intf->rsp_cons;
                prod = intf->rsp_prod;
                if (!check_indexes(cons, prod)) {
                        intf->rsp_cons = intf->rsp_prod = 0;
                        return -EIO;
                }

                src = get_input_chunk(cons, prod, intf->rsp, &avail);
                if (avail == 0)
                        continue;
                if (avail > len)
                        avail = len;

                /* Must read data /after/ reading the producer index. */
                rmb();

                memcpy(data, src, avail);
                data += avail;
                len -= avail;

                /* Other side must not see free space until we've copied out */
                mb();
                intf->rsp_cons += avail;

                pr_debug("Finished read of %i bytes (%i to go)\n", avail, len);

                /* Implies mb(): other side will see the updated consumer. */
                notify_remote_via_evtchn(xen_store_evtchn);
        }

        return 0;
}

/**
 * xb_init_comms - Set up interrupt handler off store event channel.
 */
int xb_init_comms(void)
{
        struct xenstore_domain_interface *intf = xen_store_interface;

        if (intf->req_prod != intf->req_cons)
                printk(KERN_ERR "XENBUS request ring is not quiescent "
                       "(%08x:%08x)!\n", intf->req_cons, intf->req_prod);

        if (intf->rsp_prod != intf->rsp_cons) {
                printk(KERN_WARNING "XENBUS response ring is not quiescent "
                       "(%08x:%08x): fixing up\n",
                       intf->rsp_cons, intf->rsp_prod);
                intf->rsp_cons = intf->rsp_prod;
        }

        if (xenbus_irq) {
                /* Already have an irq; assume we're resuming */
                rebind_evtchn_irq(xen_store_evtchn, xenbus_irq);
        } else {
                int err;
                err = bind_evtchn_to_irqhandler(xen_store_evtchn, wake_waiting,
                                                0, "xenbus", &xb_waitq);
                if (err <= 0) {
                        printk(KERN_ERR "XENBUS request irq failed %i\n", err);
                        return err;
                }

                xenbus_irq = err;
        }

        return 0;
}