/*
 * linux/fs/9p/trans_xen
 *
 * Xen transport layer.
 *
 * Copyright (C) 2017 by Stefano Stabellini <stefano@aporeto.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; 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 <xen/events.h>
#include <xen/grant_table.h>
#include <xen/xen.h>
#include <xen/xenbus.h>
#include <xen/interface/io/9pfs.h>

#include <linux/module.h>
#include <linux/spinlock.h>
#include <net/9p/9p.h>
#include <net/9p/client.h>
#include <net/9p/transport.h>

#define XEN_9PFS_NUM_RINGS 2
#define XEN_9PFS_RING_ORDER 9
#define XEN_9PFS_RING_SIZE(ring)  XEN_FLEX_RING_SIZE(ring->intf->ring_order)

struct xen_9pfs_header {
        uint32_t size;
        uint8_t id;
        uint16_t tag;

        /* uint8_t sdata[]; */
} __attribute__((packed));

/* One per ring, more than one per 9pfs share */
struct xen_9pfs_dataring {
        struct xen_9pfs_front_priv *priv;

        struct xen_9pfs_data_intf *intf;
        grant_ref_t ref;
        int evtchn;
        int irq;
        /* protect a ring from concurrent accesses */
        spinlock_t lock;

        struct xen_9pfs_data data;
        wait_queue_head_t wq;
        struct work_struct work;
};

/* One per 9pfs share */
struct xen_9pfs_front_priv {
        struct list_head list;
        struct xenbus_device *dev;
        char *tag;
        struct p9_client *client;

        int num_rings;
        struct xen_9pfs_dataring *rings;
};

static LIST_HEAD(xen_9pfs_devs);
static DEFINE_RWLOCK(xen_9pfs_lock);

/* We don't currently allow canceling of requests */
static int p9_xen_cancel(struct p9_client *client, struct p9_req_t *req)
{
        return 1;
}

static int p9_xen_create(struct p9_client *client, const char *addr, char *args)
{
        struct xen_9pfs_front_priv *priv;

        if (addr == NULL)
                return -EINVAL;

        read_lock(&xen_9pfs_lock);
        list_for_each_entry(priv, &xen_9pfs_devs, list) {
                if (!strcmp(priv->tag, addr)) {
                        priv->client = client;
                        read_unlock(&xen_9pfs_lock);
                        return 0;
                }
        }
        read_unlock(&xen_9pfs_lock);
        return -EINVAL;
}

static void p9_xen_close(struct p9_client *client)
{
        struct xen_9pfs_front_priv *priv;

        read_lock(&xen_9pfs_lock);
        list_for_each_entry(priv, &xen_9pfs_devs, list) {
                if (priv->client == client) {
                        priv->client = NULL;
                        read_unlock(&xen_9pfs_lock);
                        return;
                }
        }
        read_unlock(&xen_9pfs_lock);
}

static bool p9_xen_write_todo(struct xen_9pfs_dataring *ring, RING_IDX size)
{
        RING_IDX cons, prod;

        cons = ring->intf->out_cons;
        prod = ring->intf->out_prod;
        virt_mb();

        return XEN_9PFS_RING_SIZE(ring) -
                xen_9pfs_queued(prod, cons, XEN_9PFS_RING_SIZE(ring)) >= size;
}

static int p9_xen_request(struct p9_client *client, struct p9_req_t *p9_req)
{
        struct xen_9pfs_front_priv *priv;
        RING_IDX cons, prod, masked_cons, masked_prod;
        unsigned long flags;
        u32 size = p9_req->tc.size;
        struct xen_9pfs_dataring *ring;
        int num;

        read_lock(&xen_9pfs_lock);
        list_for_each_entry(priv, &xen_9pfs_devs, list) {
                if (priv->client == client)
                        break;
        }
        read_unlock(&xen_9pfs_lock);
        if (list_entry_is_head(priv, &xen_9pfs_devs, list))
                return -EINVAL;

        num = p9_req->tc.tag % priv->num_rings;
        ring = &priv->rings[num];

again:
        while (wait_event_killable(ring->wq,
                                   p9_xen_write_todo(ring, size)) != 0)
                ;

        spin_lock_irqsave(&ring->lock, flags);
        cons = ring->intf->out_cons;
        prod = ring->intf->out_prod;
        virt_mb();

        if (XEN_9PFS_RING_SIZE(ring) -
            xen_9pfs_queued(prod, cons, XEN_9PFS_RING_SIZE(ring)) < size) {
                spin_unlock_irqrestore(&ring->lock, flags);
                goto again;
        }

        masked_prod = xen_9pfs_mask(prod, XEN_9PFS_RING_SIZE(ring));
        masked_cons = xen_9pfs_mask(cons, XEN_9PFS_RING_SIZE(ring));

        xen_9pfs_write_packet(ring->data.out, p9_req->tc.sdata, size,
                              &masked_prod, masked_cons,
                              XEN_9PFS_RING_SIZE(ring));

        p9_req->status = REQ_STATUS_SENT;
        virt_wmb();                     /* write ring before updating pointer */
        prod += size;
        ring->intf->out_prod = prod;
        spin_unlock_irqrestore(&ring->lock, flags);
        notify_remote_via_irq(ring->irq);
        p9_req_put(p9_req);

        return 0;
}

static void p9_xen_response(struct work_struct *work)
{
        struct xen_9pfs_front_priv *priv;
        struct xen_9pfs_dataring *ring;
        RING_IDX cons, prod, masked_cons, masked_prod;
        struct xen_9pfs_header h;
        struct p9_req_t *req;
        int status;

        ring = container_of(work, struct xen_9pfs_dataring, work);
        priv = ring->priv;

        while (1) {
                cons = ring->intf->in_cons;
                prod = ring->intf->in_prod;
                virt_rmb();

                if (xen_9pfs_queued(prod, cons, XEN_9PFS_RING_SIZE(ring)) <
                    sizeof(h)) {
                        notify_remote_via_irq(ring->irq);
                        return;
                }

                masked_prod = xen_9pfs_mask(prod, XEN_9PFS_RING_SIZE(ring));
                masked_cons = xen_9pfs_mask(cons, XEN_9PFS_RING_SIZE(ring));

                /* First, read just the header */
                xen_9pfs_read_packet(&h, ring->data.in, sizeof(h),
                                     masked_prod, &masked_cons,
                                     XEN_9PFS_RING_SIZE(ring));

                req = p9_tag_lookup(priv->client, h.tag);
                if (!req || req->status != REQ_STATUS_SENT) {
                        dev_warn(&priv->dev->dev, "Wrong req tag=%x\n", h.tag);
                        cons += h.size;
                        virt_mb();
                        ring->intf->in_cons = cons;
                        continue;
                }

                memcpy(&req->rc, &h, sizeof(h));
                req->rc.offset = 0;

                masked_cons = xen_9pfs_mask(cons, XEN_9PFS_RING_SIZE(ring));
                /* Then, read the whole packet (including the header) */
                xen_9pfs_read_packet(req->rc.sdata, ring->data.in, h.size,
                                     masked_prod, &masked_cons,
                                     XEN_9PFS_RING_SIZE(ring));

                virt_mb();
                cons += h.size;
                ring->intf->in_cons = cons;

                status = (req->status != REQ_STATUS_ERROR) ?
                        REQ_STATUS_RCVD : REQ_STATUS_ERROR;

                p9_client_cb(priv->client, req, status);
        }
}

static irqreturn_t xen_9pfs_front_event_handler(int irq, void *r)
{
        struct xen_9pfs_dataring *ring = r;

        if (!ring || !ring->priv->client) {
                /* ignore spurious interrupt */
                return IRQ_HANDLED;
        }

        wake_up_interruptible(&ring->wq);
        schedule_work(&ring->work);

        return IRQ_HANDLED;
}

static struct p9_trans_module p9_xen_trans = {
        .name = "xen",
        .maxsize = 1 << (XEN_9PFS_RING_ORDER + XEN_PAGE_SHIFT - 2),
        .def = 1,
        .create = p9_xen_create,
        .close = p9_xen_close,
        .request = p9_xen_request,
        .cancel = p9_xen_cancel,
        .owner = THIS_MODULE,
};

static const struct xenbus_device_id xen_9pfs_front_ids[] = {
        { "9pfs" },
        { "" }
};

static void xen_9pfs_front_free(struct xen_9pfs_front_priv *priv)
{
        int i, j;

        write_lock(&xen_9pfs_lock);
        list_del(&priv->list);
        write_unlock(&xen_9pfs_lock);

        for (i = 0; i < priv->num_rings; i++) {
                if (!priv->rings[i].intf)
                        break;
                if (priv->rings[i].irq > 0)
                        unbind_from_irqhandler(priv->rings[i].irq, priv->dev);
                if (priv->rings[i].data.in) {
                        for (j = 0;
                             j < (1 << priv->rings[i].intf->ring_order);
                             j++) {
                                grant_ref_t ref;

                                ref = priv->rings[i].intf->ref[j];
                                gnttab_end_foreign_access(ref, 0, 0);
                        }
                        free_pages((unsigned long)priv->rings[i].data.in,
                                   priv->rings[i].intf->ring_order -
                                   (PAGE_SHIFT - XEN_PAGE_SHIFT));
                }
                gnttab_end_foreign_access(priv->rings[i].ref, 0, 0);
                free_page((unsigned long)priv->rings[i].intf);
        }
        kfree(priv->rings);
        kfree(priv->tag);
        kfree(priv);
}

static int xen_9pfs_front_remove(struct xenbus_device *dev)
{
        struct xen_9pfs_front_priv *priv = dev_get_drvdata(&dev->dev);

        dev_set_drvdata(&dev->dev, NULL);
        xen_9pfs_front_free(priv);
        return 0;
}

static int xen_9pfs_front_alloc_dataring(struct xenbus_device *dev,
                                         struct xen_9pfs_dataring *ring,
                                         unsigned int order)
{
        int i = 0;
        int ret = -ENOMEM;
        void *bytes = NULL;

        init_waitqueue_head(&ring->wq);
        spin_lock_init(&ring->lock);
        INIT_WORK(&ring->work, p9_xen_response);

        ring->intf = (struct xen_9pfs_data_intf *)get_zeroed_page(GFP_KERNEL);
        if (!ring->intf)
                return ret;
        ret = gnttab_grant_foreign_access(dev->otherend_id,
                                          virt_to_gfn(ring->intf), 0);
        if (ret < 0)
                goto out;
        ring->ref = ret;
        bytes = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
                        order - (PAGE_SHIFT - XEN_PAGE_SHIFT));
        if (!bytes) {
                ret = -ENOMEM;
                goto out;
        }
        for (; i < (1 << order); i++) {
                ret = gnttab_grant_foreign_access(
                                dev->otherend_id, virt_to_gfn(bytes) + i, 0);
                if (ret < 0)
                        goto out;
                ring->intf->ref[i] = ret;
        }
        ring->intf->ring_order = order;
        ring->data.in = bytes;
        ring->data.out = bytes + XEN_FLEX_RING_SIZE(order);

        ret = xenbus_alloc_evtchn(dev, &ring->evtchn);
        if (ret)
                goto out;
        ring->irq = bind_evtchn_to_irqhandler(ring->evtchn,
                                              xen_9pfs_front_event_handler,
                                              0, "xen_9pfs-frontend", ring);
        if (ring->irq >= 0)
                return 0;

        xenbus_free_evtchn(dev, ring->evtchn);
        ret = ring->irq;
out:
        if (bytes) {
                for (i--; i >= 0; i--)
                        gnttab_end_foreign_access(ring->intf->ref[i], 0, 0);
                free_pages((unsigned long)bytes,
                           ring->intf->ring_order -
                           (PAGE_SHIFT - XEN_PAGE_SHIFT));
        }
        gnttab_end_foreign_access(ring->ref, 0, 0);
        free_page((unsigned long)ring->intf);
        return ret;
}

static int xen_9pfs_front_probe(struct xenbus_device *dev,
                                const struct xenbus_device_id *id)
{
        int ret, i;
        struct xenbus_transaction xbt;
        struct xen_9pfs_front_priv *priv = NULL;
        char *versions;
        unsigned int max_rings, max_ring_order, len = 0;

        versions = xenbus_read(XBT_NIL, dev->otherend, "versions", &len);
        if (IS_ERR(versions))
                return PTR_ERR(versions);
        if (strcmp(versions, "1")) {
                kfree(versions);
                return -EINVAL;
        }
        kfree(versions);
        max_rings = xenbus_read_unsigned(dev->otherend, "max-rings", 0);
        if (max_rings < XEN_9PFS_NUM_RINGS)
                return -EINVAL;
        max_ring_order = xenbus_read_unsigned(dev->otherend,
                                              "max-ring-page-order", 0);
        if (max_ring_order > XEN_9PFS_RING_ORDER)
                max_ring_order = XEN_9PFS_RING_ORDER;
        if (p9_xen_trans.maxsize > XEN_FLEX_RING_SIZE(max_ring_order))
                p9_xen_trans.maxsize = XEN_FLEX_RING_SIZE(max_ring_order) / 2;

        priv = kzalloc(sizeof(*priv), GFP_KERNEL);
        if (!priv)
                return -ENOMEM;

        priv->dev = dev;
        priv->num_rings = XEN_9PFS_NUM_RINGS;
        priv->rings = kcalloc(priv->num_rings, sizeof(*priv->rings),
                              GFP_KERNEL);
        if (!priv->rings) {
                kfree(priv);
                return -ENOMEM;
        }

        for (i = 0; i < priv->num_rings; i++) {
                priv->rings[i].priv = priv;
                ret = xen_9pfs_front_alloc_dataring(dev, &priv->rings[i],
                                                    max_ring_order);
                if (ret < 0)
                        goto error;
        }

 again:
        ret = xenbus_transaction_start(&xbt);
        if (ret) {
                xenbus_dev_fatal(dev, ret, "starting transaction");
                goto error;
        }
        ret = xenbus_printf(xbt, dev->nodename, "version", "%u", 1);
        if (ret)
                goto error_xenbus;
        ret = xenbus_printf(xbt, dev->nodename, "num-rings", "%u",
                            priv->num_rings);
        if (ret)
                goto error_xenbus;
        for (i = 0; i < priv->num_rings; i++) {
                char str[16];

                BUILD_BUG_ON(XEN_9PFS_NUM_RINGS > 9);
                sprintf(str, "ring-ref%d", i);
                ret = xenbus_printf(xbt, dev->nodename, str, "%d",
                                    priv->rings[i].ref);
                if (ret)
                        goto error_xenbus;

                sprintf(str, "event-channel-%d", i);
                ret = xenbus_printf(xbt, dev->nodename, str, "%u",
                                    priv->rings[i].evtchn);
                if (ret)
                        goto error_xenbus;
        }
        priv->tag = xenbus_read(xbt, dev->nodename, "tag", NULL);
        if (IS_ERR(priv->tag)) {
                ret = PTR_ERR(priv->tag);
                goto error_xenbus;
        }
        ret = xenbus_transaction_end(xbt, 0);
        if (ret) {
                if (ret == -EAGAIN)
                        goto again;
                xenbus_dev_fatal(dev, ret, "completing transaction");
                goto error;
        }

        write_lock(&xen_9pfs_lock);
        list_add_tail(&priv->list, &xen_9pfs_devs);
        write_unlock(&xen_9pfs_lock);
        dev_set_drvdata(&dev->dev, priv);
        xenbus_switch_state(dev, XenbusStateInitialised);

        return 0;

 error_xenbus:
        xenbus_transaction_end(xbt, 1);
        xenbus_dev_fatal(dev, ret, "writing xenstore");
 error:
        dev_set_drvdata(&dev->dev, NULL);
        xen_9pfs_front_free(priv);
        return ret;
}

static int xen_9pfs_front_resume(struct xenbus_device *dev)
{
        dev_warn(&dev->dev, "suspend/resume unsupported\n");
        return 0;
}

static void xen_9pfs_front_changed(struct xenbus_device *dev,
                                   enum xenbus_state backend_state)
{
        switch (backend_state) {
        case XenbusStateReconfiguring:
        case XenbusStateReconfigured:
        case XenbusStateInitialising:
        case XenbusStateInitialised:
        case XenbusStateUnknown:
                break;

        case XenbusStateInitWait:
                break;

        case XenbusStateConnected:
                xenbus_switch_state(dev, XenbusStateConnected);
                break;

        case XenbusStateClosed:
                if (dev->state == XenbusStateClosed)
                        break;
                fallthrough;    /* Missed the backend's CLOSING state */
        case XenbusStateClosing:
                xenbus_frontend_closed(dev);
                break;
        }
}

static struct xenbus_driver xen_9pfs_front_driver = {
        .ids = xen_9pfs_front_ids,
        .probe = xen_9pfs_front_probe,
        .remove = xen_9pfs_front_remove,
        .resume = xen_9pfs_front_resume,
        .otherend_changed = xen_9pfs_front_changed,
};

static int p9_trans_xen_init(void)
{
        int rc;

        if (!xen_domain())
                return -ENODEV;

        pr_info("Initialising Xen transport for 9pfs\n");

        v9fs_register_trans(&p9_xen_trans);
        rc = xenbus_register_frontend(&xen_9pfs_front_driver);
        if (rc)
                v9fs_unregister_trans(&p9_xen_trans);

        return rc;
}
module_init(p9_trans_xen_init);

static void p9_trans_xen_exit(void)
{
        v9fs_unregister_trans(&p9_xen_trans);
        return xenbus_unregister_driver(&xen_9pfs_front_driver);
}
module_exit(p9_trans_xen_exit);

MODULE_AUTHOR("Stefano Stabellini <stefano@aporeto.com>");
MODULE_DESCRIPTION("Xen Transport for 9P");
MODULE_LICENSE("GPL");