/******************************************************************************
 * Talks to Xen Store to figure out what devices we have (backend half).
 *
 * Copyright (C) 2005 Rusty Russell, IBM Corporation
 * Copyright (C) 2005 Mike Wray, Hewlett-Packard
 * Copyright (C) 2005, 2006 XenSource Ltd
 * Copyright (C) 2007 Solarflare Communications, Inc.
 *
 * 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.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#define DPRINTK(fmt, ...)                               \
        pr_debug("(%s:%d) " fmt "\n",                   \
                 __func__, __LINE__, ##__VA_ARGS__)

#include <linux/kernel.h>
#include <linux/err.h>
#include <linux/string.h>
#include <linux/ctype.h>
#include <linux/fcntl.h>
#include <linux/mm.h>
#include <linux/notifier.h>
#include <linux/export.h>
#include <linux/semaphore.h>

#include <asm/page.h>
#include <asm/xen/hypervisor.h>
#include <asm/hypervisor.h>
#include <xen/xenbus.h>
#include <xen/features.h>

#include "xenbus.h"

/* backend/<type>/<fe-uuid>/<id> => <type>-<fe-domid>-<id> */
static int backend_bus_id(char bus_id[XEN_BUS_ID_SIZE], const char *nodename)
{
        int domid, err;
        const char *devid, *type, *frontend;
        unsigned int typelen;

        type = strchr(nodename, '/');
        if (!type)
                return -EINVAL;
        type++;
        typelen = strcspn(type, "/");
        if (!typelen || type[typelen] != '/')
                return -EINVAL;

        devid = strrchr(nodename, '/') + 1;

        err = xenbus_gather(XBT_NIL, nodename, "frontend-id", "%i", &domid,
                            "frontend", NULL, &frontend,
                            NULL);
        if (err)
                return err;
        if (strlen(frontend) == 0)
                err = -ERANGE;
        if (!err && !xenbus_exists(XBT_NIL, frontend, ""))
                err = -ENOENT;
        kfree(frontend);

        if (err)
                return err;

        if (snprintf(bus_id, XEN_BUS_ID_SIZE, "%.*s-%i-%s",
                     typelen, type, domid, devid) >= XEN_BUS_ID_SIZE)
                return -ENOSPC;
        return 0;
}

static int xenbus_uevent_backend(const struct device *dev,
                                 struct kobj_uevent_env *env)
{
        const struct xenbus_device *xdev;
        const struct xenbus_driver *drv;
        const struct xen_bus_type *bus;

        DPRINTK("");

        if (dev == NULL)
                return -ENODEV;

        xdev = to_xenbus_device(dev);
        bus = container_of(xdev->dev.bus, struct xen_bus_type, bus);

        if (add_uevent_var(env, "MODALIAS=xen-backend:%s", xdev->devicetype))
                return -ENOMEM;

        /* stuff we want to pass to /sbin/hotplug */
        if (add_uevent_var(env, "XENBUS_TYPE=%s", xdev->devicetype))
                return -ENOMEM;

        if (add_uevent_var(env, "XENBUS_PATH=%s", xdev->nodename))
                return -ENOMEM;

        if (add_uevent_var(env, "XENBUS_BASE_PATH=%s", bus->root))
                return -ENOMEM;

        if (dev->driver) {
                drv = to_xenbus_driver(dev->driver);
                if (drv && drv->uevent)
                        return drv->uevent(xdev, env);
        }

        return 0;
}

/* backend/<typename>/<frontend-uuid>/<name> */
static int xenbus_probe_backend_unit(struct xen_bus_type *bus,
                                     const char *dir,
                                     const char *type,
                                     const char *name)
{
        char *nodename;
        int err;

        nodename = kasprintf(GFP_KERNEL, "%s/%s", dir, name);
        if (!nodename)
                return -ENOMEM;

        DPRINTK("%s\n", nodename);

        err = xenbus_probe_node(bus, type, nodename);
        kfree(nodename);
        return err;
}

/* backend/<typename>/<frontend-domid> */
static int xenbus_probe_backend(struct xen_bus_type *bus, const char *type,
                                const char *domid)
{
        char *nodename;
        int err = 0;
        char **dir;
        unsigned int i, dir_n = 0;

        DPRINTK("");

        nodename = kasprintf(GFP_KERNEL, "%s/%s/%s", bus->root, type, domid);
        if (!nodename)
                return -ENOMEM;

        dir = xenbus_directory(XBT_NIL, nodename, "", &dir_n);
        if (IS_ERR(dir)) {
                kfree(nodename);
                return PTR_ERR(dir);
        }

        for (i = 0; i < dir_n; i++) {
                err = xenbus_probe_backend_unit(bus, nodename, type, dir[i]);
                if (err)
                        break;
        }
        kfree(dir);
        kfree(nodename);
        return err;
}

static bool frontend_will_handle(struct xenbus_watch *watch,
                                 const char *path, const char *token)
{
        return watch->nr_pending == 0;
}

static void frontend_changed(struct xenbus_watch *watch,
                             const char *path, const char *token)
{
        xenbus_otherend_changed(watch, path, token, 0);
}

static struct xen_bus_type xenbus_backend = {
        .root = "backend",
        .levels = 3,            /* backend/type/<frontend>/<id> */
        .get_bus_id = backend_bus_id,
        .probe = xenbus_probe_backend,
        .otherend_will_handle = frontend_will_handle,
        .otherend_changed = frontend_changed,
        .bus = {
                .name           = "xen-backend",
                .match          = xenbus_match,
                .uevent         = xenbus_uevent_backend,
                .probe          = xenbus_dev_probe,
                .remove         = xenbus_dev_remove,
                .dev_groups     = xenbus_dev_groups,
        },
};

static void backend_changed(struct xenbus_watch *watch,
                            const char *path, const char *token)
{
        DPRINTK("");

        xenbus_dev_changed(path, &xenbus_backend);
}

static struct xenbus_watch be_watch = {
        .node = "backend",
        .callback = backend_changed,
};

static int read_frontend_details(struct xenbus_device *xendev)
{
        return xenbus_read_otherend_details(xendev, "frontend-id", "frontend");
}

int xenbus_dev_is_online(struct xenbus_device *dev)
{
        return !!xenbus_read_unsigned(dev->nodename, "online", 0);
}
EXPORT_SYMBOL_GPL(xenbus_dev_is_online);

int __xenbus_register_backend(struct xenbus_driver *drv, struct module *owner,
                              const char *mod_name)
{
        drv->read_otherend_details = read_frontend_details;

        return xenbus_register_driver_common(drv, &xenbus_backend,
                                             owner, mod_name);
}
EXPORT_SYMBOL_GPL(__xenbus_register_backend);

static int backend_probe_and_watch(struct notifier_block *notifier,
                                   unsigned long event,
                                   void *data)
{
        /* Enumerate devices in xenstore and watch for changes. */
        xenbus_probe_devices(&xenbus_backend);
        register_xenbus_watch(&be_watch);

        return NOTIFY_DONE;
}

static int backend_reclaim_memory(struct device *dev, void *data)
{
        const struct xenbus_driver *drv;
        struct xenbus_device *xdev;

        if (!dev->driver)
                return 0;
        drv = to_xenbus_driver(dev->driver);
        if (drv && drv->reclaim_memory) {
                xdev = to_xenbus_device(dev);
                if (down_trylock(&xdev->reclaim_sem))
                        return 0;
                drv->reclaim_memory(xdev);
                up(&xdev->reclaim_sem);
        }
        return 0;
}

/*
 * Returns 0 always because we are using shrinker to only detect memory
 * pressure.
 */
static unsigned long backend_shrink_memory_count(struct shrinker *shrinker,
                                struct shrink_control *sc)
{
        bus_for_each_dev(&xenbus_backend.bus, NULL, NULL,
                        backend_reclaim_memory);
        return 0;
}

static int __init xenbus_probe_backend_init(void)
{
        struct shrinker *backend_memory_shrinker;
        static struct notifier_block xenstore_notifier = {
                .notifier_call = backend_probe_and_watch
        };
        int err;

        DPRINTK("");

        /* Register ourselves with the kernel bus subsystem */
        err = bus_register(&xenbus_backend.bus);
        if (err)
                return err;

        register_xenstore_notifier(&xenstore_notifier);

        backend_memory_shrinker = shrinker_alloc(0, "xen-backend");
        if (!backend_memory_shrinker) {
                pr_warn("shrinker allocation failed\n");
                return 0;
        }

        backend_memory_shrinker->count_objects = backend_shrink_memory_count;

        shrinker_register(backend_memory_shrinker);

        return 0;
}
subsys_initcall(xenbus_probe_backend_init);