// SPDX-License-Identifier: GPL-2.0-only
#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/proc_fs.h>
#include <linux/notifier.h>
#include <linux/kthread.h>
#include <linux/mutex.h>
#include <linux/io.h>
#include <linux/module.h>

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

#include <xen/platform_pci.h>

#include "xenbus.h"



/* device/<type>/<id> => <type>-<id> */
static int frontend_bus_id(char bus_id[XEN_BUS_ID_SIZE], const char *nodename)
{
        nodename = strchr(nodename, '/');
        if (!nodename || strlen(nodename + 1) >= XEN_BUS_ID_SIZE) {
                pr_warn("bad frontend %s\n", nodename);
                return -EINVAL;
        }

        strscpy(bus_id, nodename + 1, XEN_BUS_ID_SIZE);
        if (!strchr(bus_id, '/')) {
                pr_warn("bus_id %s no slash\n", bus_id);
                return -EINVAL;
        }
        *strchr(bus_id, '/') = '-';
        return 0;
}

/* device/<typename>/<name> */
static int xenbus_probe_frontend(struct xen_bus_type *bus, const char *type,
                                 const char *name)
{
        char *nodename;
        int err;

        /* ignore console/0 */
        if (!strncmp(type, "console", 7) && !strncmp(name, "0", 1)) {
                DPRINTK("Ignoring buggy device entry console/0");
                return 0;
        }

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

        DPRINTK("%s", nodename);

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

static int xenbus_uevent_frontend(const struct device *_dev,
                                  struct kobj_uevent_env *env)
{
        const struct xenbus_device *dev = to_xenbus_device(_dev);

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

        return 0;
}


static void backend_changed(struct xenbus_watch *watch,
                            const char *path, const char *token)
{
        xenbus_otherend_changed(watch, path, token, 1);
}

static void xenbus_frontend_delayed_restore(struct work_struct *w)
{
        struct xenbus_device *xdev = container_of(w, struct xenbus_device, work);

        xenbus_dev_restore(&xdev->dev);
}

static int xenbus_frontend_dev_restore(struct device *dev)
{
        /*
         * If xenstored is running in this domain, we cannot access the backend
         * state at the moment, so we need to defer xenbus_dev_resume
         */
        if (xen_store_domain_type == XS_LOCAL) {
                struct xenbus_device *xdev = to_xenbus_device(dev);

                schedule_work(&xdev->work);

                return 0;
        }

        return xenbus_dev_restore(dev);
}

static int xenbus_frontend_dev_probe(struct device *dev)
{
        if (xen_store_domain_type == XS_LOCAL) {
                struct xenbus_device *xdev = to_xenbus_device(dev);
                INIT_WORK(&xdev->work, xenbus_frontend_delayed_restore);
        }

        return xenbus_dev_probe(dev);
}

static void xenbus_frontend_dev_shutdown(struct device *_dev)
{
        struct xenbus_device *dev = to_xenbus_device(_dev);
        unsigned long timeout = 5*HZ;

        DPRINTK("%s", dev->nodename);

        get_device(&dev->dev);
        if (dev->state != XenbusStateConnected) {
                pr_info("%s: %s: %s != Connected, skipping\n",
                        __func__, dev->nodename, xenbus_strstate(dev->state));
                goto out;
        }
        xenbus_switch_state(dev, XenbusStateClosing);
        timeout = wait_for_completion_timeout(&dev->down, timeout);
        if (!timeout)
                pr_info("%s: %s timeout closing device\n",
                        __func__, dev->nodename);
 out:
        put_device(&dev->dev);
}

static const struct dev_pm_ops xenbus_pm_ops = {
        .freeze         = xenbus_dev_freeze,
        .thaw           = xenbus_dev_thaw,
        .restore        = xenbus_frontend_dev_restore,
};

static struct xen_bus_type xenbus_frontend = {
        .root = "device",
        .levels = 2,            /* device/type/<id> */
        .get_bus_id = frontend_bus_id,
        .probe = xenbus_probe_frontend,
        .otherend_changed = backend_changed,
        .bus = {
                .name           = "xen",
                .match          = xenbus_match,
                .uevent         = xenbus_uevent_frontend,
                .probe          = xenbus_frontend_dev_probe,
                .remove         = xenbus_dev_remove,
                .shutdown       = xenbus_frontend_dev_shutdown,
                .dev_groups     = xenbus_dev_groups,

                .pm             = &xenbus_pm_ops,
        },
};

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

        xenbus_dev_changed(path, &xenbus_frontend);
}


/* We watch for devices appearing and vanishing. */
static struct xenbus_watch fe_watch = {
        .node = "device",
        .callback = frontend_changed,
};

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

static int is_device_connecting(struct device *dev, void *data, bool ignore_nonessential)
{
        struct xenbus_device *xendev = to_xenbus_device(dev);
        struct device_driver *drv = data;
        struct xenbus_driver *xendrv;

        /*
         * A device with no driver will never connect. We care only about
         * devices which should currently be in the process of connecting.
         */
        if (!dev->driver)
                return 0;

        /* Is this search limited to a particular driver? */
        if (drv && (dev->driver != drv))
                return 0;

        xendrv = to_xenbus_driver(dev->driver);

        if (ignore_nonessential && xendrv->not_essential)
                return 0;

        return (xendev->state < XenbusStateConnected ||
                (xendev->state == XenbusStateConnected &&
                 xendrv->is_ready && !xendrv->is_ready(xendev)));
}
static int essential_device_connecting(struct device *dev, void *data)
{
        return is_device_connecting(dev, data, true /* ignore PV[KBB+FB] */);
}
static int non_essential_device_connecting(struct device *dev, void *data)
{
        return is_device_connecting(dev, data, false);
}

static int exists_essential_connecting_device(struct device_driver *drv)
{
        return bus_for_each_dev(&xenbus_frontend.bus, NULL, drv,
                                essential_device_connecting);
}
static int exists_non_essential_connecting_device(struct device_driver *drv)
{
        return bus_for_each_dev(&xenbus_frontend.bus, NULL, drv,
                                non_essential_device_connecting);
}

static int print_device_status(struct device *dev, void *data)
{
        struct xenbus_device *xendev = to_xenbus_device(dev);
        struct device_driver *drv = data;

        /* Is this operation limited to a particular driver? */
        if (drv && (dev->driver != drv))
                return 0;

        if (!dev->driver) {
                /* Information only: is this too noisy? */
                pr_info("Device with no driver: %s\n", xendev->nodename);
        } else if (xendev->state < XenbusStateConnected) {
                enum xenbus_state rstate = XenbusStateUnknown;
                if (xendev->otherend)
                        rstate = xenbus_read_driver_state(xendev, xendev->otherend);
                pr_warn("Timeout connecting to device: %s (local state %d, remote state %d)\n",
                        xendev->nodename, xendev->state, rstate);
        }

        return 0;
}

/* We only wait for device setup after most initcalls have run. */
static int ready_to_wait_for_devices;

static bool wait_loop(unsigned long start, unsigned int max_delay,
                     unsigned int *seconds_waited)
{
        if (time_after(jiffies, start + (*seconds_waited+5)*HZ)) {
                if (!*seconds_waited)
                        pr_warn("Waiting for devices to initialise: ");
                *seconds_waited += 5;
                pr_cont("%us...", max_delay - *seconds_waited);
                if (*seconds_waited == max_delay) {
                        pr_cont("\n");
                        return true;
                }
        }

        schedule_timeout_interruptible(HZ/10);

        return false;
}
/*
 * On a 5-minute timeout, wait for all devices currently configured.  We need
 * to do this to guarantee that the filesystems and / or network devices
 * needed for boot are available, before we can allow the boot to proceed.
 *
 * This needs to be on a late_initcall, to happen after the frontend device
 * drivers have been initialised, but before the root fs is mounted.
 *
 * A possible improvement here would be to have the tools add a per-device
 * flag to the store entry, indicating whether it is needed at boot time.
 * This would allow people who knew what they were doing to accelerate their
 * boot slightly, but of course needs tools or manual intervention to set up
 * those flags correctly.
 */
static void wait_for_devices(struct xenbus_driver *xendrv)
{
        unsigned long start = jiffies;
        struct device_driver *drv = xendrv ? &xendrv->driver : NULL;
        unsigned int seconds_waited = 0;

        if (!ready_to_wait_for_devices || !xen_domain())
                return;

        while (exists_non_essential_connecting_device(drv))
                if (wait_loop(start, 30, &seconds_waited))
                        break;

        /* Skips PVKB and PVFB check.*/
        while (exists_essential_connecting_device(drv))
                if (wait_loop(start, 270, &seconds_waited))
                        break;

        if (seconds_waited)
                printk("\n");

        bus_for_each_dev(&xenbus_frontend.bus, NULL, drv,
                         print_device_status);
}

int __xenbus_register_frontend(struct xenbus_driver *drv, struct module *owner,
                               const char *mod_name)
{
        int ret;

        drv->read_otherend_details = read_backend_details;

        ret = xenbus_register_driver_common(drv, &xenbus_frontend,
                                            owner, mod_name);
        if (ret)
                return ret;

        /* If this driver is loaded as a module wait for devices to attach. */
        wait_for_devices(drv);

        return 0;
}
EXPORT_SYMBOL_GPL(__xenbus_register_frontend);

static DECLARE_WAIT_QUEUE_HEAD(backend_state_wq);
static int backend_state;

static void xenbus_reset_backend_state_changed(struct xenbus_watch *w,
                                        const char *path, const char *token)
{
        if (xenbus_scanf(XBT_NIL, path, "", "%i",
                         &backend_state) != 1)
                backend_state = XenbusStateUnknown;
        printk(KERN_DEBUG "XENBUS: backend %s %s\n",
               path, xenbus_strstate(backend_state));
        wake_up(&backend_state_wq);
}

static void xenbus_reset_wait_for_backend(char *be, int expected)
{
        long timeout;
        timeout = wait_event_interruptible_timeout(backend_state_wq,
                        backend_state == expected, 5 * HZ);
        if (timeout <= 0)
                pr_info("backend %s timed out\n", be);
}

/*
 * Reset frontend if it is in Connected or Closed state.
 * Wait for backend to catch up.
 * State Connected happens during kdump, Closed after kexec.
 */
static void xenbus_reset_frontend(char *fe, char *be, int be_state)
{
        struct xenbus_watch be_watch;

        printk(KERN_DEBUG "XENBUS: backend %s %s\n",
                        be, xenbus_strstate(be_state));

        memset(&be_watch, 0, sizeof(be_watch));
        be_watch.node = kasprintf(GFP_NOIO | __GFP_HIGH, "%s/state", be);
        if (!be_watch.node)
                return;

        be_watch.callback = xenbus_reset_backend_state_changed;
        backend_state = XenbusStateUnknown;

        pr_info("triggering reconnect on %s\n", be);
        register_xenbus_watch(&be_watch);

        /* fall through to forward backend to state XenbusStateInitialising */
        switch (be_state) {
        case XenbusStateConnected:
                xenbus_printf(XBT_NIL, fe, "state", "%d", XenbusStateClosing);
                xenbus_reset_wait_for_backend(be, XenbusStateClosing);
                fallthrough;

        case XenbusStateClosing:
                xenbus_printf(XBT_NIL, fe, "state", "%d", XenbusStateClosed);
                xenbus_reset_wait_for_backend(be, XenbusStateClosed);
                fallthrough;

        case XenbusStateClosed:
                xenbus_printf(XBT_NIL, fe, "state", "%d", XenbusStateInitialising);
                xenbus_reset_wait_for_backend(be, XenbusStateInitWait);
        }

        unregister_xenbus_watch(&be_watch);
        pr_info("reconnect done on %s\n", be);
        kfree(be_watch.node);
}

static void xenbus_check_frontend(char *class, char *dev)
{
        int be_state, fe_state, err;
        char *backend, *frontend;

        frontend = kasprintf(GFP_NOIO | __GFP_HIGH, "device/%s/%s", class, dev);
        if (!frontend)
                return;

        err = xenbus_scanf(XBT_NIL, frontend, "state", "%i", &fe_state);
        if (err != 1)
                goto out;

        switch (fe_state) {
        case XenbusStateConnected:
        case XenbusStateClosed:
                printk(KERN_DEBUG "XENBUS: frontend %s %s\n",
                                frontend, xenbus_strstate(fe_state));
                backend = xenbus_read(XBT_NIL, frontend, "backend", NULL);
                if (IS_ERR_OR_NULL(backend))
                        goto out;
                err = xenbus_scanf(XBT_NIL, backend, "state", "%i", &be_state);
                if (err == 1)
                        xenbus_reset_frontend(frontend, backend, be_state);
                kfree(backend);
                break;
        default:
                break;
        }
out:
        kfree(frontend);
}

static void xenbus_reset_state(void)
{
        char **devclass, **dev;
        int devclass_n, dev_n;
        int i, j;

        devclass = xenbus_directory(XBT_NIL, "device", "", &devclass_n);
        if (IS_ERR(devclass))
                return;

        for (i = 0; i < devclass_n; i++) {
                dev = xenbus_directory(XBT_NIL, "device", devclass[i], &dev_n);
                if (IS_ERR(dev))
                        continue;
                for (j = 0; j < dev_n; j++)
                        xenbus_check_frontend(devclass[i], dev[j]);
                kfree(dev);
        }
        kfree(devclass);
}

static int frontend_probe_and_watch(struct notifier_block *notifier,
                                   unsigned long event,
                                   void *data)
{
        /* reset devices in Connected or Closed state */
        if (xen_hvm_domain())
                xenbus_reset_state();
        /* Enumerate devices in xenstore and watch for changes. */
        xenbus_probe_devices(&xenbus_frontend);
        register_xenbus_watch(&fe_watch);

        return NOTIFY_DONE;
}


static int __init xenbus_probe_frontend_init(void)
{
        static struct notifier_block xenstore_notifier = {
                .notifier_call = frontend_probe_and_watch
        };
        int err;

        DPRINTK("");

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

        register_xenstore_notifier(&xenstore_notifier);

        return 0;
}
subsys_initcall(xenbus_probe_frontend_init);

#ifndef MODULE
static int __init boot_wait_for_devices(void)
{
        if (!xen_has_pv_devices())
                return -ENODEV;

        ready_to_wait_for_devices = 1;
        wait_for_devices(NULL);
        return 0;
}

late_initcall(boot_wait_for_devices);
#endif

MODULE_DESCRIPTION("Xen PV-device frontend support");
MODULE_LICENSE("GPL");