xenbus_probe_frontend.c

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#define DPRINTK(fmt, args...)               \
    pr_debug("xenbus_probe (%s:%d) " fmt ".\n", \
         __func__, __LINE__, ##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/pgtable.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_comms.h"
#include "xenbus_probe.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) {
        printk(KERN_WARNING "XENBUS: bad frontend %s\n", nodename);
        return -EINVAL;
    }

    strlcpy(bus_id, nodename + 1, XEN_BUS_ID_SIZE);
    if (!strchr(bus_id, '/')) {
        printk(KERN_WARNING "XENBUS: 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(struct device *_dev,
                  struct kobj_uevent_env *env)
{
    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 **vec, unsigned int len)
{
    xenbus_otherend_changed(watch, vec, len, 1);
}

static const struct dev_pm_ops xenbus_pm_ops = {
    .suspend    = xenbus_dev_suspend,
    .resume     = xenbus_dev_resume,
    .freeze     = xenbus_dev_suspend,
    .thaw       = xenbus_dev_cancel,
    .restore    = xenbus_dev_resume,
};

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_dev_probe,
        .remove     = xenbus_dev_remove,
        .shutdown   = xenbus_dev_shutdown,
        .dev_attrs  = xenbus_dev_attrs,

        .pm     = &xenbus_pm_ops,
    },
};

static void frontend_changed(struct xenbus_watch *watch,
                 const char **vec, unsigned int len)
{
    DPRINTK("");

    xenbus_dev_changed(vec[XS_WATCH_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;

    if (ignore_nonessential) {
        /* With older QEMU, for PVonHVM guests the guest config files
         * could contain: vfb = [ 'vnc=1, vnclisten=0.0.0.0']
         * which is nonsensical as there is no PV FB (there can be
         * a PVKB) running as HVM guest. */

        if ((strncmp(xendev->nodename, "device/vkbd", 11) == 0))
            return 0;

        if ((strncmp(xendev->nodename, "device/vfb", 10) == 0))
            return 0;
    }
    xendrv = to_xenbus_driver(dev->driver);
    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? */
        printk(KERN_INFO "XENBUS: 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->otherend);
        printk(KERN_WARNING "XENBUS: 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)
            printk(KERN_WARNING "XENBUS: Waiting for "
                   "devices to initialise: ");
        *seconds_waited += 5;
        printk("%us...", max_delay - *seconds_waited);
        if (*seconds_waited == max_delay)
            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)
{
    int ret;

    drv->read_otherend_details = read_backend_details;

    ret = xenbus_register_driver_common(drv, &xenbus_frontend);
    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 **v, unsigned int l)
{
    xenbus_scanf(XBT_NIL, v[XS_WATCH_PATH], "", "%i", &backend_state);
    printk(KERN_DEBUG "XENBUS: backend %s %s\n",
            v[XS_WATCH_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)
        printk(KERN_INFO "XENBUS: 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;

    printk(KERN_INFO "XENBUS: 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);

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

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

    unregister_xenbus_watch(&be_watch);
    printk(KERN_INFO "XENBUS: 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 (!backend || IS_ERR(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_hvm_domain() && !xen_platform_pci_unplug)
        return -ENODEV;

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

late_initcall(boot_wait_for_devices);
#endif

MODULE_LICENSE("GPL");