1. 根目录:
2. drivers
3. xen
4. xenbus
5. xenbus_probe_frontend.c

#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 <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/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;

	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 struct device_attribute xenbus_frontend_dev_attrs[] = {
	__ATTR_NULL
};

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_frontend_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,
			       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 int frontend_probe_and_watch(struct notifier_block *notifier,
				   unsigned long event,
				   void *data)
{
	/* 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");