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    /*
     * Handle extern requests for shutdown, reboot and sysrq
     */
    #include <linux/kernel.h>
    #include <linux/err.h>
    #include <linux/slab.h>
    #include <linux/reboot.h>
    #include <linux/sysrq.h>
    #include <linux/stop_machine.h>
    #include <linux/freezer.h>
    #include <linux/syscore_ops.h>
    #include <linux/export.h>
    
    #include <xen/xen.h>
    #include <xen/xenbus.h>
    #include <xen/grant_table.h>
    #include <xen/events.h>
    #include <xen/hvc-console.h>
    #include <xen/xen-ops.h>
    
    #include <asm/xen/hypercall.h>
    #include <asm/xen/page.h>
    #include <asm/xen/hypervisor.h>
    
    enum shutdown_state {
    	SHUTDOWN_INVALID = -1,
    	SHUTDOWN_POWEROFF = 0,
    	SHUTDOWN_SUSPEND = 2,
    	/* Code 3 is SHUTDOWN_CRASH, which we don't use because the domain can only
    	   report a crash, not be instructed to crash!
    	   HALT is the same as POWEROFF, as far as we're concerned.  The tools use
    	   the distinction when we return the reason code to them.  */
    	 SHUTDOWN_HALT = 4,
    };
    
    /* Ignore multiple shutdown requests. */
    static enum shutdown_state shutting_down = SHUTDOWN_INVALID;
    
    struct suspend_info {
    	int cancelled;
    	unsigned long arg; /* extra hypercall argument */
    	void (*pre)(void);
    	void (*post)(int cancelled);
    };
    
    static void xen_hvm_post_suspend(int cancelled)
    {
    	xen_arch_hvm_post_suspend(cancelled);
    	gnttab_resume();
    }
    
    static void xen_pre_suspend(void)
    {
    	xen_mm_pin_all();
    	gnttab_suspend();
    	xen_arch_pre_suspend();
    }
    
    static void xen_post_suspend(int cancelled)
    {
    	xen_arch_post_suspend(cancelled);
    	gnttab_resume();
    	xen_mm_unpin_all();
    }
    
    #ifdef CONFIG_HIBERNATE_CALLBACKS
    static int xen_suspend(void *data)
    {
    	struct suspend_info *si = data;
    	int err;
    
    	BUG_ON(!irqs_disabled());
    
    	err = syscore_suspend();
    	if (err) {
    		printk(KERN_ERR "xen_suspend: system core suspend failed: %d\n",
    			err);
    		return err;
    	}
    
    	if (si->pre)
    		si->pre();
    
    	/*
    	 * This hypercall returns 1 if suspend was cancelled
    	 * or the domain was merely checkpointed, and 0 if it
    	 * is resuming in a new domain.
    	 */
    	si->cancelled = HYPERVISOR_suspend(si->arg);
    
    	if (si->post)
    		si->post(si->cancelled);
    
    	if (!si->cancelled) {
    		xen_irq_resume();
    		xen_console_resume();
    		xen_timer_resume();
    	}
    
    	syscore_resume();
    
    	return 0;
    }
    
    static void do_suspend(void)
    {
    	int err;
    	struct suspend_info si;
    
    	shutting_down = SHUTDOWN_SUSPEND;
    
    #ifdef CONFIG_PREEMPT
    	/* If the kernel is preemptible, we need to freeze all the processes
    	   to prevent them from being in the middle of a pagetable update
    	   during suspend. */
    	err = freeze_processes();
    	if (err) {
    		printk(KERN_ERR "xen suspend: freeze failed %d\n", err);
    		goto out;
    	}
    #endif
    
    	err = dpm_suspend_start(PMSG_FREEZE);
    	if (err) {
    		printk(KERN_ERR "xen suspend: dpm_suspend_start %d\n", err);
    		goto out_thaw;
    	}
    
    	printk(KERN_DEBUG "suspending xenstore...\n");
    	xs_suspend();
    
    	err = dpm_suspend_end(PMSG_FREEZE);
    	if (err) {
    		printk(KERN_ERR "dpm_suspend_end failed: %d\n", err);
    		si.cancelled = 0;
    		goto out_resume;
    	}
    
    	si.cancelled = 1;
    
    	if (xen_hvm_domain()) {
    		si.arg = 0UL;
    		si.pre = NULL;
    		si.post = &xen_hvm_post_suspend;
    	} else {
    		si.arg = virt_to_mfn(xen_start_info);
    		si.pre = &xen_pre_suspend;
    		si.post = &xen_post_suspend;
    	}
    
    	err = stop_machine(xen_suspend, &si, cpumask_of(0));
    
    	dpm_resume_start(si.cancelled ? PMSG_THAW : PMSG_RESTORE);
    
    	if (err) {
    		printk(KERN_ERR "failed to start xen_suspend: %d\n", err);
    		si.cancelled = 1;
    	}
    
    out_resume:
    	if (!si.cancelled) {
    		xen_arch_resume();
    		xs_resume();
    	} else
    		xs_suspend_cancel();
    
    	dpm_resume_end(si.cancelled ? PMSG_THAW : PMSG_RESTORE);
    
    	/* Make sure timer events get retriggered on all CPUs */
    	clock_was_set();
    
    out_thaw:
    #ifdef CONFIG_PREEMPT
    	thaw_processes();
    out:
    #endif
    	shutting_down = SHUTDOWN_INVALID;
    }
    #endif	/* CONFIG_HIBERNATE_CALLBACKS */
    
    struct shutdown_handler {
    	const char *command;
    	void (*cb)(void);
    };
    
    static void do_poweroff(void)
    {
    	shutting_down = SHUTDOWN_POWEROFF;
    	orderly_poweroff(false);
    }
    
    static void do_reboot(void)
    {
    	shutting_down = SHUTDOWN_POWEROFF; /* ? */
    	ctrl_alt_del();
    }
    
    static void shutdown_handler(struct xenbus_watch *watch,
    			     const char **vec, unsigned int len)
    {
    	char *str;
    	struct xenbus_transaction xbt;
    	int err;
    	static struct shutdown_handler handlers[] = {
    		{ "poweroff",	do_poweroff },
    		{ "halt",	do_poweroff },
    		{ "reboot",	do_reboot   },
    #ifdef CONFIG_HIBERNATE_CALLBACKS
    		{ "suspend",	do_suspend  },
    #endif
    		{NULL, NULL},
    	};
    	static struct shutdown_handler *handler;
    
    	if (shutting_down != SHUTDOWN_INVALID)
    		return;
    
     again:
    	err = xenbus_transaction_start(&xbt);
    	if (err)
    		return;
    
    	str = (char *)xenbus_read(xbt, "control", "shutdown", NULL);
    	/* Ignore read errors and empty reads. */
    	if (XENBUS_IS_ERR_READ(str)) {
    		xenbus_transaction_end(xbt, 1);
    		return;
    	}
    
    	for (handler = &handlers[0]; handler->command; handler++) {
    		if (strcmp(str, handler->command) == 0)
    			break;
    	}
    
    	/* Only acknowledge commands which we are prepared to handle. */
    	if (handler->cb)
    		xenbus_write(xbt, "control", "shutdown", "");
    
    	err = xenbus_transaction_end(xbt, 0);
    	if (err == -EAGAIN) {
    		kfree(str);
    		goto again;
    	}
    
    	if (handler->cb) {
    		handler->cb();
    	} else {
    		printk(KERN_INFO "Ignoring shutdown request: %s\n", str);
    		shutting_down = SHUTDOWN_INVALID;
    	}
    
    	kfree(str);
    }
    
    #ifdef CONFIG_MAGIC_SYSRQ
    static void sysrq_handler(struct xenbus_watch *watch, const char **vec,
    			  unsigned int len)
    {
    	char sysrq_key = '\0';
    	struct xenbus_transaction xbt;
    	int err;
    
     again:
    	err = xenbus_transaction_start(&xbt);
    	if (err)
    		return;
    	if (!xenbus_scanf(xbt, "control", "sysrq", "%c", &sysrq_key)) {
    		printk(KERN_ERR "Unable to read sysrq code in "
    		       "control/sysrq\n");
    		xenbus_transaction_end(xbt, 1);
    		return;
    	}
    
    	if (sysrq_key != '\0')
    		xenbus_printf(xbt, "control", "sysrq", "%c", '\0');
    
    	err = xenbus_transaction_end(xbt, 0);
    	if (err == -EAGAIN)
    		goto again;
    
    	if (sysrq_key != '\0')
    		handle_sysrq(sysrq_key);
    }
    
    static struct xenbus_watch sysrq_watch = {
    	.node = "control/sysrq",
    	.callback = sysrq_handler
    };
    #endif
    
    static struct xenbus_watch shutdown_watch = {
    	.node = "control/shutdown",
    	.callback = shutdown_handler
    };
    
    static int setup_shutdown_watcher(void)
    {
    	int err;
    
    	err = register_xenbus_watch(&shutdown_watch);
    	if (err) {
    		printk(KERN_ERR "Failed to set shutdown watcher\n");
    		return err;
    	}
    
    #ifdef CONFIG_MAGIC_SYSRQ
    	err = register_xenbus_watch(&sysrq_watch);
    	if (err) {
    		printk(KERN_ERR "Failed to set sysrq watcher\n");
    		return err;
    	}
    #endif
    
    	return 0;
    }
    
    static int shutdown_event(struct notifier_block *notifier,
    			  unsigned long event,
    			  void *data)
    {
    	setup_shutdown_watcher();
    	return NOTIFY_DONE;
    }
    
    int xen_setup_shutdown_event(void)
    {
    	static struct notifier_block xenstore_notifier = {
    		.notifier_call = shutdown_event
    	};
    
    	if (!xen_domain())
    		return -ENODEV;
    	register_xenstore_notifier(&xenstore_notifier);
    
    	return 0;
    }
    EXPORT_SYMBOL_GPL(xen_setup_shutdown_event);
    
    subsys_initcall(xen_setup_shutdown_event);