static int snapshot_open(struct inode *inode, struct file *filp)
{
	struct snapshot_data *data;
	int error;

	lock_system_sleep();

	if (!atomic_add_unless(&snapshot_device_available, -1, 0)) {
		error = -EBUSY;
		goto Unlock;
	}

	if ((filp->f_flags & O_ACCMODE) == O_RDWR) {
		atomic_inc(&snapshot_device_available);
		error = -ENOSYS;
		goto Unlock;
	}
	if(create_basic_memory_bitmaps()) {
		atomic_inc(&snapshot_device_available);
		error = -ENOMEM;
		goto Unlock;
	}
	nonseekable_open(inode, filp);
	data = &snapshot_state;
	filp->private_data = data;
	memset(&data->handle, 0, sizeof(struct snapshot_handle));
	if ((filp->f_flags & O_ACCMODE) == O_RDONLY) {
		/* Hibernating.  The image device should be accessible. */
		data->swap = swsusp_resume_device ?
			swap_type_of(swsusp_resume_device, 0, NULL) : -1;
		data->mode = O_RDONLY;
		error = pm_notifier_call_chain(PM_HIBERNATION_PREPARE);
		if (error)
			pm_notifier_call_chain(PM_POST_HIBERNATION);
	} else {
		/*
		 * Resuming.  We may need to wait for the image device to
		 * appear.
		 */
		wait_for_device_probe();

		data->swap = -1;
		data->mode = O_WRONLY;
		error = pm_notifier_call_chain(PM_RESTORE_PREPARE);
		if (error)
			pm_notifier_call_chain(PM_POST_RESTORE);
	}
	if (error) {
		free_basic_memory_bitmaps();
		atomic_inc(&snapshot_device_available);
	}
	data->frozen = 0;
	data->ready = 0;
	data->platform_support = 0;

 Unlock:
	unlock_system_sleep();

	return error;
}

static int load_image_and_restore(void)
{
	int error;
	unsigned int flags;

	pr_debug("Loading hibernation image.\n");

	lock_device_hotplug();
	error = create_basic_memory_bitmaps();
	if (error)
		goto Unlock;

	error = swsusp_read(&flags);
	swsusp_close(FMODE_READ);
	if (!error)
		hibernation_restore(flags & SF_PLATFORM_MODE);

	pr_err("Failed to load hibernation image, recovering.\n");
	swsusp_free();
	free_basic_memory_bitmaps();
 Unlock:
	unlock_device_hotplug();

	return error;
}

int hibernate(void)
{
	int error;

	mutex_lock(&pm_mutex);
	/* The snapshot device should not be opened while we're running */
	if (!atomic_add_unless(&snapshot_device_available, -1, 0)) {
		error = -EBUSY;
		goto Unlock;
	}

	error = pm_notifier_call_chain(PM_HIBERNATION_PREPARE);
	if (error)
		goto Exit;

	/* Allocate memory management structures */
	error = create_basic_memory_bitmaps();
	if (error)
		goto Exit;

	printk("Syncing filesystems ... ");
	sys_sync();
	printk("done.\n");

	error = prepare_processes();
	if (error)
		goto Finish;

	if (hibernation_mode == HIBERNATION_TESTPROC) {
		printk("swsusp debug: Waiting for 5 seconds.\n");
		mdelay(5000);
		goto Thaw;
	}
	error = hibernation_snapshot(hibernation_mode == HIBERNATION_PLATFORM);
	if (in_suspend && !error) {
		unsigned int flags = 0;

		if (hibernation_mode == HIBERNATION_PLATFORM)
			flags |= SF_PLATFORM_MODE;
		pr_debug("PM: writing image.\n");
		error = swsusp_write(flags);
		swsusp_free();
		if (!error)
			power_down();
	} else {
		pr_debug("PM: Image restored successfully.\n");
		swsusp_free();
	}
 Thaw:
	unprepare_processes();
 Finish:
	free_basic_memory_bitmaps();
 Exit:
	pm_notifier_call_chain(PM_POST_HIBERNATION);
	atomic_inc(&snapshot_device_available);
 Unlock:
	mutex_unlock(&pm_mutex);
	return error;
}

static int snapshot_release(struct inode *inode, struct file *filp)
{
	struct snapshot_data *data;

	lock_system_sleep();

	swsusp_free();
	data = filp->private_data;
	free_all_swap_pages(data->swap);
	if (data->frozen) {
		pm_restore_gfp_mask();
		free_basic_memory_bitmaps();
		thaw_processes();
	} else if (data->free_bitmaps) {
		free_basic_memory_bitmaps();
	}
	pm_notifier_call_chain(data->mode == O_RDONLY ?
			PM_POST_HIBERNATION : PM_POST_RESTORE);
	atomic_inc(&snapshot_device_available);

	unlock_system_sleep();

	return 0;
}

static int snapshot_release(struct inode *inode, struct file *filp)
{
	struct snapshot_data *data;

	swsusp_free();
	free_basic_memory_bitmaps();
	data = filp->private_data;
	free_all_swap_pages(data->swap);
	if (data->frozen) {
		mutex_lock(&pm_mutex);
		thaw_processes();
		mutex_unlock(&pm_mutex);
	}
	atomic_inc(&snapshot_device_available);
	return 0;
}

/**
 * hibernate - Carry out system hibernation, including saving the image.
 */
int hibernate(void)
{
	int error, nr_calls = 0;
	bool snapshot_test = false;

	if (!hibernation_available()) {
		pr_debug("Hibernation not available.\n");
		return -EPERM;
	}

	lock_system_sleep();
	/* The snapshot device should not be opened while we're running */
	if (!atomic_add_unless(&snapshot_device_available, -1, 0)) {
		error = -EBUSY;
		goto Unlock;
	}

	pm_prepare_console();
	error = __pm_notifier_call_chain(PM_HIBERNATION_PREPARE, -1, &nr_calls);
	if (error) {
		nr_calls--;
		goto Exit;
	}

	pr_info("Syncing filesystems ... \n");
	sys_sync();
	pr_info("done.\n");

	error = freeze_processes();
	if (error)
		goto Exit;

	lock_device_hotplug();
	/* Allocate memory management structures */
	error = create_basic_memory_bitmaps();
	if (error)
		goto Thaw;

	error = hibernation_snapshot(hibernation_mode == HIBERNATION_PLATFORM);
	if (error || freezer_test_done)
		goto Free_bitmaps;

	if (in_suspend) {
		unsigned int flags = 0;

		if (hibernation_mode == HIBERNATION_PLATFORM)
			flags |= SF_PLATFORM_MODE;
		if (nocompress)
			flags |= SF_NOCOMPRESS_MODE;
		else
		        flags |= SF_CRC32_MODE;

		pr_debug("Writing image.\n");
		error = swsusp_write(flags);
		swsusp_free();
		if (!error) {
			if (hibernation_mode == HIBERNATION_TEST_RESUME)
				snapshot_test = true;
			else
				power_down();
		}
		in_suspend = 0;
		pm_restore_gfp_mask();
	} else {
		pr_debug("Image restored successfully.\n");
	}

 Free_bitmaps:
	free_basic_memory_bitmaps();
 Thaw:
	unlock_device_hotplug();
	if (snapshot_test) {
		pr_debug("Checking hibernation image\n");
		error = swsusp_check();
		if (!error)
			error = load_image_and_restore();
	}
	thaw_processes();

	/* Don't bother checking whether freezer_test_done is true */
	freezer_test_done = false;
 Exit:
	__pm_notifier_call_chain(PM_POST_HIBERNATION, nr_calls, NULL);
	pm_restore_console();
	atomic_inc(&snapshot_device_available);
 Unlock:
	unlock_system_sleep();
	return error;
}

//.........这里部分代码省略.........
	 * which cannot happen since we're in the boot code here and
	 * sysfs can't be invoked yet. Therefore, we use a subclass
	 * here to avoid lockdep complaining.
	 */
	mutex_lock_nested(&pm_mutex, SINGLE_DEPTH_NESTING);

	if (swsusp_resume_device)
		goto Check_image;

	if (!strlen(resume_file)) {
		error = -ENOENT;
		goto Unlock;
	}

	pr_debug("PM: Checking image partition %s\n", resume_file);

	/* Check if the device is there */
	swsusp_resume_device = name_to_dev_t(resume_file);
	if (!swsusp_resume_device) {
		/*
		 * Some device discovery might still be in progress; we need
		 * to wait for this to finish.
		 */
		wait_for_device_probe();
		/*
		 * We can't depend on SCSI devices being available after loading
		 * one of their modules until scsi_complete_async_scans() is
		 * called and the resume device usually is a SCSI one.
		 */
		scsi_complete_async_scans();

		swsusp_resume_device = name_to_dev_t(resume_file);
		if (!swsusp_resume_device) {
			error = -ENODEV;
			goto Unlock;
		}
	}

 Check_image:
	pr_debug("PM: Resume from partition %d:%d\n",
		MAJOR(swsusp_resume_device), MINOR(swsusp_resume_device));

	pr_debug("PM: Checking hibernation image.\n");
	error = swsusp_check();
	if (error)
		goto Unlock;

	/* The snapshot device should not be opened while we're running */
	if (!atomic_add_unless(&snapshot_device_available, -1, 0)) {
		error = -EBUSY;
		swsusp_close(FMODE_READ);
		goto Unlock;
	}

	pm_prepare_console();
	error = pm_notifier_call_chain(PM_RESTORE_PREPARE);
	if (error)
		goto close_finish;

	error = usermodehelper_disable();
	if (error)
		goto close_finish;

	error = create_basic_memory_bitmaps();
	if (error)
		goto close_finish;

	pr_debug("PM: Preparing processes for restore.\n");
	error = prepare_processes();
	if (error) {
		swsusp_close(FMODE_READ);
		goto Done;
	}

	pr_debug("PM: Reading hibernation image.\n");

	error = swsusp_read(&flags);
	swsusp_close(FMODE_READ);
	if (!error)
		hibernation_restore(flags & SF_PLATFORM_MODE);

	printk(KERN_ERR "PM: Restore failed, recovering.\n");
	swsusp_free();
	thaw_processes();
 Done:
	free_basic_memory_bitmaps();
	usermodehelper_enable();
 Finish:
	pm_notifier_call_chain(PM_POST_RESTORE);
	pm_restore_console();
	atomic_inc(&snapshot_device_available);
	/* For success case, the suspend path will release the lock */
 Unlock:
	mutex_unlock(&pm_mutex);
	pr_debug("PM: Resume from disk failed.\n");
	return error;
close_finish:
	swsusp_close(FMODE_READ);
	goto Finish;
}

//.........这里部分代码省略.........
	}

	pr_debug("PM: Checking hibernation image partition %s\n", resume_file);

	if (resume_delay) {
		printk(KERN_INFO "Waiting %dsec before reading resume device...\n",
			resume_delay);
		ssleep(resume_delay);
	}

	/* Check if the device is there */
	swsusp_resume_device = name_to_dev_t(resume_file);

	/*
	 * name_to_dev_t is ineffective to verify parition if resume_file is in
	 * integer format. (e.g. major:minor)
	 */
	if (isdigit(resume_file[0]) && resume_wait) {
		int partno;
		while (!get_gendisk(swsusp_resume_device, &partno))
			msleep(10);
	}

	if (!swsusp_resume_device) {
		/*
		 * Some device discovery might still be in progress; we need
		 * to wait for this to finish.
		 */
		wait_for_device_probe();

		if (resume_wait) {
			while ((swsusp_resume_device = name_to_dev_t(resume_file)) == 0)
				msleep(10);
			async_synchronize_full();
		}

		swsusp_resume_device = name_to_dev_t(resume_file);
		if (!swsusp_resume_device) {
			error = -ENODEV;
			goto Unlock;
		}
	}

 Check_image:
	pr_debug("PM: Hibernation image partition %d:%d present\n",
		MAJOR(swsusp_resume_device), MINOR(swsusp_resume_device));

	pr_debug("PM: Looking for hibernation image.\n");
	error = swsusp_check();
	if (error)
		goto Unlock;

	/* The snapshot device should not be opened while we're running */
	if (!atomic_add_unless(&snapshot_device_available, -1, 0)) {
		error = -EBUSY;
		swsusp_close(FMODE_READ);
		goto Unlock;
	}

	pm_prepare_console();
	error = pm_notifier_call_chain(PM_RESTORE_PREPARE);
	if (error)
		goto Close_Finish;

	pr_debug("PM: Preparing processes for restore.\n");
	error = freeze_processes();
	if (error)
		goto Close_Finish;

	pr_debug("PM: Loading hibernation image.\n");

	lock_device_hotplug();
	error = create_basic_memory_bitmaps();
	if (error)
		goto Thaw;

	error = swsusp_read(&flags);
	swsusp_close(FMODE_READ);
	if (!error)
		hibernation_restore(flags & SF_PLATFORM_MODE);

	printk(KERN_ERR "PM: Failed to load hibernation image, recovering.\n");
	swsusp_free();
	free_basic_memory_bitmaps();
 Thaw:
	unlock_device_hotplug();
	thaw_processes();
 Finish:
	pm_notifier_call_chain(PM_POST_RESTORE);
	pm_restore_console();
	atomic_inc(&snapshot_device_available);
	/* For success case, the suspend path will release the lock */
 Unlock:
	mutex_unlock(&pm_mutex);
	pr_debug("PM: Hibernation image not present or could not be loaded.\n");
	return error;
 Close_Finish:
	swsusp_close(FMODE_READ);
	goto Finish;
}

/**
 * hibernate - Carry out system hibernation, including saving the image.
 */
int hibernate(void)
{
	int error;

	lock_system_sleep();
	/* The snapshot device should not be opened while we're running */
	if (!atomic_add_unless(&snapshot_device_available, -1, 0)) {
		error = -EBUSY;
		goto Unlock;
	}

	pm_prepare_console();
	error = pm_notifier_call_chain(PM_HIBERNATION_PREPARE);
	if (error)
		goto Exit;

	/* Allocate memory management structures */
	error = create_basic_memory_bitmaps();
	if (error)
		goto Exit;

	printk(KERN_INFO "PM: Syncing filesystems ... ");
	sys_sync();
	printk("done.\n");

	error = freeze_processes();
	if (error)
		goto Free_bitmaps;

	error = hibernation_snapshot(hibernation_mode == HIBERNATION_PLATFORM);
	if (error)
		goto Thaw;
	if (freezer_test_done) {
		freezer_test_done = false;
		goto Thaw;
	}

	if (in_suspend) {
		unsigned int flags = 0;

		if (hibernation_mode == HIBERNATION_PLATFORM)
			flags |= SF_PLATFORM_MODE;
		if (nocompress)
			flags |= SF_NOCOMPRESS_MODE;
		else
		        flags |= SF_CRC32_MODE;

		pr_debug("PM: writing image.\n");
		error = swsusp_write(flags);
		swsusp_free();
		if (!error)
			power_down();
		in_suspend = 0;
		pm_restore_gfp_mask();
	} else {
		pr_debug("PM: Image restored successfully.\n");
	}

 Thaw:
	thaw_processes();
 Free_bitmaps:
	free_basic_memory_bitmaps();
 Exit:
	pm_notifier_call_chain(PM_POST_HIBERNATION);
	pm_restore_console();
	atomic_inc(&snapshot_device_available);
 Unlock:
	unlock_system_sleep();
	return error;
}

static int software_resume(void)
{
	int error;
	unsigned int flags;

	/*
	 * name_to_dev_t() below takes a sysfs buffer mutex when sysfs
	 * is configured into the kernel. Since the regular hibernate
	 * trigger path is via sysfs which takes a buffer mutex before
	 * calling hibernate functions (which take pm_mutex) this can
	 * cause lockdep to complain about a possible ABBA deadlock
	 * which cannot happen since we're in the boot code here and
	 * sysfs can't be invoked yet. Therefore, we use a subclass
	 * here to avoid lockdep complaining.
	 */
	mutex_lock_nested(&pm_mutex, SINGLE_DEPTH_NESTING);
	if (!swsusp_resume_device) {
		if (!strlen(resume_file)) {
			mutex_unlock(&pm_mutex);
			return -ENOENT;
		}
		swsusp_resume_device = name_to_dev_t(resume_file);
		pr_debug("PM: Resume from partition %s\n", resume_file);
	} else {
		pr_debug("PM: Resume from partition %d:%d\n",
				MAJOR(swsusp_resume_device),
				MINOR(swsusp_resume_device));
	}

	if (noresume) {
		/**
		 * FIXME: If noresume is specified, we need to find the
		 * partition and reset it back to normal swap space.
		 */
		mutex_unlock(&pm_mutex);
		return 0;
	}

	pr_debug("PM: Checking hibernation image.\n");
	error = swsusp_check();
	if (error)
		goto Unlock;

	/* The snapshot device should not be opened while we're running */
	if (!atomic_add_unless(&snapshot_device_available, -1, 0)) {
		error = -EBUSY;
		goto Unlock;
	}

	pm_prepare_console();
	error = pm_notifier_call_chain(PM_RESTORE_PREPARE);
	if (error)
		goto Finish;

	error = create_basic_memory_bitmaps();
	if (error)
		goto Finish;

	pr_debug("PM: Preparing processes for restore.\n");
	error = prepare_processes();
	if (error) {
		swsusp_close();
		goto Done;
	}

	pr_debug("PM: Reading hibernation image.\n");

	error = swsusp_read(&flags);
	if (!error)
		hibernation_restore(flags & SF_PLATFORM_MODE);

	printk(KERN_ERR "PM: Restore failed, recovering.\n");
	swsusp_free();
	thaw_processes();
 Done:
	free_basic_memory_bitmaps();
 Finish:
	pm_notifier_call_chain(PM_POST_RESTORE);
	pm_restore_console();
	atomic_inc(&snapshot_device_available);
	/* For success case, the suspend path will release the lock */
 Unlock:
	mutex_unlock(&pm_mutex);
	pr_debug("PM: Resume from disk failed.\n");
	return error;
}

static int software_resume(void)
{
	int error;

	mutex_lock(&pm_mutex);
	if (!swsusp_resume_device) {
		if (!strlen(resume_file)) {
			mutex_unlock(&pm_mutex);
			return -ENOENT;
		}
		swsusp_resume_device = name_to_dev_t(resume_file);
		pr_debug("swsusp: Resume From Partition %s\n", resume_file);
	} else {
		pr_debug("swsusp: Resume From Partition %d:%d\n",
			 MAJOR(swsusp_resume_device), MINOR(swsusp_resume_device));
	}

	if (noresume) {
		/**
		 * FIXME: If noresume is specified, we need to find the partition
		 * and reset it back to normal swap space.
		 */
		mutex_unlock(&pm_mutex);
		return 0;
	}

	pr_debug("PM: Checking swsusp image.\n");
	error = swsusp_check();
	if (error)
		goto Unlock;

	error = create_basic_memory_bitmaps();
	if (error)
		goto Unlock;

	pr_debug("PM: Preparing processes for restore.\n");
	error = prepare_processes();
	if (error) {
		swsusp_close();
		goto Done;
	}

	pr_debug("PM: Reading swsusp image.\n");

	error = swsusp_read();
	if (error) {
		swsusp_free();
		goto Thaw;
	}

	pr_debug("PM: Preparing devices for restore.\n");

	suspend_console();
	error = device_suspend(PMSG_PRETHAW);
	if (error)
		goto Free;

	error = disable_nonboot_cpus();
	if (!error)
		swsusp_resume();

	enable_nonboot_cpus();
 Free:
	swsusp_free();
	device_resume();
	resume_console();
 Thaw:
	printk(KERN_ERR "PM: Restore failed, recovering.\n");
	unprepare_processes();
 Done:
	free_basic_memory_bitmaps();
	/* For success case, the suspend path will release the lock */
 Unlock:
	mutex_unlock(&pm_mutex);
	pr_debug("PM: Resume from disk failed.\n");
	return 0;
}

int pm_suspend_disk(void)
{
	int error;

	error = prepare_processes();
	if (error)
		return error;

	if (pm_disk_mode == PM_DISK_TESTPROC) {
		printk("swsusp debug: Waiting for 5 seconds.\n");
		mdelay(5000);
		goto Thaw;
	}
	/* Allocate memory management structures */
	error = create_basic_memory_bitmaps();
	if (error)
		goto Thaw;

	/* Free memory before shutting down devices. */
	error = swsusp_shrink_memory();
	if (error)
		goto Finish;

	error = platform_prepare();
	if (error)
		goto Finish;

	suspend_console();
	error = device_suspend(PMSG_FREEZE);
	if (error) {
		printk(KERN_ERR "PM: Some devices failed to suspend\n");
		goto Resume_devices;
	}
	error = disable_nonboot_cpus();
	if (error)
		goto Enable_cpus;

	if (pm_disk_mode == PM_DISK_TEST) {
		printk("swsusp debug: Waiting for 5 seconds.\n");
		mdelay(5000);
		goto Enable_cpus;
	}

	pr_debug("PM: snapshotting memory.\n");
	in_suspend = 1;
	error = swsusp_suspend();
	if (error)
		goto Enable_cpus;

	if (in_suspend) {
		enable_nonboot_cpus();
		platform_finish();
		device_resume();
		resume_console();
		pr_debug("PM: writing image.\n");
		error = swsusp_write();
		if (!error)
			power_down(pm_disk_mode);
		else {
			swsusp_free();
			goto Finish;
		}
	} else {
		pr_debug("PM: Image restored successfully.\n");
	}

	swsusp_free();
 Enable_cpus:
	enable_nonboot_cpus();
 Resume_devices:
	platform_finish();
	device_resume();
	resume_console();
 Finish:
	free_basic_memory_bitmaps();
 Thaw:
	unprepare_processes();
	return error;
}

static long snapshot_ioctl(struct file *filp, unsigned int cmd,
							unsigned long arg)
{
	int error = 0;
	struct snapshot_data *data;
	loff_t size;
	sector_t offset;

	if (_IOC_TYPE(cmd) != SNAPSHOT_IOC_MAGIC)
		return -ENOTTY;
	if (_IOC_NR(cmd) > SNAPSHOT_IOC_MAXNR)
		return -ENOTTY;
	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	if (!mutex_trylock(&pm_mutex))
		return -EBUSY;

	lock_device_hotplug();
	data = filp->private_data;

	switch (cmd) {

	case SNAPSHOT_FREEZE:
		if (data->frozen)
			break;

		printk("Syncing filesystems ... ");
		sys_sync();
		printk("done.\n");

		error = freeze_processes();
		if (error)
			break;

		error = create_basic_memory_bitmaps();
		if (error)
			thaw_processes();
		else
			data->frozen = 1;

		break;

	case SNAPSHOT_UNFREEZE:
		if (!data->frozen || data->ready)
			break;
		pm_restore_gfp_mask();
		free_basic_memory_bitmaps();
		data->free_bitmaps = false;
		thaw_processes();
		data->frozen = 0;
		break;

	case SNAPSHOT_CREATE_IMAGE:
		if (data->mode != O_RDONLY || !data->frozen  || data->ready) {
			error = -EPERM;
			break;
		}
		pm_restore_gfp_mask();
		error = hibernation_snapshot(data->platform_support);
		if (!error) {
			error = put_user(in_suspend, (int __user *)arg);
			data->ready = !freezer_test_done && !error;
			freezer_test_done = false;
		}
		break;

	case SNAPSHOT_ATOMIC_RESTORE:
		snapshot_write_finalize(&data->handle);
		if (data->mode != O_WRONLY || !data->frozen ||
		    !snapshot_image_loaded(&data->handle)) {
			error = -EPERM;
			break;
		}
		error = hibernation_restore(data->platform_support);
		break;

	case SNAPSHOT_FREE:
		swsusp_free();
		memset(&data->handle, 0, sizeof(struct snapshot_handle));
		data->ready = 0;
		/*
		 * It is necessary to thaw kernel threads here, because
		 * SNAPSHOT_CREATE_IMAGE may be invoked directly after
		 * SNAPSHOT_FREE.  In that case, if kernel threads were not
		 * thawed, the preallocation of memory carried out by
		 * hibernation_snapshot() might run into problems (i.e. it
		 * might fail or even deadlock).
		 */
		thaw_kernel_threads();
		break;

	case SNAPSHOT_PREF_IMAGE_SIZE:
		image_size = arg;
		break;

	case SNAPSHOT_GET_IMAGE_SIZE:
		if (!data->ready) {
			error = -ENODATA;
			break;
//.........这里部分代码省略.........