WSL2-Linux-Kernel/fs/super.c

/*
 *  linux/fs/super.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  super.c contains code to handle: - mount structures
 *                                   - super-block tables
 *                                   - filesystem drivers list
 *                                   - mount system call
 *                                   - umount system call
 *                                   - ustat system call
 *
 * GK 2/5/95  -  Changed to support mounting the root fs via NFS
 *
 *  Added kerneld support: Jacques Gelinas and Bjorn Ekwall
 *  Added change_root: Werner Almesberger & Hans Lermen, Feb '96
 *  Added options to /proc/mounts:
 *    Torbjörn Lindh (torbjorn.lindh@gopta.se), April 14, 1996.
 *  Added devfs support: Richard Gooch <rgooch@atnf.csiro.au>, 13-JAN-1998
 *  Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/acct.h>
#include <linux/blkdev.h>
#include <linux/mount.h>
#include <linux/security.h>
#include <linux/writeback.h>		/* for the emergency remount stuff */
#include <linux/idr.h>
#include <linux/mutex.h>
#include <linux/backing-dev.h>
#include "internal.h"


LIST_HEAD(super_blocks);
DEFINE_SPINLOCK(sb_lock);

/**
 *	alloc_super	-	create new superblock
 *	@type:	filesystem type superblock should belong to
 *
 *	Allocates and initializes a new &struct super_block.  alloc_super()
 *	returns a pointer new superblock or %NULL if allocation had failed.
 */
static struct super_block *alloc_super(struct file_system_type *type)
{
	struct super_block *s = kzalloc(sizeof(struct super_block),  GFP_USER);
	static const struct super_operations default_op;

	if (s) {
		if (security_sb_alloc(s)) {
			kfree(s);
			s = NULL;
			goto out;
		}
		INIT_LIST_HEAD(&s->s_files);
		INIT_LIST_HEAD(&s->s_instances);
		INIT_HLIST_HEAD(&s->s_anon);
		INIT_LIST_HEAD(&s->s_inodes);
		INIT_LIST_HEAD(&s->s_dentry_lru);
		init_rwsem(&s->s_umount);
		mutex_init(&s->s_lock);
		lockdep_set_class(&s->s_umount, &type->s_umount_key);
		/*
		 * The locking rules for s_lock are up to the
		 * filesystem. For example ext3fs has different
		 * lock ordering than usbfs:
		 */
		lockdep_set_class(&s->s_lock, &type->s_lock_key);
		/*
		 * sget() can have s_umount recursion.
		 *
		 * When it cannot find a suitable sb, it allocates a new
		 * one (this one), and tries again to find a suitable old
		 * one.
		 *
		 * In case that succeeds, it will acquire the s_umount
		 * lock of the old one. Since these are clearly distrinct
		 * locks, and this object isn't exposed yet, there's no
		 * risk of deadlocks.
		 *
		 * Annotate this by putting this lock in a different
		 * subclass.
		 */
		down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
		s->s_count = 1;
		atomic_set(&s->s_active, 1);
		mutex_init(&s->s_vfs_rename_mutex);
		lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
		mutex_init(&s->s_dquot.dqio_mutex);
		mutex_init(&s->s_dquot.dqonoff_mutex);
		init_rwsem(&s->s_dquot.dqptr_sem);
		init_waitqueue_head(&s->s_wait_unfrozen);
		s->s_maxbytes = MAX_NON_LFS;
		s->s_op = &default_op;
		s->s_time_gran = 1000000000;
	}
out:
	return s;
}

/**
 *	destroy_super	-	frees a superblock
 *	@s: superblock to free
 *
 *	Frees a superblock.
 */
static inline void destroy_super(struct super_block *s)
{
	security_sb_free(s);
	kfree(s->s_subtype);
	kfree(s->s_options);
	kfree(s);
}

/* Superblock refcounting  */

/*
 * Drop a superblock's refcount.  The caller must hold sb_lock.
 */
void __put_super(struct super_block *sb)
{
	if (!--sb->s_count) {
		list_del_init(&sb->s_list);
		destroy_super(sb);
	}
}

/**
 *	put_super	-	drop a temporary reference to superblock
 *	@sb: superblock in question
 *
 *	Drops a temporary reference, frees superblock if there's no
 *	references left.
 */
void put_super(struct super_block *sb)
{
	spin_lock(&sb_lock);
	__put_super(sb);
	spin_unlock(&sb_lock);
}


/**
 *	deactivate_locked_super	-	drop an active reference to superblock
 *	@s: superblock to deactivate
 *
 *	Drops an active reference to superblock, converting it into a temprory
 *	one if there is no other active references left.  In that case we
 *	tell fs driver to shut it down and drop the temporary reference we
 *	had just acquired.
 *
 *	Caller holds exclusive lock on superblock; that lock is released.
 */
void deactivate_locked_super(struct super_block *s)
{
	struct file_system_type *fs = s->s_type;
	if (atomic_dec_and_test(&s->s_active)) {
		fs->kill_sb(s);
		put_filesystem(fs);
		put_super(s);
	} else {
		up_write(&s->s_umount);
	}
}

EXPORT_SYMBOL(deactivate_locked_super);

/**
 *	deactivate_super	-	drop an active reference to superblock
 *	@s: superblock to deactivate
 *
 *	Variant of deactivate_locked_super(), except that superblock is *not*
 *	locked by caller.  If we are going to drop the final active reference,
 *	lock will be acquired prior to that.
 */
void deactivate_super(struct super_block *s)
{
        if (!atomic_add_unless(&s->s_active, -1, 1)) {
		down_write(&s->s_umount);
		deactivate_locked_super(s);
	}
}

EXPORT_SYMBOL(deactivate_super);

/**
 *	grab_super - acquire an active reference
 *	@s: reference we are trying to make active
 *
 *	Tries to acquire an active reference.  grab_super() is used when we
 * 	had just found a superblock in super_blocks or fs_type->fs_supers
 *	and want to turn it into a full-blown active reference.  grab_super()
 *	is called with sb_lock held and drops it.  Returns 1 in case of
 *	success, 0 if we had failed (superblock contents was already dead or
 *	dying when grab_super() had been called).
 */
static int grab_super(struct super_block *s) __releases(sb_lock)
{
	if (atomic_inc_not_zero(&s->s_active)) {
		spin_unlock(&sb_lock);
		return 1;
	}
	/* it's going away */
	s->s_count++;
	spin_unlock(&sb_lock);
	/* wait for it to die */
	down_write(&s->s_umount);
	up_write(&s->s_umount);
	put_super(s);
	return 0;
}

/*
 * Superblock locking.  We really ought to get rid of these two.
 */
void lock_super(struct super_block * sb)
{
	get_fs_excl();
	mutex_lock(&sb->s_lock);
}

void unlock_super(struct super_block * sb)
{
	put_fs_excl();
	mutex_unlock(&sb->s_lock);
}

EXPORT_SYMBOL(lock_super);
EXPORT_SYMBOL(unlock_super);

/**
 *	generic_shutdown_super	-	common helper for ->kill_sb()
 *	@sb: superblock to kill
 *
 *	generic_shutdown_super() does all fs-independent work on superblock
 *	shutdown.  Typical ->kill_sb() should pick all fs-specific objects
 *	that need destruction out of superblock, call generic_shutdown_super()
 *	and release aforementioned objects.  Note: dentries and inodes _are_
 *	taken care of and do not need specific handling.
 *
 *	Upon calling this function, the filesystem may no longer alter or
 *	rearrange the set of dentries belonging to this super_block, nor may it
 *	change the attachments of dentries to inodes.
 */
void generic_shutdown_super(struct super_block *sb)
{
	const struct super_operations *sop = sb->s_op;


	if (sb->s_root) {
		shrink_dcache_for_umount(sb);
		sync_filesystem(sb);
		get_fs_excl();
		sb->s_flags &= ~MS_ACTIVE;

		/* bad name - it should be evict_inodes() */
		invalidate_inodes(sb);

		if (sop->put_super)
			sop->put_super(sb);

		/* Forget any remaining inodes */
		if (invalidate_inodes(sb)) {
			printk("VFS: Busy inodes after unmount of %s. "
			   "Self-destruct in 5 seconds.  Have a nice day...\n",
			   sb->s_id);
		}
		put_fs_excl();
	}
	spin_lock(&sb_lock);
	/* should be initialized for __put_super_and_need_restart() */
	list_del_init(&sb->s_instances);
	spin_unlock(&sb_lock);
	up_write(&sb->s_umount);
}

EXPORT_SYMBOL(generic_shutdown_super);

/**
 *	sget	-	find or create a superblock
 *	@type:	filesystem type superblock should belong to
 *	@test:	comparison callback
 *	@set:	setup callback
 *	@data:	argument to each of them
 */
struct super_block *sget(struct file_system_type *type,
			int (*test)(struct super_block *,void *),
			int (*set)(struct super_block *,void *),
			void *data)
{
	struct super_block *s = NULL;
	struct super_block *old;
	int err;

retry:
	spin_lock(&sb_lock);
	if (test) {
		list_for_each_entry(old, &type->fs_supers, s_instances) {
			if (!test(old, data))
				continue;
			if (!grab_super(old))
				goto retry;
			if (s) {
				up_write(&s->s_umount);
				destroy_super(s);
			}
			down_write(&old->s_umount);
			return old;
		}
	}
	if (!s) {
		spin_unlock(&sb_lock);
		s = alloc_super(type);
		if (!s)
			return ERR_PTR(-ENOMEM);
		goto retry;
	}
		
	err = set(s, data);
	if (err) {
		spin_unlock(&sb_lock);
		up_write(&s->s_umount);
		destroy_super(s);
		return ERR_PTR(err);
	}
	s->s_type = type;
	strlcpy(s->s_id, type->name, sizeof(s->s_id));
	list_add_tail(&s->s_list, &super_blocks);
	list_add(&s->s_instances, &type->fs_supers);
	spin_unlock(&sb_lock);
	get_filesystem(type);
	return s;
}

EXPORT_SYMBOL(sget);

void drop_super(struct super_block *sb)
{
	up_read(&sb->s_umount);
	put_super(sb);
}

EXPORT_SYMBOL(drop_super);

/**
 * sync_supers - helper for periodic superblock writeback
 *
 * Call the write_super method if present on all dirty superblocks in
 * the system.  This is for the periodic writeback used by most older
 * filesystems.  For data integrity superblock writeback use
 * sync_filesystems() instead.
 *
 * Note: check the dirty flag before waiting, so we don't
 * hold up the sync while mounting a device. (The newly
 * mounted device won't need syncing.)
 */
void sync_supers(void)
{
	struct super_block *sb, *n;

	spin_lock(&sb_lock);
	list_for_each_entry_safe(sb, n, &super_blocks, s_list) {
		if (list_empty(&sb->s_instances))
			continue;
		if (sb->s_op->write_super && sb->s_dirt) {
			sb->s_count++;
			spin_unlock(&sb_lock);

			down_read(&sb->s_umount);
			if (sb->s_root && sb->s_dirt)
				sb->s_op->write_super(sb);
			up_read(&sb->s_umount);

			spin_lock(&sb_lock);
			/* lock was dropped, must reset next */
			list_safe_reset_next(sb, n, s_list);
			__put_super(sb);
		}
	}
	spin_unlock(&sb_lock);
}

/**
 *	iterate_supers - call function for all active superblocks
 *	@f: function to call
 *	@arg: argument to pass to it
 *
 *	Scans the superblock list and calls given function, passing it
 *	locked superblock and given argument.
 */
void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
{
	struct super_block *sb, *n;

	spin_lock(&sb_lock);
	list_for_each_entry_safe(sb, n, &super_blocks, s_list) {
		if (list_empty(&sb->s_instances))
			continue;
		sb->s_count++;
		spin_unlock(&sb_lock);

		down_read(&sb->s_umount);
		if (sb->s_root)
			f(sb, arg);
		up_read(&sb->s_umount);

		spin_lock(&sb_lock);
		/* lock was dropped, must reset next */
		list_safe_reset_next(sb, n, s_list);
		__put_super(sb);
	}
	spin_unlock(&sb_lock);
}

/**
 *	get_super - get the superblock of a device
 *	@bdev: device to get the superblock for
 *	
 *	Scans the superblock list and finds the superblock of the file system
 *	mounted on the device given. %NULL is returned if no match is found.
 */

struct super_block *get_super(struct block_device *bdev)
{
	struct super_block *sb;

	if (!bdev)
		return NULL;

	spin_lock(&sb_lock);
rescan:
	list_for_each_entry(sb, &super_blocks, s_list) {
		if (list_empty(&sb->s_instances))
			continue;
		if (sb->s_bdev == bdev) {
			sb->s_count++;
			spin_unlock(&sb_lock);
			down_read(&sb->s_umount);
			/* still alive? */
			if (sb->s_root)
				return sb;
			up_read(&sb->s_umount);
			/* nope, got unmounted */
			spin_lock(&sb_lock);
			__put_super(sb);
			goto rescan;
		}
	}
	spin_unlock(&sb_lock);
	return NULL;
}

EXPORT_SYMBOL(get_super);

/**
 * get_active_super - get an active reference to the superblock of a device
 * @bdev: device to get the superblock for
 *
 * Scans the superblock list and finds the superblock of the file system
 * mounted on the device given.  Returns the superblock with an active
 * reference or %NULL if none was found.
 */
struct super_block *get_active_super(struct block_device *bdev)
{
	struct super_block *sb;

	if (!bdev)
		return NULL;

restart:
	spin_lock(&sb_lock);
	list_for_each_entry(sb, &super_blocks, s_list) {
		if (list_empty(&sb->s_instances))
			continue;
		if (sb->s_bdev == bdev) {
			if (grab_super(sb)) /* drops sb_lock */
				return sb;
			else
				goto restart;
		}
	}
	spin_unlock(&sb_lock);
	return NULL;
}
 
struct super_block *user_get_super(dev_t dev)
{
	struct super_block *sb;

	spin_lock(&sb_lock);
rescan:
	list_for_each_entry(sb, &super_blocks, s_list) {
		if (list_empty(&sb->s_instances))
			continue;
		if (sb->s_dev ==  dev) {
			sb->s_count++;
			spin_unlock(&sb_lock);
			down_read(&sb->s_umount);
			/* still alive? */
			if (sb->s_root)
				return sb;
			up_read(&sb->s_umount);
			/* nope, got unmounted */
			spin_lock(&sb_lock);
			__put_super(sb);
			goto rescan;
		}
	}
	spin_unlock(&sb_lock);
	return NULL;
}

/**
 *	do_remount_sb - asks filesystem to change mount options.
 *	@sb:	superblock in question
 *	@flags:	numeric part of options
 *	@data:	the rest of options
 *      @force: whether or not to force the change
 *
 *	Alters the mount options of a mounted file system.
 */
int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
{
	int retval;
	int remount_ro;

	if (sb->s_frozen != SB_UNFROZEN)
		return -EBUSY;

#ifdef CONFIG_BLOCK
	if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
		return -EACCES;
#endif

	if (flags & MS_RDONLY)
		acct_auto_close(sb);
	shrink_dcache_sb(sb);
	sync_filesystem(sb);

	remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);

	/* If we are remounting RDONLY and current sb is read/write,
	   make sure there are no rw files opened */
	if (remount_ro) {
		if (force)
			mark_files_ro(sb);
		else if (!fs_may_remount_ro(sb))
			return -EBUSY;
	}

	if (sb->s_op->remount_fs) {
		retval = sb->s_op->remount_fs(sb, &flags, data);
		if (retval)
			return retval;
	}
	sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);

	/*
	 * Some filesystems modify their metadata via some other path than the
	 * bdev buffer cache (eg. use a private mapping, or directories in
	 * pagecache, etc). Also file data modifications go via their own
	 * mappings. So If we try to mount readonly then copy the filesystem
	 * from bdev, we could get stale data, so invalidate it to give a best
	 * effort at coherency.
	 */
	if (remount_ro && sb->s_bdev)
		invalidate_bdev(sb->s_bdev);
	return 0;
}

static void do_emergency_remount(struct work_struct *work)
{
	struct super_block *sb, *n;

	spin_lock(&sb_lock);
	list_for_each_entry_safe(sb, n, &super_blocks, s_list) {
		if (list_empty(&sb->s_instances))
			continue;
		sb->s_count++;
		spin_unlock(&sb_lock);
		down_write(&sb->s_umount);
		if (sb->s_root && sb->s_bdev && !(sb->s_flags & MS_RDONLY)) {
			/*
			 * What lock protects sb->s_flags??
			 */
			do_remount_sb(sb, MS_RDONLY, NULL, 1);
		}
		up_write(&sb->s_umount);
		spin_lock(&sb_lock);
		/* lock was dropped, must reset next */
		list_safe_reset_next(sb, n, s_list);
		__put_super(sb);
	}
	spin_unlock(&sb_lock);
	kfree(work);
	printk("Emergency Remount complete\n");
}

void emergency_remount(void)
{
	struct work_struct *work;

	work = kmalloc(sizeof(*work), GFP_ATOMIC);
	if (work) {
		INIT_WORK(work, do_emergency_remount);
		schedule_work(work);
	}
}

/*
 * Unnamed block devices are dummy devices used by virtual
 * filesystems which don't use real block-devices.  -- jrs
 */

static DEFINE_IDA(unnamed_dev_ida);
static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
static int unnamed_dev_start = 0; /* don't bother trying below it */

int set_anon_super(struct super_block *s, void *data)
{
	int dev;
	int error;

 retry:
	if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0)
		return -ENOMEM;
	spin_lock(&unnamed_dev_lock);
	error = ida_get_new_above(&unnamed_dev_ida, unnamed_dev_start, &dev);
	if (!error)
		unnamed_dev_start = dev + 1;
	spin_unlock(&unnamed_dev_lock);
	if (error == -EAGAIN)
		/* We raced and lost with another CPU. */
		goto retry;
	else if (error)
		return -EAGAIN;

	if ((dev & MAX_ID_MASK) == (1 << MINORBITS)) {
		spin_lock(&unnamed_dev_lock);
		ida_remove(&unnamed_dev_ida, dev);
		if (unnamed_dev_start > dev)
			unnamed_dev_start = dev;
		spin_unlock(&unnamed_dev_lock);
		return -EMFILE;
	}
	s->s_dev = MKDEV(0, dev & MINORMASK);
	s->s_bdi = &noop_backing_dev_info;
	return 0;
}

EXPORT_SYMBOL(set_anon_super);

void kill_anon_super(struct super_block *sb)
{
	int slot = MINOR(sb->s_dev);

	generic_shutdown_super(sb);
	spin_lock(&unnamed_dev_lock);
	ida_remove(&unnamed_dev_ida, slot);
	if (slot < unnamed_dev_start)
		unnamed_dev_start = slot;
	spin_unlock(&unnamed_dev_lock);
}

EXPORT_SYMBOL(kill_anon_super);

void kill_litter_super(struct super_block *sb)
{
	if (sb->s_root)
		d_genocide(sb->s_root);
	kill_anon_super(sb);
}

EXPORT_SYMBOL(kill_litter_super);

static int ns_test_super(struct super_block *sb, void *data)
{
	return sb->s_fs_info == data;
}

static int ns_set_super(struct super_block *sb, void *data)
{
	sb->s_fs_info = data;
	return set_anon_super(sb, NULL);
}

int get_sb_ns(struct file_system_type *fs_type, int flags, void *data,
	int (*fill_super)(struct super_block *, void *, int),
	struct vfsmount *mnt)
{
	struct super_block *sb;

	sb = sget(fs_type, ns_test_super, ns_set_super, data);
	if (IS_ERR(sb))
		return PTR_ERR(sb);

	if (!sb->s_root) {
		int err;
		sb->s_flags = flags;
		err = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
		if (err) {
			deactivate_locked_super(sb);
			return err;
		}

		sb->s_flags |= MS_ACTIVE;
	}

	simple_set_mnt(mnt, sb);
	return 0;
}

EXPORT_SYMBOL(get_sb_ns);

#ifdef CONFIG_BLOCK
static int set_bdev_super(struct super_block *s, void *data)
{
	s->s_bdev = data;
	s->s_dev = s->s_bdev->bd_dev;

	/*
	 * We set the bdi here to the queue backing, file systems can
	 * overwrite this in ->fill_super()
	 */
	s->s_bdi = &bdev_get_queue(s->s_bdev)->backing_dev_info;
	return 0;
}

static int test_bdev_super(struct super_block *s, void *data)
{
	return (void *)s->s_bdev == data;
}

int get_sb_bdev(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data,
	int (*fill_super)(struct super_block *, void *, int),
	struct vfsmount *mnt)
{
	struct block_device *bdev;
	struct super_block *s;
	fmode_t mode = FMODE_READ;
	int error = 0;

	if (!(flags & MS_RDONLY))
		mode |= FMODE_WRITE;

	bdev = open_bdev_exclusive(dev_name, mode, fs_type);
	if (IS_ERR(bdev))
		return PTR_ERR(bdev);

	/*
	 * once the super is inserted into the list by sget, s_umount
	 * will protect the lockfs code from trying to start a snapshot
	 * while we are mounting
	 */
	mutex_lock(&bdev->bd_fsfreeze_mutex);
	if (bdev->bd_fsfreeze_count > 0) {
		mutex_unlock(&bdev->bd_fsfreeze_mutex);
		error = -EBUSY;
		goto error_bdev;
	}
	s = sget(fs_type, test_bdev_super, set_bdev_super, bdev);
	mutex_unlock(&bdev->bd_fsfreeze_mutex);
	if (IS_ERR(s))
		goto error_s;

	if (s->s_root) {
		if ((flags ^ s->s_flags) & MS_RDONLY) {
			deactivate_locked_super(s);
			error = -EBUSY;
			goto error_bdev;
		}

		close_bdev_exclusive(bdev, mode);
	} else {
		char b[BDEVNAME_SIZE];

		s->s_flags = flags;
		s->s_mode = mode;
		strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
		sb_set_blocksize(s, block_size(bdev));
		error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
		if (error) {
			deactivate_locked_super(s);
			goto error;
		}

		s->s_flags |= MS_ACTIVE;
		bdev->bd_super = s;
	}

	simple_set_mnt(mnt, s);
	return 0;

error_s:
	error = PTR_ERR(s);
error_bdev:
	close_bdev_exclusive(bdev, mode);
error:
	return error;
}

EXPORT_SYMBOL(get_sb_bdev);

void kill_block_super(struct super_block *sb)
{
	struct block_device *bdev = sb->s_bdev;
	fmode_t mode = sb->s_mode;

	bdev->bd_super = NULL;
	generic_shutdown_super(sb);
	sync_blockdev(bdev);
	close_bdev_exclusive(bdev, mode);
}

EXPORT_SYMBOL(kill_block_super);
#endif

int get_sb_nodev(struct file_system_type *fs_type,
	int flags, void *data,
	int (*fill_super)(struct super_block *, void *, int),
	struct vfsmount *mnt)
{
	int error;
	struct super_block *s = sget(fs_type, NULL, set_anon_super, NULL);

	if (IS_ERR(s))
		return PTR_ERR(s);

	s->s_flags = flags;

	error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
	if (error) {
		deactivate_locked_super(s);
		return error;
	}
	s->s_flags |= MS_ACTIVE;
	simple_set_mnt(mnt, s);
	return 0;
}

EXPORT_SYMBOL(get_sb_nodev);

static int compare_single(struct super_block *s, void *p)
{
	return 1;
}

int get_sb_single(struct file_system_type *fs_type,
	int flags, void *data,
	int (*fill_super)(struct super_block *, void *, int),
	struct vfsmount *mnt)
{
	struct super_block *s;
	int error;

	s = sget(fs_type, compare_single, set_anon_super, NULL);
	if (IS_ERR(s))
		return PTR_ERR(s);
	if (!s->s_root) {
		s->s_flags = flags;
		error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
		if (error) {
			deactivate_locked_super(s);
			return error;
		}
		s->s_flags |= MS_ACTIVE;
	} else {
		do_remount_sb(s, flags, data, 0);
	}
	simple_set_mnt(mnt, s);
	return 0;
}

EXPORT_SYMBOL(get_sb_single);

struct vfsmount *
vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
{
	struct vfsmount *mnt;
	char *secdata = NULL;
	int error;

	if (!type)
		return ERR_PTR(-ENODEV);

	error = -ENOMEM;
	mnt = alloc_vfsmnt(name);
	if (!mnt)
		goto out;

	if (flags & MS_KERNMOUNT)
		mnt->mnt_flags = MNT_INTERNAL;

	if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
		secdata = alloc_secdata();
		if (!secdata)
			goto out_mnt;

		error = security_sb_copy_data(data, secdata);
		if (error)
			goto out_free_secdata;
	}

	error = type->get_sb(type, flags, name, data, mnt);
	if (error < 0)
		goto out_free_secdata;
	BUG_ON(!mnt->mnt_sb);
	WARN_ON(!mnt->mnt_sb->s_bdi);

	error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);
	if (error)
		goto out_sb;

	/*
	 * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
	 * but s_maxbytes was an unsigned long long for many releases. Throw
	 * this warning for a little while to try and catch filesystems that
	 * violate this rule. This warning should be either removed or
	 * converted to a BUG() in 2.6.34.
	 */
	WARN((mnt->mnt_sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
		"negative value (%lld)\n", type->name, mnt->mnt_sb->s_maxbytes);

	mnt->mnt_mountpoint = mnt->mnt_root;
	mnt->mnt_parent = mnt;
	up_write(&mnt->mnt_sb->s_umount);
	free_secdata(secdata);
	return mnt;
out_sb:
	dput(mnt->mnt_root);
	deactivate_locked_super(mnt->mnt_sb);
out_free_secdata:
	free_secdata(secdata);
out_mnt:
	free_vfsmnt(mnt);
out:
	return ERR_PTR(error);
}

EXPORT_SYMBOL_GPL(vfs_kern_mount);

/**
 * freeze_super - lock the filesystem and force it into a consistent state
 * @sb: the super to lock
 *
 * Syncs the super to make sure the filesystem is consistent and calls the fs's
 * freeze_fs.  Subsequent calls to this without first thawing the fs will return
 * -EBUSY.
 */
int freeze_super(struct super_block *sb)
{
	int ret;

	atomic_inc(&sb->s_active);
	down_write(&sb->s_umount);
	if (sb->s_frozen) {
		deactivate_locked_super(sb);
		return -EBUSY;
	}

	if (sb->s_flags & MS_RDONLY) {
		sb->s_frozen = SB_FREEZE_TRANS;
		smp_wmb();
		up_write(&sb->s_umount);
		return 0;
	}

	sb->s_frozen = SB_FREEZE_WRITE;
	smp_wmb();

	sync_filesystem(sb);

	sb->s_frozen = SB_FREEZE_TRANS;
	smp_wmb();

	sync_blockdev(sb->s_bdev);
	if (sb->s_op->freeze_fs) {
		ret = sb->s_op->freeze_fs(sb);
		if (ret) {
			printk(KERN_ERR
				"VFS:Filesystem freeze failed\n");
			sb->s_frozen = SB_UNFROZEN;
			deactivate_locked_super(sb);
			return ret;
		}
	}
	up_write(&sb->s_umount);
	return 0;
}
EXPORT_SYMBOL(freeze_super);

/**
 * thaw_super -- unlock filesystem
 * @sb: the super to thaw
 *
 * Unlocks the filesystem and marks it writeable again after freeze_super().
 */
int thaw_super(struct super_block *sb)
{
	int error;

	down_write(&sb->s_umount);
	if (sb->s_frozen == SB_UNFROZEN) {
		up_write(&sb->s_umount);
		return -EINVAL;
	}

	if (sb->s_flags & MS_RDONLY)
		goto out;

	if (sb->s_op->unfreeze_fs) {
		error = sb->s_op->unfreeze_fs(sb);
		if (error) {
			printk(KERN_ERR
				"VFS:Filesystem thaw failed\n");
			sb->s_frozen = SB_FREEZE_TRANS;
			up_write(&sb->s_umount);
			return error;
		}
	}

out:
	sb->s_frozen = SB_UNFROZEN;
	smp_wmb();
	wake_up(&sb->s_wait_unfrozen);
	deactivate_locked_super(sb);

	return 0;
}
EXPORT_SYMBOL(thaw_super);

static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
{
	int err;
	const char *subtype = strchr(fstype, '.');
	if (subtype) {
		subtype++;
		err = -EINVAL;
		if (!subtype[0])
			goto err;
	} else
		subtype = "";

	mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
	err = -ENOMEM;
	if (!mnt->mnt_sb->s_subtype)
		goto err;
	return mnt;

 err:
	mntput(mnt);
	return ERR_PTR(err);
}

struct vfsmount *
do_kern_mount(const char *fstype, int flags, const char *name, void *data)
{
	struct file_system_type *type = get_fs_type(fstype);
	struct vfsmount *mnt;
	if (!type)
		return ERR_PTR(-ENODEV);
	mnt = vfs_kern_mount(type, flags, name, data);
	if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
	    !mnt->mnt_sb->s_subtype)
		mnt = fs_set_subtype(mnt, fstype);
	put_filesystem(type);
	return mnt;
}
EXPORT_SYMBOL_GPL(do_kern_mount);

struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
{
	return vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);
}

EXPORT_SYMBOL_GPL(kern_mount_data);