/*
 *  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 <linux/rculist_bl.h>
#include <linux/cleancache.h>
#include <linux/lockdep.h>
#include "internal.h"


LIST_HEAD(super_blocks);
DEFINE_SPINLOCK(sb_lock);

static struct lock_class_key sb_writers_key[SB_FREEZE_LEVELS-1];

static int init_sb_writers(struct super_block *s, int level, char *lockname)
{
	struct sb_writers_level *sl = &s->s_writers[level-1];
	int err;
    
	err = percpu_counter_init(&sl->counter, 0);
	if (err < 0)
		return err;
	init_waitqueue_head(&sl->wait);
	lockdep_init_map(&sl->lock_map, lockname, &sb_writers_key[level-1], 0);
	return 0;
}

static void destroy_sb_writers(struct super_block *s, int level)
{
	percpu_counter_destroy(&s->s_writers[level-1].counter);
}

/**
 *	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)) {
            /*
             * We cannot call security_sb_free() without
             * security_sb_alloc() succeeding. So bail out manually
             */
			kfree(s);
			s = NULL;
			goto out;
		}
#ifdef CONFIG_SMP
        s->s_files = alloc_percpu(struct list_head);
        if (!s->s_files)
            goto err_out;
        else {
        
            int i;

			for_each_possible_cpu(i)
				INIT_LIST_HEAD(per_cpu_ptr(s->s_files, i));
		}
#else
		INIT_LIST_HEAD(&s->s_files);
#endif
		
        if (init_sb_writers(s, SB_FREEZE_WRITE, "sb_writers_write"))
            goto err_out;
        if (init_sb_writers(s, SB_FREEZE_TRANS, "sb_writers_trans"))
            goto err_out;
        s->s_bdi = &default_backing_dev_info;
		INIT_LIST_HEAD(&s->s_instances);
		INIT_HLIST_BL_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;
		s->cleancache_poolid = -1;
	}
out:
	return s;
err_out:
	security_sb_free(s);
#ifdef CONFIG_SMP
    if (s->s_files)
        free_percpu(s->s_files);
#endif
    destroy_sb_writers(s, SB_FREEZE_WRITE);
    destroy_sb_writers(s, SB_FREEZE_TRANS);
    kfree(s);
    s = NULL;
    goto out;
}


/**
 *	destroy_super	-	frees a superblock
 *	@s: superblock to free
 *
 *	Frees a superblock.
 */
static inline void destroy_super(struct super_block *s)
{
#ifdef CONFIG_SMP
	free_percpu(s->s_files);
#endif
	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)) {
		cleancache_flush_fs(s);
		fs->kill_sb(s);
		/*
		 * We need to call rcu_barrier so all the delayed rcu free
		 * inodes are flushed before we release the fs module.
		 */
		rcu_barrier();
		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;
}

/*
 *	grab_super_passive - acquire a passive reference
 *	@s: reference we are trying to grab
 *
 *	Tries to acquire a passive reference. This is used in places where we
 *	cannot take an active reference but we need to ensure that the
 *	superblock does not go away while we are working on it. It returns
 *	false if a reference was not gained, and returns true with the s_umount
 *	lock held in read mode if a reference is gained. On successful return,
 *	the caller must drop the s_umount lock and the passive reference when
 *	done.
 */
bool grab_super_passive(struct super_block *sb)
{
	spin_lock(&sb_lock);
	if (list_empty(&sb->s_instances)) {
		spin_unlock(&sb_lock);
		return false;
	}

	sb->s_count++;
	spin_unlock(&sb_lock);

	if (down_read_trylock(&sb->s_umount)) {
		if (sb->s_root)
			return true;
		up_read(&sb->s_umount);
	}

	put_super(sb);
	return false;
}

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

void unlock_super(struct super_block * sb)
{
	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;

		fsnotify_unmount_inodes(&sb->s_inodes);

		evict_inodes(sb);

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

		if (!list_empty(&sb->s_inodes)) {
			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);
				s = NULL;
			}
			down_write(&old->s_umount);
			if (unlikely(!(old->s_flags & MS_BORN))) {
				deactivate_locked_super(old);
				goto retry;
			}
			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, *p = NULL;

	spin_lock(&sb_lock);
	list_for_each_entry(sb, &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);
			if (p)
				__put_super(p);
			p = sb;
		}
	}
	if (p)
		__put_super(p);
	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, *p = NULL;

	spin_lock(&sb_lock);
	list_for_each_entry(sb, &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);
		if (p)
			__put_super(p);
		p = sb;
	}
	if (p)
		__put_super(p);
	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, *p = NULL;

	spin_lock(&sb_lock);
	list_for_each_entry(sb, &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);
		if (p)
			__put_super(p);
		p = sb;
	}
	if (p)
		__put_super(p);
	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);
}

struct dentry *mount_ns(struct file_system_type *fs_type, int flags,
	void *data, int (*fill_super)(struct super_block *, void *, int))
{
	struct super_block *sb;

	sb = sget(fs_type, ns_test_super, ns_set_super, data);
	if (IS_ERR(sb))
		return ERR_CAST(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_PTR(err);
		}

		sb->s_flags |= MS_ACTIVE;
	}

	return dget(sb->s_root);
}

EXPORT_SYMBOL(mount_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;
}

struct dentry *mount_bdev(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data,
	int (*fill_super)(struct super_block *, void *, int))
{
	struct block_device *bdev;
	struct super_block *s;
	fmode_t mode = FMODE_READ | FMODE_EXCL;
	int error = 0;

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

	bdev = blkdev_get_by_path(dev_name, mode, fs_type);
	if (IS_ERR(bdev))
		return ERR_CAST(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;
		}

		/*
		 * s_umount nests inside bd_mutex during
		 * __invalidate_device().  blkdev_put() acquires
		 * bd_mutex and can't be called under s_umount.  Drop
		 * s_umount temporarily.  This is safe as we're
		 * holding an active reference.
		 */
		up_write(&s->s_umount);
		blkdev_put(bdev, mode);
		down_write(&s->s_umount);
	} 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;
	}

	return dget(s->s_root);

error_s:
	error = PTR_ERR(s);
error_bdev:
	blkdev_put(bdev, mode);
error:
	return ERR_PTR(error);
}
EXPORT_SYMBOL(mount_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);
	WARN_ON_ONCE(!(mode & FMODE_EXCL));
	blkdev_put(bdev, mode | FMODE_EXCL);
}

EXPORT_SYMBOL(kill_block_super);
#endif

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

	if (IS_ERR(s))
		return ERR_CAST(s);

	s->s_flags = flags;

	error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
	if (error) {
		deactivate_locked_super(s);
		return ERR_PTR(error);
	}
	s->s_flags |= MS_ACTIVE;
	return dget(s->s_root);
}
EXPORT_SYMBOL(mount_nodev);

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

struct dentry *mount_single(struct file_system_type *fs_type,
	int flags, void *data,
	int (*fill_super)(struct super_block *, void *, int))
{
	struct super_block *s;
	int error;

	s = sget(fs_type, compare_single, set_anon_super, NULL);
	if (IS_ERR(s))
		return ERR_CAST(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 ERR_PTR(error);
		}
		s->s_flags |= MS_ACTIVE;
	} else {
		do_remount_sb(s, flags, data, 0);
	}
	return dget(s->s_root);
}
EXPORT_SYMBOL(mount_single);

struct dentry *
mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
{
	struct dentry *root;
	struct super_block *sb;
	char *secdata = NULL;
	int error = -ENOMEM;

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

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

	root = type->mount(type, flags, name, data);
	if (IS_ERR(root)) {
		error = PTR_ERR(root);
		goto out_free_secdata;
	}
	sb = root->d_sb;
	BUG_ON(!sb);
	WARN_ON(!sb->s_bdi);
	WARN_ON(sb->s_bdi == &default_backing_dev_info);
	sb->s_flags |= MS_BORN;

	error = security_sb_kern_mount(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.
	 */
	WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
		"negative value (%lld)\n", type->name, sb->s_maxbytes);

	up_write(&sb->s_umount);
	free_secdata(secdata);
	return root;
out_sb:
	dput(root);
	deactivate_locked_super(sb);
out_free_secdata:
	free_secdata(secdata);
out:
	return ERR_PTR(error);
}

/**
 * sb_end_write - drop write access to a superblock
 * @sb: the super we wrote to
 * @level: the lowest level of freezing which we blocked
 *
 * Decrement number of writers to the filesystem preventing freezing of
 * given level. Wake up possible waiters wanting to freeze the filesystem.
 */
void sb_end_write(struct super_block *sb, int level)
{
	struct sb_writers_level *sl = &sb->s_writers[level-1];

	percpu_counter_dec(&sl->counter);
	/*
	 * Make sure s_writers are updated before we wake up waiters in
	 * freeze_super().
	 */
	smp_mb();
	if (waitqueue_active(&sl->wait))
		wake_up(&sl->wait);
	rwsem_release(&sl->lock_map, 1, _RET_IP_);
}
EXPORT_SYMBOL(sb_end_write);

/**
 * sb_start_write - get write access to a superblock
 * @sb: the super we write to
 * @level: the lowest level of freezing which we block
 *
 * When a process wants to write data to a filesystem (i.e. dirty a page), it
 * should embed the operation in a sb_start_write() - sb_end_write() pair to
 * get exclusion against filesystem freezing. This function increments number
 * of writers preventing freezing of given level to proceed.  If the file
 * system is already frozen it waits until it is thawed.
 *
 * The lock orderding constraints of sb_start_write() for level SB_FREEZE_WRITE
 * are following:
 * mmap_sem			(page-fault)
 *   -> s_writers		(block_page_mkwrite or equivalent)
 *
 * i_mutex			(do_truncate, __generic_file_aio_write)
 *   -> s_writers
 *
 * s_umount			(freeze_super)
 *   -> s_writers
 *
 * For level SB_FREEZE_TRANS lock constraints are rather file system dependent,
 * in most cases equivalent to constraints for starting a fs transaction.
 */
void sb_start_write(struct super_block *sb, int level)
{
retry:
	rwsem_acquire_read(&sb->s_writers[level-1].lock_map, 0, 0, _RET_IP_);
	vfs_check_frozen(sb, level);
	percpu_counter_inc(&sb->s_writers[level-1].counter);
	/*
	 * Make sure s_writers are updated before we check s_frozen.
	 * freeze_super() first sets s_frozen and then checks s_writers.
	 */
	smp_mb();
	if (sb->s_frozen >= level) {
		sb_end_write(sb, level);
		goto retry;
	}
}
EXPORT_SYMBOL(sb_start_write);

/**
 * sb_dup_write - get write access to a superblock without blocking
 * @sb: the super we write to
 * @level: the lowest level of freezing which we block
 *
 * This function is like sb_start_write() only that it does not check s_frozen
 * in the superblock. The caller can call this function only when it already
 * holds write access to the superblock at this level (i.e., called
 * sb_start_write(sb, level) previously).
 */
void sb_dup_write(struct super_block *sb, int level)
{
	/*
	 * Trick lockdep into acquiring read lock again without complaining
	 * about lock recursion
	 */
	rwsem_acquire_read(&sb->s_writers[level-1].lock_map, 0, 1, _RET_IP_);
	percpu_counter_inc(&sb->s_writers[level-1].counter);
}
EXPORT_SYMBOL(sb_dup_write);

/**
 * sb_wait_write - wait until all writers at given level finish
 * @sb: the super for which we wait
 * @level: the level at which we wait for writers
 *
 * This function waits until there are no writers at given level. Caller
 * of this function should make sure there can be no new writers at required
 * level before calling this function. Otherwise this function can livelock.
 */
void sb_wait_write(struct super_block *sb, int level)
{
	s64 writers;
	struct sb_writers_level *sl = &sb->s_writers[level-1];

	do {
		DEFINE_WAIT(wait);

		/*
		 * We use a barrier in prepare_to_wait() to separate setting
		 * of s_frozen and checking of s_writers
		 */
		prepare_to_wait(&sl->wait, &wait, TASK_UNINTERRUPTIBLE);

		writers = percpu_counter_sum(&sl->counter);
		if (writers)
			schedule();

		finish_wait(&sl->wait, &wait);
	} while (writers);
}
EXPORT_SYMBOL(sb_wait_write);

/*
 * Freeze superblock to given level, wait for writers at given level
 * to finish.
 */
static void sb_freeze_to_level(struct super_block *sb, int level)
{
	sb->s_frozen = level;

	/*
	 * We just cycle-through lockdep here so that it does not complain
	 * about returning with lock to userspace
	 */
	rwsem_acquire(&sb->s_writers[level-1].lock_map, 0, 0, _THIS_IP_);
	rwsem_release(&sb->s_writers[level-1].lock_map, 1, _THIS_IP_);

	/*
	 * Now wait for writers to finish. As s_frozen is already set to
	 * 'level' we are guaranteed there are no new writers at given level.
	 */
	sb_wait_write(sb, level);
}

/**
 * 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_freeze_to_level(sb, SB_FREEZE_WRITE);
	sync_filesystem(sb);
	sb_freeze_to_level(sb, SB_FREEZE_TRANS);
	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);
