Push BKL down into do_remount_sb()

[safe/jmp/linux-2.6] / 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/init.h>
#include <linux/smp_lock.h>
#include <linux/acct.h>
#include <linux/blkdev.h>
#include <linux/quotaops.h>
#include <linux/namei.h>
#include <linux/mount.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/vfs.h>
#include <linux/writeback.h>            /* for the emergency remount stuff */
#include <linux/idr.h>
#include <linux/kobject.h>
#include <linux/mutex.h>
#include <linux/file.h>
#include <asm/uaccess.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 struct super_operations default_op;

        if (s) {
                if (security_sb_alloc(s)) {
                        kfree(s);
                        s = NULL;
                        goto out;
                }
                INIT_LIST_HEAD(&s->s_dirty);
                INIT_LIST_HEAD(&s->s_io);
                INIT_LIST_HEAD(&s->s_more_io);
                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 = S_BIAS;
                atomic_set(&s->s_active, 1);
                mutex_init(&s->s_vfs_rename_mutex);
                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->dq_op = sb_dquot_ops;
                s->s_qcop = sb_quotactl_ops;
                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.  Returns non-zero if the superblock was
 * destroyed.  The caller must hold sb_lock.
 */
static int __put_super(struct super_block *sb)
{
        int ret = 0;

        if (!--sb->s_count) {
                destroy_super(sb);
                ret = 1;
        }
        return ret;
}

/*
 * Drop a superblock's refcount.
 * Returns non-zero if the superblock is about to be destroyed and
 * at least is already removed from super_blocks list, so if we are
 * making a loop through super blocks then we need to restart.
 * The caller must hold sb_lock.
 */
int __put_super_and_need_restart(struct super_block *sb)
{
        /* check for race with generic_shutdown_super() */
        if (list_empty(&sb->s_list)) {
                /* super block is removed, need to restart... */
                __put_super(sb);
                return 1;
        }
        /* can't be the last, since s_list is still in use */
        sb->s_count--;
        BUG_ON(sb->s_count == 0);
        return 0;
}

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


/**
 *      deactivate_super        -       drop an active reference to superblock
 *      @s: superblock to deactivate
 *
 *      Drops an active reference to superblock, acquiring a temprory one if
 *      there is no active references left.  In that case we lock superblock,
 *      tell fs driver to shut it down and drop the temporary reference we
 *      had just acquired.
 */
void deactivate_super(struct super_block *s)
{
        struct file_system_type *fs = s->s_type;
        if (atomic_dec_and_lock(&s->s_active, &sb_lock)) {
                s->s_count -= S_BIAS-1;
                spin_unlock(&sb_lock);
                vfs_dq_off(s, 0);
                down_write(&s->s_umount);
                fs->kill_sb(s);
                put_filesystem(fs);
                put_super(s);
        }
}

EXPORT_SYMBOL(deactivate_super);

/**
 *      deactivate_locked_super -       drop an active reference to superblock
 *      @s: superblock to deactivate
 *
 *      Equivalent of up_write(&s->s_umount); deactivate_super(s);, except that
 *      it does not unlock it until it's all over.  As the result, it's safe to
 *      use to dispose of new superblock on ->get_sb() failure exits - nobody
 *      will see the sucker until it's all over.  Equivalent using up_write +
 *      deactivate_super is safe for that purpose only if superblock is either
 *      safe to use or has NULL ->s_root when we unlock.
 */
void deactivate_locked_super(struct super_block *s)
{
        struct file_system_type *fs = s->s_type;
        if (atomic_dec_and_lock(&s->s_active, &sb_lock)) {
                s->s_count -= S_BIAS-1;
                spin_unlock(&sb_lock);
                vfs_dq_off(s, 0);
                fs->kill_sb(s);
                put_filesystem(fs);
                put_super(s);
        } else {
                up_write(&s->s_umount);
        }
}

EXPORT_SYMBOL(deactivate_locked_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)
{
        s->s_count++;
        spin_unlock(&sb_lock);
        down_write(&s->s_umount);
        if (s->s_root) {
                spin_lock(&sb_lock);
                if (s->s_count > S_BIAS) {
                        atomic_inc(&s->s_active);
                        s->s_count--;
                        spin_unlock(&sb_lock);
                        return 1;
                }
                spin_unlock(&sb_lock);
        }
        up_write(&s->s_umount);
        put_super(s);
        yield();
        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_list);
        list_del(&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);
                        }
                        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;

        spin_lock(&sb_lock);
restart:
        list_for_each_entry(sb, &super_blocks, s_list) {
                if (sb->s_op->write_super && sb->s_dirt) {
                        sb->s_count++;
                        spin_unlock(&sb_lock);

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

                        spin_lock(&sb_lock);
                        if (__put_super_and_need_restart(sb))
                                goto restart;
                }
        }
        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 (sb->s_bdev == bdev) {
                        sb->s_count++;
                        spin_unlock(&sb_lock);
                        down_read(&sb->s_umount);
                        if (sb->s_root)
                                return sb;
                        up_read(&sb->s_umount);
                        /* restart only when sb is no longer on the list */
                        spin_lock(&sb_lock);
                        if (__put_super_and_need_restart(sb))
                                goto rescan;
                }
        }
        spin_unlock(&sb_lock);
        return NULL;
}

EXPORT_SYMBOL(get_super);
 
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 (sb->s_dev ==  dev) {
                        sb->s_count++;
                        spin_unlock(&sb_lock);
                        down_read(&sb->s_umount);
                        if (sb->s_root)
                                return sb;
                        up_read(&sb->s_umount);
                        /* restart only when sb is no longer on the list */
                        spin_lock(&sb_lock);
                        if (__put_super_and_need_restart(sb))
                                goto rescan;
                }
        }
        spin_unlock(&sb_lock);
        return NULL;
}

SYSCALL_DEFINE2(ustat, unsigned, dev, struct ustat __user *, ubuf)
{
        struct super_block *s;
        struct ustat tmp;
        struct kstatfs sbuf;
        int err = -EINVAL;

        s = user_get_super(new_decode_dev(dev));
        if (s == NULL)
                goto out;
        err = vfs_statfs(s->s_root, &sbuf);
        drop_super(s);
        if (err)
                goto out;

        memset(&tmp,0,sizeof(struct ustat));
        tmp.f_tfree = sbuf.f_bfree;
        tmp.f_tinode = sbuf.f_ffree;

        err = copy_to_user(ubuf,&tmp,sizeof(struct ustat)) ? -EFAULT : 0;
out:
        return err;
}

/**
 *      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_rw;
        
#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);

        lock_kernel();
        /* If we are remounting RDONLY and current sb is read/write,
           make sure there are no rw files opened */
        if ((flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY)) {
                if (force)
                        mark_files_ro(sb);
                else if (!fs_may_remount_ro(sb)) {
                        unlock_kernel();
                        return -EBUSY;
                }
                retval = vfs_dq_off(sb, 1);
                if (retval < 0 && retval != -ENOSYS) {
                        unlock_kernel();
                        return -EBUSY;
                }
        }
        remount_rw = !(flags & MS_RDONLY) && (sb->s_flags & MS_RDONLY);

        if (sb->s_op->remount_fs) {
                retval = sb->s_op->remount_fs(sb, &flags, data);
                if (retval) {
                        unlock_kernel();
                        return retval;
                }
        }
        sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);
        unlock_kernel();
        if (remount_rw)
                vfs_dq_quota_on_remount(sb);
        return 0;
}

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

        spin_lock(&sb_lock);
        list_for_each_entry(sb, &super_blocks, s_list) {
                sb->s_count++;
                spin_unlock(&sb_lock);
                down_write(&sb->s_umount);
                if (sb->s_root && sb->s_bdev && !(sb->s_flags & MS_RDONLY)) {
                        /*
                         * ->remount_fs needs lock_kernel().
                         *
                         * What lock protects sb->s_flags??
                         */
                        do_remount_sb(sb, MS_RDONLY, NULL, 1);
                }
                up_write(&sb->s_umount);
                put_super(sb);
                spin_lock(&sb_lock);
        }
        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 */

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(&unnamed_dev_ida, &dev);
        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);
                spin_unlock(&unnamed_dev_lock);
                return -EMFILE;
        }
        s->s_dev = MKDEV(0, dev & MINORMASK);
        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);
        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;
        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
         */
        down(&bdev->bd_mount_sem);
        s = sget(fs_type, test_bdev_super, set_bdev_super, bdev);
        up(&bdev->bd_mount_sem);
        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;
        }
        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 (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);

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

        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);

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);