Merge with Linux 2.4.0-test6-pre9.

[linux-2.6/linux-mips.git] / 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
 *
 *  Added options to /proc/mounts
 *  Torbjörn Lindh (torbjorn.lindh@gopta.se), April 14, 1996.
 *
 * 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 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/config.h>
#include <linux/string.h>
#include <linux/malloc.h>
#include <linux/locks.h>
#include <linux/smp_lock.h>
#include <linux/devfs_fs_kernel.h>
#include <linux/fd.h>
#include <linux/init.h>
#include <linux/quotaops.h>
#include <linux/acct.h>

#include <asm/uaccess.h>

#include <linux/nfs_fs.h>
#include <linux/nfs_fs_sb.h>
#include <linux/nfs_mount.h>

#include <linux/kmod.h>
#define __NO_VERSION__
#include <linux/module.h>

/*
 * We use a semaphore to synchronize all mount/umount
 * activity - imagine the mess if we have a race between
 * unmounting a filesystem and re-mounting it (or something
 * else).
 */
static DECLARE_MUTEX(mount_sem);

extern void wait_for_keypress(void);

extern int root_mountflags;

static int do_remount_sb(struct super_block *sb, int flags, char * data);

/* this is initialized in init/main.c */
kdev_t ROOT_DEV;

int nr_super_blocks;
int max_super_blocks = NR_SUPER;
LIST_HEAD(super_blocks);

/*
 * Handling of filesystem drivers list.
 * Rules:
 *      Inclusion to/removals from/scanning of list are protected by spinlock.
 *      During the unload module must call unregister_filesystem().
 *      We can access the fields of list element if:
 *              1) spinlock is held or
 *              2) we hold the reference to the module.
 *      The latter can be guaranteed by call of try_inc_mod_count(); if it
 *      returned 0 we must skip the element, otherwise we got the reference.
 *      Once the reference is obtained we can drop the spinlock.
 */

static struct file_system_type *file_systems;
static rwlock_t file_systems_lock = RW_LOCK_UNLOCKED;

/* WARNING: This can be used only if we _already_ own a reference */
static void get_filesystem(struct file_system_type *fs)
{
        if (fs->owner)
                __MOD_INC_USE_COUNT(fs->owner);
}

static void put_filesystem(struct file_system_type *fs)
{
        if (fs->owner)
                __MOD_DEC_USE_COUNT(fs->owner);
}

static struct file_system_type **find_filesystem(const char *name)
{
        struct file_system_type **p;
        for (p=&file_systems; *p; p=&(*p)->next)
                if (strcmp((*p)->name,name) == 0)
                        break;
        return p;
}

/**
 *      register_filesystem - register a new filesystem
 *      @fs: the file system structure
 *
 *      Adds the file system passed to the list of file systems the kernel
 *      is aware of for mount and other syscalls. Returns 0 on success,
 *      or a negative errno code on an error.
 *
 *      The &struct file_system_type that is passed is linked into the kernel 
 *      structures and must not be freed until the file system has been
 *      unregistered.
 */
 
int register_filesystem(struct file_system_type * fs)
{
        int res = 0;
        struct file_system_type ** p;

        if (!fs)
                return -EINVAL;
        if (fs->next)
                return -EBUSY;
        write_lock(&file_systems_lock);
        p = find_filesystem(fs->name);
        if (*p)
                res = -EBUSY;
        else
                *p = fs;
        write_unlock(&file_systems_lock);
        return res;
}

/**
 *      unregister_filesystem - unregister a file system
 *      @fs: filesystem to unregister
 *
 *      Remove a file system that was previously successfully registered
 *      with the kernel. An error is returned if the file system is not found.
 *      Zero is returned on a success.
 *      
 *      Once this function has returned the &struct file_system_type structure
 *      may be freed or reused.
 */
 
int unregister_filesystem(struct file_system_type * fs)
{
        struct file_system_type ** tmp;

        write_lock(&file_systems_lock);
        tmp = &file_systems;
        while (*tmp) {
                if (fs == *tmp) {
                        *tmp = fs->next;
                        fs->next = NULL;
                        write_unlock(&file_systems_lock);
                        return 0;
                }
                tmp = &(*tmp)->next;
        }
        write_unlock(&file_systems_lock);
        return -EINVAL;
}

static int fs_index(const char * __name)
{
        struct file_system_type * tmp;
        char * name;
        int err, index;

        name = getname(__name);
        err = PTR_ERR(name);
        if (IS_ERR(name))
                return err;

        err = -EINVAL;
        read_lock(&file_systems_lock);
        for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
                if (strcmp(tmp->name,name) == 0) {
                        err = index;
                        break;
                }
        }
        read_unlock(&file_systems_lock);
        putname(name);
        return err;
}

static int fs_name(unsigned int index, char * buf)
{
        struct file_system_type * tmp;
        int len, res;

        read_lock(&file_systems_lock);
        for (tmp = file_systems; tmp; tmp = tmp->next, index--)
                if (index <= 0 && try_inc_mod_count(tmp->owner))
                                break;
        read_unlock(&file_systems_lock);
        if (!tmp)
                return -EINVAL;

        /* OK, we got the reference, so we can safely block */
        len = strlen(tmp->name) + 1;
        res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
        put_filesystem(tmp);
        return res;
}

static int fs_maxindex(void)
{
        struct file_system_type * tmp;
        int index;

        read_lock(&file_systems_lock);
        for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
                ;
        read_unlock(&file_systems_lock);
        return index;
}

/*
 * Whee.. Weird sysv syscall. 
 */
asmlinkage long sys_sysfs(int option, unsigned long arg1, unsigned long arg2)
{
        int retval = -EINVAL;

        switch (option) {
                case 1:
                        retval = fs_index((const char *) arg1);
                        break;

                case 2:
                        retval = fs_name(arg1, (char *) arg2);
                        break;

                case 3:
                        retval = fs_maxindex();
                        break;
        }
        return retval;
}

int get_filesystem_list(char * buf)
{
        int len = 0;
        struct file_system_type * tmp;

        read_lock(&file_systems_lock);
        tmp = file_systems;
        while (tmp && len < PAGE_SIZE - 80) {
                len += sprintf(buf+len, "%s\t%s\n",
                        (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
                        tmp->name);
                tmp = tmp->next;
        }
        read_unlock(&file_systems_lock);
        return len;
}

struct file_system_type *get_fs_type(const char *name)
{
        struct file_system_type *fs;
        
        read_lock(&file_systems_lock);
        fs = *(find_filesystem(name));
        if (fs && !try_inc_mod_count(fs->owner))
                fs = NULL;
        read_unlock(&file_systems_lock);
        if (!fs && (request_module(name) == 0)) {
                read_lock(&file_systems_lock);
                fs = *(find_filesystem(name));
                if (fs && !try_inc_mod_count(fs->owner))
                        fs = NULL;
                read_unlock(&file_systems_lock);
        }
        return fs;
}

static LIST_HEAD(vfsmntlist);

/**
 *      add_vfsmnt - add a new mount node
 *      @nd: location of mountpoint or %NULL if we want a root node
 *      @root: root of (sub)tree to be mounted
 *      @dev_name: device name to show in /proc/mounts or %NULL (for "none").
 *
 *      This is VFS idea of mount. New node is allocated, bound to a tree
 *      we are mounting and optionally (OK, usually) registered as mounted
 *      on a given mountpoint. Returns a pointer to new node or %NULL in
 *      case of failure.
 *
 *      Potential reason for failure (aside of trivial lack of memory) is a
 *      deleted mountpoint. Caller must hold ->i_zombie on mountpoint
 *      dentry (if any).
 *
 *      Node is marked as MNT_VISIBLE (visible in /proc/mounts) unless both
 *      @nd and @devname are %NULL. It works since we pass non-%NULL @devname
 *      when we are mounting root and kern_mount() filesystems are deviceless.
 *      If we will get a kern_mount() filesystem with nontrivial @devname we
 *      will have to pass the visibility flag explicitly, so if we will add
 *      support for such beasts we'll have to change prototype.
 */

static struct vfsmount *add_vfsmnt(struct nameidata *nd,
                                struct dentry *root,
                                const char *dev_name)
{
        struct vfsmount *mnt;
        struct super_block *sb = root->d_inode->i_sb;
        char *name;

        mnt = kmalloc(sizeof(struct vfsmount), GFP_KERNEL);
        if (!mnt)
                goto out;
        memset(mnt, 0, sizeof(struct vfsmount));

        if (nd || dev_name)
                mnt->mnt_flags = MNT_VISIBLE;

        /* It may be NULL, but who cares? */
        if (dev_name) {
                name = kmalloc(strlen(dev_name)+1, GFP_KERNEL);
                if (name) {
                        strcpy(name, dev_name);
                        mnt->mnt_devname = name;
                }
        }
        mnt->mnt_owner = current->uid;
        atomic_set(&mnt->mnt_count,1);
        mnt->mnt_sb = sb;

        spin_lock(&dcache_lock);
        if (nd && !IS_ROOT(nd->dentry) && d_unhashed(nd->dentry))
                goto fail;
        mnt->mnt_root = dget(root);
        mnt->mnt_mountpoint = nd ? dget(nd->dentry) : dget(root);
        mnt->mnt_parent = nd ? mntget(nd->mnt) : mnt;

        if (nd) {
                list_add(&mnt->mnt_child, &nd->mnt->mnt_mounts);
                list_add(&mnt->mnt_clash, &nd->dentry->d_vfsmnt);
        } else {
                INIT_LIST_HEAD(&mnt->mnt_child);
                INIT_LIST_HEAD(&mnt->mnt_clash);
        }
        INIT_LIST_HEAD(&mnt->mnt_mounts);
        list_add(&mnt->mnt_instances, &sb->s_mounts);
        list_add(&mnt->mnt_list, vfsmntlist.prev);
        spin_unlock(&dcache_lock);
out:
        return mnt;
fail:
        spin_unlock(&dcache_lock);
        if (mnt->mnt_devname)
                kfree(mnt->mnt_devname);
        kfree(mnt);
        return NULL;
}

static void move_vfsmnt(struct vfsmount *mnt,
                        struct dentry *mountpoint,
                        struct vfsmount *parent,
                        const char *dev_name)
{
        struct dentry *old_mountpoint;
        struct vfsmount *old_parent;
        char *new_devname = NULL;

        if (dev_name) {
                new_devname = kmalloc(strlen(dev_name)+1, GFP_KERNEL);
                if (new_devname)
                        strcpy(new_devname, dev_name);
        }

        spin_lock(&dcache_lock);
        old_mountpoint = mnt->mnt_mountpoint;
        old_parent = mnt->mnt_parent;

        /* flip names */
        if (new_devname) {
                if (mnt->mnt_devname)
                        kfree(mnt->mnt_devname);
                mnt->mnt_devname = new_devname;
        }

        /* flip the linkage */
        mnt->mnt_mountpoint = dget(mountpoint);
        mnt->mnt_parent = parent ? mntget(parent) : mnt;
        list_del(&mnt->mnt_clash);
        list_del(&mnt->mnt_child);
        if (parent) {
                list_add(&mnt->mnt_child, &parent->mnt_mounts);
                list_add(&mnt->mnt_clash, &mountpoint->d_vfsmnt);
        } else {
                INIT_LIST_HEAD(&mnt->mnt_child);
                INIT_LIST_HEAD(&mnt->mnt_clash);
        }
        spin_unlock(&dcache_lock);

        /* put the old stuff */
        dput(old_mountpoint);
        if (old_parent != mnt)
                mntput(old_parent);
}

/*
 * Called with spinlock held, releases it.
 */
static void remove_vfsmnt(struct vfsmount *mnt)
{
        /* First of all, remove it from all lists */
        list_del(&mnt->mnt_instances);
        list_del(&mnt->mnt_clash);
        list_del(&mnt->mnt_list);
        list_del(&mnt->mnt_child);
        spin_unlock(&dcache_lock);
        /* Now we can work safely */
        if (mnt->mnt_parent != mnt)
                mntput(mnt->mnt_parent);

        dput(mnt->mnt_mountpoint);
        dput(mnt->mnt_root);
        if (mnt->mnt_devname)
                kfree(mnt->mnt_devname);
        kfree(mnt);
}

static struct proc_fs_info {
        int flag;
        char *str;
} fs_info[] = {
        { MS_NOEXEC, ",noexec" },
        { MS_NOSUID, ",nosuid" },
        { MS_NODEV, ",nodev" },
        { MS_SYNCHRONOUS, ",sync" },
        { MS_MANDLOCK, ",mand" },
        { MS_NOATIME, ",noatime" },
        { MS_NODIRATIME, ",nodiratime" },
#ifdef MS_NOSUB                 /* Can't find this except in mount.c */
        { MS_NOSUB, ",nosub" },
#endif
        { 0, NULL }
};

static struct proc_nfs_info {
        int flag;
        char *str;
        char *nostr;
} nfs_info[] = {
        { NFS_MOUNT_SOFT, ",soft", ",hard" },
        { NFS_MOUNT_INTR, ",intr", "" },
        { NFS_MOUNT_POSIX, ",posix", "" },
        { NFS_MOUNT_TCP, ",tcp", ",udp" },
        { NFS_MOUNT_NOCTO, ",nocto", "" },
        { NFS_MOUNT_NOAC, ",noac", "" },
        { NFS_MOUNT_NONLM, ",nolock", ",lock" },
        { 0, NULL, NULL }
};

int get_filesystem_info( char *buf )
{
        struct list_head *p;
        struct proc_fs_info *fs_infop;
        struct proc_nfs_info *nfs_infop;
        struct nfs_server *nfss;
        int len = 0;
        char *path,*buffer = (char *) __get_free_page(GFP_KERNEL);

        if (!buffer) return 0;
        for (p = vfsmntlist.next; p!=&vfsmntlist && len < PAGE_SIZE - 160;
            p = p->next) {
                struct vfsmount *tmp = list_entry(p, struct vfsmount, mnt_list);
                if (!(tmp->mnt_flags & MNT_VISIBLE))
                        continue;
                path = d_path(tmp->mnt_root, tmp, buffer, PAGE_SIZE);
                if (!path)
                        continue;
                len += sprintf( buf + len, "%s %s %s %s",
                        tmp->mnt_devname ? tmp->mnt_devname : "none", path,
                        tmp->mnt_sb->s_type->name,
                        tmp->mnt_sb->s_flags & MS_RDONLY ? "ro" : "rw" );
                for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
                  if (tmp->mnt_sb->s_flags & fs_infop->flag) {
                    strcpy(buf + len, fs_infop->str);
                    len += strlen(fs_infop->str);
                  }
                }
                if (!strcmp("nfs", tmp->mnt_sb->s_type->name)) {
                        nfss = &tmp->mnt_sb->u.nfs_sb.s_server;
                        len += sprintf(buf+len, ",v%d", nfss->rpc_ops->version);

                        len += sprintf(buf+len, ",rsize=%d", nfss->rsize);

                        len += sprintf(buf+len, ",wsize=%d", nfss->wsize);
#if 0
                        if (nfss->timeo != 7*HZ/10) {
                                len += sprintf(buf+len, ",timeo=%d",
                                               nfss->timeo*10/HZ);
                        }
                        if (nfss->retrans != 3) {
                                len += sprintf(buf+len, ",retrans=%d",
                                               nfss->retrans);
                        }
#endif
                        if (nfss->acregmin != 3*HZ) {
                                len += sprintf(buf+len, ",acregmin=%d",
                                               nfss->acregmin/HZ);
                        }
                        if (nfss->acregmax != 60*HZ) {
                                len += sprintf(buf+len, ",acregmax=%d",
                                               nfss->acregmax/HZ);
                        }
                        if (nfss->acdirmin != 30*HZ) {
                                len += sprintf(buf+len, ",acdirmin=%d",
                                               nfss->acdirmin/HZ);
                        }
                        if (nfss->acdirmax != 60*HZ) {
                                len += sprintf(buf+len, ",acdirmax=%d",
                                               nfss->acdirmax/HZ);
                        }
                        for (nfs_infop = nfs_info; nfs_infop->flag; nfs_infop++) {
                                char *str;
                                if (nfss->flags & nfs_infop->flag)
                                        str = nfs_infop->str;
                                else
                                        str = nfs_infop->nostr;
                                strcpy(buf + len, str);
                                len += strlen(str);
                        }
                        len += sprintf(buf+len, ",addr=%s",
                                       nfss->hostname);
                }
                len += sprintf( buf + len, " 0 0\n" );
        }

        free_page((unsigned long) buffer);
        return len;
}

/**
 *      __wait_on_super - wait on a superblock
 *      @sb: superblock to wait on
 *
 *      Waits for a superblock to become unlocked and then returns. It does
 *      not take the lock. This is an internal function. See wait_on_super().
 */
 
void __wait_on_super(struct super_block * sb)
{
        DECLARE_WAITQUEUE(wait, current);

        add_wait_queue(&sb->s_wait, &wait);
repeat:
        set_current_state(TASK_UNINTERRUPTIBLE);
        if (sb->s_lock) {
                schedule();
                goto repeat;
        }
        remove_wait_queue(&sb->s_wait, &wait);
        current->state = TASK_RUNNING;
}

/*
 * 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(kdev_t dev)
{
        struct super_block * sb;

        for (sb = sb_entry(super_blocks.next);
             sb != sb_entry(&super_blocks); 
             sb = sb_entry(sb->s_list.next)) {
                if (!sb->s_dev)
                        continue;
                if (dev && sb->s_dev != dev)
                        continue;
                if (!sb->s_dirt)
                        continue;
                lock_super(sb);
                if (sb->s_dev && sb->s_dirt && (!dev || dev == sb->s_dev))
                        if (sb->s_op && sb->s_op->write_super)
                                sb->s_op->write_super(sb);
                unlock_super(sb);
        }
}

/**
 *      get_super       -       get the superblock of a device
 *      @dev: 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(kdev_t dev)
{
        struct super_block * s;

        if (!dev)
                return NULL;
restart:
        s = sb_entry(super_blocks.next);
        while (s != sb_entry(&super_blocks))
                if (s->s_dev == dev) {
                        wait_on_super(s);
                        if (s->s_dev == dev)
                                return s;
                        goto restart;
                } else
                        s = sb_entry(s->s_list.next);
        return NULL;
}

asmlinkage long sys_ustat(dev_t dev, struct ustat * ubuf)
{
        struct super_block *s;
        struct ustat tmp;
        struct statfs sbuf;
        int err = -EINVAL;

        lock_kernel();
        s = get_super(to_kdev_t(dev));
        unlock_kernel();
        if (s == NULL)
                goto out;
        err = vfs_statfs(s, &sbuf);
        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;
}

/**
 *      get_empty_super -       find empty superblocks
 *
 *      Find a superblock with no device assigned. A free superblock is 
 *      found and returned. If neccessary new superblocks are allocated.
 *      %NULL is returned if there are insufficient resources to complete
 *      the request.
 */
 
struct super_block *get_empty_super(void)
{
        struct super_block *s;

        for (s  = sb_entry(super_blocks.next);
             s != sb_entry(&super_blocks); 
             s  = sb_entry(s->s_list.next)) {
                if (s->s_dev)
                        continue;
                if (!s->s_lock)
                        return s;
                printk("VFS: empty superblock %p locked!\n", s);
        }
        /* Need a new one... */
        if (nr_super_blocks >= max_super_blocks)
                return NULL;
        s = kmalloc(sizeof(struct super_block),  GFP_USER);
        if (s) {
                nr_super_blocks++;
                memset(s, 0, sizeof(struct super_block));
                INIT_LIST_HEAD(&s->s_dirty);
                list_add (&s->s_list, super_blocks.prev);
                init_waitqueue_head(&s->s_wait);
                INIT_LIST_HEAD(&s->s_files);
                INIT_LIST_HEAD(&s->s_mounts);
        }
        return s;
}

static struct super_block * read_super(kdev_t dev, struct block_device *bdev,
                                       struct file_system_type *type, int flags,
                                       void *data, int silent)
{
        struct super_block * s;
        s = get_empty_super();
        if (!s)
                goto out;
        s->s_dev = dev;
        s->s_bdev = bdev;
        s->s_flags = flags;
        s->s_dirt = 0;
        sema_init(&s->s_vfs_rename_sem,1);
        sema_init(&s->s_nfsd_free_path_sem,1);
        s->s_type = type;
        sema_init(&s->s_dquot.dqio_sem, 1);
        sema_init(&s->s_dquot.dqoff_sem, 1);
        s->s_dquot.flags = 0;
        lock_super(s);
        if (!type->read_super(s, data, silent))
                goto out_fail;
        unlock_super(s);
        /* tell bdcache that we are going to keep this one */
        if (bdev)
                atomic_inc(&bdev->bd_count);
out:
        return s;

out_fail:
        s->s_dev = 0;
        s->s_bdev = 0;
        s->s_type = NULL;
        unlock_super(s);
        return NULL;
}

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

static unsigned int unnamed_dev_in_use[256/(8*sizeof(unsigned int))];

kdev_t get_unnamed_dev(void)
{
        int i;

        for (i = 1; i < 256; i++) {
                if (!test_and_set_bit(i,unnamed_dev_in_use))
                        return MKDEV(UNNAMED_MAJOR, i);
        }
        return 0;
}

void put_unnamed_dev(kdev_t dev)
{
        if (!dev || MAJOR(dev) != UNNAMED_MAJOR)
                return;
        if (test_and_clear_bit(MINOR(dev), unnamed_dev_in_use))
                return;
        printk("VFS: put_unnamed_dev: freeing unused device %s\n",
                        kdevname(dev));
}

static struct super_block *get_sb_bdev(struct file_system_type *fs_type,
        char *dev_name, int flags, void * data)
{
        struct inode *inode;
        struct block_device *bdev;
        struct block_device_operations *bdops;
        struct super_block * sb;
        struct nameidata nd;
        kdev_t dev;
        int error = 0;
        /* What device it is? */
        if (!dev_name || !*dev_name)
                return ERR_PTR(-EINVAL);
        if (path_init(dev_name, LOOKUP_FOLLOW|LOOKUP_POSITIVE, &nd))
                error = path_walk(dev_name, &nd);
        if (error)
                return ERR_PTR(error);
        inode = nd.dentry->d_inode;
        error = -ENOTBLK;
        if (!S_ISBLK(inode->i_mode))
                goto out;
        error = -EACCES;
        if (IS_NODEV(inode))
                goto out;
        bdev = inode->i_bdev;
        bdops = devfs_get_ops ( devfs_get_handle_from_inode (inode) );
        if (bdops) bdev->bd_op = bdops;
        /* Done with lookups, semaphore down */
        down(&mount_sem);
        dev = to_kdev_t(bdev->bd_dev);
        sb = get_super(dev);
        if (sb) {
                if (fs_type == sb->s_type) {
                        path_release(&nd);
                        return sb;
                }
        } else {
                mode_t mode = FMODE_READ; /* we always need it ;-) */
                if (!(flags & MS_RDONLY))
                        mode |= FMODE_WRITE;
                error = blkdev_get(bdev, mode, 0, BDEV_FS);
                if (error)
                        goto out;
                check_disk_change(dev);
                error = -EACCES;
                if (!(flags & MS_RDONLY) && is_read_only(dev))
                        goto out1;
                error = -EINVAL;
                sb = read_super(dev, bdev, fs_type, flags, data, 0);
                if (sb) {
                        get_filesystem(fs_type);
                        path_release(&nd);
                        return sb;
                }
out1:
                blkdev_put(bdev, BDEV_FS);
        }
out:
        path_release(&nd);
        up(&mount_sem);
        return ERR_PTR(error);
}

static struct super_block *get_sb_nodev(struct file_system_type *fs_type,
        int flags, void * data)
{
        kdev_t dev;
        int error = -EMFILE;
        down(&mount_sem);
        dev = get_unnamed_dev();
        if (dev) {
                struct super_block * sb;
                error = -EINVAL;
                sb = read_super(dev, NULL, fs_type, flags, data, 0);
                if (sb) {
                        get_filesystem(fs_type);
                        return sb;
                }
                put_unnamed_dev(dev);
        }
        up(&mount_sem);
        return ERR_PTR(error);
}

static struct super_block *get_sb_single(struct file_system_type *fs_type,
        int flags, void *data)
{
        struct super_block * sb;
        /*
         * Get the superblock of kernel-wide instance, but
         * keep the reference to fs_type.
         */
        down(&mount_sem);
        sb = fs_type->kern_mnt->mnt_sb;
        if (!sb)
                BUG();
        get_filesystem(fs_type);
        do_remount_sb(sb, flags, data);
        return sb;
}

static struct block_device *kill_super(struct super_block *sb, int umount_root)
{
        struct block_device *bdev;
        kdev_t dev;
        struct dentry *root = sb->s_root;
        sb->s_root = NULL;
        /* Need to clean after the sucker */
        if (sb->s_type->fs_flags & FS_LITTER)
                d_genocide(root);
        if (sb->s_type->fs_flags & (FS_SINGLE|FS_LITTER))
                shrink_dcache_parent(root);
        dput(root);
        lock_super(sb);
        if (sb->s_op) {
                if (sb->s_op->write_super && sb->s_dirt)
                        sb->s_op->write_super(sb);
                if (sb->s_op->put_super)
                        sb->s_op->put_super(sb);
        }

        /* Forget any remaining inodes */
        if (invalidate_inodes(sb)) {
                printk("VFS: Busy inodes after unmount. "
                        "Self-destruct in 5 seconds.  Have a nice day...\n");
        }

        dev = sb->s_dev;
        sb->s_dev = 0;          /* Free the superblock */
        bdev = sb->s_bdev;
        sb->s_bdev = NULL;
        put_filesystem(sb->s_type);
        sb->s_type = NULL;
        unlock_super(sb);
        if (umount_root) {
                /* special: the old device driver is going to be
                   a ramdisk and the point of this call is to free its
                   protected memory (even if dirty). */
                destroy_buffers(dev);
        }
        if (bdev) {
                blkdev_put(bdev, BDEV_FS);
                bdput(bdev);
        } else
                put_unnamed_dev(dev);
        return bdev;
}

/*
 * Alters the mount flags of a mounted file system. Only the mount point
 * is used as a reference - file system type and the device are ignored.
 */

static int do_remount_sb(struct super_block *sb, int flags, char *data)
{
        int retval;
        
        if (!(flags & MS_RDONLY) && sb->s_dev && is_read_only(sb->s_dev))
                return -EACCES;
                /*flags |= MS_RDONLY;*/
        /* If we are remounting RDONLY, make sure there are no rw files open */
        if ((flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY))
                if (!fs_may_remount_ro(sb))
                        return -EBUSY;
        if (sb->s_op && sb->s_op->remount_fs) {
                lock_super(sb);
                retval = sb->s_op->remount_fs(sb, &flags, data);
                unlock_super(sb);
                if (retval)
                        return retval;
        }
        sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);

        /*
         * We can't invalidate inodes as we can loose data when remounting
         * (someone might manage to alter data while we are waiting in lock_super()
         * or in foo_remount_fs()))
         */

        return 0;
}

struct vfsmount *kern_mount(struct file_system_type *type)
{
        kdev_t dev = get_unnamed_dev();
        struct super_block *sb;
        struct vfsmount *mnt;
        if (!dev)
                return ERR_PTR(-EMFILE);
        sb = read_super(dev, NULL, type, 0, NULL, 0);
        if (!sb) {
                put_unnamed_dev(dev);
                return ERR_PTR(-EINVAL);
        }
        mnt = add_vfsmnt(NULL, sb->s_root, NULL);
        if (!mnt) {
                kill_super(sb, 0);
                return ERR_PTR(-ENOMEM);
        }
        type->kern_mnt = mnt;
        return mnt;
}

/* Call only after unregister_filesystem() - it's a final cleanup */

void kern_umount(struct vfsmount *mnt)
{
        struct super_block *sb = mnt->mnt_sb;
        spin_lock(&dcache_lock);
        remove_vfsmnt(mnt);
        kill_super(sb, 0);
}

/*
 * Doesn't take quota and stuff into account. IOW, in some cases it will
 * give false negatives. The main reason why it's here is that we need
 * a non-destructive way to look for easily umountable filesystems.
 */
int may_umount(struct vfsmount *mnt)
{
        if (atomic_read(&mnt->mnt_count) > 2)
                return -EBUSY;
        return 0;
}

static int do_umount(struct vfsmount *mnt, int umount_root, int flags)
{
        struct super_block * sb = mnt->mnt_sb;

        /*
         * No sense to grab the lock for this test, but test itself looks
         * somewhat bogus. Suggestions for better replacement?
         * Ho-hum... In principle, we might treat that as umount + switch
         * to rootfs. GC would eventually take care of the old vfsmount.
         * The problem being: we have to implement rootfs and GC for that ;-)
         * Actually it makes sense, especially if rootfs would contain a
         * /reboot - static binary that would close all descriptors and
         * call reboot(9). Then init(8) could umount root and exec /reboot.
         */
        if (mnt == current->fs->rootmnt && !umount_root) {
                int retval = 0;
                /*
                 * Special case for "unmounting" root ...
                 * we just try to remount it readonly.
                 */
                mntput(mnt);
                if (!(sb->s_flags & MS_RDONLY))
                        retval = do_remount_sb(sb, MS_RDONLY, 0);
                return retval;
        }

        spin_lock(&dcache_lock);
        if (atomic_read(&mnt->mnt_count) > 2) {
                spin_unlock(&dcache_lock);
                mntput(mnt);
                return -EBUSY;
        }

        if (mnt->mnt_instances.next != mnt->mnt_instances.prev) {
                if (sb->s_type->fs_flags & FS_SINGLE)
                        put_filesystem(sb->s_type);
                /* We hold two references, so mntput() is safe */
                mntput(mnt);
                remove_vfsmnt(mnt);
                return 0;
        }
        spin_unlock(&dcache_lock);

        /*
         * Before checking whether the filesystem is still busy,
         * make sure the kernel doesn't hold any quota files open
         * on the device. If the umount fails, too bad -- there
         * are no quotas running any more. Just turn them on again.
         */
        DQUOT_OFF(sb);
        acct_auto_close(sb->s_dev);

        /*
         * If we may have to abort operations to get out of this
         * mount, and they will themselves hold resources we must
         * allow the fs to do things. In the Unix tradition of
         * 'Gee thats tricky lets do it in userspace' the umount_begin
         * might fail to complete on the first run through as other tasks
         * must return, and the like. Thats for the mount program to worry
         * about for the moment.
         */

        if( (flags&MNT_FORCE) && sb->s_op->umount_begin)
                sb->s_op->umount_begin(sb);

        /*
         * Shrink dcache, then fsync. This guarantees that if the
         * filesystem is quiescent at this point, then (a) only the
         * root entry should be in use and (b) that root entry is
         * clean.
         */
        shrink_dcache_sb(sb);
        fsync_dev(sb->s_dev);

        if (sb->s_root->d_inode->i_state) {
                mntput(mnt);
                return -EBUSY;
        }

        /* Something might grab it again - redo checks */

        spin_lock(&dcache_lock);
        if (atomic_read(&mnt->mnt_count) > 2) {
                spin_unlock(&dcache_lock);
                mntput(mnt);
                return -EBUSY;
        }

        /* OK, that's the point of no return */
        mntput(mnt);
        remove_vfsmnt(mnt);

        kill_super(sb, umount_root);
        return 0;
}

/*
 * Now umount can handle mount points as well as block devices.
 * This is important for filesystems which use unnamed block devices.
 *
 * We now support a flag for forced unmount like the other 'big iron'
 * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
 */

asmlinkage long sys_umount(char * name, int flags)
{
        struct nameidata nd;
        char *kname;
        int retval;

        lock_kernel();
        kname = getname(name);
        retval = PTR_ERR(kname);
        if (IS_ERR(kname))
                goto out;
        retval = 0;
        if (path_init(kname, LOOKUP_POSITIVE|LOOKUP_FOLLOW, &nd))
                retval = path_walk(kname, &nd);
        putname(kname);
        if (retval)
                goto out;
        retval = -EINVAL;
        if (nd.dentry!=nd.mnt->mnt_root)
                goto dput_and_out;

        retval = -EPERM;
        if (!capable(CAP_SYS_ADMIN) && current->uid!=nd.mnt->mnt_owner)
                goto dput_and_out;

        dput(nd.dentry);
        /* puts nd.mnt */
        down(&mount_sem);
        retval = do_umount(nd.mnt, 0, flags);
        up(&mount_sem);
        goto out;
dput_and_out:
        path_release(&nd);
out:
        unlock_kernel();
        return retval;
}

/*
 *      The 2.0 compatible umount. No flags. 
 */
 
asmlinkage long sys_oldumount(char * name)
{
        return sys_umount(name,0);
}

static int mount_is_safe(struct nameidata *nd)
{
        if (capable(CAP_SYS_ADMIN))
                return 0;
        return -EPERM;
#ifdef notyet
        if (S_ISLNK(nd->dentry->d_inode->i_mode))
                return -EPERM;
        if (nd->dentry->d_inode->i_mode & S_ISVTX) {
                if (current->uid != nd->dentry->d_inode->i_uid)
                        return -EPERM;
        }
        if (permission(nd->dentry->d_inode, MAY_WRITE))
                return -EPERM;
        return 0;
#endif
}

/*
 * do loopback mount.
 */
static int do_loopback(char *old_name, char *new_name)
{
        struct nameidata old_nd, new_nd;
        int err = 0;
        if (!old_name || !*old_name)
                return -EINVAL;
        if (path_init(old_name, LOOKUP_POSITIVE, &old_nd))
                err = path_walk(old_name, &old_nd);
        if (err)
                goto out;
        if (path_init(new_name, LOOKUP_POSITIVE, &new_nd))
                err = path_walk(new_name, &new_nd);
        if (err)
                goto out1;
        err = mount_is_safe(&new_nd);
        if (err)
                goto out2;
        err = -EINVAL;
        if (S_ISDIR(new_nd.dentry->d_inode->i_mode) !=
              S_ISDIR(old_nd.dentry->d_inode->i_mode))
                goto out2;

        err = -ENOMEM;
        if (old_nd.mnt->mnt_sb->s_type->fs_flags & FS_SINGLE)
                get_filesystem(old_nd.mnt->mnt_sb->s_type);
                
        down(&mount_sem);
        /* there we go */
        down(&new_nd.dentry->d_inode->i_zombie);
        if (IS_DEADDIR(new_nd.dentry->d_inode))
                err = -ENOENT;
        else if (add_vfsmnt(&new_nd, old_nd.dentry, old_nd.mnt->mnt_devname))
                err = 0;
        up(&new_nd.dentry->d_inode->i_zombie);
        up(&mount_sem);
        if (err && old_nd.mnt->mnt_sb->s_type->fs_flags & FS_SINGLE)
                put_filesystem(old_nd.mnt->mnt_sb->s_type);
out2:
        path_release(&new_nd);
out1:
        path_release(&old_nd);
out:
        return err;
}

/*
 * change filesystem flags. dir should be a physical root of filesystem.
 * If you've mounted a non-root directory somewhere and want to do remount
 * on it - tough luck.
 */

static int do_remount(const char *dir,int flags,char *data)
{
        struct nameidata nd;
        int retval = 0;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        if (path_init(dir, LOOKUP_FOLLOW|LOOKUP_POSITIVE, &nd))
                retval = path_walk(dir, &nd);
        if (!retval) {
                struct super_block * sb = nd.dentry->d_inode->i_sb;
                retval = -ENODEV;
                if (sb) {
                        retval = -EINVAL;
                        if (nd.dentry == sb->s_root) {
                                /*
                                 * Shrink the dcache and sync the device.
                                 */
                                shrink_dcache_sb(sb);
                                fsync_dev(sb->s_dev);
                                if (flags & MS_RDONLY)
                                        acct_auto_close(sb->s_dev);
                                retval = do_remount_sb(sb, flags, data);
                        }
                }
                path_release(&nd);
        }
        return retval;
}

static int copy_mount_options (const void *data, unsigned long *where)
{
        int i;
        unsigned long page;
        unsigned long size;
        
        *where = 0;
        if (!data)
                return 0;

        if (!(page = __get_free_page(GFP_KERNEL)))
                return -ENOMEM;

        /* We only care that *some* data at the address the user
         * gave us is valid.  Just in case, we'll zero
         * the remainder of the page.
         */
        /* copy_from_user cannot cross TASK_SIZE ! */
        size = TASK_SIZE - (unsigned long)data;
        if (size > PAGE_SIZE)
                size = PAGE_SIZE;

        i = size - copy_from_user((void *)page, data, size);
        if (!i) {
                free_page(page); 
                return -EFAULT;
        }
        if (i != PAGE_SIZE)
                memset((char *)page + i, 0, PAGE_SIZE - i);
        *where = page;
        return 0;
}

/*
 * Flags is a 16-bit value that allows up to 16 non-fs dependent flags to
 * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
 *
 * data is a (void *) that can point to any structure up to
 * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
 * information (or be NULL).
 *
 * NOTE! As old versions of mount() didn't use this setup, the flags
 * have to have a special 16-bit magic number in the high word:
 * 0xC0ED. If this magic word isn't present, the flags and data info
 * aren't used, as the syscall assumes we are talking to an older
 * version that didn't understand them.
 */
long do_mount(char * dev_name, char * dir_name, char *type_page,
                  unsigned long new_flags, void *data_page)
{
        struct file_system_type * fstype;
        struct nameidata nd;
        struct vfsmount *mnt = NULL;
        struct super_block *sb;
        int retval = 0;
        unsigned long flags = 0;
 
        /* Basic sanity checks */

        if (!dir_name || !*dir_name || !memchr(dir_name, 0, PAGE_SIZE))
                return -EINVAL;
        if (dev_name && !memchr(dev_name, 0, PAGE_SIZE))
                return -EINVAL;

        /* OK, looks good, now let's see what do they want */

        /* just change the flags? - capabilities are checked in do_remount() */
        if ((new_flags & (MS_MGC_MSK|MS_REMOUNT)) == (MS_MGC_VAL|MS_REMOUNT))
                return do_remount(dir_name, new_flags&~(MS_MGC_MSK|MS_REMOUNT),
                                    (char *) data_page);

        if ((new_flags & MS_MGC_MSK) == MS_MGC_VAL)
                flags = new_flags & ~MS_MGC_MSK;

        /* For the rest we need the type */

        if (!type_page || !memchr(type_page, 0, PAGE_SIZE))
                return -EINVAL;

        /* loopback mount? This is special - requires fewer capabilities */
        if (strcmp(type_page, "bind")==0)
                return do_loopback(dev_name, dir_name);

        /* for the rest we _really_ need capabilities... */
        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        /* ... filesystem driver... */
        fstype = get_fs_type(type_page);
        if (!fstype)            
                return -ENODEV;

        /* ... and mountpoint. Do the lookup first to force automounting. */
        if (path_init(dir_name, LOOKUP_FOLLOW|LOOKUP_POSITIVE|LOOKUP_DIRECTORY, &nd))
                retval = path_walk(dir_name, &nd);
        if (retval)
                goto fs_out;

        /* get superblock, locks mount_sem on success */
        if (fstype->fs_flags & FS_NOMOUNT)
                sb = ERR_PTR(-EINVAL);
        else if (fstype->fs_flags & FS_REQUIRES_DEV)
                sb = get_sb_bdev(fstype, dev_name,flags, data_page);
        else if (fstype->fs_flags & FS_SINGLE)
                sb = get_sb_single(fstype, flags, data_page);
        else
                sb = get_sb_nodev(fstype, flags, data_page);

        retval = PTR_ERR(sb);
        if (IS_ERR(sb))
                goto dput_out;

        /* Something was mounted here while we slept */
        while(d_mountpoint(nd.dentry) && follow_down(&nd.mnt, &nd.dentry))
                ;
        retval = -ENOENT;
        if (!nd.dentry->d_inode)
                goto fail;
        down(&nd.dentry->d_inode->i_zombie);
        if (!IS_DEADDIR(nd.dentry->d_inode)) {
                retval = -ENOMEM;
                mnt = add_vfsmnt(&nd, sb->s_root, dev_name);
        }
        up(&nd.dentry->d_inode->i_zombie);
        if (!mnt)
                goto fail;
        retval = 0;
unlock_out:
        up(&mount_sem);
dput_out:
        path_release(&nd);
fs_out:
        put_filesystem(fstype);
        return retval;

fail:
        if (list_empty(&sb->s_mounts))
                kill_super(sb, 0);
        goto unlock_out;
}

asmlinkage long sys_mount(char * dev_name, char * dir_name, char * type,
                          unsigned long new_flags, void * data)
{
        int retval;
        unsigned long data_page;
        unsigned long type_page;
        unsigned long dev_page;
        char *dir_page;

        retval = copy_mount_options (type, &type_page);
        if (retval < 0)
                return retval;

        dir_page = getname(dir_name);
        retval = PTR_ERR(dir_page);
        if (IS_ERR(dir_page))
                goto out1;

        retval = copy_mount_options (dev_name, &dev_page);
        if (retval < 0)
                goto out2;
        retval = copy_mount_options (data, &data_page);
        if (retval >= 0) {
                lock_kernel();
                retval = do_mount((char*)dev_page,dir_page,(char*)type_page,
                                      new_flags, (void*)data_page);
                unlock_kernel();
                free_page(data_page);
        }
        free_page(dev_page);
out2:
        putname(dir_page);
out1:
        free_page(type_page);
        return retval;
}

void __init mount_root(void)
{
        struct file_system_type * fs_type;
        struct super_block * sb;
        struct vfsmount *vfsmnt;
        struct block_device *bdev = NULL;
        mode_t mode;
        int retval;
        void *handle;
        char path[64];
        int path_start = -1;

#ifdef CONFIG_ROOT_NFS
        void *data;
        if (MAJOR(ROOT_DEV) != UNNAMED_MAJOR)
                goto skip_nfs;
        fs_type = get_fs_type("nfs");
        if (!fs_type)
                goto no_nfs;
        ROOT_DEV = get_unnamed_dev();
        if (!ROOT_DEV)
                /*
                 * Your /linuxrc sucks worse than MSExchange - that's the
                 * only way you could run out of anon devices at that point.
                 */
                goto no_anon;
        data = nfs_root_data();
        if (!data)
                goto no_server;
        sb = read_super(ROOT_DEV, NULL, fs_type, root_mountflags, data, 1);
        if (sb)
                /*
                 * We _can_ fail there, but if that will happen we have no
                 * chance anyway (no memory for vfsmnt and we _will_ need it,
                 * no matter which fs we try to mount).
                 */
                goto mount_it;
no_server:
        put_unnamed_dev(ROOT_DEV);
no_anon:
        put_filesystem(fs_type);
no_nfs:
        printk(KERN_ERR "VFS: Unable to mount root fs via NFS, trying floppy.\n");
        ROOT_DEV = MKDEV(FLOPPY_MAJOR, 0);
skip_nfs:
#endif

#ifdef CONFIG_BLK_DEV_FD
        if (MAJOR(ROOT_DEV) == FLOPPY_MAJOR) {
#ifdef CONFIG_BLK_DEV_RAM
                extern int rd_doload;
                extern void rd_load_secondary(void);
#endif
                floppy_eject();
#ifndef CONFIG_BLK_DEV_RAM
                printk(KERN_NOTICE "(Warning, this kernel has no ramdisk support)\n");
#else
                /* rd_doload is 2 for a dual initrd/ramload setup */
                if(rd_doload==2)
                        rd_load_secondary();
                else
#endif
                {
                        printk(KERN_NOTICE "VFS: Insert root floppy and press ENTER\n");
                        wait_for_keypress();
                }
        }
#endif

        devfs_make_root (root_device_name);
        handle = devfs_find_handle (NULL, ROOT_DEVICE_NAME,
                                    MAJOR (ROOT_DEV), MINOR (ROOT_DEV),
                                    DEVFS_SPECIAL_BLK, 1);
        if (handle)  /*  Sigh: bd*() functions only paper over the cracks  */
        {
            unsigned major, minor;

            devfs_get_maj_min (handle, &major, &minor);
            ROOT_DEV = MKDEV (major, minor);
        }

        /*
         * Probably pure paranoia, but I'm less than happy about delving into
         * devfs crap and checking it right now. Later.
         */
        if (!ROOT_DEV)
                panic("I have no root and I want to scream");

        bdev = bdget(kdev_t_to_nr(ROOT_DEV));
        if (!bdev)
                panic(__FUNCTION__ ": unable to allocate root device");
        bdev->bd_op = devfs_get_ops (handle);
        path_start = devfs_generate_path (handle, path + 5, sizeof (path) - 5);
        mode = FMODE_READ;
        if (!(root_mountflags & MS_RDONLY))
                mode |= FMODE_WRITE;
        retval = blkdev_get(bdev, mode, 0, BDEV_FS);
        if (retval == -EROFS) {
                root_mountflags |= MS_RDONLY;
                retval = blkdev_get(bdev, FMODE_READ, 0, BDEV_FS);
        }
        if (retval) {
                /*
                 * Allow the user to distinguish between failed open
                 * and bad superblock on root device.
                 */
                printk ("VFS: Cannot open root device \"%s\" or %s\n",
                        root_device_name, kdevname (ROOT_DEV));
                printk ("Please append a correct \"root=\" boot option\n");
                panic("VFS: Unable to mount root fs on %s",
                        kdevname(ROOT_DEV));
        }

        check_disk_change(ROOT_DEV);
        sb = get_super(ROOT_DEV);
        if (sb) {
                fs_type = sb->s_type;
                goto mount_it;
        }

        read_lock(&file_systems_lock);
        for (fs_type = file_systems ; fs_type ; fs_type = fs_type->next) {
                if (!(fs_type->fs_flags & FS_REQUIRES_DEV))
                        continue;
                if (!try_inc_mod_count(fs_type->owner))
                        continue;
                read_unlock(&file_systems_lock);
                sb = read_super(ROOT_DEV,bdev,fs_type,root_mountflags,NULL,1);
                if (sb) 
                        goto mount_it;
                read_lock(&file_systems_lock);
                put_filesystem(fs_type);
        }
        read_unlock(&file_systems_lock);
        panic("VFS: Unable to mount root fs on %s", kdevname(ROOT_DEV));

mount_it:
        printk ("VFS: Mounted root (%s filesystem)%s.\n",
                fs_type->name,
                (sb->s_flags & MS_RDONLY) ? " readonly" : "");
        if (path_start >= 0) {
                devfs_mk_symlink (NULL, "root", DEVFS_FL_DEFAULT,
                                  path + 5 + path_start, NULL, NULL);
                memcpy (path + path_start, "/dev/", 5);
                vfsmnt = add_vfsmnt(NULL, sb->s_root, path + path_start);
        }
        else
                vfsmnt = add_vfsmnt(NULL, sb->s_root, "/dev/root");
        /* FIXME: if something will try to umount us right now... */
        if (vfsmnt) {
                set_fs_root(current->fs, vfsmnt, sb->s_root);
                set_fs_pwd(current->fs, vfsmnt, sb->s_root);
                if (bdev)
                        bdput(bdev); /* sb holds a reference */
                return;
        }
        panic("VFS: add_vfsmnt failed for root fs");
}


static void chroot_fs_refs(struct dentry *old_root,
                           struct vfsmount *old_rootmnt,
                           struct dentry *new_root,
                           struct vfsmount *new_rootmnt)
{
        struct task_struct *p;
        struct fs_struct *fs;

        read_lock(&tasklist_lock);
        for_each_task(p) {
                task_lock(p);
                fs = p->fs;
                if (fs) {
                        atomic_inc(&fs->count);
                        task_unlock(p);
                        if (fs->root==old_root && fs->rootmnt==old_rootmnt)
                                set_fs_root(fs, new_rootmnt, new_root);
                        if (fs->pwd==old_root && fs->pwdmnt==old_rootmnt)
                                set_fs_pwd(fs, new_rootmnt, new_root);
                        put_fs_struct(fs);
                } else
                        task_unlock(p);
        }
        read_unlock(&tasklist_lock);
}

/*
 * Moves the current root to put_root, and sets root/cwd of all processes
 * which had them on the old root to new_root.
 *
 * Note:
 *  - we don't move root/cwd if they are not at the root (reason: if something
 *    cared enough to change them, it's probably wrong to force them elsewhere)
 *  - it's okay to pick a root that isn't the root of a file system, e.g.
 *    /nfs/my_root where /nfs is the mount point. Better avoid creating
 *    unreachable mount points this way, though.
 */

asmlinkage long sys_pivot_root(const char *new_root, const char *put_old)
{
        struct dentry *root;
        struct vfsmount *root_mnt;
        struct vfsmount *tmp;
        struct nameidata new_nd, old_nd;
        char *name;
        int error;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        lock_kernel();

        name = getname(new_root);
        error = PTR_ERR(name);
        if (IS_ERR(name))
                goto out0;
        error = 0;
        if (path_init(name, LOOKUP_POSITIVE|LOOKUP_FOLLOW|LOOKUP_DIRECTORY, &new_nd))
                error = path_walk(name, &new_nd);
        putname(name);
        if (error)
                goto out0;

        name = getname(put_old);
        error = PTR_ERR(name);
        if (IS_ERR(name))
                goto out0;
        error = 0;
        if (path_init(name, LOOKUP_POSITIVE|LOOKUP_FOLLOW|LOOKUP_DIRECTORY, &old_nd))
                error = path_walk(name, &old_nd);
        putname(name);
        if (error)
                goto out1;

        read_lock(&current->fs->lock);
        root_mnt = mntget(current->fs->rootmnt);
        root = dget(current->fs->root);
        read_unlock(&current->fs->lock);
        down(&mount_sem);
        down(&old_nd.dentry->d_inode->i_zombie);
        error = -ENOENT;
        if (IS_DEADDIR(new_nd.dentry->d_inode))
                goto out2;
        if (d_unhashed(new_nd.dentry) && !IS_ROOT(new_nd.dentry))
                goto out2;
        if (d_unhashed(old_nd.dentry) && !IS_ROOT(old_nd.dentry))
                goto out2;
        error = -EBUSY;
        if (new_nd.mnt == root_mnt || old_nd.mnt == root_mnt)
                goto out2; /* loop */
        error = -EINVAL;
        tmp = old_nd.mnt; /* make sure we can reach put_old from new_root */
        spin_lock(&dcache_lock);
        if (tmp != new_nd.mnt) {
                for (;;) {
                        if (tmp->mnt_parent == tmp)
                                goto out3;
                        if (tmp->mnt_parent == new_nd.mnt)
                                break;
                        tmp = tmp->mnt_parent;
                }
                if (!is_subdir(tmp->mnt_mountpoint, new_nd.dentry))
                        goto out3;
        } else if (!is_subdir(old_nd.dentry, new_nd.dentry))
                goto out3;
        spin_unlock(&dcache_lock);

        move_vfsmnt(new_nd.mnt, new_nd.dentry, NULL, NULL);
        move_vfsmnt(root_mnt, old_nd.dentry, old_nd.mnt, NULL);
        chroot_fs_refs(root,root_mnt,new_nd.dentry,new_nd.mnt);
        error = 0;
out2:
        up(&old_nd.dentry->d_inode->i_zombie);
        up(&mount_sem);
        dput(root);
        mntput(root_mnt);
        path_release(&old_nd);
out1:
        path_release(&new_nd);
out0:
        unlock_kernel();
        return error;
out3:
        spin_unlock(&dcache_lock);
        goto out2;
}


#ifdef CONFIG_BLK_DEV_INITRD

int __init change_root(kdev_t new_root_dev,const char *put_old)
{
        struct vfsmount *old_rootmnt;
        struct nameidata devfs_nd, nd;
        int error = 0;

        read_lock(&current->fs->lock);
        old_rootmnt = mntget(current->fs->rootmnt);
        read_unlock(&current->fs->lock);
        /*  First unmount devfs if mounted  */
        if (path_init("/dev", LOOKUP_FOLLOW|LOOKUP_POSITIVE, &devfs_nd))
                error = path_walk("/dev", &devfs_nd);
        if (!error) {
                if (devfs_nd.mnt->mnt_sb->s_magic == DEVFS_SUPER_MAGIC &&
                    devfs_nd.dentry == devfs_nd.mnt->mnt_root) {
                        dput(devfs_nd.dentry);
                        down(&mount_sem);
                        /* puts devfs_nd.mnt */
                        do_umount(devfs_nd.mnt, 0, 0);
                        up(&mount_sem);
                } else 
                        path_release(&devfs_nd);
        }
        ROOT_DEV = new_root_dev;
        mount_root();
#if 1
        shrink_dcache();
        printk("change_root: old root has d_count=%d\n", 
               atomic_read(&old_rootmnt->mnt_root->d_count));
#endif
        mount_devfs_fs ();
        /*
         * Get the new mount directory
         */
        error = 0;
        if (path_init(put_old, LOOKUP_FOLLOW|LOOKUP_POSITIVE|LOOKUP_DIRECTORY, &nd))
                error = path_walk(put_old, &nd);
        if (error) {
                int blivet;

                printk(KERN_NOTICE "Trying to unmount old root ... ");
                blivet = do_umount(old_rootmnt, 1, 0);
                if (!blivet) {
                        printk("okay\n");
                        return 0;
                }
                printk(KERN_ERR "error %d\n",blivet);
                return error;
        }
        /* FIXME: we should hold i_zombie on nd.dentry */
        move_vfsmnt(old_rootmnt, nd.dentry, nd.mnt, "/dev/root.old");
        mntput(old_rootmnt);
        path_release(&nd);
        return 0;
}

#endif