Logo Search packages:      
Sourcecode: linux version File versions  Download package

namespace.c

/*
 *  linux/fs/namespace.c
 *
 * (C) Copyright Al Viro 2000, 2001
 *    Released under GPL v2.
 *
 * Based on code from fs/super.c, copyright Linus Torvalds and others.
 * Heavily rewritten.
 */

#include <linux/syscalls.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/smp_lock.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/quotaops.h>
#include <linux/acct.h>
#include <linux/capability.h>
#include <linux/module.h>
#include <linux/sysfs.h>
#include <linux/seq_file.h>
#include <linux/mnt_namespace.h>
#include <linux/namei.h>
#include <linux/security.h>
#include <linux/mount.h>
#include <linux/ramfs.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
#include "pnode.h"
#include "internal.h"

/* spinlock for vfsmount related operations, inplace of dcache_lock */
__cacheline_aligned_in_smp DEFINE_SPINLOCK(vfsmount_lock);

static int event;

static struct list_head *mount_hashtable __read_mostly;
static int hash_mask __read_mostly, hash_bits __read_mostly;
static struct kmem_cache *mnt_cache __read_mostly;
static struct rw_semaphore namespace_sem;

/* /sys/fs */
decl_subsys(fs, NULL, NULL);
EXPORT_SYMBOL_GPL(fs_subsys);

static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
{
      unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
      tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
      tmp = tmp + (tmp >> hash_bits);
      return tmp & hash_mask;
}

struct vfsmount *alloc_vfsmnt(const char *name)
{
      struct vfsmount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
      if (mnt) {
            atomic_set(&mnt->mnt_count, 1);
            INIT_LIST_HEAD(&mnt->mnt_hash);
            INIT_LIST_HEAD(&mnt->mnt_child);
            INIT_LIST_HEAD(&mnt->mnt_mounts);
            INIT_LIST_HEAD(&mnt->mnt_list);
            INIT_LIST_HEAD(&mnt->mnt_expire);
            INIT_LIST_HEAD(&mnt->mnt_share);
            INIT_LIST_HEAD(&mnt->mnt_slave_list);
            INIT_LIST_HEAD(&mnt->mnt_slave);
            if (name) {
                  int size = strlen(name) + 1;
                  char *newname = kmalloc(size, GFP_KERNEL);
                  if (newname) {
                        memcpy(newname, name, size);
                        mnt->mnt_devname = newname;
                  }
            }
      }
      return mnt;
}

int simple_set_mnt(struct vfsmount *mnt, struct super_block *sb)
{
      mnt->mnt_sb = sb;
      mnt->mnt_root = dget(sb->s_root);
      return 0;
}

EXPORT_SYMBOL(simple_set_mnt);

void free_vfsmnt(struct vfsmount *mnt)
{
      kfree(mnt->mnt_devname);
      kmem_cache_free(mnt_cache, mnt);
}

/*
 * find the first or last mount at @dentry on vfsmount @mnt depending on
 * @dir. If @dir is set return the first mount else return the last mount.
 */
struct vfsmount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,
                        int dir)
{
      struct list_head *head = mount_hashtable + hash(mnt, dentry);
      struct list_head *tmp = head;
      struct vfsmount *p, *found = NULL;

      for (;;) {
            tmp = dir ? tmp->next : tmp->prev;
            p = NULL;
            if (tmp == head)
                  break;
            p = list_entry(tmp, struct vfsmount, mnt_hash);
            if (p->mnt_parent == mnt && p->mnt_mountpoint == dentry) {
                  found = p;
                  break;
            }
      }
      return found;
}

/*
 * lookup_mnt increments the ref count before returning
 * the vfsmount struct.
 */
struct vfsmount *lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
{
      struct vfsmount *child_mnt;
      spin_lock(&vfsmount_lock);
      if ((child_mnt = __lookup_mnt(mnt, dentry, 1)))
            mntget(child_mnt);
      spin_unlock(&vfsmount_lock);
      return child_mnt;
}

static inline int check_mnt(struct vfsmount *mnt)
{
      return mnt->mnt_ns == current->nsproxy->mnt_ns;
}

static void touch_mnt_namespace(struct mnt_namespace *ns)
{
      if (ns) {
            ns->event = ++event;
            wake_up_interruptible(&ns->poll);
      }
}

static void __touch_mnt_namespace(struct mnt_namespace *ns)
{
      if (ns && ns->event != event) {
            ns->event = event;
            wake_up_interruptible(&ns->poll);
      }
}

static void detach_mnt(struct vfsmount *mnt, struct nameidata *old_nd)
{
      old_nd->dentry = mnt->mnt_mountpoint;
      old_nd->mnt = mnt->mnt_parent;
      mnt->mnt_parent = mnt;
      mnt->mnt_mountpoint = mnt->mnt_root;
      list_del_init(&mnt->mnt_child);
      list_del_init(&mnt->mnt_hash);
      old_nd->dentry->d_mounted--;
}

void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry,
                  struct vfsmount *child_mnt)
{
      child_mnt->mnt_parent = mntget(mnt);
      child_mnt->mnt_mountpoint = dget(dentry);
      dentry->d_mounted++;
}

static void attach_mnt(struct vfsmount *mnt, struct nameidata *nd)
{
      mnt_set_mountpoint(nd->mnt, nd->dentry, mnt);
      list_add_tail(&mnt->mnt_hash, mount_hashtable +
                  hash(nd->mnt, nd->dentry));
      list_add_tail(&mnt->mnt_child, &nd->mnt->mnt_mounts);
}

/*
 * the caller must hold vfsmount_lock
 */
static void commit_tree(struct vfsmount *mnt)
{
      struct vfsmount *parent = mnt->mnt_parent;
      struct vfsmount *m;
      LIST_HEAD(head);
      struct mnt_namespace *n = parent->mnt_ns;

      BUG_ON(parent == mnt);

      list_add_tail(&head, &mnt->mnt_list);
      list_for_each_entry(m, &head, mnt_list)
            m->mnt_ns = n;
      list_splice(&head, n->list.prev);

      list_add_tail(&mnt->mnt_hash, mount_hashtable +
                        hash(parent, mnt->mnt_mountpoint));
      list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
      touch_mnt_namespace(n);
}

static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
{
      struct list_head *next = p->mnt_mounts.next;
      if (next == &p->mnt_mounts) {
            while (1) {
                  if (p == root)
                        return NULL;
                  next = p->mnt_child.next;
                  if (next != &p->mnt_parent->mnt_mounts)
                        break;
                  p = p->mnt_parent;
            }
      }
      return list_entry(next, struct vfsmount, mnt_child);
}

static struct vfsmount *skip_mnt_tree(struct vfsmount *p)
{
      struct list_head *prev = p->mnt_mounts.prev;
      while (prev != &p->mnt_mounts) {
            p = list_entry(prev, struct vfsmount, mnt_child);
            prev = p->mnt_mounts.prev;
      }
      return p;
}

static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
                              int flag)
{
      struct super_block *sb = old->mnt_sb;
      struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);

      if (mnt) {
            mnt->mnt_flags = old->mnt_flags;
            atomic_inc(&sb->s_active);
            mnt->mnt_sb = sb;
            mnt->mnt_root = dget(root);
            mnt->mnt_mountpoint = mnt->mnt_root;
            mnt->mnt_parent = mnt;

            if (flag & CL_SLAVE) {
                  list_add(&mnt->mnt_slave, &old->mnt_slave_list);
                  mnt->mnt_master = old;
                  CLEAR_MNT_SHARED(mnt);
            } else if (!(flag & CL_PRIVATE)) {
                  if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
                        list_add(&mnt->mnt_share, &old->mnt_share);
                  if (IS_MNT_SLAVE(old))
                        list_add(&mnt->mnt_slave, &old->mnt_slave);
                  mnt->mnt_master = old->mnt_master;
            }
            if (flag & CL_MAKE_SHARED)
                  set_mnt_shared(mnt);

            /* stick the duplicate mount on the same expiry list
             * as the original if that was on one */
            if (flag & CL_EXPIRE) {
                  spin_lock(&vfsmount_lock);
                  if (!list_empty(&old->mnt_expire))
                        list_add(&mnt->mnt_expire, &old->mnt_expire);
                  spin_unlock(&vfsmount_lock);
            }
      }
      return mnt;
}

static inline void __mntput(struct vfsmount *mnt)
{
      struct super_block *sb = mnt->mnt_sb;
      dput(mnt->mnt_root);
      free_vfsmnt(mnt);
      deactivate_super(sb);
}

void mntput_no_expire(struct vfsmount *mnt)
{
repeat:
      if (atomic_dec_and_lock(&mnt->mnt_count, &vfsmount_lock)) {
            if (likely(!mnt->mnt_pinned)) {
                  spin_unlock(&vfsmount_lock);
                  __mntput(mnt);
                  return;
            }
            atomic_add(mnt->mnt_pinned + 1, &mnt->mnt_count);
            mnt->mnt_pinned = 0;
            spin_unlock(&vfsmount_lock);
            acct_auto_close_mnt(mnt);
            security_sb_umount_close(mnt);
            goto repeat;
      }
}

EXPORT_SYMBOL(mntput_no_expire);

void mnt_pin(struct vfsmount *mnt)
{
      spin_lock(&vfsmount_lock);
      mnt->mnt_pinned++;
      spin_unlock(&vfsmount_lock);
}

EXPORT_SYMBOL(mnt_pin);

void mnt_unpin(struct vfsmount *mnt)
{
      spin_lock(&vfsmount_lock);
      if (mnt->mnt_pinned) {
            atomic_inc(&mnt->mnt_count);
            mnt->mnt_pinned--;
      }
      spin_unlock(&vfsmount_lock);
}

EXPORT_SYMBOL(mnt_unpin);

/* iterator */
static void *m_start(struct seq_file *m, loff_t *pos)
{
      struct mnt_namespace *n = m->private;

      down_read(&namespace_sem);
      return seq_list_start(&n->list, *pos);
}

static void *m_next(struct seq_file *m, void *v, loff_t *pos)
{
      struct mnt_namespace *n = m->private;

      return seq_list_next(v, &n->list, pos);
}

static void m_stop(struct seq_file *m, void *v)
{
      up_read(&namespace_sem);
}

static inline void mangle(struct seq_file *m, const char *s)
{
      seq_escape(m, s, " \t\n\\");
}

static int show_vfsmnt(struct seq_file *m, void *v)
{
      struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
      int err = 0;
      static struct proc_fs_info {
            int flag;
            char *str;
      } fs_info[] = {
            { MS_SYNCHRONOUS, ",sync" },
            { MS_DIRSYNC, ",dirsync" },
            { MS_MANDLOCK, ",mand" },
            { 0, NULL }
      };
      static struct proc_fs_info mnt_info[] = {
            { MNT_NOSUID, ",nosuid" },
            { MNT_NODEV, ",nodev" },
            { MNT_NOEXEC, ",noexec" },
            { MNT_NOATIME, ",noatime" },
            { MNT_NODIRATIME, ",nodiratime" },
            { MNT_RELATIME, ",relatime" },
            { 0, NULL }
      };
      struct proc_fs_info *fs_infop;

      mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
      seq_putc(m, ' ');
      seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
      seq_putc(m, ' ');
      mangle(m, mnt->mnt_sb->s_type->name);
      if (mnt->mnt_sb->s_subtype && mnt->mnt_sb->s_subtype[0]) {
            seq_putc(m, '.');
            mangle(m, mnt->mnt_sb->s_subtype);
      }
      seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");
      for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
            if (mnt->mnt_sb->s_flags & fs_infop->flag)
                  seq_puts(m, fs_infop->str);
      }
      for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
            if (mnt->mnt_flags & fs_infop->flag)
                  seq_puts(m, fs_infop->str);
      }
      if (mnt->mnt_sb->s_op->show_options)
            err = mnt->mnt_sb->s_op->show_options(m, mnt);
      seq_puts(m, " 0 0\n");
      return err;
}

struct seq_operations mounts_op = {
      .start      = m_start,
      .next = m_next,
      .stop = m_stop,
      .show = show_vfsmnt
};

static int show_vfsstat(struct seq_file *m, void *v)
{
      struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
      int err = 0;

      /* device */
      if (mnt->mnt_devname) {
            seq_puts(m, "device ");
            mangle(m, mnt->mnt_devname);
      } else
            seq_puts(m, "no device");

      /* mount point */
      seq_puts(m, " mounted on ");
      seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
      seq_putc(m, ' ');

      /* file system type */
      seq_puts(m, "with fstype ");
      mangle(m, mnt->mnt_sb->s_type->name);

      /* optional statistics */
      if (mnt->mnt_sb->s_op->show_stats) {
            seq_putc(m, ' ');
            err = mnt->mnt_sb->s_op->show_stats(m, mnt);
      }

      seq_putc(m, '\n');
      return err;
}

struct seq_operations mountstats_op = {
      .start      = m_start,
      .next = m_next,
      .stop = m_stop,
      .show = show_vfsstat,
};

/**
 * may_umount_tree - check if a mount tree is busy
 * @mnt: root of mount tree
 *
 * This is called to check if a tree of mounts has any
 * open files, pwds, chroots or sub mounts that are
 * busy.
 */
int may_umount_tree(struct vfsmount *mnt)
{
      int actual_refs = 0;
      int minimum_refs = 0;
      struct vfsmount *p;

      spin_lock(&vfsmount_lock);
      for (p = mnt; p; p = next_mnt(p, mnt)) {
            actual_refs += atomic_read(&p->mnt_count);
            minimum_refs += 2;
      }
      spin_unlock(&vfsmount_lock);

      if (actual_refs > minimum_refs)
            return 0;

      return 1;
}

EXPORT_SYMBOL(may_umount_tree);

/**
 * may_umount - check if a mount point is busy
 * @mnt: root of mount
 *
 * This is called to check if a mount point has any
 * open files, pwds, chroots or sub mounts. If the
 * mount has sub mounts this will return busy
 * regardless of whether the sub mounts are busy.
 *
 * 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)
{
      int ret = 1;
      spin_lock(&vfsmount_lock);
      if (propagate_mount_busy(mnt, 2))
            ret = 0;
      spin_unlock(&vfsmount_lock);
      return ret;
}

EXPORT_SYMBOL(may_umount);

void release_mounts(struct list_head *head)
{
      struct vfsmount *mnt;
      while (!list_empty(head)) {
            mnt = list_first_entry(head, struct vfsmount, mnt_hash);
            list_del_init(&mnt->mnt_hash);
            if (mnt->mnt_parent != mnt) {
                  struct dentry *dentry;
                  struct vfsmount *m;
                  spin_lock(&vfsmount_lock);
                  dentry = mnt->mnt_mountpoint;
                  m = mnt->mnt_parent;
                  mnt->mnt_mountpoint = mnt->mnt_root;
                  mnt->mnt_parent = mnt;
                  spin_unlock(&vfsmount_lock);
                  dput(dentry);
                  mntput(m);
            }
            mntput(mnt);
      }
}

void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)
{
      struct vfsmount *p;

      for (p = mnt; p; p = next_mnt(p, mnt))
            list_move(&p->mnt_hash, kill);

      if (propagate)
            propagate_umount(kill);

      list_for_each_entry(p, kill, mnt_hash) {
            list_del_init(&p->mnt_expire);
            list_del_init(&p->mnt_list);
            __touch_mnt_namespace(p->mnt_ns);
            p->mnt_ns = NULL;
            list_del_init(&p->mnt_child);
            if (p->mnt_parent != p)
                  p->mnt_mountpoint->d_mounted--;
            change_mnt_propagation(p, MS_PRIVATE);
      }
}

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

      retval = security_sb_umount(mnt, flags);
      if (retval)
            return retval;

      /*
       * Allow userspace to request a mountpoint be expired rather than
       * unmounting unconditionally. Unmount only happens if:
       *  (1) the mark is already set (the mark is cleared by mntput())
       *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
       */
      if (flags & MNT_EXPIRE) {
            if (mnt == current->fs->rootmnt ||
                flags & (MNT_FORCE | MNT_DETACH))
                  return -EINVAL;

            if (atomic_read(&mnt->mnt_count) != 2)
                  return -EBUSY;

            if (!xchg(&mnt->mnt_expiry_mark, 1))
                  return -EAGAIN;
      }

      /*
       * 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.
       */

      lock_kernel();
      if (sb->s_op->umount_begin)
            sb->s_op->umount_begin(mnt, flags);
      unlock_kernel();

      /*
       * 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.
       * 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 && !(flags & MNT_DETACH)) {
            /*
             * Special case for "unmounting" root ...
             * we just try to remount it readonly.
             */
            down_write(&sb->s_umount);
            if (!(sb->s_flags & MS_RDONLY)) {
                  lock_kernel();
                  DQUOT_OFF(sb);
                  retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
                  unlock_kernel();
            }
            up_write(&sb->s_umount);
            return retval;
      }

      down_write(&namespace_sem);
      spin_lock(&vfsmount_lock);
      event++;

      retval = -EBUSY;
      if (flags & MNT_DETACH || !propagate_mount_busy(mnt, 2)) {
            if (!list_empty(&mnt->mnt_list))
                  umount_tree(mnt, 1, &umount_list);
            retval = 0;
      }
      spin_unlock(&vfsmount_lock);
      if (retval)
            security_sb_umount_busy(mnt);
      up_write(&namespace_sem);
      release_mounts(&umount_list);
      return retval;
}

/*
 * 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 __user * name, int flags)
{
      struct nameidata nd;
      int retval;

      retval = __user_walk(name, LOOKUP_FOLLOW, &nd);
      if (retval)
            goto out;
      retval = -EINVAL;
      if (nd.dentry != nd.mnt->mnt_root)
            goto dput_and_out;
      if (!check_mnt(nd.mnt))
            goto dput_and_out;

      retval = -EPERM;
      if (!capable(CAP_SYS_ADMIN))
            goto dput_and_out;

      retval = do_umount(nd.mnt, flags);
dput_and_out:
      path_release_on_umount(&nd);
out:
      return retval;
}

#ifdef __ARCH_WANT_SYS_OLDUMOUNT

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

#endif

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 (vfs_permission(nd, MAY_WRITE))
            return -EPERM;
      return 0;
#endif
}

static int lives_below_in_same_fs(struct dentry *d, struct dentry *dentry)
{
      while (1) {
            if (d == dentry)
                  return 1;
            if (d == NULL || d == d->d_parent)
                  return 0;
            d = d->d_parent;
      }
}

struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
                              int flag)
{
      struct vfsmount *res, *p, *q, *r, *s;
      struct nameidata nd;

      if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
            return NULL;

      res = q = clone_mnt(mnt, dentry, flag);
      if (!q)
            goto Enomem;
      q->mnt_mountpoint = mnt->mnt_mountpoint;

      p = mnt;
      list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
            if (!lives_below_in_same_fs(r->mnt_mountpoint, dentry))
                  continue;

            for (s = r; s; s = next_mnt(s, r)) {
                  if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(s)) {
                        s = skip_mnt_tree(s);
                        continue;
                  }
                  while (p != s->mnt_parent) {
                        p = p->mnt_parent;
                        q = q->mnt_parent;
                  }
                  p = s;
                  nd.mnt = q;
                  nd.dentry = p->mnt_mountpoint;
                  q = clone_mnt(p, p->mnt_root, flag);
                  if (!q)
                        goto Enomem;
                  spin_lock(&vfsmount_lock);
                  list_add_tail(&q->mnt_list, &res->mnt_list);
                  attach_mnt(q, &nd);
                  spin_unlock(&vfsmount_lock);
            }
      }
      return res;
Enomem:
      if (res) {
            LIST_HEAD(umount_list);
            spin_lock(&vfsmount_lock);
            umount_tree(res, 0, &umount_list);
            spin_unlock(&vfsmount_lock);
            release_mounts(&umount_list);
      }
      return NULL;
}

struct vfsmount *collect_mounts(struct vfsmount *mnt, struct dentry *dentry)
{
      struct vfsmount *tree;
      down_read(&namespace_sem);
      tree = copy_tree(mnt, dentry, CL_COPY_ALL | CL_PRIVATE);
      up_read(&namespace_sem);
      return tree;
}

void drop_collected_mounts(struct vfsmount *mnt)
{
      LIST_HEAD(umount_list);
      down_read(&namespace_sem);
      spin_lock(&vfsmount_lock);
      umount_tree(mnt, 0, &umount_list);
      spin_unlock(&vfsmount_lock);
      up_read(&namespace_sem);
      release_mounts(&umount_list);
}

/*
 *  @source_mnt : mount tree to be attached
 *  @nd         : place the mount tree @source_mnt is attached
 *  @parent_nd  : if non-null, detach the source_mnt from its parent and
 *             store the parent mount and mountpoint dentry.
 *             (done when source_mnt is moved)
 *
 *  NOTE: in the table below explains the semantics when a source mount
 *  of a given type is attached to a destination mount of a given type.
 * ---------------------------------------------------------------------------
 * |         BIND MOUNT OPERATION                                            |
 * |**************************************************************************
 * | source-->| shared        |       private  |       slave    | unbindable |
 * | dest     |               |                |                |            |
 * |   |      |               |                |                |            |
 * |   v      |               |                |                |            |
 * |**************************************************************************
 * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
 * |          |               |                |                |            |
 * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
 * ***************************************************************************
 * A bind operation clones the source mount and mounts the clone on the
 * destination mount.
 *
 * (++)  the cloned mount is propagated to all the mounts in the propagation
 *     tree of the destination mount and the cloned mount is added to
 *     the peer group of the source mount.
 * (+)   the cloned mount is created under the destination mount and is marked
 *       as shared. The cloned mount is added to the peer group of the source
 *       mount.
 * (+++) the mount is propagated to all the mounts in the propagation tree
 *       of the destination mount and the cloned mount is made slave
 *       of the same master as that of the source mount. The cloned mount
 *       is marked as 'shared and slave'.
 * (*)   the cloned mount is made a slave of the same master as that of the
 *     source mount.
 *
 * ---------------------------------------------------------------------------
 * |                    MOVE MOUNT OPERATION                                 |
 * |**************************************************************************
 * | source-->| shared        |       private  |       slave    | unbindable |
 * | dest     |               |                |                |            |
 * |   |      |               |                |                |            |
 * |   v      |               |                |                |            |
 * |**************************************************************************
 * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
 * |          |               |                |                |            |
 * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
 * ***************************************************************************
 *
 * (+)  the mount is moved to the destination. And is then propagated to
 *    all the mounts in the propagation tree of the destination mount.
 * (+*)  the mount is moved to the destination.
 * (+++)  the mount is moved to the destination and is then propagated to
 *    all the mounts belonging to the destination mount's propagation tree.
 *    the mount is marked as 'shared and slave'.
 * (*)      the mount continues to be a slave at the new location.
 *
 * if the source mount is a tree, the operations explained above is
 * applied to each mount in the tree.
 * Must be called without spinlocks held, since this function can sleep
 * in allocations.
 */
static int attach_recursive_mnt(struct vfsmount *source_mnt,
                  struct nameidata *nd, struct nameidata *parent_nd)
{
      LIST_HEAD(tree_list);
      struct vfsmount *dest_mnt = nd->mnt;
      struct dentry *dest_dentry = nd->dentry;
      struct vfsmount *child, *p;

      if (propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list))
            return -EINVAL;

      if (IS_MNT_SHARED(dest_mnt)) {
            for (p = source_mnt; p; p = next_mnt(p, source_mnt))
                  set_mnt_shared(p);
      }

      spin_lock(&vfsmount_lock);
      if (parent_nd) {
            detach_mnt(source_mnt, parent_nd);
            attach_mnt(source_mnt, nd);
            touch_mnt_namespace(current->nsproxy->mnt_ns);
      } else {
            mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
            commit_tree(source_mnt);
      }

      list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
            list_del_init(&child->mnt_hash);
            commit_tree(child);
      }
      spin_unlock(&vfsmount_lock);
      return 0;
}

static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
{
      int err;
      if (mnt->mnt_sb->s_flags & MS_NOUSER)
            return -EINVAL;

      if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
            S_ISDIR(mnt->mnt_root->d_inode->i_mode))
            return -ENOTDIR;

      err = -ENOENT;
      mutex_lock(&nd->dentry->d_inode->i_mutex);
      if (IS_DEADDIR(nd->dentry->d_inode))
            goto out_unlock;

      err = security_sb_check_sb(mnt, nd);
      if (err)
            goto out_unlock;

      err = -ENOENT;
      if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry))
            err = attach_recursive_mnt(mnt, nd, NULL);
out_unlock:
      mutex_unlock(&nd->dentry->d_inode->i_mutex);
      if (!err)
            security_sb_post_addmount(mnt, nd);
      return err;
}

/*
 * recursively change the type of the mountpoint.
 */
static int do_change_type(struct nameidata *nd, int flag)
{
      struct vfsmount *m, *mnt = nd->mnt;
      int recurse = flag & MS_REC;
      int type = flag & ~MS_REC;

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

      if (nd->dentry != nd->mnt->mnt_root)
            return -EINVAL;

      down_write(&namespace_sem);
      spin_lock(&vfsmount_lock);
      for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
            change_mnt_propagation(m, type);
      spin_unlock(&vfsmount_lock);
      up_write(&namespace_sem);
      return 0;
}

/*
 * do loopback mount.
 */
static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
{
      struct nameidata old_nd;
      struct vfsmount *mnt = NULL;
      int err = mount_is_safe(nd);
      if (err)
            return err;
      if (!old_name || !*old_name)
            return -EINVAL;
      err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
      if (err)
            return err;

      down_write(&namespace_sem);
      err = -EINVAL;
      if (IS_MNT_UNBINDABLE(old_nd.mnt))
            goto out;

      if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
            goto out;

      err = -ENOMEM;
      if (recurse)
            mnt = copy_tree(old_nd.mnt, old_nd.dentry, 0);
      else
            mnt = clone_mnt(old_nd.mnt, old_nd.dentry, 0);

      if (!mnt)
            goto out;

      err = graft_tree(mnt, nd);
      if (err) {
            LIST_HEAD(umount_list);
            spin_lock(&vfsmount_lock);
            umount_tree(mnt, 0, &umount_list);
            spin_unlock(&vfsmount_lock);
            release_mounts(&umount_list);
      }

out:
      up_write(&namespace_sem);
      path_release(&old_nd);
      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(struct nameidata *nd, int flags, int mnt_flags,
                  void *data)
{
      int err;
      struct super_block *sb = nd->mnt->mnt_sb;

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

      if (!check_mnt(nd->mnt))
            return -EINVAL;

      if (nd->dentry != nd->mnt->mnt_root)
            return -EINVAL;

      down_write(&sb->s_umount);
      err = do_remount_sb(sb, flags, data, 0);
      if (!err)
            nd->mnt->mnt_flags = mnt_flags;
      up_write(&sb->s_umount);
      if (!err)
            security_sb_post_remount(nd->mnt, flags, data);
      return err;
}

static inline int tree_contains_unbindable(struct vfsmount *mnt)
{
      struct vfsmount *p;
      for (p = mnt; p; p = next_mnt(p, mnt)) {
            if (IS_MNT_UNBINDABLE(p))
                  return 1;
      }
      return 0;
}

static int do_move_mount(struct nameidata *nd, char *old_name)
{
      struct nameidata old_nd, parent_nd;
      struct vfsmount *p;
      int err = 0;
      if (!capable(CAP_SYS_ADMIN))
            return -EPERM;
      if (!old_name || !*old_name)
            return -EINVAL;
      err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
      if (err)
            return err;

      down_write(&namespace_sem);
      while (d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
            ;
      err = -EINVAL;
      if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
            goto out;

      err = -ENOENT;
      mutex_lock(&nd->dentry->d_inode->i_mutex);
      if (IS_DEADDIR(nd->dentry->d_inode))
            goto out1;

      if (!IS_ROOT(nd->dentry) && d_unhashed(nd->dentry))
            goto out1;

      err = -EINVAL;
      if (old_nd.dentry != old_nd.mnt->mnt_root)
            goto out1;

      if (old_nd.mnt == old_nd.mnt->mnt_parent)
            goto out1;

      if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
            S_ISDIR(old_nd.dentry->d_inode->i_mode))
            goto out1;
      /*
       * Don't move a mount residing in a shared parent.
       */
      if (old_nd.mnt->mnt_parent && IS_MNT_SHARED(old_nd.mnt->mnt_parent))
            goto out1;
      /*
       * Don't move a mount tree containing unbindable mounts to a destination
       * mount which is shared.
       */
      if (IS_MNT_SHARED(nd->mnt) && tree_contains_unbindable(old_nd.mnt))
            goto out1;
      err = -ELOOP;
      for (p = nd->mnt; p->mnt_parent != p; p = p->mnt_parent)
            if (p == old_nd.mnt)
                  goto out1;

      if ((err = attach_recursive_mnt(old_nd.mnt, nd, &parent_nd)))
            goto out1;

      spin_lock(&vfsmount_lock);
      /* if the mount is moved, it should no longer be expire
       * automatically */
      list_del_init(&old_nd.mnt->mnt_expire);
      spin_unlock(&vfsmount_lock);
out1:
      mutex_unlock(&nd->dentry->d_inode->i_mutex);
out:
      up_write(&namespace_sem);
      if (!err)
            path_release(&parent_nd);
      path_release(&old_nd);
      return err;
}

/*
 * create a new mount for userspace and request it to be added into the
 * namespace's tree
 */
static int do_new_mount(struct nameidata *nd, char *type, int flags,
                  int mnt_flags, char *name, void *data)
{
      struct vfsmount *mnt;

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

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

      mnt = do_kern_mount(type, flags, name, data);
      if (IS_ERR(mnt))
            return PTR_ERR(mnt);

      return do_add_mount(mnt, nd, mnt_flags, NULL);
}

/*
 * add a mount into a namespace's mount tree
 * - provide the option of adding the new mount to an expiration list
 */
int do_add_mount(struct vfsmount *newmnt, struct nameidata *nd,
             int mnt_flags, struct list_head *fslist)
{
      int err;

      down_write(&namespace_sem);
      /* Something was mounted here while we slept */
      while (d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
            ;
      err = -EINVAL;
      if (!check_mnt(nd->mnt))
            goto unlock;

      /* Refuse the same filesystem on the same mount point */
      err = -EBUSY;
      if (nd->mnt->mnt_sb == newmnt->mnt_sb &&
          nd->mnt->mnt_root == nd->dentry)
            goto unlock;

      err = -EINVAL;
      if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
            goto unlock;

      newmnt->mnt_flags = mnt_flags;
      if ((err = graft_tree(newmnt, nd)))
            goto unlock;

      if (fslist) {
            /* add to the specified expiration list */
            spin_lock(&vfsmount_lock);
            list_add_tail(&newmnt->mnt_expire, fslist);
            spin_unlock(&vfsmount_lock);
      }
      up_write(&namespace_sem);
      return 0;

unlock:
      up_write(&namespace_sem);
      mntput(newmnt);
      return err;
}

EXPORT_SYMBOL_GPL(do_add_mount);

static void expire_mount(struct vfsmount *mnt, struct list_head *mounts,
                        struct list_head *umounts)
{
      spin_lock(&vfsmount_lock);

      /*
       * Check if mount is still attached, if not, let whoever holds it deal
       * with the sucker
       */
      if (mnt->mnt_parent == mnt) {
            spin_unlock(&vfsmount_lock);
            return;
      }

      /*
       * Check that it is still dead: the count should now be 2 - as
       * contributed by the vfsmount parent and the mntget above
       */
      if (!propagate_mount_busy(mnt, 2)) {
            /* delete from the namespace */
            touch_mnt_namespace(mnt->mnt_ns);
            list_del_init(&mnt->mnt_list);
            mnt->mnt_ns = NULL;
            umount_tree(mnt, 1, umounts);
            spin_unlock(&vfsmount_lock);
      } else {
            /*
             * Someone brought it back to life whilst we didn't have any
             * locks held so return it to the expiration list
             */
            list_add_tail(&mnt->mnt_expire, mounts);
            spin_unlock(&vfsmount_lock);
      }
}

/*
 * go through the vfsmounts we've just consigned to the graveyard to
 * - check that they're still dead
 * - delete the vfsmount from the appropriate namespace under lock
 * - dispose of the corpse
 */
static void expire_mount_list(struct list_head *graveyard, struct list_head *mounts)
{
      struct mnt_namespace *ns;
      struct vfsmount *mnt;

      while (!list_empty(graveyard)) {
            LIST_HEAD(umounts);
            mnt = list_first_entry(graveyard, struct vfsmount, mnt_expire);
            list_del_init(&mnt->mnt_expire);

            /* don't do anything if the namespace is dead - all the
             * vfsmounts from it are going away anyway */
            ns = mnt->mnt_ns;
            if (!ns || !ns->root)
                  continue;
            get_mnt_ns(ns);

            spin_unlock(&vfsmount_lock);
            down_write(&namespace_sem);
            expire_mount(mnt, mounts, &umounts);
            up_write(&namespace_sem);
            release_mounts(&umounts);
            mntput(mnt);
            put_mnt_ns(ns);
            spin_lock(&vfsmount_lock);
      }
}

/*
 * process a list of expirable mountpoints with the intent of discarding any
 * mountpoints that aren't in use and haven't been touched since last we came
 * here
 */
void mark_mounts_for_expiry(struct list_head *mounts)
{
      struct vfsmount *mnt, *next;
      LIST_HEAD(graveyard);

      if (list_empty(mounts))
            return;

      spin_lock(&vfsmount_lock);

      /* extract from the expiration list every vfsmount that matches the
       * following criteria:
       * - only referenced by its parent vfsmount
       * - still marked for expiry (marked on the last call here; marks are
       *   cleared by mntput())
       */
      list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
            if (!xchg(&mnt->mnt_expiry_mark, 1) ||
                atomic_read(&mnt->mnt_count) != 1)
                  continue;

            mntget(mnt);
            list_move(&mnt->mnt_expire, &graveyard);
      }

      expire_mount_list(&graveyard, mounts);

      spin_unlock(&vfsmount_lock);
}

EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);

/*
 * Ripoff of 'select_parent()'
 *
 * search the list of submounts for a given mountpoint, and move any
 * shrinkable submounts to the 'graveyard' list.
 */
static int select_submounts(struct vfsmount *parent, struct list_head *graveyard)
{
      struct vfsmount *this_parent = parent;
      struct list_head *next;
      int found = 0;

repeat:
      next = this_parent->mnt_mounts.next;
resume:
      while (next != &this_parent->mnt_mounts) {
            struct list_head *tmp = next;
            struct vfsmount *mnt = list_entry(tmp, struct vfsmount, mnt_child);

            next = tmp->next;
            if (!(mnt->mnt_flags & MNT_SHRINKABLE))
                  continue;
            /*
             * Descend a level if the d_mounts list is non-empty.
             */
            if (!list_empty(&mnt->mnt_mounts)) {
                  this_parent = mnt;
                  goto repeat;
            }

            if (!propagate_mount_busy(mnt, 1)) {
                  mntget(mnt);
                  list_move_tail(&mnt->mnt_expire, graveyard);
                  found++;
            }
      }
      /*
       * All done at this level ... ascend and resume the search
       */
      if (this_parent != parent) {
            next = this_parent->mnt_child.next;
            this_parent = this_parent->mnt_parent;
            goto resume;
      }
      return found;
}

/*
 * process a list of expirable mountpoints with the intent of discarding any
 * submounts of a specific parent mountpoint
 */
void shrink_submounts(struct vfsmount *mountpoint, struct list_head *mounts)
{
      LIST_HEAD(graveyard);
      int found;

      spin_lock(&vfsmount_lock);

      /* extract submounts of 'mountpoint' from the expiration list */
      while ((found = select_submounts(mountpoint, &graveyard)) != 0)
            expire_mount_list(&graveyard, mounts);

      spin_unlock(&vfsmount_lock);
}

EXPORT_SYMBOL_GPL(shrink_submounts);

/*
 * Some copy_from_user() implementations do not return the exact number of
 * bytes remaining to copy on a fault.  But copy_mount_options() requires that.
 * Note that this function differs from copy_from_user() in that it will oops
 * on bad values of `to', rather than returning a short copy.
 */
static long exact_copy_from_user(void *to, const void __user * from,
                         unsigned long n)
{
      char *t = to;
      const char __user *f = from;
      char c;

      if (!access_ok(VERIFY_READ, from, n))
            return n;

      while (n) {
            if (__get_user(c, f)) {
                  memset(t, 0, n);
                  break;
            }
            *t++ = c;
            f++;
            n--;
      }
      return n;
}

int copy_mount_options(const void __user * 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 - exact_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 32-bit value that allows up to 31 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).
 *
 * Pre-0.97 versions of mount() didn't have a flags word.
 * When the flags word was introduced its top half was required
 * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
 * Therefore, if this magic number is present, it carries no information
 * and must be discarded.
 */
long do_mount(char *dev_name, char *dir_name, char *type_page,
              unsigned long flags, void *data_page)
{
      struct nameidata nd;
      int retval = 0;
      int mnt_flags = 0;

      /* Discard magic */
      if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
            flags &= ~MS_MGC_MSK;

      /* 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;

      if (data_page)
            ((char *)data_page)[PAGE_SIZE - 1] = 0;

      /* Separate the per-mountpoint flags */
      if (flags & MS_NOSUID)
            mnt_flags |= MNT_NOSUID;
      if (flags & MS_NODEV)
            mnt_flags |= MNT_NODEV;
      if (flags & MS_NOEXEC)
            mnt_flags |= MNT_NOEXEC;
      if (flags & MS_NOATIME)
            mnt_flags |= MNT_NOATIME;
      if (flags & MS_NODIRATIME)
            mnt_flags |= MNT_NODIRATIME;
      if (flags & MS_RELATIME)
            mnt_flags |= MNT_RELATIME;

      flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
               MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT);

      /* ... and get the mountpoint */
      retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd);
      if (retval)
            return retval;

      retval = security_sb_mount(dev_name, &nd, type_page, flags, data_page);
      if (retval)
            goto dput_out;

      if (flags & MS_REMOUNT)
            retval = do_remount(&nd, flags & ~MS_REMOUNT, mnt_flags,
                            data_page);
      else if (flags & MS_BIND)
            retval = do_loopback(&nd, dev_name, flags & MS_REC);
      else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
            retval = do_change_type(&nd, flags);
      else if (flags & MS_MOVE)
            retval = do_move_mount(&nd, dev_name);
      else
            retval = do_new_mount(&nd, type_page, flags, mnt_flags,
                              dev_name, data_page);
dput_out:
      path_release(&nd);
      return retval;
}

/*
 * Allocate a new namespace structure and populate it with contents
 * copied from the namespace of the passed in task structure.
 */
static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
            struct fs_struct *fs)
{
      struct mnt_namespace *new_ns;
      struct vfsmount *rootmnt = NULL, *pwdmnt = NULL, *altrootmnt = NULL;
      struct vfsmount *p, *q;

      new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
      if (!new_ns)
            return ERR_PTR(-ENOMEM);

      atomic_set(&new_ns->count, 1);
      INIT_LIST_HEAD(&new_ns->list);
      init_waitqueue_head(&new_ns->poll);
      new_ns->event = 0;

      down_write(&namespace_sem);
      /* First pass: copy the tree topology */
      new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,
                              CL_COPY_ALL | CL_EXPIRE);
      if (!new_ns->root) {
            up_write(&namespace_sem);
            kfree(new_ns);
            return ERR_PTR(-ENOMEM);;
      }
      spin_lock(&vfsmount_lock);
      list_add_tail(&new_ns->list, &new_ns->root->mnt_list);
      spin_unlock(&vfsmount_lock);

      /*
       * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
       * as belonging to new namespace.  We have already acquired a private
       * fs_struct, so tsk->fs->lock is not needed.
       */
      p = mnt_ns->root;
      q = new_ns->root;
      while (p) {
            q->mnt_ns = new_ns;
            if (fs) {
                  if (p == fs->rootmnt) {
                        rootmnt = p;
                        fs->rootmnt = mntget(q);
                  }
                  if (p == fs->pwdmnt) {
                        pwdmnt = p;
                        fs->pwdmnt = mntget(q);
                  }
                  if (p == fs->altrootmnt) {
                        altrootmnt = p;
                        fs->altrootmnt = mntget(q);
                  }
            }
            p = next_mnt(p, mnt_ns->root);
            q = next_mnt(q, new_ns->root);
      }
      up_write(&namespace_sem);

      if (rootmnt)
            mntput(rootmnt);
      if (pwdmnt)
            mntput(pwdmnt);
      if (altrootmnt)
            mntput(altrootmnt);

      return new_ns;
}

struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
            struct fs_struct *new_fs)
{
      struct mnt_namespace *new_ns;

      BUG_ON(!ns);
      get_mnt_ns(ns);

      if (!(flags & CLONE_NEWNS))
            return ns;

      new_ns = dup_mnt_ns(ns, new_fs);

      put_mnt_ns(ns);
      return new_ns;
}

asmlinkage long sys_mount(char __user * dev_name, char __user * dir_name,
                    char __user * type, unsigned long flags,
                    void __user * 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)
            goto out3;

      lock_kernel();
      retval = do_mount((char *)dev_page, dir_page, (char *)type_page,
                    flags, (void *)data_page);
      unlock_kernel();
      free_page(data_page);

out3:
      free_page(dev_page);
out2:
      putname(dir_page);
out1:
      free_page(type_page);
      return retval;
}

/*
 * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
 * It can block. Requires the big lock held.
 */
void set_fs_root(struct fs_struct *fs, struct vfsmount *mnt,
             struct dentry *dentry)
{
      struct dentry *old_root;
      struct vfsmount *old_rootmnt;
      write_lock(&fs->lock);
      old_root = fs->root;
      old_rootmnt = fs->rootmnt;
      fs->rootmnt = mntget(mnt);
      fs->root = dget(dentry);
      write_unlock(&fs->lock);
      if (old_root) {
            dput(old_root);
            mntput(old_rootmnt);
      }
}

/*
 * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
 * It can block. Requires the big lock held.
 */
void set_fs_pwd(struct fs_struct *fs, struct vfsmount *mnt,
            struct dentry *dentry)
{
      struct dentry *old_pwd;
      struct vfsmount *old_pwdmnt;

      write_lock(&fs->lock);
      old_pwd = fs->pwd;
      old_pwdmnt = fs->pwdmnt;
      fs->pwdmnt = mntget(mnt);
      fs->pwd = dget(dentry);
      write_unlock(&fs->lock);

      if (old_pwd) {
            dput(old_pwd);
            mntput(old_pwdmnt);
      }
}

static void chroot_fs_refs(struct nameidata *old_nd, struct nameidata *new_nd)
{
      struct task_struct *g, *p;
      struct fs_struct *fs;

      read_lock(&tasklist_lock);
      do_each_thread(g, p) {
            task_lock(p);
            fs = p->fs;
            if (fs) {
                  atomic_inc(&fs->count);
                  task_unlock(p);
                  if (fs->root == old_nd->dentry
                      && fs->rootmnt == old_nd->mnt)
                        set_fs_root(fs, new_nd->mnt, new_nd->dentry);
                  if (fs->pwd == old_nd->dentry
                      && fs->pwdmnt == old_nd->mnt)
                        set_fs_pwd(fs, new_nd->mnt, new_nd->dentry);
                  put_fs_struct(fs);
            } else
                  task_unlock(p);
      } while_each_thread(g, p);
      read_unlock(&tasklist_lock);
}

/*
 * pivot_root Semantics:
 * Moves the root file system of the current process to the directory put_old,
 * makes new_root as the new root file system of the current process, and sets
 * root/cwd of all processes which had them on the current root to new_root.
 *
 * Restrictions:
 * The new_root and put_old must be directories, and  must not be on the
 * same file  system as the current process root. The put_old  must  be
 * underneath new_root,  i.e. adding a non-zero number of /.. to the string
 * pointed to by put_old must yield the same directory as new_root. No other
 * file system may be mounted on put_old. After all, new_root is a mountpoint.
 *
 * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
 * See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
 * in this situation.
 *
 * Notes:
 *  - 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. It must be a mountpoint,
 *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
 *    first.
 */
asmlinkage long sys_pivot_root(const char __user * new_root,
                         const char __user * put_old)
{
      struct vfsmount *tmp;
      struct nameidata new_nd, old_nd, parent_nd, root_parent, user_nd;
      int error;

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

      lock_kernel();

      error = __user_walk(new_root, LOOKUP_FOLLOW | LOOKUP_DIRECTORY,
                      &new_nd);
      if (error)
            goto out0;
      error = -EINVAL;
      if (!check_mnt(new_nd.mnt))
            goto out1;

      error = __user_walk(put_old, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &old_nd);
      if (error)
            goto out1;

      error = security_sb_pivotroot(&old_nd, &new_nd);
      if (error) {
            path_release(&old_nd);
            goto out1;
      }

      read_lock(&current->fs->lock);
      user_nd.mnt = mntget(current->fs->rootmnt);
      user_nd.dentry = dget(current->fs->root);
      read_unlock(&current->fs->lock);
      down_write(&namespace_sem);
      mutex_lock(&old_nd.dentry->d_inode->i_mutex);
      error = -EINVAL;
      if (IS_MNT_SHARED(old_nd.mnt) ||
            IS_MNT_SHARED(new_nd.mnt->mnt_parent) ||
            IS_MNT_SHARED(user_nd.mnt->mnt_parent))
            goto out2;
      if (!check_mnt(user_nd.mnt))
            goto out2;
      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 == user_nd.mnt || old_nd.mnt == user_nd.mnt)
            goto out2; /* loop, on the same file system  */
      error = -EINVAL;
      if (user_nd.mnt->mnt_root != user_nd.dentry)
            goto out2; /* not a mountpoint */
      if (user_nd.mnt->mnt_parent == user_nd.mnt)
            goto out2; /* not attached */
      if (new_nd.mnt->mnt_root != new_nd.dentry)
            goto out2; /* not a mountpoint */
      if (new_nd.mnt->mnt_parent == new_nd.mnt)
            goto out2; /* not attached */
      tmp = old_nd.mnt; /* make sure we can reach put_old from new_root */
      spin_lock(&vfsmount_lock);
      if (tmp != new_nd.mnt) {
            for (;;) {
                  if (tmp->mnt_parent == tmp)
                        goto out3; /* already mounted on put_old */
                  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;
      detach_mnt(new_nd.mnt, &parent_nd);
      detach_mnt(user_nd.mnt, &root_parent);
      attach_mnt(user_nd.mnt, &old_nd);     /* mount old root on put_old */
      attach_mnt(new_nd.mnt, &root_parent); /* mount new_root on / */
      touch_mnt_namespace(current->nsproxy->mnt_ns);
      spin_unlock(&vfsmount_lock);
      chroot_fs_refs(&user_nd, &new_nd);
      security_sb_post_pivotroot(&user_nd, &new_nd);
      error = 0;
      path_release(&root_parent);
      path_release(&parent_nd);
out2:
      mutex_unlock(&old_nd.dentry->d_inode->i_mutex);
      up_write(&namespace_sem);
      path_release(&user_nd);
      path_release(&old_nd);
out1:
      path_release(&new_nd);
out0:
      unlock_kernel();
      return error;
out3:
      spin_unlock(&vfsmount_lock);
      goto out2;
}

static void __init init_mount_tree(void)
{
      struct vfsmount *mnt;
      struct mnt_namespace *ns;

      mnt = do_kern_mount("rootfs", 0, "rootfs", NULL);
      if (IS_ERR(mnt))
            panic("Can't create rootfs");
      ns = kmalloc(sizeof(*ns), GFP_KERNEL);
      if (!ns)
            panic("Can't allocate initial namespace");
      atomic_set(&ns->count, 1);
      INIT_LIST_HEAD(&ns->list);
      init_waitqueue_head(&ns->poll);
      ns->event = 0;
      list_add(&mnt->mnt_list, &ns->list);
      ns->root = mnt;
      mnt->mnt_ns = ns;

      init_task.nsproxy->mnt_ns = ns;
      get_mnt_ns(ns);

      set_fs_pwd(current->fs, ns->root, ns->root->mnt_root);
      set_fs_root(current->fs, ns->root, ns->root->mnt_root);
}

void __init mnt_init(void)
{
      struct list_head *d;
      unsigned int nr_hash;
      int i;
      int err;

      init_rwsem(&namespace_sem);

      mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct vfsmount),
                  0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);

      mount_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);

      if (!mount_hashtable)
            panic("Failed to allocate mount hash table\n");

      /*
       * Find the power-of-two list-heads that can fit into the allocation..
       * We don't guarantee that "sizeof(struct list_head)" is necessarily
       * a power-of-two.
       */
      nr_hash = PAGE_SIZE / sizeof(struct list_head);
      hash_bits = 0;
      do {
            hash_bits++;
      } while ((nr_hash >> hash_bits) != 0);
      hash_bits--;

      /*
       * Re-calculate the actual number of entries and the mask
       * from the number of bits we can fit.
       */
      nr_hash = 1UL << hash_bits;
      hash_mask = nr_hash - 1;

      printk("Mount-cache hash table entries: %d\n", nr_hash);

      /* And initialize the newly allocated array */
      d = mount_hashtable;
      i = nr_hash;
      do {
            INIT_LIST_HEAD(d);
            d++;
            i--;
      } while (i);
      err = sysfs_init();
      if (err)
            printk(KERN_WARNING "%s: sysfs_init error: %d\n",
                  __FUNCTION__, err);
      err = subsystem_register(&fs_subsys);
      if (err)
            printk(KERN_WARNING "%s: subsystem_register error: %d\n",
                  __FUNCTION__, err);
      init_rootfs();
      init_mount_tree();
}

void __put_mnt_ns(struct mnt_namespace *ns)
{
      struct vfsmount *root = ns->root;
      LIST_HEAD(umount_list);
      ns->root = NULL;
      spin_unlock(&vfsmount_lock);
      down_write(&namespace_sem);
      spin_lock(&vfsmount_lock);
      umount_tree(root, 0, &umount_list);
      spin_unlock(&vfsmount_lock);
      up_write(&namespace_sem);
      release_mounts(&umount_list);
      kfree(ns);
}

Generated by  Doxygen 1.6.0   Back to index