/*
   *  linux/fs/namei.c
   *
   *  Copyright (C) 1991, 1992  Linus Torvalds
   */
  
  /*
   * Some corrections by tytso.
   */
  
  /* [Feb 1997 T. Schoebel-Theuer] Complete rewrite of the pathname
   * lookup logic.
   */
  /* [Feb-Apr 2000, AV] Rewrite to the new namespace architecture.
   */
  
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/fs.h>
  #include <linux/namei.h>

  #include <linux/pagemap.h>

  #include <linux/fsnotify.h>

  #include <linux/personality.h>
  #include <linux/security.h>

  #include <linux/ima.h>

  #include <linux/syscalls.h>
  #include <linux/mount.h>
  #include <linux/audit.h>

  #include <linux/capability.h>

  #include <linux/file.h>

  #include <linux/fcntl.h>

  #include <linux/device_cgroup.h>

  #include <linux/fs_struct.h>

  #include <asm/uaccess.h>

  #include "internal.h"

  /* [Feb-1997 T. Schoebel-Theuer]
   * Fundamental changes in the pathname lookup mechanisms (namei)
   * were necessary because of omirr.  The reason is that omirr needs
   * to know the _real_ pathname, not the user-supplied one, in case
   * of symlinks (and also when transname replacements occur).
   *
   * The new code replaces the old recursive symlink resolution with
   * an iterative one (in case of non-nested symlink chains).  It does
   * this with calls to <fs>_follow_link().
   * As a side effect, dir_namei(), _namei() and follow_link() are now 
   * replaced with a single function lookup_dentry() that can handle all 
   * the special cases of the former code.
   *
   * With the new dcache, the pathname is stored at each inode, at least as
   * long as the refcount of the inode is positive.  As a side effect, the
   * size of the dcache depends on the inode cache and thus is dynamic.
   *
   * [29-Apr-1998 C. Scott Ananian] Updated above description of symlink
   * resolution to correspond with current state of the code.
   *
   * Note that the symlink resolution is not *completely* iterative.
   * There is still a significant amount of tail- and mid- recursion in
   * the algorithm.  Also, note that <fs>_readlink() is not used in
   * lookup_dentry(): lookup_dentry() on the result of <fs>_readlink()
   * may return different results than <fs>_follow_link().  Many virtual
   * filesystems (including /proc) exhibit this behavior.
   */
  
  /* [24-Feb-97 T. Schoebel-Theuer] Side effects caused by new implementation:
   * New symlink semantics: when open() is called with flags O_CREAT | O_EXCL
   * and the name already exists in form of a symlink, try to create the new
   * name indicated by the symlink. The old code always complained that the
   * name already exists, due to not following the symlink even if its target
   * is nonexistent.  The new semantics affects also mknod() and link() when

   * the name is a symlink pointing to a non-existent name.

   *
   * I don't know which semantics is the right one, since I have no access
   * to standards. But I found by trial that HP-UX 9.0 has the full "new"
   * semantics implemented, while SunOS 4.1.1 and Solaris (SunOS 5.4) have the
   * "old" one. Personally, I think the new semantics is much more logical.
   * Note that "ln old new" where "new" is a symlink pointing to a non-existing
   * file does succeed in both HP-UX and SunOs, but not in Solaris
   * and in the old Linux semantics.
   */
  
  /* [16-Dec-97 Kevin Buhr] For security reasons, we change some symlink
   * semantics.  See the comments in "open_namei" and "do_link" below.
   *
   * [10-Sep-98 Alan Modra] Another symlink change.
   */
  
  /* [Feb-Apr 2000 AV] Complete rewrite. Rules for symlinks:
   *	inside the path - always follow.
   *	in the last component in creation/removal/renaming - never follow.
   *	if LOOKUP_FOLLOW passed - follow.
   *	if the pathname has trailing slashes - follow.
   *	otherwise - don't follow.
   * (applied in that order).
   *
   * [Jun 2000 AV] Inconsistent behaviour of open() in case if flags==O_CREAT
   * restored for 2.4. This is the last surviving part of old 4.2BSD bug.
   * During the 2.4 we need to fix the userland stuff depending on it -
   * hopefully we will be able to get rid of that wart in 2.5. So far only
   * XEmacs seems to be relying on it...
   */
  /*
   * [Sep 2001 AV] Single-semaphore locking scheme (kudos to David Holland)

   * implemented.  Let's see if raised priority of ->s_vfs_rename_mutex gives

   * any extra contention...
   */
  
  /* In order to reduce some races, while at the same time doing additional
   * checking and hopefully speeding things up, we copy filenames to the
   * kernel data space before using them..
   *
   * POSIX.1 2.4: an empty pathname is invalid (ENOENT).
   * PATH_MAX includes the nul terminator --RR.
   */

  static int do_getname(const char __user *filename, char *page)

  {
  	int retval;
  	unsigned long len = PATH_MAX;
  
  	if (!segment_eq(get_fs(), KERNEL_DS)) {
  		if ((unsigned long) filename >= TASK_SIZE)
  			return -EFAULT;
  		if (TASK_SIZE - (unsigned long) filename < PATH_MAX)
  			len = TASK_SIZE - (unsigned long) filename;
  	}
  
  	retval = strncpy_from_user(page, filename, len);
  	if (retval > 0) {
  		if (retval < len)
  			return 0;
  		return -ENAMETOOLONG;
  	} else if (!retval)
  		retval = -ENOENT;
  	return retval;
  }

  static char *getname_flags(const char __user * filename, int flags)

  {
  	char *tmp, *result;
  
  	result = ERR_PTR(-ENOMEM);
  	tmp = __getname();
  	if (tmp)  {
  		int retval = do_getname(filename, tmp);
  
  		result = tmp;
  		if (retval < 0) {

  			if (retval != -ENOENT || !(flags & LOOKUP_EMPTY)) {
  				__putname(tmp);
  				result = ERR_PTR(retval);
  			}

  		}
  	}
  	audit_getname(result);
  	return result;
  }

  char *getname(const char __user * filename)
  {
  	return getname_flags(filename, 0);
  }

  #ifdef CONFIG_AUDITSYSCALL
  void putname(const char *name)
  {

  	if (unlikely(!audit_dummy_context()))

  		audit_putname(name);
  	else
  		__putname(name);
  }
  EXPORT_SYMBOL(putname);
  #endif

  /*
   * This does basic POSIX ACL permission checking

   */

  static int acl_permission_check(struct inode *inode, int mask, unsigned int flags,
  		int (*check_acl)(struct inode *inode, int mask, unsigned int flags))

  {

  	unsigned int mode = inode->i_mode;

  	mask &= MAY_READ | MAY_WRITE | MAY_EXEC;

  	if (current_user_ns() != inode_userns(inode))
  		goto other_perms;

  	if (current_fsuid() == inode->i_uid)

  		mode >>= 6;
  	else {
  		if (IS_POSIXACL(inode) && (mode & S_IRWXG) && check_acl) {

  			int error = check_acl(inode, mask, flags);
  			if (error != -EAGAIN)
  				return error;

  		}
  
  		if (in_group_p(inode->i_gid))
  			mode >>= 3;
  	}

  other_perms:

  	/*
  	 * If the DACs are ok we don't need any capability check.
  	 */

  	if ((mask & ~mode) == 0)

  		return 0;

  	return -EACCES;
  }
  
  /**

   * generic_permission -  check for access rights on a Posix-like filesystem

   * @inode:	inode to check access rights for
   * @mask:	right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
   * @check_acl:	optional callback to check for Posix ACLs

   * @flags:	IPERM_FLAG_ flags.

   *
   * Used to check for read/write/execute permissions on a file.
   * We use "fsuid" for this, letting us set arbitrary permissions
   * for filesystem access without changing the "normal" uids which

   * are used for other things.
   *
   * generic_permission is rcu-walk aware. It returns -ECHILD in case an rcu-walk
   * request cannot be satisfied (eg. requires blocking or too much complexity).
   * It would then be called again in ref-walk mode.

   */

  int generic_permission(struct inode *inode, int mask, unsigned int flags,
  	int (*check_acl)(struct inode *inode, int mask, unsigned int flags))

  {
  	int ret;
  
  	/*
  	 * Do the basic POSIX ACL permission checks.
  	 */

  	ret = acl_permission_check(inode, mask, flags, check_acl);

  	if (ret != -EACCES)
  		return ret;

  	/*
  	 * Read/write DACs are always overridable.

  	 * Executable DACs are overridable for all directories and
  	 * for non-directories that have least one exec bit set.

  	 */

  	if (!(mask & MAY_EXEC) || execute_ok(inode))

  		if (ns_capable(inode_userns(inode), CAP_DAC_OVERRIDE))

  			return 0;
  
  	/*
  	 * Searching includes executable on directories, else just read.
  	 */

  	mask &= MAY_READ | MAY_WRITE | MAY_EXEC;

  	if (mask == MAY_READ || (S_ISDIR(inode->i_mode) && !(mask & MAY_WRITE)))

  		if (ns_capable(inode_userns(inode), CAP_DAC_READ_SEARCH))

  			return 0;
  
  	return -EACCES;
  }

  /**
   * inode_permission  -  check for access rights to a given inode
   * @inode:	inode to check permission on
   * @mask:	right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
   *
   * Used to check for read/write/execute permissions on an inode.
   * We use "fsuid" for this, letting us set arbitrary permissions
   * for filesystem access without changing the "normal" uids which
   * are used for other things.
   */

  int inode_permission(struct inode *inode, int mask)

  {

  	int retval;

  
  	if (mask & MAY_WRITE) {

  		umode_t mode = inode->i_mode;

  
  		/*
  		 * Nobody gets write access to a read-only fs.
  		 */
  		if (IS_RDONLY(inode) &&
  		    (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
  			return -EROFS;
  
  		/*
  		 * Nobody gets write access to an immutable file.
  		 */
  		if (IS_IMMUTABLE(inode))
  			return -EACCES;
  	}

  	if (inode->i_op->permission)

  		retval = inode->i_op->permission(inode, mask, 0);

  	else

  		retval = generic_permission(inode, mask, 0,
  				inode->i_op->check_acl);

  	if (retval)
  		return retval;

  	retval = devcgroup_inode_permission(inode, mask);
  	if (retval)
  		return retval;

  	return security_inode_permission(inode, mask);

  }

  /**

   * file_permission  -  check for additional access rights to a given file
   * @file:	file to check access rights for
   * @mask:	right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
   *
   * Used to check for read/write/execute permissions on an already opened
   * file.
   *
   * Note:
   *	Do not use this function in new code.  All access checks should

   *	be done using inode_permission().

   */
  int file_permission(struct file *file, int mask)
  {

  	return inode_permission(file->f_path.dentry->d_inode, mask);

  }

  /*
   * get_write_access() gets write permission for a file.
   * put_write_access() releases this write permission.
   * This is used for regular files.
   * We cannot support write (and maybe mmap read-write shared) accesses and
   * MAP_DENYWRITE mmappings simultaneously. The i_writecount field of an inode
   * can have the following values:
   * 0: no writers, no VM_DENYWRITE mappings
   * < 0: (-i_writecount) vm_area_structs with VM_DENYWRITE set exist
   * > 0: (i_writecount) users are writing to the file.
   *
   * Normally we operate on that counter with atomic_{inc,dec} and it's safe
   * except for the cases where we don't hold i_writecount yet. Then we need to
   * use {get,deny}_write_access() - these functions check the sign and refuse
   * to do the change if sign is wrong. Exclusion between them is provided by
   * the inode->i_lock spinlock.
   */
  
  int get_write_access(struct inode * inode)
  {
  	spin_lock(&inode->i_lock);
  	if (atomic_read(&inode->i_writecount) < 0) {
  		spin_unlock(&inode->i_lock);
  		return -ETXTBSY;
  	}
  	atomic_inc(&inode->i_writecount);
  	spin_unlock(&inode->i_lock);
  
  	return 0;
  }
  
  int deny_write_access(struct file * file)
  {

  	struct inode *inode = file->f_path.dentry->d_inode;

  
  	spin_lock(&inode->i_lock);
  	if (atomic_read(&inode->i_writecount) > 0) {
  		spin_unlock(&inode->i_lock);
  		return -ETXTBSY;
  	}
  	atomic_dec(&inode->i_writecount);
  	spin_unlock(&inode->i_lock);
  
  	return 0;
  }

  /**

   * path_get - get a reference to a path
   * @path: path to get the reference to
   *
   * Given a path increment the reference count to the dentry and the vfsmount.
   */
  void path_get(struct path *path)
  {
  	mntget(path->mnt);
  	dget(path->dentry);
  }
  EXPORT_SYMBOL(path_get);
  
  /**

   * path_put - put a reference to a path
   * @path: path to put the reference to
   *
   * Given a path decrement the reference count to the dentry and the vfsmount.
   */
  void path_put(struct path *path)

  {

  	dput(path->dentry);
  	mntput(path->mnt);

  }

  EXPORT_SYMBOL(path_put);

  /*

   * Path walking has 2 modes, rcu-walk and ref-walk (see

   * Documentation/filesystems/path-lookup.txt).  In situations when we can't
   * continue in RCU mode, we attempt to drop out of rcu-walk mode and grab
   * normal reference counts on dentries and vfsmounts to transition to rcu-walk
   * mode.  Refcounts are grabbed at the last known good point before rcu-walk
   * got stuck, so ref-walk may continue from there. If this is not successful
   * (eg. a seqcount has changed), then failure is returned and it's up to caller
   * to restart the path walk from the beginning in ref-walk mode.

   */

  
  /**

   * unlazy_walk - try to switch to ref-walk mode.
   * @nd: nameidata pathwalk data
   * @dentry: child of nd->path.dentry or NULL

   * Returns: 0 on success, -ECHILD on failure

   *

   * unlazy_walk attempts to legitimize the current nd->path, nd->root and dentry
   * for ref-walk mode.  @dentry must be a path found by a do_lookup call on
   * @nd or NULL.  Must be called from rcu-walk context.

   */

  static int unlazy_walk(struct nameidata *nd, struct dentry *dentry)

  {
  	struct fs_struct *fs = current->fs;
  	struct dentry *parent = nd->path.dentry;

  	int want_root = 0;

  
  	BUG_ON(!(nd->flags & LOOKUP_RCU));

  	if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
  		want_root = 1;

  		spin_lock(&fs->lock);
  		if (nd->root.mnt != fs->root.mnt ||
  				nd->root.dentry != fs->root.dentry)
  			goto err_root;
  	}
  	spin_lock(&parent->d_lock);

  	if (!dentry) {
  		if (!__d_rcu_to_refcount(parent, nd->seq))
  			goto err_parent;
  		BUG_ON(nd->inode != parent->d_inode);
  	} else {
  		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
  		if (!__d_rcu_to_refcount(dentry, nd->seq))
  			goto err_child;
  		/*
  		 * If the sequence check on the child dentry passed, then
  		 * the child has not been removed from its parent. This
  		 * means the parent dentry must be valid and able to take
  		 * a reference at this point.
  		 */
  		BUG_ON(!IS_ROOT(dentry) && dentry->d_parent != parent);
  		BUG_ON(!parent->d_count);
  		parent->d_count++;
  		spin_unlock(&dentry->d_lock);
  	}

  	spin_unlock(&parent->d_lock);

  	if (want_root) {

  		path_get(&nd->root);
  		spin_unlock(&fs->lock);
  	}
  	mntget(nd->path.mnt);
  
  	rcu_read_unlock();
  	br_read_unlock(vfsmount_lock);
  	nd->flags &= ~LOOKUP_RCU;
  	return 0;

  
  err_child:

  	spin_unlock(&dentry->d_lock);

  err_parent:

  	spin_unlock(&parent->d_lock);
  err_root:

  	if (want_root)

  		spin_unlock(&fs->lock);
  	return -ECHILD;
  }

  /**

   * release_open_intent - free up open intent resources
   * @nd: pointer to nameidata
   */
  void release_open_intent(struct nameidata *nd)
  {

  	struct file *file = nd->intent.open.file;
  
  	if (file && !IS_ERR(file)) {
  		if (file->f_path.dentry == NULL)
  			put_filp(file);
  		else
  			fput(file);
  	}

  }

  static inline int d_revalidate(struct dentry *dentry, struct nameidata *nd)

  {

  	return dentry->d_op->d_revalidate(dentry, nd);

  }

  static struct dentry *

  do_revalidate(struct dentry *dentry, struct nameidata *nd)
  {

  	int status = d_revalidate(dentry, nd);

  	if (unlikely(status <= 0)) {
  		/*
  		 * The dentry failed validation.
  		 * If d_revalidate returned 0 attempt to invalidate
  		 * the dentry otherwise d_revalidate is asking us
  		 * to return a fail status.
  		 */

  		if (status < 0) {

  			dput(dentry);

  			dentry = ERR_PTR(status);

  		} else if (!d_invalidate(dentry)) {
  			dput(dentry);
  			dentry = NULL;

  		}
  	}
  	return dentry;
  }

  /**
   * complete_walk - successful completion of path walk
   * @nd:  pointer nameidata

   *

   * If we had been in RCU mode, drop out of it and legitimize nd->path.
   * Revalidate the final result, unless we'd already done that during
   * the path walk or the filesystem doesn't ask for it.  Return 0 on
   * success, -error on failure.  In case of failure caller does not
   * need to drop nd->path.

   */

  static int complete_walk(struct nameidata *nd)

  {

  	struct dentry *dentry = nd->path.dentry;

  	int status;

  	if (nd->flags & LOOKUP_RCU) {
  		nd->flags &= ~LOOKUP_RCU;
  		if (!(nd->flags & LOOKUP_ROOT))
  			nd->root.mnt = NULL;
  		spin_lock(&dentry->d_lock);
  		if (unlikely(!__d_rcu_to_refcount(dentry, nd->seq))) {
  			spin_unlock(&dentry->d_lock);
  			rcu_read_unlock();
  			br_read_unlock(vfsmount_lock);
  			return -ECHILD;
  		}
  		BUG_ON(nd->inode != dentry->d_inode);
  		spin_unlock(&dentry->d_lock);
  		mntget(nd->path.mnt);
  		rcu_read_unlock();
  		br_read_unlock(vfsmount_lock);
  	}

  	if (likely(!(nd->flags & LOOKUP_JUMPED)))
  		return 0;
  
  	if (likely(!(dentry->d_flags & DCACHE_OP_REVALIDATE)))

  		return 0;

  	if (likely(!(dentry->d_sb->s_type->fs_flags & FS_REVAL_DOT)))
  		return 0;
  
  	/* Note: we do not d_invalidate() */

  	status = d_revalidate(dentry, nd);

  	if (status > 0)
  		return 0;

  	if (!status)

  		status = -ESTALE;

  	path_put(&nd->path);

  	return status;
  }
  
  /*

   * Short-cut version of permission(), for calling on directories
   * during pathname resolution.  Combines parts of permission()
   * and generic_permission(), and tests ONLY for MAY_EXEC permission.

   *
   * If appropriate, check DAC only.  If not appropriate, or

   * short-cut DAC fails, then call ->permission() to do more

   * complete permission check.
   */

  static inline int exec_permission(struct inode *inode, unsigned int flags)

  {

  	int ret;

  	struct user_namespace *ns = inode_userns(inode);

  	if (inode->i_op->permission) {

  		ret = inode->i_op->permission(inode, MAY_EXEC, flags);
  	} else {
  		ret = acl_permission_check(inode, MAY_EXEC, flags,
  				inode->i_op->check_acl);

  	}

  	if (likely(!ret))

  		goto ok;

  	if (ret == -ECHILD)

  		return ret;

  	if (ns_capable(ns, CAP_DAC_OVERRIDE) ||
  			ns_capable(ns, CAP_DAC_READ_SEARCH))

  		goto ok;

  	return ret;

  ok:

  	return security_inode_exec_permission(inode, flags);

  }

  static __always_inline void set_root(struct nameidata *nd)
  {

  	if (!nd->root.mnt)
  		get_fs_root(current->fs, &nd->root);

  }

  static int link_path_walk(const char *, struct nameidata *);

  static __always_inline void set_root_rcu(struct nameidata *nd)
  {
  	if (!nd->root.mnt) {
  		struct fs_struct *fs = current->fs;

  		unsigned seq;
  
  		do {
  			seq = read_seqcount_begin(&fs->seq);
  			nd->root = fs->root;

  			nd->seq = __read_seqcount_begin(&nd->root.dentry->d_seq);

  		} while (read_seqcount_retry(&fs->seq, seq));

  	}
  }

  static __always_inline int __vfs_follow_link(struct nameidata *nd, const char *link)

  {

  	int ret;

  	if (IS_ERR(link))
  		goto fail;
  
  	if (*link == '/') {

  		set_root(nd);

  		path_put(&nd->path);

  		nd->path = nd->root;
  		path_get(&nd->root);

  		nd->flags |= LOOKUP_JUMPED;

  	}

  	nd->inode = nd->path.dentry->d_inode;

  	ret = link_path_walk(link, nd);
  	return ret;

  fail:

  	path_put(&nd->path);

  	return PTR_ERR(link);
  }

  static void path_put_conditional(struct path *path, struct nameidata *nd)

  {
  	dput(path->dentry);

  	if (path->mnt != nd->path.mnt)

  		mntput(path->mnt);
  }

  static inline void path_to_nameidata(const struct path *path,
  					struct nameidata *nd)

  {

  	if (!(nd->flags & LOOKUP_RCU)) {
  		dput(nd->path.dentry);
  		if (nd->path.mnt != path->mnt)
  			mntput(nd->path.mnt);

  	}

  	nd->path.mnt = path->mnt;

  	nd->path.dentry = path->dentry;

  }

  static inline void put_link(struct nameidata *nd, struct path *link, void *cookie)
  {
  	struct inode *inode = link->dentry->d_inode;
  	if (!IS_ERR(cookie) && inode->i_op->put_link)
  		inode->i_op->put_link(link->dentry, nd, cookie);
  	path_put(link);
  }

  static __always_inline int

  follow_link(struct path *link, struct nameidata *nd, void **p)

  {
  	int error;

  	struct dentry *dentry = link->dentry;

  	BUG_ON(nd->flags & LOOKUP_RCU);

  	if (link->mnt == nd->path.mnt)
  		mntget(link->mnt);

  	if (unlikely(current->total_link_count >= 40)) {
  		*p = ERR_PTR(-ELOOP); /* no ->put_link(), please */

  		path_put(&nd->path);
  		return -ELOOP;
  	}
  	cond_resched();
  	current->total_link_count++;

  	touch_atime(link->mnt, dentry);

  	nd_set_link(nd, NULL);

  	error = security_inode_follow_link(link->dentry, nd);
  	if (error) {
  		*p = ERR_PTR(error); /* no ->put_link(), please */
  		path_put(&nd->path);
  		return error;
  	}

  	nd->last_type = LAST_BIND;

  	*p = dentry->d_inode->i_op->follow_link(dentry, nd);
  	error = PTR_ERR(*p);
  	if (!IS_ERR(*p)) {

  		char *s = nd_get_link(nd);

  		error = 0;

  		if (s)
  			error = __vfs_follow_link(nd, s);

  		else if (nd->last_type == LAST_BIND) {

  			nd->flags |= LOOKUP_JUMPED;

  			nd->inode = nd->path.dentry->d_inode;
  			if (nd->inode->i_op->follow_link) {

  				/* stepped on a _really_ weird one */
  				path_put(&nd->path);
  				error = -ELOOP;
  			}
  		}

  	}

  	return error;
  }

  static int follow_up_rcu(struct path *path)
  {
  	struct vfsmount *parent;
  	struct dentry *mountpoint;
  
  	parent = path->mnt->mnt_parent;
  	if (parent == path->mnt)
  		return 0;
  	mountpoint = path->mnt->mnt_mountpoint;
  	path->dentry = mountpoint;
  	path->mnt = parent;
  	return 1;
  }

  int follow_up(struct path *path)

  {
  	struct vfsmount *parent;
  	struct dentry *mountpoint;

  
  	br_read_lock(vfsmount_lock);

  	parent = path->mnt->mnt_parent;
  	if (parent == path->mnt) {

  		br_read_unlock(vfsmount_lock);

  		return 0;
  	}
  	mntget(parent);

  	mountpoint = dget(path->mnt->mnt_mountpoint);

  	br_read_unlock(vfsmount_lock);

  	dput(path->dentry);
  	path->dentry = mountpoint;
  	mntput(path->mnt);
  	path->mnt = parent;

  	return 1;
  }

  /*

   * Perform an automount
   * - return -EISDIR to tell follow_managed() to stop and return the path we
   *   were called with.

   */

  static int follow_automount(struct path *path, unsigned flags,
  			    bool *need_mntput)

  {

  	struct vfsmount *mnt;

  	int err;

  
  	if (!path->dentry->d_op || !path->dentry->d_op->d_automount)
  		return -EREMOTE;

  	/* We don't want to mount if someone supplied AT_NO_AUTOMOUNT
  	 * and this is the terminal part of the path.
  	 */
  	if ((flags & LOOKUP_NO_AUTOMOUNT) && !(flags & LOOKUP_CONTINUE))
  		return -EISDIR; /* we actually want to stop here */

  	/* We want to mount if someone is trying to open/create a file of any
  	 * type under the mountpoint, wants to traverse through the mountpoint
  	 * or wants to open the mounted directory.
  	 *
  	 * We don't want to mount if someone's just doing a stat and they've
  	 * set AT_SYMLINK_NOFOLLOW - unless they're stat'ing a directory and
  	 * appended a '/' to the name.
  	 */
  	if (!(flags & LOOKUP_FOLLOW) &&
  	    !(flags & (LOOKUP_CONTINUE | LOOKUP_DIRECTORY |
  		       LOOKUP_OPEN | LOOKUP_CREATE)))
  		return -EISDIR;
  
  	current->total_link_count++;
  	if (current->total_link_count >= 40)
  		return -ELOOP;
  
  	mnt = path->dentry->d_op->d_automount(path);
  	if (IS_ERR(mnt)) {
  		/*
  		 * The filesystem is allowed to return -EISDIR here to indicate
  		 * it doesn't want to automount.  For instance, autofs would do
  		 * this so that its userspace daemon can mount on this dentry.
  		 *
  		 * However, we can only permit this if it's a terminal point in
  		 * the path being looked up; if it wasn't then the remainder of
  		 * the path is inaccessible and we should say so.
  		 */
  		if (PTR_ERR(mnt) == -EISDIR && (flags & LOOKUP_CONTINUE))
  			return -EREMOTE;
  		return PTR_ERR(mnt);

  	}

  	if (!mnt) /* mount collision */
  		return 0;

  	if (!*need_mntput) {
  		/* lock_mount() may release path->mnt on error */
  		mntget(path->mnt);
  		*need_mntput = true;
  	}

  	err = finish_automount(mnt, path);

  	switch (err) {
  	case -EBUSY:
  		/* Someone else made a mount here whilst we were busy */

  		return 0;

  	case 0:

  		path_put(path);

  		path->mnt = mnt;
  		path->dentry = dget(mnt->mnt_root);

  		return 0;

  	default:
  		return err;

  	}

  }

  /*
   * Handle a dentry that is managed in some way.

   * - Flagged for transit management (autofs)

   * - Flagged as mountpoint
   * - Flagged as automount point
   *
   * This may only be called in refwalk mode.
   *
   * Serialization is taken care of in namespace.c
   */
  static int follow_managed(struct path *path, unsigned flags)

  {

  	struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */

  	unsigned managed;
  	bool need_mntput = false;

  	int ret = 0;

  
  	/* Given that we're not holding a lock here, we retain the value in a
  	 * local variable for each dentry as we look at it so that we don't see
  	 * the components of that value change under us */
  	while (managed = ACCESS_ONCE(path->dentry->d_flags),
  	       managed &= DCACHE_MANAGED_DENTRY,
  	       unlikely(managed != 0)) {

  		/* Allow the filesystem to manage the transit without i_mutex
  		 * being held. */
  		if (managed & DCACHE_MANAGE_TRANSIT) {
  			BUG_ON(!path->dentry->d_op);
  			BUG_ON(!path->dentry->d_op->d_manage);

  			ret = path->dentry->d_op->d_manage(path->dentry, false);

  			if (ret < 0)

  				break;

  		}

  		/* Transit to a mounted filesystem. */
  		if (managed & DCACHE_MOUNTED) {
  			struct vfsmount *mounted = lookup_mnt(path);
  			if (mounted) {
  				dput(path->dentry);
  				if (need_mntput)
  					mntput(path->mnt);
  				path->mnt = mounted;
  				path->dentry = dget(mounted->mnt_root);
  				need_mntput = true;
  				continue;
  			}
  
  			/* Something is mounted on this dentry in another
  			 * namespace and/or whatever was mounted there in this
  			 * namespace got unmounted before we managed to get the
  			 * vfsmount_lock */
  		}
  
  		/* Handle an automount point */
  		if (managed & DCACHE_NEED_AUTOMOUNT) {
  			ret = follow_automount(path, flags, &need_mntput);
  			if (ret < 0)

  				break;

  			continue;
  		}
  
  		/* We didn't change the current path point */
  		break;

  	}

  
  	if (need_mntput && path->mnt == mnt)
  		mntput(path->mnt);
  	if (ret == -EISDIR)
  		ret = 0;
  	return ret;

  }

  int follow_down_one(struct path *path)

  {
  	struct vfsmount *mounted;

  	mounted = lookup_mnt(path);

  	if (mounted) {

  		dput(path->dentry);
  		mntput(path->mnt);
  		path->mnt = mounted;
  		path->dentry = dget(mounted->mnt_root);

  		return 1;
  	}
  	return 0;
  }

  static inline bool managed_dentry_might_block(struct dentry *dentry)
  {
  	return (dentry->d_flags & DCACHE_MANAGE_TRANSIT &&
  		dentry->d_op->d_manage(dentry, true) < 0);
  }

  /*

   * Try to skip to top of mountpoint pile in rcuwalk mode.  Fail if
   * we meet a managed dentry that would need blocking.

   */
  static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,

  			       struct inode **inode)

  {

  	for (;;) {

  		struct vfsmount *mounted;

  		/*
  		 * Don't forget we might have a non-mountpoint managed dentry
  		 * that wants to block transit.
  		 */
  		*inode = path->dentry->d_inode;

  		if (unlikely(managed_dentry_might_block(path->dentry)))

  			return false;

  
  		if (!d_mountpoint(path->dentry))
  			break;

  		mounted = __lookup_mnt(path->mnt, path->dentry, 1);
  		if (!mounted)
  			break;
  		path->mnt = mounted;
  		path->dentry = mounted->mnt_root;
  		nd->seq = read_seqcount_begin(&path->dentry->d_seq);

  	}

  	return true;
  }

  static void follow_mount_rcu(struct nameidata *nd)

  {

  	while (d_mountpoint(nd->path.dentry)) {

  		struct vfsmount *mounted;

  		mounted = __lookup_mnt(nd->path.mnt, nd->path.dentry, 1);

  		if (!mounted)
  			break;

  		nd->path.mnt = mounted;
  		nd->path.dentry = mounted->mnt_root;
  		nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);

  	}
  }

  static int follow_dotdot_rcu(struct nameidata *nd)
  {

  	set_root_rcu(nd);

  	while (1) {

  		if (nd->path.dentry == nd->root.dentry &&
  		    nd->path.mnt == nd->root.mnt) {
  			break;
  		}
  		if (nd->path.dentry != nd->path.mnt->mnt_root) {
  			struct dentry *old = nd->path.dentry;
  			struct dentry *parent = old->d_parent;
  			unsigned seq;
  
  			seq = read_seqcount_begin(&parent->d_seq);
  			if (read_seqcount_retry(&old->d_seq, nd->seq))

  				goto failed;

  			nd->path.dentry = parent;
  			nd->seq = seq;
  			break;
  		}
  		if (!follow_up_rcu(&nd->path))
  			break;
  		nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);

  	}

  	follow_mount_rcu(nd);
  	nd->inode = nd->path.dentry->d_inode;

  	return 0;

  
  failed:
  	nd->flags &= ~LOOKUP_RCU;

  	if (!(nd->flags & LOOKUP_ROOT))
  		nd->root.mnt = NULL;

  	rcu_read_unlock();
  	br_read_unlock(vfsmount_lock);
  	return -ECHILD;

  }

  /*

   * Follow down to the covering mount currently visible to userspace.  At each
   * point, the filesystem owning that dentry may be queried as to whether the
   * caller is permitted to proceed or not.

   */

  int follow_down(struct path *path)

  {
  	unsigned managed;
  	int ret;
  
  	while (managed = ACCESS_ONCE(path->dentry->d_flags),
  	       unlikely(managed & DCACHE_MANAGED_DENTRY)) {
  		/* Allow the filesystem to manage the transit without i_mutex
  		 * being held.
  		 *
  		 * We indicate to the filesystem if someone is trying to mount
  		 * something here.  This gives autofs the chance to deny anyone
  		 * other than its daemon the right to mount on its
  		 * superstructure.
  		 *
  		 * The filesystem may sleep at this point.
  		 */
  		if (managed & DCACHE_MANAGE_TRANSIT) {
  			BUG_ON(!path->dentry->d_op);
  			BUG_ON(!path->dentry->d_op->d_manage);

  			ret = path->dentry->d_op->d_manage(

  				path->dentry, false);

  			if (ret < 0)
  				return ret == -EISDIR ? 0 : ret;
  		}
  
  		/* Transit to a mounted filesystem. */
  		if (managed & DCACHE_MOUNTED) {
  			struct vfsmount *mounted = lookup_mnt(path);
  			if (!mounted)
  				break;
  			dput(path->dentry);
  			mntput(path->mnt);
  			path->mnt = mounted;
  			path->dentry = dget(mounted->mnt_root);
  			continue;
  		}
  
  		/* Don't handle automount points here */
  		break;
  	}
  	return 0;
  }
  
  /*

   * Skip to top of mountpoint pile in refwalk mode for follow_dotdot()
   */
  static void follow_mount(struct path *path)
  {
  	while (d_mountpoint(path->dentry)) {
  		struct vfsmount *mounted = lookup_mnt(path);
  		if (!mounted)
  			break;
  		dput(path->dentry);
  		mntput(path->mnt);
  		path->mnt = mounted;
  		path->dentry = dget(mounted->mnt_root);
  	}
  }

  static void follow_dotdot(struct nameidata *nd)

  {

  	set_root(nd);

  	while(1) {

  		struct dentry *old = nd->path.dentry;

  		if (nd->path.dentry == nd->root.dentry &&
  		    nd->path.mnt == nd->root.mnt) {

  			break;
  		}

  		if (nd->path.dentry != nd->path.mnt->mnt_root) {

  			/* rare case of legitimate dget_parent()... */
  			nd->path.dentry = dget_parent(nd->path.dentry);

  			dput(old);
  			break;
  		}

  		if (!follow_up(&nd->path))

  			break;

  	}

  	follow_mount(&nd->path);

  	nd->inode = nd->path.dentry->d_inode;

  }

  /*

   * Allocate a dentry with name and parent, and perform a parent
   * directory ->lookup on it. Returns the new dentry, or ERR_PTR
   * on error. parent->d_inode->i_mutex must be held. d_lookup must
   * have verified that no child exists while under i_mutex.
   */
  static struct dentry *d_alloc_and_lookup(struct dentry *parent,
  				struct qstr *name, struct nameidata *nd)
  {
  	struct inode *inode = parent->d_inode;
  	struct dentry *dentry;
  	struct dentry *old;
  
  	/* Don't create child dentry for a dead directory. */
  	if (unlikely(IS_DEADDIR(inode)))
  		return ERR_PTR(-ENOENT);
  
  	dentry = d_alloc(parent, name);
  	if (unlikely(!dentry))
  		return ERR_PTR(-ENOMEM);
  
  	old = inode->i_op->lookup(inode, dentry, nd);
  	if (unlikely(old)) {
  		dput(dentry);
  		dentry = old;
  	}
  	return dentry;
  }
  
  /*

   *  It's more convoluted than I'd like it to be, but... it's still fairly
   *  small and for now I'd prefer to have fast path as straight as possible.
   *  It _is_ time-critical.
   */
  static int do_lookup(struct nameidata *nd, struct qstr *name,

  			struct path *path, struct inode **inode)

  {

  	struct vfsmount *mnt = nd->path.mnt;

  	struct dentry *dentry, *parent = nd->path.dentry;

  	int need_reval = 1;
  	int status = 1;

  	int err;

  	/*

  	 * Rename seqlock is not required here because in the off chance
  	 * of a false negative due to a concurrent rename, we're going to
  	 * do the non-racy lookup, below.
  	 */

  	if (nd->flags & LOOKUP_RCU) {
  		unsigned seq;

  		*inode = nd->inode;
  		dentry = __d_lookup_rcu(parent, name, &seq, inode);

  		if (!dentry)
  			goto unlazy;

  		/* Memory barrier in read_seqcount_begin of child is enough */
  		if (__read_seqcount_retry(&parent->d_seq, nd->seq))
  			return -ECHILD;

  		nd->seq = seq;

  		if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) {

  			status = d_revalidate(dentry, nd);
  			if (unlikely(status <= 0)) {
  				if (status != -ECHILD)
  					need_reval = 0;
  				goto unlazy;
  			}

  		}

  		path->mnt = mnt;
  		path->dentry = dentry;

  		if (unlikely(!__follow_mount_rcu(nd, path, inode)))
  			goto unlazy;
  		if (unlikely(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT))
  			goto unlazy;
  		return 0;

  unlazy:

  		if (unlazy_walk(nd, dentry))
  			return -ECHILD;

  	} else {
  		dentry = __d_lookup(parent, name);

  	}

  
  retry:
  	if (unlikely(!dentry)) {
  		struct inode *dir = parent->d_inode;
  		BUG_ON(nd->inode != dir);
  
  		mutex_lock(&dir->i_mutex);
  		dentry = d_lookup(parent, name);
  		if (likely(!dentry)) {
  			dentry = d_alloc_and_lookup(parent, name, nd);
  			if (IS_ERR(dentry)) {
  				mutex_unlock(&dir->i_mutex);
  				return PTR_ERR(dentry);
  			}
  			/* known good */
  			need_reval = 0;
  			status = 1;
  		}
  		mutex_unlock(&dir->i_mutex);
  	}
  	if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE) && need_reval)
  		status = d_revalidate(dentry, nd);
  	if (unlikely(status <= 0)) {
  		if (status < 0) {
  			dput(dentry);
  			return status;
  		}
  		if (!d_invalidate(dentry)) {
  			dput(dentry);
  			dentry = NULL;
  			need_reval = 1;
  			goto retry;
  		}

  	}

  	path->mnt = mnt;
  	path->dentry = dentry;
  	err = follow_managed(path, nd->flags);

  	if (unlikely(err < 0)) {
  		path_put_conditional(path, nd);

  		return err;

  	}

  	*inode = path->dentry->d_inode;

  	return 0;

  }

  static inline int may_lookup(struct nameidata *nd)
  {
  	if (nd->flags & LOOKUP_RCU) {
  		int err = exec_permission(nd->inode, IPERM_FLAG_RCU);
  		if (err != -ECHILD)
  			return err;

  		if (unlazy_walk(nd, NULL))

  			return -ECHILD;
  	}
  	return exec_permission(nd->inode, 0);
  }

  static inline int handle_dots(struct nameidata *nd, int type)
  {
  	if (type == LAST_DOTDOT) {
  		if (nd->flags & LOOKUP_RCU) {
  			if (follow_dotdot_rcu(nd))
  				return -ECHILD;
  		} else
  			follow_dotdot(nd);
  	}
  	return 0;
  }

  static void terminate_walk(struct nameidata *nd)
  {
  	if (!(nd->flags & LOOKUP_RCU)) {
  		path_put(&nd->path);
  	} else {
  		nd->flags &= ~LOOKUP_RCU;

  		if (!(nd->flags & LOOKUP_ROOT))
  			nd->root.mnt = NULL;

  		rcu_read_unlock();
  		br_read_unlock(vfsmount_lock);
  	}
  }

  static inline int walk_component(struct nameidata *nd, struct path *path,
  		struct qstr *name, int type, int follow)
  {
  	struct inode *inode;
  	int err;
  	/*
  	 * "." and ".." are special - ".." especially so because it has
  	 * to be able to know about the current root directory and
  	 * parent relationships.
  	 */
  	if (unlikely(type != LAST_NORM))
  		return handle_dots(nd, type);
  	err = do_lookup(nd, name, path, &inode);
  	if (unlikely(err)) {
  		terminate_walk(nd);
  		return err;
  	}
  	if (!inode) {
  		path_to_nameidata(path, nd);
  		terminate_walk(nd);
  		return -ENOENT;
  	}
  	if (unlikely(inode->i_op->follow_link) && follow) {

  		if (nd->flags & LOOKUP_RCU) {
  			if (unlikely(unlazy_walk(nd, path->dentry))) {
  				terminate_walk(nd);
  				return -ECHILD;
  			}
  		}

  		BUG_ON(inode != path->dentry->d_inode);
  		return 1;
  	}
  	path_to_nameidata(path, nd);
  	nd->inode = inode;
  	return 0;
  }

  /*

   * This limits recursive symlink follows to 8, while
   * limiting consecutive symlinks to 40.
   *
   * Without that kind of total limit, nasty chains of consecutive
   * symlinks can cause almost arbitrarily long lookups.
   */
  static inline int nested_symlink(struct path *path, struct nameidata *nd)
  {
  	int res;

  	if (unlikely(current->link_count >= MAX_NESTED_LINKS)) {
  		path_put_conditional(path, nd);
  		path_put(&nd->path);
  		return -ELOOP;
  	}

  	BUG_ON(nd->depth >= MAX_NESTED_LINKS);

  
  	nd->depth++;
  	current->link_count++;
  
  	do {
  		struct path link = *path;
  		void *cookie;

  
  		res = follow_link(&link, nd, &cookie);

  		if (!res)
  			res = walk_component(nd, path, &nd->last,
  					     nd->last_type, LOOKUP_FOLLOW);

  		put_link(nd, &link, cookie);

  	} while (res > 0);
  
  	current->link_count--;
  	nd->depth--;
  	return res;
  }
  
  /*

   * Name resolution.

   * This is the basic name resolution function, turning a pathname into
   * the final dentry. We expect 'base' to be positive and a directory.

   *

   * Returns 0 and nd will have valid dentry and mnt on success.
   * Returns error and drops reference to input namei data on failure.

   */

  static int link_path_walk(const char *name, struct nameidata *nd)

  {
  	struct path next;

  	int err;
  	unsigned int lookup_flags = nd->flags;
  	
  	while (*name=='/')
  		name++;
  	if (!*name)

  		return 0;

  	/* At this point we know we have a real path component. */
  	for(;;) {
  		unsigned long hash;
  		struct qstr this;
  		unsigned int c;

  		int type;

  		nd->flags |= LOOKUP_CONTINUE;

  
  		err = may_lookup(nd);

   		if (err)
  			break;
  
  		this.name = name;
  		c = *(const unsigned char *)name;
  
  		hash = init_name_hash();
  		do {
  			name++;
  			hash = partial_name_hash(c, hash);
  			c = *(const unsigned char *)name;
  		} while (c && (c != '/'));
  		this.len = name - (const char *) this.name;
  		this.hash = end_name_hash(hash);

  		type = LAST_NORM;
  		if (this.name[0] == '.') switch (this.len) {
  			case 2:

  				if (this.name[1] == '.') {

  					type = LAST_DOTDOT;

  					nd->flags |= LOOKUP_JUMPED;
  				}

  				break;
  			case 1:
  				type = LAST_DOT;
  		}

  		if (likely(type == LAST_NORM)) {
  			struct dentry *parent = nd->path.dentry;

  			nd->flags &= ~LOOKUP_JUMPED;

  			if (unlikely(parent->d_flags & DCACHE_OP_HASH)) {
  				err = parent->d_op->d_hash(parent, nd->inode,
  							   &this);
  				if (err < 0)
  					break;
  			}
  		}

  		/* remove trailing slashes? */
  		if (!c)
  			goto last_component;
  		while (*++name == '/');
  		if (!*name)

  			goto last_component;

  		err = walk_component(nd, &next, &this, type, LOOKUP_FOLLOW);
  		if (err < 0)
  			return err;

  		if (err) {

  			err = nested_symlink(&next, nd);

  			if (err)

  				return err;

  		}

  		err = -ENOTDIR; 

  		if (!nd->inode->i_op->lookup)

  			break;
  		continue;
  		/* here ends the main loop */

  last_component:

  		/* Clear LOOKUP_CONTINUE iff it was previously unset */
  		nd->flags &= lookup_flags | ~LOOKUP_CONTINUE;

  		nd->last = this;
  		nd->last_type = type;

  		return 0;

  	}

  	terminate_walk(nd);

  	return err;
  }

  static int path_init(int dfd, const char *name, unsigned int flags,
  		     struct nameidata *nd, struct file **fp)

  {
  	int retval = 0;
  	int fput_needed;
  	struct file *file;
  
  	nd->last_type = LAST_ROOT; /* if there are only slashes... */

  	nd->flags = flags | LOOKUP_JUMPED;

  	nd->depth = 0;

  	if (flags & LOOKUP_ROOT) {
  		struct inode *inode = nd->root.dentry->d_inode;

  		if (*name) {
  			if (!inode->i_op->lookup)
  				return -ENOTDIR;
  			retval = inode_permission(inode, MAY_EXEC);
  			if (retval)
  				return retval;
  		}

  		nd->path = nd->root;
  		nd->inode = inode;
  		if (flags & LOOKUP_RCU) {
  			br_read_lock(vfsmount_lock);
  			rcu_read_lock();
  			nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
  		} else {
  			path_get(&nd->path);
  		}
  		return 0;
  	}

  	nd->root.mnt = NULL;

  
  	if (*name=='/') {

  		if (flags & LOOKUP_RCU) {
  			br_read_lock(vfsmount_lock);
  			rcu_read_lock();
  			set_root_rcu(nd);
  		} else {
  			set_root(nd);
  			path_get(&nd->root);
  		}
  		nd->path = nd->root;

  	} else if (dfd == AT_FDCWD) {

  		if (flags & LOOKUP_RCU) {
  			struct fs_struct *fs = current->fs;
  			unsigned seq;

  			br_read_lock(vfsmount_lock);
  			rcu_read_lock();

  			do {
  				seq = read_seqcount_begin(&fs->seq);
  				nd->path = fs->pwd;
  				nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
  			} while (read_seqcount_retry(&fs->seq, seq));
  		} else {
  			get_fs_pwd(current->fs, &nd->path);
  		}

  	} else {
  		struct dentry *dentry;

  		file = fget_raw_light(dfd, &fput_needed);

  		retval = -EBADF;
  		if (!file)
  			goto out_fail;
  
  		dentry = file->f_path.dentry;

  		if (*name) {
  			retval = -ENOTDIR;
  			if (!S_ISDIR(dentry->d_inode->i_mode))
  				goto fput_fail;

  			retval = file_permission(file, MAY_EXEC);
  			if (retval)
  				goto fput_fail;
  		}

  
  		nd->path = file->f_path;

  		if (flags & LOOKUP_RCU) {
  			if (fput_needed)

  				*fp = file;

  			nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
  			br_read_lock(vfsmount_lock);
  			rcu_read_lock();
  		} else {
  			path_get(&file->f_path);
  			fput_light(file, fput_needed);
  		}

  	}

  	nd->inode = nd->path.dentry->d_inode;

  	return 0;

  fput_fail:
  	fput_light(file, fput_needed);
  out_fail:
  	return retval;
  }

  static inline int lookup_last(struct nameidata *nd, struct path *path)
  {
  	if (nd->last_type == LAST_NORM && nd->last.name[nd->last.len])
  		nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
  
  	nd->flags &= ~LOOKUP_PARENT;
  	return walk_component(nd, path, &nd->last, nd->last_type,
  					nd->flags & LOOKUP_FOLLOW);
  }

  /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */

  static int path_lookupat(int dfd, const char *name,

  				unsigned int flags, struct nameidata *nd)
  {

  	struct file *base = NULL;

  	struct path path;
  	int err;

  
  	/*
  	 * Path walking is largely split up into 2 different synchronisation
  	 * schemes, rcu-walk and ref-walk (explained in
  	 * Documentation/filesystems/path-lookup.txt). These share much of the
  	 * path walk code, but some things particularly setup, cleanup, and
  	 * following mounts are sufficiently divergent that functions are
  	 * duplicated. Typically there is a function foo(), and its RCU
  	 * analogue, foo_rcu().
  	 *
  	 * -ECHILD is the error number of choice (just to avoid clashes) that
  	 * is returned if some aspect of an rcu-walk fails. Such an error must
  	 * be handled by restarting a traditional ref-walk (which will always
  	 * be able to complete).
  	 */

  	err = path_init(dfd, name, flags | LOOKUP_PARENT, nd, &base);

  	if (unlikely(err))
  		return err;

  
  	current->total_link_count = 0;

  	err = link_path_walk(name, nd);
  
  	if (!err && !(flags & LOOKUP_PARENT)) {

  		err = lookup_last(nd, &path);
  		while (err > 0) {
  			void *cookie;
  			struct path link = path;

  			nd->flags |= LOOKUP_PARENT;

  			err = follow_link(&link, nd, &cookie);

  			if (!err)
  				err = lookup_last(nd, &path);

  			put_link(nd, &link, cookie);

  		}
  	}

  	if (!err)
  		err = complete_walk(nd);

  
  	if (!err && nd->flags & LOOKUP_DIRECTORY) {
  		if (!nd->inode->i_op->lookup) {
  			path_put(&nd->path);

  			err = -ENOTDIR;

  		}
  	}

  	if (base)
  		fput(base);

  	if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {

  		path_put(&nd->root);
  		nd->root.mnt = NULL;
  	}

  	return err;

  }

  static int do_path_lookup(int dfd, const char *name,
  				unsigned int flags, struct nameidata *nd)
  {
  	int retval = path_lookupat(dfd, name, flags | LOOKUP_RCU, nd);
  	if (unlikely(retval == -ECHILD))
  		retval = path_lookupat(dfd, name, flags, nd);
  	if (unlikely(retval == -ESTALE))
  		retval = path_lookupat(dfd, name, flags | LOOKUP_REVAL, nd);

  
  	if (likely(!retval)) {
  		if (unlikely(!audit_dummy_context())) {
  			if (nd->path.dentry && nd->inode)
  				audit_inode(name, nd->path.dentry);
  		}
  	}

  	return retval;

  }

  int kern_path_parent(const char *name, struct nameidata *nd)

  {

  	return do_path_lookup(AT_FDCWD, name, LOOKUP_PARENT, nd);

  }

  int kern_path(const char *name, unsigned int flags, struct path *path)
  {
  	struct nameidata nd;
  	int res = do_path_lookup(AT_FDCWD, name, flags, &nd);
  	if (!res)
  		*path = nd.path;
  	return res;
  }

  /**
   * vfs_path_lookup - lookup a file path relative to a dentry-vfsmount pair
   * @dentry:  pointer to dentry of the base directory
   * @mnt: pointer to vfs mount of the base directory
   * @name: pointer to file name
   * @flags: lookup flags
   * @nd: pointer to nameidata
   */
  int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
  		    const char *name, unsigned int flags,
  		    struct nameidata *nd)
  {

  	nd->root.dentry = dentry;
  	nd->root.mnt = mnt;
  	/* the first argument of do_path_lookup() is ignored with LOOKUP_ROOT */
  	return do_path_lookup(AT_FDCWD, name, flags | LOOKUP_ROOT, nd);

  }

  static struct dentry *__lookup_hash(struct qstr *name,
  		struct dentry *base, struct nameidata *nd)

  {

  	struct inode *inode = base->d_inode;

  	struct dentry *dentry;

  	int err;

  	err = exec_permission(inode, 0);

  	if (err)
  		return ERR_PTR(err);

  
  	/*

  	 * Don't bother with __d_lookup: callers are for creat as
  	 * well as unlink, so a lot of the time it would cost
  	 * a double lookup.

  	 */

  	dentry = d_lookup(base, name);

  	if (dentry && (dentry->d_flags & DCACHE_OP_REVALIDATE))

  		dentry = do_revalidate(dentry, nd);

  	if (!dentry)
  		dentry = d_alloc_and_lookup(base, name, nd);

  	return dentry;
  }

  /*
   * Restricted form of lookup. Doesn't follow links, single-component only,
   * needs parent already locked. Doesn't follow mounts.
   * SMP-safe.
   */

  static struct dentry *lookup_hash(struct nameidata *nd)

  {

  	return __lookup_hash(&nd->last, nd->path.dentry, nd);

  }

  /**

   * lookup_one_len - filesystem helper to lookup single pathname component

   * @name:	pathname component to lookup
   * @base:	base directory to lookup from
   * @len:	maximum length @len should be interpreted to
   *

   * Note that this routine is purely a helper for filesystem usage and should
   * not be called by generic code.  Also note that by using this function the

   * nameidata argument is passed to the filesystem methods and a filesystem
   * using this helper needs to be prepared for that.
   */

  struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
  {

  	struct qstr this;

  	unsigned long hash;
  	unsigned int c;

  	WARN_ON_ONCE(!mutex_is_locked(&base->d_inode->i_mutex));

  	this.name = name;
  	this.len = len;
  	if (!len)
  		return ERR_PTR(-EACCES);
  
  	hash = init_name_hash();
  	while (len--) {
  		c = *(const unsigned char *)name++;
  		if (c == '/' || c == '\0')
  			return ERR_PTR(-EACCES);
  		hash = partial_name_hash(c, hash);
  	}
  	this.hash = end_name_hash(hash);

  	/*
  	 * See if the low-level filesystem might want
  	 * to use its own hash..
  	 */
  	if (base->d_flags & DCACHE_OP_HASH) {
  		int err = base->d_op->d_hash(base, base->d_inode, &this);
  		if (err < 0)
  			return ERR_PTR(err);
  	}

  	return __lookup_hash(&this, base, NULL);

  }

  int user_path_at(int dfd, const char __user *name, unsigned flags,
  		 struct path *path)

  {

  	struct nameidata nd;

  	char *tmp = getname_flags(name, flags);

  	int err = PTR_ERR(tmp);

  	if (!IS_ERR(tmp)) {

  
  		BUG_ON(flags & LOOKUP_PARENT);
  
  		err = do_path_lookup(dfd, tmp, flags, &nd);

  		putname(tmp);

  		if (!err)
  			*path = nd.path;

  	}
  	return err;
  }

  static int user_path_parent(int dfd, const char __user *path,
  			struct nameidata *nd, char **name)
  {
  	char *s = getname(path);
  	int error;
  
  	if (IS_ERR(s))
  		return PTR_ERR(s);
  
  	error = do_path_lookup(dfd, s, LOOKUP_PARENT, nd);
  	if (error)
  		putname(s);
  	else
  		*name = s;
  
  	return error;
  }

  /*
   * It's inline, so penalty for filesystems that don't use sticky bit is
   * minimal.
   */
  static inline int check_sticky(struct inode *dir, struct inode *inode)
  {

  	uid_t fsuid = current_fsuid();

  	if (!(dir->i_mode & S_ISVTX))
  		return 0;

  	if (current_user_ns() != inode_userns(inode))
  		goto other_userns;

  	if (inode->i_uid == fsuid)

  		return 0;

  	if (dir->i_uid == fsuid)

  		return 0;

  
  other_userns:
  	return !ns_capable(inode_userns(inode), CAP_FOWNER);

  }
  
  /*
   *	Check whether we can remove a link victim from directory dir, check
   *  whether the type of victim is right.
   *  1. We can't do it if dir is read-only (done in permission())
   *  2. We should have write and exec permissions on dir
   *  3. We can't remove anything from append-only dir
   *  4. We can't do anything with immutable dir (done in permission())
   *  5. If the sticky bit on dir is set we should either
   *	a. be owner of dir, or
   *	b. be owner of victim, or
   *	c. have CAP_FOWNER capability
   *  6. If the victim is append-only or immutable we can't do antyhing with
   *     links pointing to it.
   *  7. If we were asked to remove a directory and victim isn't one - ENOTDIR.
   *  8. If we were asked to remove a non-directory and victim isn't one - EISDIR.
   *  9. We can't remove a root or mountpoint.
   * 10. We don't allow removal of NFS sillyrenamed files; it's handled by
   *     nfs_async_unlink().
   */

  static int may_delete(struct inode *dir,struct dentry *victim,int isdir)

  {
  	int error;
  
  	if (!victim->d_inode)
  		return -ENOENT;
  
  	BUG_ON(victim->d_parent->d_inode != dir);

  	audit_inode_child(victim, dir);

  	error = inode_permission(dir, MAY_WRITE | MAY_EXEC);

  	if (error)
  		return error;
  	if (IS_APPEND(dir))
  		return -EPERM;
  	if (check_sticky(dir, victim->d_inode)||IS_APPEND(victim->d_inode)||

  	    IS_IMMUTABLE(victim->d_inode) || IS_SWAPFILE(victim->d_inode))

  		return -EPERM;
  	if (isdir) {
  		if (!S_ISDIR(victim->d_inode->i_mode))
  			return -ENOTDIR;
  		if (IS_ROOT(victim))
  			return -EBUSY;
  	} else if (S_ISDIR(victim->d_inode->i_mode))
  		return -EISDIR;
  	if (IS_DEADDIR(dir))
  		return -ENOENT;
  	if (victim->d_flags & DCACHE_NFSFS_RENAMED)
  		return -EBUSY;
  	return 0;
  }
  
  /*	Check whether we can create an object with dentry child in directory
   *  dir.
   *  1. We can't do it if child already exists (open has special treatment for
   *     this case, but since we are inlined it's OK)
   *  2. We can't do it if dir is read-only (done in permission())
   *  3. We should have write and exec permissions on dir
   *  4. We can't do it if dir is immutable (done in permission())
   */

  static inline int may_create(struct inode *dir, struct dentry *child)

  {
  	if (child->d_inode)
  		return -EEXIST;
  	if (IS_DEADDIR(dir))
  		return -ENOENT;

  	return inode_permission(dir, MAY_WRITE | MAY_EXEC);

  }

  /*
   * p1 and p2 should be directories on the same fs.
   */
  struct dentry *lock_rename(struct dentry *p1, struct dentry *p2)
  {
  	struct dentry *p;
  
  	if (p1 == p2) {

  		mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);

  		return NULL;
  	}

  	mutex_lock(&p1->d_inode->i_sb->s_vfs_rename_mutex);

  	p = d_ancestor(p2, p1);
  	if (p) {
  		mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_PARENT);
  		mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_CHILD);
  		return p;

  	}

  	p = d_ancestor(p1, p2);
  	if (p) {
  		mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
  		mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_CHILD);
  		return p;

  	}

  	mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
  	mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_CHILD);

  	return NULL;
  }
  
  void unlock_rename(struct dentry *p1, struct dentry *p2)
  {

  	mutex_unlock(&p1->d_inode->i_mutex);

  	if (p1 != p2) {

  		mutex_unlock(&p2->d_inode->i_mutex);

  		mutex_unlock(&p1->d_inode->i_sb->s_vfs_rename_mutex);

  	}
  }
  
  int vfs_create(struct inode *dir, struct dentry *dentry, int mode,
  		struct nameidata *nd)
  {

  	int error = may_create(dir, dentry);

  
  	if (error)
  		return error;

  	if (!dir->i_op->create)

  		return -EACCES;	/* shouldn't it be ENOSYS? */
  	mode &= S_IALLUGO;
  	mode |= S_IFREG;
  	error = security_inode_create(dir, dentry, mode);
  	if (error)
  		return error;

  	error = dir->i_op->create(dir, dentry, mode, nd);

  	if (!error)

  		fsnotify_create(dir, dentry);

  	return error;
  }

  static int may_open(struct path *path, int acc_mode, int flag)

  {

  	struct dentry *dentry = path->dentry;

  	struct inode *inode = dentry->d_inode;
  	int error;

  	/* O_PATH? */
  	if (!acc_mode)
  		return 0;

  	if (!inode)
  		return -ENOENT;

  	switch (inode->i_mode & S_IFMT) {
  	case S_IFLNK:

  		return -ELOOP;

  	case S_IFDIR:
  		if (acc_mode & MAY_WRITE)
  			return -EISDIR;
  		break;
  	case S_IFBLK:
  	case S_IFCHR:

  		if (path->mnt->mnt_flags & MNT_NODEV)

  			return -EACCES;

  		/*FALLTHRU*/
  	case S_IFIFO:
  	case S_IFSOCK:

  		flag &= ~O_TRUNC;

  		break;

  	}

  	error = inode_permission(inode, acc_mode);

  	if (error)
  		return error;

  	/*
  	 * An append-only file must be opened in append mode for writing.
  	 */
  	if (IS_APPEND(inode)) {

  		if  ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND))

  			return -EPERM;

  		if (flag & O_TRUNC)