namei.c

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		}
		/*
		 * See if the low-level filesystem might want
		 * to use its own hash..
		 */
		if (nd->dentry->d_op && nd->dentry->d_op->d_hash) {
			err = nd->dentry->d_op->d_hash(nd->dentry, &this);
			if (err < 0)
				break;
		}
		/* This does the actual lookups.. */
		dentry = cached_lookup(nd->dentry, &this, LOOKUP_CONTINUE);
		if (!dentry) {
			dentry = real_lookup(nd->dentry, &this, LOOKUP_CONTINUE);
			err = PTR_ERR(dentry);
			if (IS_ERR(dentry))
				break;
		}
		/* Check mountpoints.. */
		while (d_mountpoint(dentry) && __follow_down(&nd->mnt, &dentry))
			;

		err = -ENOENT;
		inode = dentry->d_inode;
		if (!inode)
			goto out_dput;
		err = -ENOTDIR; 
		if (!inode->i_op)
			goto out_dput;

		if (inode->i_op->follow_link) {
			err = do_follow_link(dentry, nd);
			dput(dentry);
			if (err)
				goto return_err;
			err = -ENOENT;
			inode = nd->dentry->d_inode;
			if (!inode)
				break;
			err = -ENOTDIR; 
			if (!inode->i_op)
				break;
		} else {
			dput(nd->dentry);
			nd->dentry = dentry;
		}
		err = -ENOTDIR; 
		if (!inode->i_op->lookup)
			break;
		continue;
		/* here ends the main loop */

last_with_slashes:
		lookup_flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
last_component:
		if (lookup_flags & LOOKUP_PARENT)
			goto lookup_parent;
		if (this.name[0] == '.') switch (this.len) {
			default:
				break;
			case 2:	
				if (this.name[1] != '.')
					break;
				follow_dotdot(nd);
				inode = nd->dentry->d_inode;
				/* fallthrough */
			case 1:
				goto return_base;
		}
		if (nd->dentry->d_op && nd->dentry->d_op->d_hash) {
			err = nd->dentry->d_op->d_hash(nd->dentry, &this);
			if (err < 0)
				break;
		}
		dentry = cached_lookup(nd->dentry, &this, 0);
		if (!dentry) {
			dentry = real_lookup(nd->dentry, &this, 0);
			err = PTR_ERR(dentry);
			if (IS_ERR(dentry))
				break;
		}
		while (d_mountpoint(dentry) && __follow_down(&nd->mnt, &dentry))
			;
		inode = dentry->d_inode;
		if ((lookup_flags & LOOKUP_FOLLOW)
		    && inode && inode->i_op && inode->i_op->follow_link) {
			err = do_follow_link(dentry, nd);
			dput(dentry);
			if (err)
				goto return_err;
			inode = nd->dentry->d_inode;
		} else {
			dput(nd->dentry);
			nd->dentry = dentry;
		}
		err = -ENOENT;
		if (!inode)
			goto no_inode;
		if (lookup_flags & LOOKUP_DIRECTORY) {
			err = -ENOTDIR; 
			if (!inode->i_op || !inode->i_op->lookup)
				break;
		}
		goto return_base;
no_inode:
		err = -ENOENT;
		if (lookup_flags & (LOOKUP_POSITIVE|LOOKUP_DIRECTORY))
			break;
		goto return_base;
lookup_parent:
		nd->last = this;
		nd->last_type = LAST_NORM;
		if (this.name[0] != '.')
			goto return_base;
		if (this.len == 1)
			nd->last_type = LAST_DOT;
		else if (this.len == 2 && this.name[1] == '.')
			nd->last_type = LAST_DOTDOT;
return_base:
		return 0;
out_dput:
		dput(dentry);
		break;
	}
	path_release(nd);
return_err:
	return err;
}

int path_walk(const char * name, struct nameidata *nd)
{
	current->total_link_count = 0;
	return link_path_walk(name, nd);
}

/* SMP-safe */
/* returns 1 if everything is done */
static int __emul_lookup_dentry(const char *name, struct nameidata *nd)
{
	if (path_walk(name, nd))
		return 0;		/* something went wrong... */

	if (!nd->dentry->d_inode || S_ISDIR(nd->dentry->d_inode->i_mode)) {
		struct nameidata nd_root;
		/*
		 * NAME was not found in alternate root or it's a directory.  Try to find
		 * it in the normal root:
		 */
		nd_root.last_type = LAST_ROOT;
		nd_root.flags = nd->flags;
		read_lock(&current->fs->lock);
		nd_root.mnt = mntget(current->fs->rootmnt);
		nd_root.dentry = dget(current->fs->root);
		read_unlock(&current->fs->lock);
		if (path_walk(name, &nd_root))
			return 1;
		if (nd_root.dentry->d_inode) {
			path_release(nd);
			nd->dentry = nd_root.dentry;
			nd->mnt = nd_root.mnt;
			nd->last = nd_root.last;
			return 1;
		}
		path_release(&nd_root);
	}
	return 1;
}

void set_fs_altroot(void)
{
	char *emul = __emul_prefix();
	struct nameidata nd;
	struct vfsmount *mnt = NULL, *oldmnt;
	struct dentry *dentry = NULL, *olddentry;
	if (emul) {
		read_lock(&current->fs->lock);
		nd.mnt = mntget(current->fs->rootmnt);
		nd.dentry = dget(current->fs->root);
		read_unlock(&current->fs->lock);
		nd.flags = LOOKUP_FOLLOW|LOOKUP_DIRECTORY|LOOKUP_POSITIVE;
		if (path_walk(emul,&nd) == 0) {
			mnt = nd.mnt;
			dentry = nd.dentry;
		}
	}
	write_lock(&current->fs->lock);
	oldmnt = current->fs->altrootmnt;
	olddentry = current->fs->altroot;
	current->fs->altrootmnt = mnt;
	current->fs->altroot = dentry;
	write_unlock(&current->fs->lock);
	if (olddentry) {
		dput(olddentry);
		mntput(oldmnt);
	}
}

/* SMP-safe */
static inline int
walk_init_root(const char *name, struct nameidata *nd)
{
	read_lock(&current->fs->lock);
	if (current->fs->altroot && !(nd->flags & LOOKUP_NOALT)) {
		nd->mnt = mntget(current->fs->altrootmnt);
		nd->dentry = dget(current->fs->altroot);
		read_unlock(&current->fs->lock);
		if (__emul_lookup_dentry(name,nd))
			return 0;
		read_lock(&current->fs->lock);
	}
	nd->mnt = mntget(current->fs->rootmnt);
	nd->dentry = dget(current->fs->root);
	read_unlock(&current->fs->lock);
	return 1;
}

/* SMP-safe */
int path_init(const char *name, unsigned int flags, struct nameidata *nd)
{
	nd->last_type = LAST_ROOT; /* if there are only slashes... */
	nd->flags = flags;
	if (*name=='/')
		return walk_init_root(name,nd);
	read_lock(&current->fs->lock);
	nd->mnt = mntget(current->fs->pwdmnt);
	nd->dentry = dget(current->fs->pwd);
	read_unlock(&current->fs->lock);
	return 1;
}

/*
 * Restricted form of lookup. Doesn't follow links, single-component only,
 * needs parent already locked. Doesn't follow mounts.
 * SMP-safe.
 */
struct dentry * lookup_hash(struct qstr *name, struct dentry * base)
{
	struct dentry * dentry;
	struct inode *inode;
	int err;

	inode = base->d_inode;
	err = permission(inode, MAY_EXEC);
	dentry = ERR_PTR(err);
	if (err)
		goto out;

	/*
	 * See if the low-level filesystem might want
	 * to use its own hash..
	 */
	if (base->d_op && base->d_op->d_hash) {
		err = base->d_op->d_hash(base, name);
		dentry = ERR_PTR(err);
		if (err < 0)
			goto out;
	}

	dentry = cached_lookup(base, name, 0);
	if (!dentry) {
		struct dentry *new = d_alloc(base, name);
		dentry = ERR_PTR(-ENOMEM);
		if (!new)
			goto out;
		lock_kernel();
		dentry = inode->i_op->lookup(inode, new);
		unlock_kernel();
		if (!dentry)
			dentry = new;
		else
			dput(new);
	}
out:
	return dentry;
}

/* SMP-safe */
struct dentry * lookup_one_len(const char * name, struct dentry * base, int len)
{
	unsigned long hash;
	struct qstr this;
	unsigned int c;

	this.name = name;
	this.len = len;
	if (!len)
		goto access;

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

	return lookup_hash(&this, base);
access:
	return ERR_PTR(-EACCES);
}

/*
 *	namei()
 *
 * is used by most simple commands to get the inode of a specified name.
 * Open, link etc use their own routines, but this is enough for things
 * like 'chmod' etc.
 *
 * namei exists in two versions: namei/lnamei. The only difference is
 * that namei follows links, while lnamei does not.
 * SMP-safe
 */
int __user_walk(const char *name, unsigned flags, struct nameidata *nd)
{
	char *tmp;
	int err;

	tmp = getname(name);
	err = PTR_ERR(tmp);
	if (!IS_ERR(tmp)) {
		err = 0;
		if (path_init(tmp, flags, nd))
			err = path_walk(tmp, nd);
		putname(tmp);
	}
	return err;
}

/*
 * 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)
{
	if (!(dir->i_mode & S_ISVTX))
		return 0;
	if (inode->i_uid == current->fsuid)
		return 0;
	if (dir->i_uid == current->fsuid)
		return 0;
	return !capable(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.
 */
static inline int may_delete(struct inode *dir,struct dentry *victim, int isdir)
{
	int error;
	if (!victim->d_inode || victim->d_parent->d_inode != dir)
		return -ENOENT;
	error = 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))
		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;
	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 permission(dir,MAY_WRITE | MAY_EXEC);
}

/* 
 * Special case: O_CREAT|O_EXCL implies O_NOFOLLOW for security
 * reasons.
 *
 * O_DIRECTORY translates into forcing a directory lookup.
 */
static inline int lookup_flags(unsigned int f)
{
	unsigned long retval = LOOKUP_FOLLOW;

	if (f & O_NOFOLLOW)
		retval &= ~LOOKUP_FOLLOW;
	
	if ((f & (O_CREAT|O_EXCL)) == (O_CREAT|O_EXCL))
		retval &= ~LOOKUP_FOLLOW;
	
	if (f & O_DIRECTORY)
		retval |= LOOKUP_DIRECTORY;

	return retval;
}

int vfs_create(struct inode *dir, struct dentry *dentry, int mode)
{
	int error;

	mode &= S_IALLUGO;
	mode |= S_IFREG;

	down(&dir->i_zombie);
	error = may_create(dir, dentry);
	if (error)
		goto exit_lock;

	error = -EACCES;	/* shouldn't it be ENOSYS? */
	if (!dir->i_op || !dir->i_op->create)
		goto exit_lock;

	DQUOT_INIT(dir);
	lock_kernel();
	error = dir->i_op->create(dir, dentry, mode);
	unlock_kernel();
exit_lock:
	up(&dir->i_zombie);
	if (!error)
		inode_dir_notify(dir, DN_CREATE);
	return error;
}

/*
 *	open_namei()
 *
 * namei for open - this is in fact almost the whole open-routine.
 *
 * Note that the low bits of "flag" aren't the same as in the open
 * system call - they are 00 - no permissions needed
 *			  01 - read permission needed
 *			  10 - write permission needed
 *			  11 - read/write permissions needed
 * which is a lot more logical, and also allows the "no perm" needed
 * for symlinks (where the permissions are checked later).
 * SMP-safe
 */
int open_namei(const char * pathname, int flag, int mode, struct nameidata *nd)
{
	int acc_mode, error = 0;
	struct inode *inode;
	struct dentry *dentry;
	struct dentry *dir;
	int count = 0;

	acc_mode = ACC_MODE(flag);

	/*
	 * The simplest case - just a plain lookup.
	 */
	if (!(flag & O_CREAT)) {
		if (path_init(pathname, lookup_flags(flag), nd))
			error = path_walk(pathname, nd);
		if (error)
			return error;
		dentry = nd->dentry;
		goto ok;
	}

	/*
	 * Create - we need to know the parent.
	 */
	if (path_init(pathname, LOOKUP_PARENT, nd))
		error = path_walk(pathname, nd);
	if (error)
		return error;

	/*
	 * We have the parent and last component. First of all, check
	 * that we are not asked to creat(2) an obvious directory - that
	 * will not do.
	 */
	error = -EISDIR;
	if (nd->last_type != LAST_NORM || nd->last.name[nd->last.len])
		goto exit;

	dir = nd->dentry;
	down(&dir->d_inode->i_sem);
	dentry = lookup_hash(&nd->last, nd->dentry);

do_last:
	error = PTR_ERR(dentry);
	if (IS_ERR(dentry)) {