link_path_walk

link_path_walk.c

*
 * 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.
 */
int fastcall link_path_walk(const char * name, struct nameidata *nd)
{
	struct path next;
	struct inode *inode;
	int err;
	unsigned int lookup_flags = nd->flags;
  // 	
	while (*name=='/')
		name++;
	if (!*name)
		goto return_reval;
	inode = nd->dentry->d_inode;
	if (nd->depth)
		lookup_flags = LOOKUP_FOLLOW;
	/* At this point we know we have a real path component. */
	for(;;) {
		unsigned long hash;
		struct qstr this;
		unsigned int c;
		err = exec_permission_lite(inode, nd);
		if (err == -EAGAIN) { 
			err = permission(inode, MAY_EXEC, 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);
		/* remove trailing slashes? */
		if (!c)
			goto last_component;
		while (*++name == '/');
		if (!*name)
			goto last_with_slashes;
		/*
		 * "." and ".." are special - ".." especially so because it has
		 * to be able to know about the current root directory and
		 * parent relationships.
		 */
		if (this.name[0] == '.') switch (this.len) {
			default:
				break;
			case 2:	
				if (this.name[1] != '.')
					break;
				follow_dotdot(&nd->mnt, &nd->dentry);
				inode = nd->dentry->d_inode;
				/* fallthrough */
			case 1:
				continue;
		}
		/*
		 * 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;
		}
		nd->flags |= LOOKUP_CONTINUE;
		/* This does the actual lookups.. */
		err = do_lookup(nd, &this, &next);
		if (err)
			break;
		/* Check mountpoints.. */
		follow_mount(&next.mnt, &next.dentry);
		err = -ENOENT;
		inode = next.dentry->d_inode;
		if (!inode)
			goto out_dput;
		err = -ENOTDIR; 
		if (!inode->i_op)
			goto out_dput;
		if (inode->i_op->follow_link) {
			mntget(next.mnt);
			err = do_follow_link(next.dentry, nd);
			dput(next.dentry);
			mntput(next.mnt);
			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->mnt = next.mnt;
			nd->dentry = next.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:
		nd->flags &= ~LOOKUP_CONTINUE;
		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->mnt, &nd->dentry);
				inode = nd->dentry->d_inode;
				/* fallthrough */
			case 1:
				goto return_reval;
		}
		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;
		}
		err = do_lookup(nd, &this, &next);
		if (err)
			break;
		follow_mount(&next.mnt, &next.dentry);
		inode = next.dentry->d_inode;
		if ((lookup_flags & LOOKUP_FOLLOW)
		    && inode && inode->i_op && inode->i_op->follow_link) {
			mntget(next.mnt);
			err = do_follow_link(next.dentry, nd);
			dput(next.dentry);
			mntput(next.mnt);
			if (err)
				goto return_err;
			inode = nd->dentry->d_inode;
		} else {
			dput(nd->dentry);
			nd->mnt = next.mnt;
			nd->dentry = next.dentry;
		}
		err = -ENOENT;
		if (!inode)
			break;
		if (lookup_flags & LOOKUP_DIRECTORY) {
			err = -ENOTDIR; 
			if (!inode->i_op || !inode->i_op->lookup)
				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;
		else
			goto return_base;
return_reval:
		/*
		 * We bypassed the ordinary revalidation routines.
		 * We may need to check the cached dentry for staleness.
		 */
		if (nd->dentry && nd->dentry->d_sb &&
		    (nd->dentry->d_sb->s_type->fs_flags & FS_REVAL_DOT)) {
			err = -ESTALE;
			/* Note: we do not d_invalidate() */
			if (!nd->dentry->d_op->d_revalidate(nd->dentry, nd))
				break;
		}
return_base:
		return 0;
out_dput:
		dput(next.dentry);
		break;
	}
	path_release(nd);
return_err:
	return err;
}