get rid of s_files and files_lock

The only thing we need it for is alt-sysrq-r (emergency remount r/o)
and these days we can do just as well without going through the
list of files.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
SYSCALL_DEFINE1(fchdir, unsigned int, fd)
{
	struct fd f = fdget_raw(fd);
	struct inode *inode;
	int error = -EBADF;

	error = -EBADF;
	if (!f.file)
		goto out;

	inode = file_inode(f.file);

	error = -ENOTDIR;
	if (!S_ISDIR(inode->i_mode))
		goto out_putf;

	error = inode_permission(inode, MAY_EXEC | MAY_CHDIR);
	if (!error)
		set_fs_pwd(current->fs, &f.file->f_path);
out_putf:
	fdput(f);
out:
	return error;
}

SYSCALL_DEFINE1(fchdir, unsigned int, fd)
{
	struct fd f = fdget_raw(fd);
	struct inode *inode;
	int error = -EBADF;

	error = -EBADF;
	if (!f.file)
		goto out;

	inode = file_inode(f.file);

	error = -ENOTDIR;
	if (!S_ISDIR(inode->i_mode))
		goto out_putf;

	error = inode_permission(inode, MAY_EXEC | MAY_CHDIR);
	if (!error)
		set_fs_pwd(current->fs, &f.file->f_path);
out_putf:
	fdput(f);
out:
	return error;
}
