Function svn_fs_file_length 

pub unsafe extern "C" fn svn_fs_file_length(
    length_p: *mut svn_filesize_t,
    root: *mut svn_fs_root_t,
    path: *const c_char,
    pool: *mut apr_pool_t,
) -> *mut svn_error_t

Set @a *length_p to the length of the file @a path in @a root, in bytes. Do any necessary temporary allocation in @a pool.