You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: result.rs
    path of file: ./repos/kerla/kernel
    
    the code of the file until where you have to start completion: use core::fmt;

use kerla_runtime::{
    address::{AccessError, NullUserPointerError},
    page_allocator::PageAllocError,
};

#[cfg(debug_assertions)]
use kerla_runtime::backtrace::CapturedBacktrace;

#[derive(Debug, Copy, Clone, Eq, PartialEq)]
#[repr(i32)]
#[allow(unused)]
#[allow(clippy::upper_case_acronyms)]
pub enum Errno {
    EPERM = 1,
    ENOENT = 2,
    ESRCH = 3,
    EINTR = 4,
    EIO = 5,
    ENXIO = 6,
    E2BIG = 7,
    ENOEXEC = 8,
    EBADF = 9,
    ECHILD = 10,
 
    
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if let Some(message) = self.message.as_ref() {
            match message {
                ErrorMessage::StaticStr(message) => {
                    if let Some(ref trace) = self.backtrace {
                        write!(
                            f,
                            "[{:?}] {}\n    This error originates from:\n{:?}",
                            self.errno, message, trace
                        )
                    } else {
                        write!(f, "[{:?}] {}", self.errno, message)
                    }
                }
            }
        } else if let Some(ref trace) = self.backtrace {
            write!(
                f,
                "{:?}: This error originates from:\n{:?}",
                self.errno, trace
            )
        } else {
            write!(f, "{:?}", self.errno)
        }
    }