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Print out errname in impl Debug for Error #287

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Merged
merged 1 commit into from
May 26, 2021
Merged

Print out errname in impl Debug for Error #287

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1 change: 1 addition & 0 deletions rust/kernel/bindings_helper.h
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
/* SPDX-License-Identifier: GPL-2.0 */

#include <linux/cdev.h>
#include <linux/errname.h>
#include <linux/fs.h>
#include <linux/module.h>
#include <linux/random.h>
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28 changes: 26 additions & 2 deletions rust/kernel/error.rs
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Expand Up @@ -4,16 +4,19 @@
//!
//! C header: [`include/uapi/asm-generic/errno-base.h`](../../../include/uapi/asm-generic/errno-base.h)

use crate::str::CStr;
use crate::{bindings, c_types};
use alloc::{alloc::AllocError, collections::TryReserveError};
use core::convert::From;
use core::{num::TryFromIntError, str::Utf8Error};
use core::fmt;
use core::num::TryFromIntError;
use core::str::{self, Utf8Error};

/// Generic integer kernel error.
///
/// The kernel defines a set of integer generic error codes based on C and
/// POSIX ones. These codes may have a more specific meaning in some contexts.
#[derive(Debug)]
#[derive(Clone, Copy, PartialEq, Eq)]
pub struct Error(c_types::c_int);

impl Error {
Expand Down Expand Up @@ -61,6 +64,27 @@ impl Error {
}
}

impl fmt::Debug for Error {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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I like the idea that we could have names instead of values for the Debug::fmt of Error. However, I think it's better that we don't need to call errname if we already have the corresponding const, e.g. Error::EINVAL, because having the const actually means we have names for the error numbers at Rust side.

Thoughts?

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We don't currently have constants for all errors defined in Rust. Plus, defining them in Rust essentially requires us to have a giant match, or define a lookup table like errname.c did. It might be better just to reuse errname, C side needs it anyway.

// SAFETY: FFI call.
#[cfg(CONFIG_SYMBOLIC_ERRNAME)]
let name = unsafe { crate::bindings::errname(-self.0) };
#[cfg(not(CONFIG_SYMBOLIC_ERRNAME))]
let name: *const c_types::c_char = core::ptr::null();

if name.is_null() {
// Print out number if no name can be found.
return f.debug_tuple("Error").field(&-self.0).finish();
}

// SAFETY: `'static` string from C, and is not NULL.
let cstr = unsafe { CStr::from_char_ptr(name) };
// SAFETY: These strings are ASCII-only.
let str = unsafe { str::from_utf8_unchecked(&cstr) };
f.debug_tuple(str).finish()
}
}

impl From<TryFromIntError> for Error {
fn from(_: TryFromIntError) -> Error {
Error::EINVAL
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