kernel/
error.rs

1// SPDX-License-Identifier: GPL-2.0
2
3//! Kernel errors.
4//!
5//! C header: [`include/uapi/asm-generic/errno-base.h`](srctree/include/uapi/asm-generic/errno-base.h)
6
7use crate::{
8    alloc::{layout::LayoutError, AllocError},
9    str::CStr,
10};
11
12use core::fmt;
13use core::num::NonZeroI32;
14use core::num::TryFromIntError;
15use core::str::Utf8Error;
16
17/// Contains the C-compatible error codes.
18#[rustfmt::skip]
19pub mod code {
20    macro_rules! declare_err {
21        ($err:tt $(,)? $($doc:expr),+) => {
22            $(
23            #[doc = $doc]
24            )*
25            pub const $err: super::Error =
26                match super::Error::try_from_errno(-(crate::bindings::$err as i32)) {
27                    Some(err) => err,
28                    None => panic!("Invalid errno in `declare_err!`"),
29                };
30        };
31    }
32
33    declare_err!(EPERM, "Operation not permitted.");
34    declare_err!(ENOENT, "No such file or directory.");
35    declare_err!(ESRCH, "No such process.");
36    declare_err!(EINTR, "Interrupted system call.");
37    declare_err!(EIO, "I/O error.");
38    declare_err!(ENXIO, "No such device or address.");
39    declare_err!(E2BIG, "Argument list too long.");
40    declare_err!(ENOEXEC, "Exec format error.");
41    declare_err!(EBADF, "Bad file number.");
42    declare_err!(ECHILD, "No child processes.");
43    declare_err!(EAGAIN, "Try again.");
44    declare_err!(ENOMEM, "Out of memory.");
45    declare_err!(EACCES, "Permission denied.");
46    declare_err!(EFAULT, "Bad address.");
47    declare_err!(ENOTBLK, "Block device required.");
48    declare_err!(EBUSY, "Device or resource busy.");
49    declare_err!(EEXIST, "File exists.");
50    declare_err!(EXDEV, "Cross-device link.");
51    declare_err!(ENODEV, "No such device.");
52    declare_err!(ENOTDIR, "Not a directory.");
53    declare_err!(EISDIR, "Is a directory.");
54    declare_err!(EINVAL, "Invalid argument.");
55    declare_err!(ENFILE, "File table overflow.");
56    declare_err!(EMFILE, "Too many open files.");
57    declare_err!(ENOTTY, "Not a typewriter.");
58    declare_err!(ETXTBSY, "Text file busy.");
59    declare_err!(EFBIG, "File too large.");
60    declare_err!(ENOSPC, "No space left on device.");
61    declare_err!(ESPIPE, "Illegal seek.");
62    declare_err!(EROFS, "Read-only file system.");
63    declare_err!(EMLINK, "Too many links.");
64    declare_err!(EPIPE, "Broken pipe.");
65    declare_err!(EDOM, "Math argument out of domain of func.");
66    declare_err!(ERANGE, "Math result not representable.");
67    declare_err!(ERESTARTSYS, "Restart the system call.");
68    declare_err!(ERESTARTNOINTR, "System call was interrupted by a signal and will be restarted.");
69    declare_err!(ERESTARTNOHAND, "Restart if no handler.");
70    declare_err!(ENOIOCTLCMD, "No ioctl command.");
71    declare_err!(ERESTART_RESTARTBLOCK, "Restart by calling sys_restart_syscall.");
72    declare_err!(EPROBE_DEFER, "Driver requests probe retry.");
73    declare_err!(EOPENSTALE, "Open found a stale dentry.");
74    declare_err!(ENOPARAM, "Parameter not supported.");
75    declare_err!(EBADHANDLE, "Illegal NFS file handle.");
76    declare_err!(ENOTSYNC, "Update synchronization mismatch.");
77    declare_err!(EBADCOOKIE, "Cookie is stale.");
78    declare_err!(ENOTSUPP, "Operation is not supported.");
79    declare_err!(ETOOSMALL, "Buffer or request is too small.");
80    declare_err!(ESERVERFAULT, "An untranslatable error occurred.");
81    declare_err!(EBADTYPE, "Type not supported by server.");
82    declare_err!(EJUKEBOX, "Request initiated, but will not complete before timeout.");
83    declare_err!(EIOCBQUEUED, "iocb queued, will get completion event.");
84    declare_err!(ERECALLCONFLICT, "Conflict with recalled state.");
85    declare_err!(ENOGRACE, "NFS file lock reclaim refused.");
86}
87
88/// Generic integer kernel error.
89///
90/// The kernel defines a set of integer generic error codes based on C and
91/// POSIX ones. These codes may have a more specific meaning in some contexts.
92///
93/// # Invariants
94///
95/// The value is a valid `errno` (i.e. `>= -MAX_ERRNO && < 0`).
96#[derive(Clone, Copy, PartialEq, Eq)]
97pub struct Error(NonZeroI32);
98
99impl Error {
100    /// Creates an [`Error`] from a kernel error code.
101    ///
102    /// It is a bug to pass an out-of-range `errno`. `EINVAL` would
103    /// be returned in such a case.
104    pub fn from_errno(errno: crate::ffi::c_int) -> Error {
105        if let Some(error) = Self::try_from_errno(errno) {
106            error
107        } else {
108            // TODO: Make it a `WARN_ONCE` once available.
109            crate::pr_warn!(
110                "attempted to create `Error` with out of range `errno`: {}\n",
111                errno
112            );
113            code::EINVAL
114        }
115    }
116
117    /// Creates an [`Error`] from a kernel error code.
118    ///
119    /// Returns [`None`] if `errno` is out-of-range.
120    const fn try_from_errno(errno: crate::ffi::c_int) -> Option<Error> {
121        if errno < -(bindings::MAX_ERRNO as i32) || errno >= 0 {
122            return None;
123        }
124
125        // SAFETY: `errno` is checked above to be in a valid range.
126        Some(unsafe { Error::from_errno_unchecked(errno) })
127    }
128
129    /// Creates an [`Error`] from a kernel error code.
130    ///
131    /// # Safety
132    ///
133    /// `errno` must be within error code range (i.e. `>= -MAX_ERRNO && < 0`).
134    const unsafe fn from_errno_unchecked(errno: crate::ffi::c_int) -> Error {
135        // INVARIANT: The contract ensures the type invariant
136        // will hold.
137        // SAFETY: The caller guarantees `errno` is non-zero.
138        Error(unsafe { NonZeroI32::new_unchecked(errno) })
139    }
140
141    /// Returns the kernel error code.
142    pub fn to_errno(self) -> crate::ffi::c_int {
143        self.0.get()
144    }
145
146    #[cfg(CONFIG_BLOCK)]
147    pub(crate) fn to_blk_status(self) -> bindings::blk_status_t {
148        // SAFETY: `self.0` is a valid error due to its invariant.
149        unsafe { bindings::errno_to_blk_status(self.0.get()) }
150    }
151
152    /// Returns the error encoded as a pointer.
153    pub fn to_ptr<T>(self) -> *mut T {
154        // SAFETY: `self.0` is a valid error due to its invariant.
155        unsafe { bindings::ERR_PTR(self.0.get() as _) as *mut _ }
156    }
157
158    /// Returns a string representing the error, if one exists.
159    #[cfg(not(any(test, testlib)))]
160    pub fn name(&self) -> Option<&'static CStr> {
161        // SAFETY: Just an FFI call, there are no extra safety requirements.
162        let ptr = unsafe { bindings::errname(-self.0.get()) };
163        if ptr.is_null() {
164            None
165        } else {
166            // SAFETY: The string returned by `errname` is static and `NUL`-terminated.
167            Some(unsafe { CStr::from_char_ptr(ptr) })
168        }
169    }
170
171    /// Returns a string representing the error, if one exists.
172    ///
173    /// When `testlib` is configured, this always returns `None` to avoid the dependency on a
174    /// kernel function so that tests that use this (e.g., by calling [`Result::unwrap`]) can still
175    /// run in userspace.
176    #[cfg(any(test, testlib))]
177    pub fn name(&self) -> Option<&'static CStr> {
178        None
179    }
180}
181
182impl fmt::Debug for Error {
183    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
184        match self.name() {
185            // Print out number if no name can be found.
186            None => f.debug_tuple("Error").field(&-self.0).finish(),
187            Some(name) => f
188                .debug_tuple(
189                    // SAFETY: These strings are ASCII-only.
190                    unsafe { core::str::from_utf8_unchecked(name) },
191                )
192                .finish(),
193        }
194    }
195}
196
197impl From<AllocError> for Error {
198    fn from(_: AllocError) -> Error {
199        code::ENOMEM
200    }
201}
202
203impl From<TryFromIntError> for Error {
204    fn from(_: TryFromIntError) -> Error {
205        code::EINVAL
206    }
207}
208
209impl From<Utf8Error> for Error {
210    fn from(_: Utf8Error) -> Error {
211        code::EINVAL
212    }
213}
214
215impl From<LayoutError> for Error {
216    fn from(_: LayoutError) -> Error {
217        code::ENOMEM
218    }
219}
220
221impl From<core::fmt::Error> for Error {
222    fn from(_: core::fmt::Error) -> Error {
223        code::EINVAL
224    }
225}
226
227impl From<core::convert::Infallible> for Error {
228    fn from(e: core::convert::Infallible) -> Error {
229        match e {}
230    }
231}
232
233/// A [`Result`] with an [`Error`] error type.
234///
235/// To be used as the return type for functions that may fail.
236///
237/// # Error codes in C and Rust
238///
239/// In C, it is common that functions indicate success or failure through
240/// their return value; modifying or returning extra data through non-`const`
241/// pointer parameters. In particular, in the kernel, functions that may fail
242/// typically return an `int` that represents a generic error code. We model
243/// those as [`Error`].
244///
245/// In Rust, it is idiomatic to model functions that may fail as returning
246/// a [`Result`]. Since in the kernel many functions return an error code,
247/// [`Result`] is a type alias for a [`core::result::Result`] that uses
248/// [`Error`] as its error type.
249///
250/// Note that even if a function does not return anything when it succeeds,
251/// it should still be modeled as returning a `Result` rather than
252/// just an [`Error`].
253pub type Result<T = (), E = Error> = core::result::Result<T, E>;
254
255/// Converts an integer as returned by a C kernel function to an error if it's negative, and
256/// `Ok(())` otherwise.
257pub fn to_result(err: crate::ffi::c_int) -> Result {
258    if err < 0 {
259        Err(Error::from_errno(err))
260    } else {
261        Ok(())
262    }
263}
264
265/// Transform a kernel "error pointer" to a normal pointer.
266///
267/// Some kernel C API functions return an "error pointer" which optionally
268/// embeds an `errno`. Callers are supposed to check the returned pointer
269/// for errors. This function performs the check and converts the "error pointer"
270/// to a normal pointer in an idiomatic fashion.
271///
272/// # Examples
273///
274/// ```ignore
275/// # use kernel::from_err_ptr;
276/// # use kernel::bindings;
277/// fn devm_platform_ioremap_resource(
278///     pdev: &mut PlatformDevice,
279///     index: u32,
280/// ) -> Result<*mut kernel::ffi::c_void> {
281///     // SAFETY: `pdev` points to a valid platform device. There are no safety requirements
282///     // on `index`.
283///     from_err_ptr(unsafe { bindings::devm_platform_ioremap_resource(pdev.to_ptr(), index) })
284/// }
285/// ```
286pub fn from_err_ptr<T>(ptr: *mut T) -> Result<*mut T> {
287    // CAST: Casting a pointer to `*const crate::ffi::c_void` is always valid.
288    let const_ptr: *const crate::ffi::c_void = ptr.cast();
289    // SAFETY: The FFI function does not deref the pointer.
290    if unsafe { bindings::IS_ERR(const_ptr) } {
291        // SAFETY: The FFI function does not deref the pointer.
292        let err = unsafe { bindings::PTR_ERR(const_ptr) };
293
294        #[allow(clippy::unnecessary_cast)]
295        // CAST: If `IS_ERR()` returns `true`,
296        // then `PTR_ERR()` is guaranteed to return a
297        // negative value greater-or-equal to `-bindings::MAX_ERRNO`,
298        // which always fits in an `i16`, as per the invariant above.
299        // And an `i16` always fits in an `i32`. So casting `err` to
300        // an `i32` can never overflow, and is always valid.
301        //
302        // SAFETY: `IS_ERR()` ensures `err` is a
303        // negative value greater-or-equal to `-bindings::MAX_ERRNO`.
304        return Err(unsafe { Error::from_errno_unchecked(err as crate::ffi::c_int) });
305    }
306    Ok(ptr)
307}
308
309/// Calls a closure returning a [`crate::error::Result<T>`] and converts the result to
310/// a C integer result.
311///
312/// This is useful when calling Rust functions that return [`crate::error::Result<T>`]
313/// from inside `extern "C"` functions that need to return an integer error result.
314///
315/// `T` should be convertible from an `i16` via `From<i16>`.
316///
317/// # Examples
318///
319/// ```ignore
320/// # use kernel::from_result;
321/// # use kernel::bindings;
322/// unsafe extern "C" fn probe_callback(
323///     pdev: *mut bindings::platform_device,
324/// ) -> kernel::ffi::c_int {
325///     from_result(|| {
326///         let ptr = devm_alloc(pdev)?;
327///         bindings::platform_set_drvdata(pdev, ptr);
328///         Ok(0)
329///     })
330/// }
331/// ```
332pub fn from_result<T, F>(f: F) -> T
333where
334    T: From<i16>,
335    F: FnOnce() -> Result<T>,
336{
337    match f() {
338        Ok(v) => v,
339        // NO-OVERFLOW: negative `errno`s are no smaller than `-bindings::MAX_ERRNO`,
340        // `-bindings::MAX_ERRNO` fits in an `i16` as per invariant above,
341        // therefore a negative `errno` always fits in an `i16` and will not overflow.
342        Err(e) => T::from(e.to_errno() as i16),
343    }
344}
345
346/// Error message for calling a default function of a [`#[vtable]`](macros::vtable) trait.
347pub const VTABLE_DEFAULT_ERROR: &str =
348    "This function must not be called, see the #[vtable] documentation.";