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