summaryrefslogtreecommitdiff
path: root/rust/kernel/error.rs
blob: e53466937796eda4d0331fd675c7fa272e6c08f2 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
// SPDX-License-Identifier: GPL-2.0

//! Kernel errors.
//!
//! C header: [`include/uapi/asm-generic/errno-base.h`](srctree/include/uapi/asm-generic/errno-base.h)

use crate::str::CStr;

use alloc::alloc::{AllocError, LayoutError};

use core::convert::From;
use core::fmt;
use core::num::TryFromIntError;
use core::str::Utf8Error;

/// Contains the C-compatible error codes.
#[rustfmt::skip]
pub mod code {
    macro_rules! declare_err {
        ($err:tt $(,)? $($doc:expr),+) => {
            $(
            #[doc = $doc]
            )*
            pub const $err: super::Error = super::Error(-(crate::bindings::$err as i32));
        };
    }

    declare_err!(EPERM, "Operation not permitted.");
    declare_err!(ENOENT, "No such file or directory.");
    declare_err!(ESRCH, "No such process.");
    declare_err!(EINTR, "Interrupted system call.");
    declare_err!(EIO, "I/O error.");
    declare_err!(ENXIO, "No such device or address.");
    declare_err!(E2BIG, "Argument list too long.");
    declare_err!(ENOEXEC, "Exec format error.");
    declare_err!(EBADF, "Bad file number.");
    declare_err!(ECHILD, "No child processes.");
    declare_err!(EAGAIN, "Try again.");
    declare_err!(ENOMEM, "Out of memory.");
    declare_err!(EACCES, "Permission denied.");
    declare_err!(EFAULT, "Bad address.");
    declare_err!(ENOTBLK, "Block device required.");
    declare_err!(EBUSY, "Device or resource busy.");
    declare_err!(EEXIST, "File exists.");
    declare_err!(EXDEV, "Cross-device link.");
    declare_err!(ENODEV, "No such device.");
    declare_err!(ENOTDIR, "Not a directory.");
    declare_err!(EISDIR, "Is a directory.");
    declare_err!(EINVAL, "Invalid argument.");
    declare_err!(ENFILE, "File table overflow.");
    declare_err!(EMFILE, "Too many open files.");
    declare_err!(ENOTTY, "Not a typewriter.");
    declare_err!(ETXTBSY, "Text file busy.");
    declare_err!(EFBIG, "File too large.");
    declare_err!(ENOSPC, "No space left on device.");
    declare_err!(ESPIPE, "Illegal seek.");
    declare_err!(EROFS, "Read-only file system.");
    declare_err!(EMLINK, "Too many links.");
    declare_err!(EPIPE, "Broken pipe.");
    declare_err!(EDOM, "Math argument out of domain of func.");
    declare_err!(ERANGE, "Math result not representable.");
    declare_err!(ERESTARTSYS, "Restart the system call.");
    declare_err!(ERESTARTNOINTR, "System call was interrupted by a signal and will be restarted.");
    declare_err!(ERESTARTNOHAND, "Restart if no handler.");
    declare_err!(ENOIOCTLCMD, "No ioctl command.");
    declare_err!(ERESTART_RESTARTBLOCK, "Restart by calling sys_restart_syscall.");
    declare_err!(EPROBE_DEFER, "Driver requests probe retry.");
    declare_err!(EOPENSTALE, "Open found a stale dentry.");
    declare_err!(ENOPARAM, "Parameter not supported.");
    declare_err!(EBADHANDLE, "Illegal NFS file handle.");
    declare_err!(ENOTSYNC, "Update synchronization mismatch.");
    declare_err!(EBADCOOKIE, "Cookie is stale.");
    declare_err!(ENOTSUPP, "Operation is not supported.");
    declare_err!(ETOOSMALL, "Buffer or request is too small.");
    declare_err!(ESERVERFAULT, "An untranslatable error occurred.");
    declare_err!(EBADTYPE, "Type not supported by server.");
    declare_err!(EJUKEBOX, "Request initiated, but will not complete before timeout.");
    declare_err!(EIOCBQUEUED, "iocb queued, will get completion event.");
    declare_err!(ERECALLCONFLICT, "Conflict with recalled state.");
    declare_err!(ENOGRACE, "NFS file lock reclaim refused.");
}

/// 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.
///
/// # Invariants
///
/// The value is a valid `errno` (i.e. `>= -MAX_ERRNO && < 0`).
#[derive(Clone, Copy, PartialEq, Eq)]
pub struct Error(core::ffi::c_int);

impl Error {
    /// Creates an [`Error`] from a kernel error code.
    ///
    /// It is a bug to pass an out-of-range `errno`. `EINVAL` would
    /// be returned in such a case.
    pub(crate) fn from_errno(errno: core::ffi::c_int) -> Error {
        if errno < -(bindings::MAX_ERRNO as i32) || errno >= 0 {
            // TODO: Make it a `WARN_ONCE` once available.
            crate::pr_warn!(
                "attempted to create `Error` with out of range `errno`: {}",
                errno
            );
            return code::EINVAL;
        }

        // INVARIANT: The check above ensures the type invariant
        // will hold.
        Error(errno)
    }

    /// Creates an [`Error`] from a kernel error code.
    ///
    /// # Safety
    ///
    /// `errno` must be within error code range (i.e. `>= -MAX_ERRNO && < 0`).
    unsafe fn from_errno_unchecked(errno: core::ffi::c_int) -> Error {
        // INVARIANT: The contract ensures the type invariant
        // will hold.
        Error(errno)
    }

    /// Returns the kernel error code.
    pub fn to_errno(self) -> core::ffi::c_int {
        self.0
    }

    /// Returns the error encoded as a pointer.
    #[allow(dead_code)]
    pub(crate) fn to_ptr<T>(self) -> *mut T {
        // SAFETY: `self.0` is a valid error due to its invariant.
        unsafe { bindings::ERR_PTR(self.0.into()) as *mut _ }
    }

    /// Returns a string representing the error, if one exists.
    #[cfg(not(testlib))]
    pub fn name(&self) -> Option<&'static CStr> {
        // SAFETY: Just an FFI call, there are no extra safety requirements.
        let ptr = unsafe { bindings::errname(-self.0) };
        if ptr.is_null() {
            None
        } else {
            // SAFETY: The string returned by `errname` is static and `NUL`-terminated.
            Some(unsafe { CStr::from_char_ptr(ptr) })
        }
    }

    /// Returns a string representing the error, if one exists.
    ///
    /// When `testlib` is configured, this always returns `None` to avoid the dependency on a
    /// kernel function so that tests that use this (e.g., by calling [`Result::unwrap`]) can still
    /// run in userspace.
    #[cfg(testlib)]
    pub fn name(&self) -> Option<&'static CStr> {
        None
    }
}

impl fmt::Debug for Error {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self.name() {
            // Print out number if no name can be found.
            None => f.debug_tuple("Error").field(&-self.0).finish(),
            // SAFETY: These strings are ASCII-only.
            Some(name) => f
                .debug_tuple(unsafe { core::str::from_utf8_unchecked(name) })
                .finish(),
        }
    }
}

impl From<AllocError> for Error {
    fn from(_: AllocError) -> Error {
        code::ENOMEM
    }
}

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

impl From<Utf8Error> for Error {
    fn from(_: Utf8Error) -> Error {
        code::EINVAL
    }
}

impl From<LayoutError> for Error {
    fn from(_: LayoutError) -> Error {
        code::ENOMEM
    }
}

impl From<core::fmt::Error> for Error {
    fn from(_: core::fmt::Error) -> Error {
        code::EINVAL
    }
}

impl From<core::convert::Infallible> for Error {
    fn from(e: core::convert::Infallible) -> Error {
        match e {}
    }
}

/// A [`Result`] with an [`Error`] error type.
///
/// To be used as the return type for functions that may fail.
///
/// # Error codes in C and Rust
///
/// In C, it is common that functions indicate success or failure through
/// their return value; modifying or returning extra data through non-`const`
/// pointer parameters. In particular, in the kernel, functions that may fail
/// typically return an `int` that represents a generic error code. We model
/// those as [`Error`].
///
/// In Rust, it is idiomatic to model functions that may fail as returning
/// a [`Result`]. Since in the kernel many functions return an error code,
/// [`Result`] is a type alias for a [`core::result::Result`] that uses
/// [`Error`] as its error type.
///
/// Note that even if a function does not return anything when it succeeds,
/// it should still be modeled as returning a `Result` rather than
/// just an [`Error`].
pub type Result<T = (), E = Error> = core::result::Result<T, E>;

/// Converts an integer as returned by a C kernel function to an error if it's negative, and
/// `Ok(())` otherwise.
pub fn to_result(err: core::ffi::c_int) -> Result {
    if err < 0 {
        Err(Error::from_errno(err))
    } else {
        Ok(())
    }
}

/// Transform a kernel "error pointer" to a normal pointer.
///
/// Some kernel C API functions return an "error pointer" which optionally
/// embeds an `errno`. Callers are supposed to check the returned pointer
/// for errors. This function performs the check and converts the "error pointer"
/// to a normal pointer in an idiomatic fashion.
///
/// # Examples
///
/// ```ignore
/// # use kernel::from_err_ptr;
/// # use kernel::bindings;
/// fn devm_platform_ioremap_resource(
///     pdev: &mut PlatformDevice,
///     index: u32,
/// ) -> Result<*mut core::ffi::c_void> {
///     // SAFETY: `pdev` points to a valid platform device. There are no safety requirements
///     // on `index`.
///     from_err_ptr(unsafe { bindings::devm_platform_ioremap_resource(pdev.to_ptr(), index) })
/// }
/// ```
// TODO: Remove `dead_code` marker once an in-kernel client is available.
#[allow(dead_code)]
pub(crate) fn from_err_ptr<T>(ptr: *mut T) -> Result<*mut T> {
    // CAST: Casting a pointer to `*const core::ffi::c_void` is always valid.
    let const_ptr: *const core::ffi::c_void = ptr.cast();
    // SAFETY: The FFI function does not deref the pointer.
    if unsafe { bindings::IS_ERR(const_ptr) } {
        // SAFETY: The FFI function does not deref the pointer.
        let err = unsafe { bindings::PTR_ERR(const_ptr) };
        // CAST: If `IS_ERR()` returns `true`,
        // then `PTR_ERR()` is guaranteed to return a
        // negative value greater-or-equal to `-bindings::MAX_ERRNO`,
        // which always fits in an `i16`, as per the invariant above.
        // And an `i16` always fits in an `i32`. So casting `err` to
        // an `i32` can never overflow, and is always valid.
        //
        // SAFETY: `IS_ERR()` ensures `err` is a
        // negative value greater-or-equal to `-bindings::MAX_ERRNO`.
        #[allow(clippy::unnecessary_cast)]
        return Err(unsafe { Error::from_errno_unchecked(err as core::ffi::c_int) });
    }
    Ok(ptr)
}

/// Calls a closure returning a [`crate::error::Result<T>`] and converts the result to
/// a C integer result.
///
/// This is useful when calling Rust functions that return [`crate::error::Result<T>`]
/// from inside `extern "C"` functions that need to return an integer error result.
///
/// `T` should be convertible from an `i16` via `From<i16>`.
///
/// # Examples
///
/// ```ignore
/// # use kernel::from_result;
/// # use kernel::bindings;
/// unsafe extern "C" fn probe_callback(
///     pdev: *mut bindings::platform_device,
/// ) -> core::ffi::c_int {
///     from_result(|| {
///         let ptr = devm_alloc(pdev)?;
///         bindings::platform_set_drvdata(pdev, ptr);
///         Ok(0)
///     })
/// }
/// ```
// TODO: Remove `dead_code` marker once an in-kernel client is available.
#[allow(dead_code)]
pub(crate) fn from_result<T, F>(f: F) -> T
where
    T: From<i16>,
    F: FnOnce() -> Result<T>,
{
    match f() {
        Ok(v) => v,
        // NO-OVERFLOW: negative `errno`s are no smaller than `-bindings::MAX_ERRNO`,
        // `-bindings::MAX_ERRNO` fits in an `i16` as per invariant above,
        // therefore a negative `errno` always fits in an `i16` and will not overflow.
        Err(e) => T::from(e.to_errno() as i16),
    }
}

/// Error message for calling a default function of a [`#[vtable]`](macros::vtable) trait.
pub const VTABLE_DEFAULT_ERROR: &str =
    "This function must not be called, see the #[vtable] documentation.";