rust/kernel/error.rs - linux - Git at Google

 // 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::{alloc::AllocError, str::CStr};

 use alloc::alloc::LayoutError;

 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
     }

     #[cfg(CONFIG_BLOCK)]
     pub(crate) fn to_blk_status(self) -> bindings::blk_status_t {
         // SAFETY: `self.0` is a valid error due to its invariant.
         unsafe { bindings::errno_to_blk_status(self.0) }
     }

     /// Returns the error encoded as a pointer.
     #[allow(dead_code)]
     pub(crate) fn to_ptr<T>(self) -> *mut T {
         #[cfg_attr(target_pointer_width = "32", allow(clippy::useless_conversion))]
         // 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.";
	// 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::{alloc::AllocError, str::CStr};

	use alloc::alloc::LayoutError;

	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
	}

	#[cfg(CONFIG_BLOCK)]
	pub(crate) fn to_blk_status(self) -> bindings::blk_status_t {
	// SAFETY: `self.0` is a valid error due to its invariant.
	unsafe { bindings::errno_to_blk_status(self.0) }
	}

	/// Returns the error encoded as a pointer.
	#[allow(dead_code)]
	pub(crate) fn to_ptr<T>(self) -> *mut T {
	#[cfg_attr(target_pointer_width = "32", allow(clippy::useless_conversion))]
	// 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.";