1//! Unsafe `ioctl` API.
2//!
3//! Unix systems expose a number of `ioctl`'s. `ioctl`s have been adopted as a
4//! general purpose system call for making calls into the kernel. In addition
5//! to the wide variety of system calls that are included by default in the
6//! kernel, many drivers expose their own `ioctl`'s for controlling their
7//! behavior, some of which are proprietary. Therefore it is impossible to make
8//! a safe interface for every `ioctl` call, as they all have wildly varying
9//! semantics.
10//!
11//! This module provides an unsafe interface to write your own `ioctl` API. To
12//! start, create a type that implements [`Ioctl`]. Then, pass it to [`ioctl`]
13//! to make the `ioctl` call.
14
15#![allow(unsafe_code)]
16
17use crate::backend::c;
18use crate::fd::{AsFd, BorrowedFd};
19use crate::io::Result;
20
21#[cfg(any(linux_kernel, bsd))]
22use core::mem;
23
24pub use patterns::*;
25
26mod patterns;
27
28#[cfg(linux_kernel)]
29mod linux;
30
31#[cfg(bsd)]
32mod bsd;
33
34#[cfg(linux_kernel)]
35use linux as platform;
36
37#[cfg(bsd)]
38use bsd as platform;
39
40/// Perform an `ioctl` call.
41///
42/// `ioctl` was originally intended to act as a way of modifying the behavior
43/// of files, but has since been adopted as a general purpose system call for
44/// making calls into the kernel. In addition to the default calls exposed by
45/// generic file descriptors, many drivers expose their own `ioctl` calls for
46/// controlling their behavior, some of which are proprietary.
47///
48/// This crate exposes many other `ioctl` interfaces with safe and idiomatic
49/// wrappers, like [`ioctl_fionbio`](crate::io::ioctl_fionbio) and
50/// [`ioctl_fionread`](crate::io::ioctl_fionread). It is recommended to use
51/// those instead of this function, as they are safer and more idiomatic.
52/// For other cases, implement the [`Ioctl`] API and pass it to this function.
53///
54/// See documentation for [`Ioctl`] for more information.
55///
56/// # Safety
57///
58/// While [`Ioctl`] takes much of the unsafety out of `ioctl` calls, it is
59/// still unsafe to call this code with arbitrary device drivers, as it is up
60/// to the device driver to implement the `ioctl` call correctly. It is on the
61/// onus of the protocol between the user and the driver to ensure that the
62/// `ioctl` call is safe to make.
63///
64/// # References
65///
66/// - [Linux]
67/// - [WinSock2]
68/// - [FreeBSD]
69/// - [NetBSD]
70/// - [OpenBSD]
71/// - [Apple]
72/// - [Solaris]
73/// - [illumos]
74///
75/// [Linux]: https://man7.org/linux/man-pages/man2/ioctl.2.html
76/// [Winsock2]: https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-ioctlsocket
77/// [FreeBSD]: https://man.freebsd.org/cgi/man.cgi?query=ioctl&sektion=2
78/// [NetBSD]: https://man.netbsd.org/ioctl.2
79/// [OpenBSD]: https://man.openbsd.org/ioctl.2
80/// [Apple]: https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/ioctl.2.html
81/// [Solaris]: https://docs.oracle.com/cd/E23824_01/html/821-1463/ioctl-2.html
82/// [illumos]: https://illumos.org/man/2/ioctl
83#[inline]
84pub unsafe fn ioctl<F: AsFd, I: Ioctl>(fd: F, mut ioctl: I) -> Result<I::Output> {
85 let fd: BorrowedFd<'_> = fd.as_fd();
86 let request: u32 = I::OPCODE.raw();
87 let arg: *mut c_void = ioctl.as_ptr();
88
89 // SAFETY: The variant of `Ioctl` asserts that this is a valid IOCTL call
90 // to make.
91 let output: i32 = if I::IS_MUTATING {
92 _ioctl(fd, request, arg)?
93 } else {
94 _ioctl_readonly(fd, request, arg)?
95 };
96
97 // SAFETY: The variant of `Ioctl` asserts that this is a valid pointer to
98 // the output data.
99 I::output_from_ptr(out:output, extract_output:arg)
100}
101
102unsafe fn _ioctl(
103 fd: BorrowedFd<'_>,
104 request: RawOpcode,
105 arg: *mut c::c_void,
106) -> Result<IoctlOutput> {
107 crate::backend::io::syscalls::ioctl(fd, request, arg)
108}
109
110unsafe fn _ioctl_readonly(
111 fd: BorrowedFd<'_>,
112 request: RawOpcode,
113 arg: *mut c::c_void,
114) -> Result<IoctlOutput> {
115 crate::backend::io::syscalls::ioctl_readonly(fd, request, arg)
116}
117
118/// A trait defining the properties of an `ioctl` command.
119///
120/// Objects implementing this trait can be passed to [`ioctl`] to make an
121/// `ioctl` call. The contents of the object represent the inputs to the
122/// `ioctl` call. The inputs must be convertible to a pointer through the
123/// `as_ptr` method. In most cases, this involves either casting a number to a
124/// pointer, or creating a pointer to the actual data. The latter case is
125/// necessary for `ioctl` calls that modify userspace data.
126///
127/// # Safety
128///
129/// This trait is unsafe to implement because it is impossible to guarantee
130/// that the `ioctl` call is safe. The `ioctl` call may be proprietary, or it
131/// may be unsafe to call in certain circumstances.
132///
133/// By implementing this trait, you guarantee that:
134///
135/// - The `ioctl` call expects the input provided by `as_ptr` and produces the
136/// output as indicated by `output`.
137/// - That `output_from_ptr` can safely take the pointer from `as_ptr` and cast
138/// it to the correct type, *only* after the `ioctl` call.
139/// - That `OPCODE` uniquely identifies the `ioctl` call.
140/// - That, for whatever platforms you are targeting, the `ioctl` call is safe
141/// to make.
142/// - If `IS_MUTATING` is false, that no userspace data will be modified by the
143/// `ioctl` call.
144pub unsafe trait Ioctl {
145 /// The type of the output data.
146 ///
147 /// Given a pointer, one should be able to construct an instance of this
148 /// type.
149 type Output;
150
151 /// The opcode used by this `ioctl` command.
152 ///
153 /// There are different types of opcode depending on the operation. See
154 /// documentation for the [`Opcode`] struct for more information.
155 const OPCODE: Opcode;
156
157 /// Does the `ioctl` mutate any data in the userspace?
158 ///
159 /// If the `ioctl` call does not mutate any data in the userspace, then
160 /// making this `false` enables optimizations that can make the call
161 /// faster. When in doubt, set this to `true`.
162 ///
163 /// # Safety
164 ///
165 /// This should only be set to `false` if the `ioctl` call does not mutate
166 /// any data in the userspace. Undefined behavior may occur if this is set
167 /// to `false` when it should be `true`.
168 const IS_MUTATING: bool;
169
170 /// Get a pointer to the data to be passed to the `ioctl` command.
171 ///
172 /// See trait-level documentation for more information.
173 fn as_ptr(&mut self) -> *mut c::c_void;
174
175 /// Cast the output data to the correct type.
176 ///
177 /// # Safety
178 ///
179 /// The `extract_output` value must be the resulting value after a
180 /// successful `ioctl` call, and `out` is the direct return value of an
181 /// `ioctl` call that did not fail. In this case `extract_output` is the
182 /// pointer that was passed to the `ioctl` call.
183 unsafe fn output_from_ptr(
184 out: IoctlOutput,
185 extract_output: *mut c::c_void,
186 ) -> Result<Self::Output>;
187}
188
189/// The opcode used by an `Ioctl`.
190#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
191pub struct Opcode {
192 /// The raw opcode.
193 raw: RawOpcode,
194}
195
196impl Opcode {
197 /// Create a new old `Opcode` from a raw opcode.
198 ///
199 /// Rather than being a composition of several attributes, old opcodes are
200 /// just numbers. In general most drivers follow stricter conventions, but
201 /// older drivers may still use this strategy.
202 #[inline]
203 pub const fn old(raw: RawOpcode) -> Self {
204 Self { raw }
205 }
206
207 /// Create a new opcode from a direction, group, number and size.
208 ///
209 /// This corresponds to the C macro `_IOC(direction, group, number, size)`
210 #[cfg(any(linux_kernel, bsd))]
211 #[inline]
212 pub const fn from_components(
213 direction: Direction,
214 group: u8,
215 number: u8,
216 data_size: usize,
217 ) -> Self {
218 if data_size > RawOpcode::MAX as usize {
219 panic!("data size is too large");
220 }
221
222 Self::old(platform::compose_opcode(
223 direction,
224 group as RawOpcode,
225 number as RawOpcode,
226 data_size as RawOpcode,
227 ))
228 }
229
230 /// Create a new non-mutating opcode from a group, a number and the type of
231 /// data.
232 ///
233 /// This corresponds to the C macro `_IO(group, number)` when `T` is zero
234 /// sized.
235 #[cfg(any(linux_kernel, bsd))]
236 #[inline]
237 pub const fn none<T>(group: u8, number: u8) -> Self {
238 Self::from_components(Direction::None, group, number, mem::size_of::<T>())
239 }
240
241 /// Create a new reading opcode from a group, a number and the type of
242 /// data.
243 ///
244 /// This corresponds to the C macro `_IOR(group, number, T)`.
245 #[cfg(any(linux_kernel, bsd))]
246 #[inline]
247 pub const fn read<T>(group: u8, number: u8) -> Self {
248 Self::from_components(Direction::Read, group, number, mem::size_of::<T>())
249 }
250
251 /// Create a new writing opcode from a group, a number and the type of
252 /// data.
253 ///
254 /// This corresponds to the C macro `_IOW(group, number, T)`.
255 #[cfg(any(linux_kernel, bsd))]
256 #[inline]
257 pub const fn write<T>(group: u8, number: u8) -> Self {
258 Self::from_components(Direction::Write, group, number, mem::size_of::<T>())
259 }
260
261 /// Create a new reading and writing opcode from a group, a number and the
262 /// type of data.
263 ///
264 /// This corresponds to the C macro `_IOWR(group, number, T)`.
265 #[cfg(any(linux_kernel, bsd))]
266 #[inline]
267 pub const fn read_write<T>(group: u8, number: u8) -> Self {
268 Self::from_components(Direction::ReadWrite, group, number, mem::size_of::<T>())
269 }
270
271 /// Get the raw opcode.
272 #[inline]
273 pub fn raw(self) -> RawOpcode {
274 self.raw
275 }
276}
277
278/// The direction that an `ioctl` is going.
279///
280/// Note that this is relative to userspace. `Read` means reading data from the
281/// kernel, and write means the kernel writing data to userspace.
282#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
283pub enum Direction {
284 /// None of the above.
285 None,
286
287 /// Read data from the kernel.
288 Read,
289
290 /// Write data to the kernel.
291 Write,
292
293 /// Read and write data to the kernel.
294 ReadWrite,
295}
296
297/// The type used by the `ioctl` to signify the output.
298pub type IoctlOutput = c::c_int;
299
300/// The type used by the `ioctl` to signify the command.
301pub type RawOpcode = _RawOpcode;
302
303// Under raw Linux, this is an `unsigned int`.
304#[cfg(linux_raw)]
305type _RawOpcode = c::c_uint;
306
307// On libc Linux with GNU libc or uclibc, this is an `unsigned long`.
308#[cfg(all(
309 not(linux_raw),
310 target_os = "linux",
311 any(target_env = "gnu", target_env = "uclibc")
312))]
313type _RawOpcode = c::c_ulong;
314
315// Musl uses `c_int`.
316#[cfg(all(
317 not(linux_raw),
318 target_os = "linux",
319 not(target_env = "gnu"),
320 not(target_env = "uclibc")
321))]
322type _RawOpcode = c::c_int;
323
324// Android uses `c_int`.
325#[cfg(all(not(linux_raw), target_os = "android"))]
326type _RawOpcode = c::c_int;
327
328// BSD, Haiku, Hurd, and Redox use `unsigned long`.
329#[cfg(any(bsd, target_os = "redox", target_os = "haiku", target_os = "hurd"))]
330type _RawOpcode = c::c_ulong;
331
332// AIX, Emscripten, Fuchsia, Solaris, and WASI use a `int`.
333#[cfg(any(
334 solarish,
335 target_os = "aix",
336 target_os = "fuchsia",
337 target_os = "emscripten",
338 target_os = "wasi",
339 target_os = "nto"
340))]
341type _RawOpcode = c::c_int;
342
343// ESP-IDF uses a `c_uint`.
344#[cfg(target_os = "espidf")]
345type _RawOpcode = c::c_uint;
346
347// Windows has `ioctlsocket`, which uses `i32`.
348#[cfg(windows)]
349type _RawOpcode = i32;
350