path: root/src/sys/ioctl/mod.rs

//! Provide helpers for making ioctl system calls.
//!
//! This library is pretty low-level and messy. `ioctl` is not fun.
//!
//! What is an `ioctl`?
//! ===================
//!
//! The `ioctl` syscall is the grab-bag syscall on POSIX systems. Don't want to add a new
//! syscall? Make it an `ioctl`! `ioctl` refers to both the syscall, and the commands that can be
//! sent with it. `ioctl` stands for "IO control", and the commands are always sent to a file
//! descriptor.
//!
//! It is common to see `ioctl`s used for the following purposes:
//!
//!   * Provide read/write access to out-of-band data related to a device such as configuration
//!     (for instance, setting serial port options)
//!   * Provide a mechanism for performing full-duplex data transfers (for instance, xfer on SPI
//!     devices).
//!   * Provide access to control functions on a device (for example, on Linux you can send
//!     commands like pause, resume, and eject to the CDROM device.
//!   * Do whatever else the device driver creator thought made most sense.
//!
//! `ioctl`s are synchronous system calls and are similar to read and write calls in that regard.
//! They operate on file descriptors and have an identifier that specifies what the ioctl is.
//! Additionally they may read or write data and therefore need to pass along a data pointer.
//! Besides the semantics of the ioctls being confusing, the generation of this identifer can also
//! be difficult.
//!
//! Historically `ioctl` numbers were arbitrary hard-coded values. In Linux (before 2.6) and some
//! unices this has changed to a more-ordered system where the ioctl numbers are partitioned into
//! subcomponents (For linux this is documented in
//! [`Documentation/ioctl/ioctl-number.txt`](http://elixir.free-electrons.com/linux/latest/source/Documentation/ioctl/ioctl-number.txt)):
//!
//!   * Number: The actual ioctl ID
//!   * Type: A grouping of ioctls for a common purpose or driver
//!   * Size: The size in bytes of the data that will be transferred
//!   * Direction: Whether there is any data and if it's read, write, or both
//!
//! Newer drivers should not generate complete integer identifiers for their `ioctl`s instead
//! preferring to use the 4 components above to generate the final ioctl identifier. Because of
//! how old `ioctl`s are, however, there are many hard-coded `ioctl` identifiers. These are
//! commonly referred to as "bad" in `ioctl` documentation.
//!
//! Defining ioctls
//! ===============
//!
//! This library provides the `ioctl!` macro, for binding `ioctl`s. This macro generates public
//! unsafe functions that can then be used for calling the ioctl. This macro has a few different
//! ways it can be used depending on the specific ioctl you're working with.
//!
//! A simple `ioctl` is `SPI_IOC_RD_MODE`. This ioctl works with the SPI interface on Linux. This
//! specific `ioctl` reads the mode of the SPI device as a `u8`. It's declared in
//! `/include/uapi/linux/spi/spidev.h` as `_IOR(SPI_IOC_MAGIC, 1, __u8)`. Since it uses the `_IOR`
//! macro, we know it's a `read` ioctl and can use the `ioctl!` macro as follows:
//!
//! ```
//! # #[macro_use] extern crate nix;
//! const SPI_IOC_MAGIC: u8 = b'k'; // Defined in linux/spi/spidev.h
//! const SPI_IOC_TYPE_MODE: u8 = 1;
//! ioctl!(read spi_read_mode with SPI_IOC_MAGIC, SPI_IOC_TYPE_MODE; u8);
//! # fn main() {}
//! ```
//!
//! This generates the function:
//!
//! ```
//! # #[macro_use] extern crate nix;
//! # use std::mem;
//! # use nix::{Errno, libc, Result};
//! # use nix::libc::c_int as c_int;
//! # const SPI_IOC_MAGIC: u8 = b'k'; // Defined in linux/spi/spidev.h
//! # const SPI_IOC_TYPE_MODE: u8 = 1;
//! pub unsafe fn spi_read_mode(fd: c_int, data: *mut u8) -> Result<c_int> {
//!     let res = libc::ioctl(fd, ior!(SPI_IOC_MAGIC, SPI_IOC_TYPE_MODE, mem::size_of::<u8>()), data);
//!     Errno::result(res)
//! }
//! # fn main() {}
//! ```
//!
//! The return value for `ioctl` functions generated by the `ioctl!` macro are `nix::Error`s.
//! These are generated by assuming the return value of the ioctl is `-1` on error and everything
//! else is a valid return value. If this is not the case, `Result::map` can be used to map some
//! of the range of "good" values (-2..-Inf, 0..Inf) into a smaller range in a helper function.
//!
//! The mode for a given `ioctl` should be clear from the documentation if it has good
//! documentation. Otherwise it will be clear based on the macro used to generate the `ioctl`
//! number where `_IO`, `_IOR`, `_IOW`, and `_IORW` map to "none", "read", "write_*", and "readwrite"
//! respectively. To determine the specific `write_` variant to use you'll need to find
//! what the argument type is supposed to be. If it's an `int`, then `write_int` should be used,
//! otherwise it should be a pointer and `write_ptr` should be used. On Linux the
//! [`ioctl_list` man page](http://man7.org/linux/man-pages/man2/ioctl_list.2.html) describes a
//! large number of `ioctl`s and describes their argument data type.
//!
//! More examples on using `ioctl!` can be found in the [rust-spidev crate](https://github.com/rust-embedded/rust-spidev).
//!
//! ```text
//! pub unsafe fn $NAME(fd: c_int, val: *mut u8, len: usize) -> Result<c_int>;
//! ```
//!
//! As mentioned earlier, there are many old `ioctl`s that do not use the newer method of
//! generating `ioctl` numbers and instead use hardcoded values. These can be used with the `bad`
//! form of the `ioctl!` macro (there is no data transfer direction used with `bad`). The naming of
//! this comes from the Linux kernel which refers to these `ioctl`s as "bad".
//!
//! For example the `TCGETS` `ioctl` reads a `termios` data structure for a given file descriptor.
//! It can be implemented as:
//!
//! ```
//! # #[macro_use] extern crate nix;
//! # #[cfg(any(target_os = "android", target_os = "linux"))]
//! # use nix::libc::TCGETS as TCGETS;
//! # #[cfg(any(target_os = "android", target_os = "linux"))]
//! ioctl!(bad tcgets with TCGETS);
//! # fn main() {}
//! ```
//!
//! The generated function has the same form as that generated by `read`:
//!
//! ```text
//! pub unsafe fn tcgets(fd: c_int, val: *mut u8) -> Result<c_int>;
//! ```
//!
//! There is also a `bad none` form for use with hard-coded `ioctl`s that do not transfer data.
//! The `TIOCEXCL` `ioctl` that's part of the termios API can be implemented as:
//!
//! ```
//! # #[macro_use] extern crate nix;
//! # use nix::libc::TIOCEXCL as TIOCEXCL;
//! ioctl!(bad none tiocexcl with TIOCEXCL);
//! # fn main() {}
//! ```
//!
//! More examples on using `ioctl!` can be found in the [rust-spidev crate](https://github.com/rust-embedded/rust-spidev).
//!
//! Finding ioctl documentation
//! ---------------------------
//!
//! For Linux, look at your system's headers. For example, `/usr/include/linux/input.h` has a lot
//! of lines defining macros which use `_IO`, `_IOR`, `_IOW`, `_IOC`, and `_IORW`. Some `ioctl`s are
//! documented directly in the headers defining their constants, but others have more extensive
//! documentation in man pages (like termios' `ioctl`s which are in `tty_ioctl(4)`).
#[cfg(any(target_os = "linux", target_os = "android"))]
#[path = "platform/linux.rs"]
#[macro_use]
mod platform;

#[cfg(any(target_os = "macos",
          target_os = "ios",
          target_os = "netbsd",
          target_os = "openbsd",
          target_os = "freebsd",
          target_os = "dragonfly"))]
#[path = "platform/bsd.rs"]
#[macro_use]
mod platform;

pub use self::platform::*;

/// Convert raw ioctl return value to a Nix result
#[macro_export]
#[doc(hidden)]
macro_rules! convert_ioctl_res {
    ($w:expr) => (
        {
            $crate::Errno::result($w)
        }
    );
}

/// Generates ioctl functions. See [::sys::ioctl](sys/ioctl/index.html).
#[macro_export]
macro_rules! ioctl {
    (bad $name:ident with $nr:expr) => (
        pub unsafe fn $name(fd: $crate::libc::c_int,
                            data: *mut u8)
                            -> $crate::Result<$crate::libc::c_int> {
            convert_ioctl_res!($crate::libc::ioctl(fd, $nr as $crate::sys::ioctl::ioctl_num_type, data))
        }
        );
    (bad none $name:ident with $nr:expr) => (
        pub unsafe fn $name(fd: $crate::libc::c_int)
                            -> $crate::Result<$crate::libc::c_int> {
            convert_ioctl_res!($crate::libc::ioctl(fd, $nr as $crate::sys::ioctl::ioctl_num_type))
        }
        );
    (none $name:ident with $ioty:expr, $nr:expr) => (
        pub unsafe fn $name(fd: $crate::libc::c_int)
                            -> $crate::Result<$crate::libc::c_int> {
            convert_ioctl_res!($crate::libc::ioctl(fd, io!($ioty, $nr) as $crate::sys::ioctl::ioctl_num_type))
        }
        );
    (read $name:ident with $ioty:expr, $nr:expr; $ty:ty) => (
        pub unsafe fn $name(fd: $crate::libc::c_int,
                            val: *mut $ty)
                            -> $crate::Result<$crate::libc::c_int> {
            convert_ioctl_res!($crate::libc::ioctl(fd, ior!($ioty, $nr, ::std::mem::size_of::<$ty>()) as $crate::sys::ioctl::ioctl_num_type, val))
        }
        );
    (write $name:ident with $ioty:expr, $nr:expr; $ty:ty) => (
        pub unsafe fn $name(fd: $crate::libc::c_int,
                            val: $ty)
                            -> $crate::Result<$crate::libc::c_int> {
            convert_ioctl_res!($crate::libc::ioctl(fd, iow!($ioty, $nr, ::std::mem::size_of::<$ty>()) as $crate::sys::ioctl::ioctl_num_type, val))
        }
        );
    (readwrite $name:ident with $ioty:expr, $nr:expr; $ty:ty) => (
        pub unsafe fn $name(fd: $crate::libc::c_int,
                            val: *mut $ty)
                            -> $crate::Result<$crate::libc::c_int> {
            convert_ioctl_res!($crate::libc::ioctl(fd, iorw!($ioty, $nr, ::std::mem::size_of::<$ty>()) as $crate::sys::ioctl::ioctl_num_type, val))
        }
        );
    (read buf $name:ident with $ioty:expr, $nr:expr; $ty:ty) => (
        pub unsafe fn $name(fd: $crate::libc::c_int,
                            val: *mut $ty,
                            len: usize)
                            -> $crate::Result<$crate::libc::c_int> {
            convert_ioctl_res!($crate::libc::ioctl(fd, ior!($ioty, $nr, len) as $crate::sys::ioctl::ioctl_num_type, val))
        }
        );
    (write buf $name:ident with $ioty:expr, $nr:expr; $ty:ty) => (
        pub unsafe fn $name(fd: $crate::libc::c_int,
                            val: *const $ty,
                            len: usize) -> $crate::Result<$crate::libc::c_int> {
            convert_ioctl_res!($crate::libc::ioctl(fd, iow!($ioty, $nr, len) as $crate::sys::ioctl::ioctl_num_type, val))
        }
        );
    (readwrite buf $name:ident with $ioty:expr, $nr:expr; $ty:ty) => (
        pub unsafe fn $name(fd: $crate::libc::c_int,
                            val: *mut $ty,
                            len: usize)
                            -> $crate::Result<$crate::libc::c_int> {
            convert_ioctl_res!($crate::libc::ioctl(fd, iorw!($ioty, $nr, len) as $crate::sys::ioctl::ioctl_num_type, val))
        }
        );
}