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Use termios2 on Linux
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The termios2 struct with TCSETS2/TCGETS2 ioctls is the modern way to set
arbitrary baud rates on Linux. This commit does *not* implement custom
baud rates (dcuddeback#49), but lays the groundwork for doing so by replacing the
POSIX termios API with the Linux-specific termios2 API when Linux is the
compilation target.

Since this is an alternative to the termios(3) API, it was necessary to
manually modify baud rates in c_cflags, c_ospeed, and c_ispeed members
of termios2 in order to implement replacements for cfsetspeed(),
cfgetispeed(), and cfgetospeed(). Helpful documentation can be found in
Picocom's writeup of termios2 [1] and drivers/tty/tty_baudrate.c from
the Linux kernel source [2].

No behavior should change due to this commit.

The termios2 struct was added to libc in v0.2.33.

[1]: https://github.com/npat-efault/picocom/blob/1acf1ddabaf3576b4023c4f6f09c5a3e4b086fb8/termios2.txt
[2]: https://github.com/torvalds/linux/blob/ba4dbdedd3edc2798659bcd8b1a184ea8bdd04dc/drivers/tty/tty_baudrate.c#L49-L121
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@dcuddeback @KoffeinFlummi
dcuddeback authored and KoffeinFlummi committed Aug 23, 2020
1 parent 5fe2a1b commit 4587b89
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Showing 2 changed files with 126 additions and 7 deletions.
2 changes: 1 addition & 1 deletion serial-unix/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -13,4 +13,4 @@ categories = ["hardware-support", "os", "os::unix-apis"]

[dependencies]
serial-core = { version = "0.4", path = "../serial-core" }
libc = "0.2.21"
libc = "0.2.33"
131 changes: 125 additions & 6 deletions serial-unix/src/tty.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,60 @@ use libc::{c_int, c_void, size_t};
use core::{SerialDevice, SerialPortSettings};


#[cfg(target_os = "linux")]
const IBSHIFT: usize = 16;

#[cfg(all(target_os = "linux",
not(any(target_env = "musl",
target_env = "android"))))]
#[allow(non_camel_case_types)]
type ioctl_request = libc::c_ulong;

#[cfg(all(target_os = "linux",
any(target_env = "musl",
target_env = "android")))]
#[allow(non_camel_case_types)]
type ioctl_request = libc::c_int;

#[cfg(all(target_os = "linux",
any(target_arch = "x86",
target_arch = "x86_64",
target_arch = "arm",
target_arch = "aarch64",
target_arch = "s390x")))]
// Suppress warning on targets with libc that use c_int for ioctl request type. Binary
// representation is unaffected, so ioctl() will be interpreted correctly.
#[allow(overflowing_literals)]
const TCGETS2: ioctl_request = 0x802C542A;

#[cfg(all(target_os = "linux",
any(target_arch = "x86",
target_arch = "x86_64",
target_arch = "arm",
target_arch = "aarch64",
target_arch = "s390x")))]
const TCSETS2: ioctl_request = 0x402C542B;

#[cfg(all(target_os = "linux",
any(target_arch = "mips",
target_arch = "mips64",
target_arch = "powerpc",
target_arch = "powerpc64",
target_arch = "sparc64")))]
const TCGETS2: ioctl_request = 0x402C542A;

#[cfg(all(target_os = "linux",
any(target_arch = "mips",
target_arch = "mips64",
target_arch = "powerpc",
target_arch = "powerpc64",
target_arch = "sparc64")))]
// Suppress warning on targets with libc that use c_int for ioctl request type. Binary
// representation is unaffected, so ioctl() will be interpreted correctly.
#[allow(overflowing_literals)]
const TCSETS2: ioctl_request = 0x802C542B;


/// A TTY-based serial port implementation.
///
/// The port will be closed when the value is dropped.
Expand Down Expand Up @@ -204,14 +258,26 @@ impl SerialDevice for TTYPort {
use libc::{INLCR, IGNCR, ICRNL, IGNBRK}; // iflags
use libc::{VMIN, VTIME}; // c_cc indexes

let mut termios = unsafe { mem::uninitialized() };
#[cfg(not(target_os = "linux"))]
let mut termios: libc::termios = unsafe { mem::uninitialized() };

#[cfg(target_os = "linux")]
let mut termios: libc::termios2 = unsafe { mem::uninitialized() };

#[cfg(not(target_os = "linux"))]
unsafe {
if libc::tcgetattr(self.fd, &mut termios) < 0 {
return Err(super::error::last_os_error());
}
}

#[cfg(target_os = "linux")]
unsafe {
if libc::ioctl(self.fd, TCGETS2, &mut termios) < 0 {
return Err(super::error::last_os_error());
}
}

// setup TTY for binary serial port access
termios.c_cflag |= CREAD | CLOCAL;
termios.c_lflag &= !(ICANON | ECHO | ECHOE | ECHOK | ECHONL | ISIG | IEXTEN);
Expand All @@ -225,14 +291,26 @@ impl SerialDevice for TTYPort {
}

fn write_settings(&mut self, settings: &TTYSettings) -> core::Result<()> {
use libc::{TCSANOW, TCIOFLUSH};
#[cfg(not(target_os = "linux"))]
use libc::{TCSANOW};
use libc::{TCIOFLUSH};

// write settings to TTY
#[cfg(not(target_os = "linux"))]
unsafe {
if libc::tcsetattr(self.fd, TCSANOW, &settings.termios) < 0 {
return Err(super::error::last_os_error());
}
}

#[cfg(target_os = "linux")]
unsafe {
if libc::ioctl(self.fd, TCSETS2, &settings.termios) < 0 {
return Err(super::error::last_os_error());
}
}

unsafe {
if libc::tcflush(self.fd, TCIOFLUSH) < 0 {
return Err(super::error::last_os_error());
}
Expand Down Expand Up @@ -278,18 +356,30 @@ impl SerialDevice for TTYPort {
/// Serial port settings for TTY devices.
#[derive(Copy,Clone)]
pub struct TTYSettings {
#[cfg(not(target_os = "linux"))]
termios: libc::termios,
#[cfg(target_os = "linux")]
termios: libc::termios2,
}

impl TTYSettings {
#[cfg(not(target_os = "linux"))]
fn new(termios: libc::termios) -> Self {
TTYSettings { termios: termios }
}

#[cfg(target_os = "linux")]
fn new(termios: libc::termios2) -> Self {
TTYSettings { termios: termios }
}
}

impl fmt::Debug for TTYSettings {
fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
#[cfg(not(target_os = "linux"))]
struct TermiosFormatter(libc::termios);
#[cfg(target_os = "linux")]
struct TermiosFormatter(libc::termios2);

impl fmt::Debug for TermiosFormatter {
fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
Expand All @@ -315,7 +405,7 @@ impl SerialPortSettings for TTYSettings {
use libc::{B57600, B115200, B230400};

#[cfg(target_os = "linux")]
use libc::{B460800, B500000, B576000, B921600, B1000000, B1152000, B1500000, B2000000, B2500000, B3000000, B3500000, B4000000};
use libc::{B0, B460800, B500000, B576000, B921600, B1000000, B1152000, B1500000, B2000000, B2500000, B3000000, B3500000, B4000000};

#[cfg(target_os = "macos")]
use libc::{B7200, B14400, B28800, B76800};
Expand All @@ -326,8 +416,27 @@ impl SerialPortSettings for TTYSettings {
#[cfg(target_os = "openbsd")]
use libc::{B7200, B14400, B28800, B76800};

let ospeed = unsafe { libc::cfgetospeed(&self.termios) };
let ispeed = unsafe { libc::cfgetispeed(&self.termios) };
#[cfg(target_os = "linux")]
use libc::CBAUD;

#[cfg(not(target_os = "linux"))]
let (ospeed, ispeed) = unsafe {
(
libc::cfgetospeed(&self.termios),
libc::cfgetispeed(&self.termios),
)
};

#[cfg(target_os = "linux")]
let (ospeed, ispeed) = {
let ospeed = self.termios.c_cflag & CBAUD;
let ispeed = self.termios.c_cflag >> IBSHIFT & CBAUD;

match ispeed {
B0 => (ospeed, ospeed),
_ => (ospeed, ispeed),
}
};

if ospeed != ispeed {
return None;
Expand Down Expand Up @@ -450,7 +559,7 @@ impl SerialPortSettings for TTYSettings {
use libc::{B57600, B115200, B230400};

#[cfg(target_os = "linux")]
use libc::{B460800, B500000, B576000, B921600, B1000000, B1152000, B1500000, B2000000, B2500000, B3000000, B3500000, B4000000};
use libc::{B0, B460800, B500000, B576000, B921600, B1000000, B1152000, B1500000, B2000000, B2500000, B3000000, B3500000, B4000000};

#[cfg(target_os = "macos")]
use libc::{B7200, B14400, B28800, B76800};
Expand All @@ -461,6 +570,9 @@ impl SerialPortSettings for TTYSettings {
#[cfg(target_os = "openbsd")]
use libc::{B7200, B14400, B28800, B76800};

#[cfg(target_os = "linux")]
use libc::CBAUD;

let baud = match baud_rate {
core::BaudOther(50) => B50,
core::BaudOther(75) => B75,
Expand Down Expand Up @@ -516,12 +628,19 @@ impl SerialPortSettings for TTYSettings {
core::BaudOther(_) => return Err(super::error::from_raw_os_error(EINVAL)),
};

#[cfg(not(target_os = "linux"))]
unsafe {
if libc::cfsetspeed(&mut self.termios, baud) < 0 {
return Err(super::error::last_os_error());
}
}

#[cfg(target_os = "linux")]
{
self.termios.c_cflag &= !(CBAUD | CBAUD << IBSHIFT);
self.termios.c_cflag |= baud | B0 << IBSHIFT;
}

Ok(())
}

Expand Down

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