Add termios constant for VDISABLE

_POSIX_VDISABLE is an extension that disables terminal special
characters.

See:
* redox-os/termios!3
* redox-os/base!27

src/header/fcntl/linux.rs

@@ -6,6 +6,7 @@ pub const O_RDWR: c_int = 0x0002;
 pub const O_ACCMODE: c_int = 0x0003;
 pub const O_CREAT: c_int = 0x0040;
 pub const O_EXCL: c_int = 0x0080;
+pub const O_NOCTTY: c_int = 0x0100;
 pub const O_TRUNC: c_int = 0x0200;
 pub const O_APPEND: c_int = 0x0400;
 pub const O_NONBLOCK: c_int = 0x0800;

src/header/pty/linux.rs

@@ -5,10 +5,8 @@ use crate::{
 };
 
 pub(super) unsafe fn openpty(name: &mut [u8]) -> Result<(c_int, c_int), ()> {
-    const O_NOCTTY: c_int = 0x100;
-
     //TODO: wrap in auto-close struct
-    let master = fcntl::open(c"/dev/ptmx".as_ptr(), fcntl::O_RDWR | O_NOCTTY, 0);
+    let master = fcntl::open(c"/dev/ptmx".as_ptr(), fcntl::O_RDWR | fcntl::O_NOCTTY, 0);
     if master < 0 {
         return Err(());
     }
@@ -40,7 +38,7 @@ pub(super) unsafe fn openpty(name: &mut [u8]) -> Result<(c_int, c_int), ()> {
 
     let slave = fcntl::open(
         cursor.get_ref().as_ptr() as *const c_char,
-        fcntl::O_RDWR | O_NOCTTY,
+        fcntl::O_RDWR | fcntl::O_NOCTTY,
         0,
     );
     if slave < 0 {

src/header/termios/linux.rs

@@ -111,3 +111,7 @@ pub const NOFLSH: usize = 0o000_200;
 pub const TOSTOP: usize = 0o000_400;
 pub const IEXTEN: usize = 0o100_000;
 /* } c_lflag */
+
+// POSIX extensions
+/// Sentinel value to disable a control char.
+pub const _POSIX_VDISABLE: u8 = 0;

src/header/termios/redox.rs

@@ -104,3 +104,7 @@ pub const NOFLSH: usize = 0x8000_0000;
 pub const TOSTOP: usize = 0x0040_0000;
 pub const IEXTEN: usize = 0x0000_0400;
 /* } c_lflag */
+
+// POSIX extensions
+/// Sentinel value to disable a control char.
+pub const _POSIX_VDISABLE: u8 = 0;

src/header/unistd/pathconf.rs

@@ -1,5 +1,5 @@
 use crate::{
-    header::errno,
+    header::{errno, termios::_POSIX_VDISABLE},
     platform::{self, types::*},
 };
 
@@ -11,6 +11,7 @@ pub const _PC_PATH_MAX: c_int = 4;
 pub const _PC_PIPE_BUF: c_int = 5;
 pub const _PC_CHOWN_RESTRICTED: c_int = 6;
 pub const _PC_NO_TRUNC: c_int = 7;
+/// Check if file (terminal) supports disabling control chars (CC)
 pub const _PC_VDISABLE: c_int = 8;
 pub const _PC_SYNC_IO: c_int = 9;
 pub const _PC_ASYNC_IO: c_int = 10;
@@ -36,7 +37,7 @@ fn pc(name: c_int) -> c_long {
         _PC_PIPE_BUF => 4096,
         _PC_CHOWN_RESTRICTED => 1,
         _PC_NO_TRUNC => 1,
-        _PC_VDISABLE => 0,
+        _PC_VDISABLE => _POSIX_VDISABLE.into(),
         _PC_SYNC_IO => 1,
         _PC_ASYNC_IO => -1,
         _PC_PRIO_IO => -1,

tests/termios.c

@@ -0,0 +1,57 @@
+#include <assert.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <termios.h>
+#include <unistd.h>
+
+int main(void) {
+    // Check that the tty supports VDISABLE
+    int vdisable = pathconf("/dev/tty", _PC_VDISABLE);
+    assert(vdisable == _POSIX_VDISABLE);
+
+    int termfd = open("/dev/tty", O_RDWR, O_NDELAY | O_NOCTTY);
+    if (termfd < 0) {
+        perror("open");
+        return EXIT_FAILURE;
+    }
+
+    // Currently set/default options
+    struct termios termios = {0};
+    if (tcgetattr(termfd, &termios) < 0) {
+        perror("tcgetattr");
+        close(termfd);
+        return EXIT_FAILURE;
+    }
+    struct termios term_restore = termios;
+
+    const cc_t verase = termios.c_cc[VERASE];
+    assert(verase != _POSIX_VDISABLE);
+    // Disable backspace key control char
+    termios.c_cc[VERASE] = _POSIX_VDISABLE;
+
+    if (tcsetattr(termfd, TCSANOW, &termios) < 0) {
+        perror("tcsetattr (setting VDISABLE)");
+        close(termfd);
+        return EXIT_FAILURE;
+    }
+
+    // Check that it was actually set
+    struct termios term_vdisable = {0};
+    if (tcgetattr(termfd, &term_vdisable) < 0) {
+        perror("tcgetattr (after setting VDISABLE)");
+        close(termfd);
+        return EXIT_FAILURE;
+    }
+    assert(term_vdisable.c_cc[VERASE] == _POSIX_VDISABLE);
+
+    // Restore old config
+    if (tcsetattr(termfd, TCSAFLUSH, &term_restore) < 0) {
+        perror("tcsetattr (restoring settings)");
+        close(termfd);
+        return EXIT_FAILURE;
+    }
+
+    close(termfd);
+    return EXIT_SUCCESS;
+}