Magisk/pts.c

/*
 * Copyright 2013, Tan Chee Eng (@tan-ce)
 */

 /*
 * pts.c
 *
 * Manages the pseudo-terminal driver on Linux/Android and provides some
 * helper functions to handle raw input mode and terminal window resizing
 */

#define _GNU_SOURCE 
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>
#include <termios.h>
#include <errno.h>
#include <pthread.h>

#include "magisk.h"
#include "pts.h"

/**
 * Helper functions
 */
// Ensures all the data is written out
static int write_blocking(int fd, char *buf, ssize_t bufsz) {
	ssize_t ret, written;

	written = 0;
	do {
		ret = write(fd, buf + written, bufsz - written);
		if (ret == -1) return -1;
		written += ret;
	} while (written < bufsz);

	return 0;
}

/**
 * Pump data from input FD to output FD. If close_output is
 * true, then close the output FD when we're done.
 */
static void pump_ex(int input, int output, int close_output) {
	char buf[4096];
	int len;
	while ((len = read(input, buf, 4096)) > 0) {
		if (write_blocking(output, buf, len) == -1) break;
	}
	close(input);
	if (close_output) close(output);
}

/**
 * Pump data from input FD to output FD. Will close the
 * output FD when done.
 */
static void pump(int input, int output) {
	pump_ex(input, output, 1);
}

static void* pump_thread(void* data) {
	int* files = (int*)data;
	int input = files[0];
	int output = files[1];
	pump(input, output);
	free(data);
	return NULL;
}

static void pump_async(int input, int output) {
	pthread_t writer;
	int* files = (int*)malloc(sizeof(int) * 2);
	if (files == NULL) {
		exit(-1);
	}
	files[0] = input;
	files[1] = output;
	pthread_create(&writer, NULL, pump_thread, files);
}


/**
 * pts_open
 *
 * Opens a pts device and returns the name of the slave tty device.
 *
 * Arguments
 * slave_name       the name of the slave device
 * slave_name_size  the size of the buffer passed via slave_name
 *
 * Return Values
 * on failure either -2 or -1 (errno set) is returned.
 * on success, the file descriptor of the master device is returned.
 */
int pts_open(char *slave_name, size_t slave_name_size) {
	int fdm;
	char sn_tmp[256];

	// Open master ptmx device
	fdm = open("/dev/ptmx", O_RDWR);
	if (fdm == -1)
		goto error;

	// Get the slave name
	if (ptsname_r(fdm, slave_name, slave_name_size-1))
		goto error;

	slave_name[slave_name_size - 1] = '\0';

	// Grant, then unlock
	if (grantpt(fdm) == -1)
		goto error;

	if (unlockpt(fdm) == -1)
		goto error;

	return fdm;
error:
	close(fdm);
	PLOGE("pts_open");
	return -1;
}

// Stores the previous termios of stdin
static struct termios old_stdin;
static int stdin_is_raw = 0;

/**
 * set_stdin_raw
 *
 * Changes stdin to raw unbuffered mode, disables echo, 
 * auto carriage return, etc.
 *
 * Return Value
 * on failure -1, and errno is set
 * on success 0
 */
int set_stdin_raw(void) {
	struct termios new_termios;

	// Save the current stdin termios
	if (tcgetattr(STDIN_FILENO, &old_stdin) < 0) {
		return -1;
	}

	// Start from the current settings
	new_termios = old_stdin;

	// Make the terminal like an SSH or telnet client
	new_termios.c_iflag |= IGNPAR;
	new_termios.c_iflag &= ~(ISTRIP | INLCR | IGNCR | ICRNL | IXON | IXANY | IXOFF);
	new_termios.c_lflag &= ~(ISIG | ICANON | ECHO | ECHOE | ECHOK | ECHONL);
	new_termios.c_oflag &= ~OPOST;
	new_termios.c_cc[VMIN] = 1;
	new_termios.c_cc[VTIME] = 0;

	if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &new_termios) < 0) {
		return -1;
	}

	stdin_is_raw = 1;

	return 0;
}

/**
 * restore_stdin
 *
 * Restore termios on stdin to the state it was before
 * set_stdin_raw() was called. If set_stdin_raw() was
 * never called, does nothing and doesn't return an error.
 *
 * This function is async-safe.
 *
 * Return Value
 * on failure, -1 and errno is set
 * on success, 0
 */
int restore_stdin(void) {
	if (!stdin_is_raw) return 0;

	if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &old_stdin) < 0) {
		return -1;
	}

	stdin_is_raw = 0;

	return 0;
}

// Flag indicating whether the sigwinch watcher should terminate.
static volatile int closing_time = 0;

/**
 * Thread process. Wait for a SIGWINCH to be received, then update 
 * the terminal size.
 */
static void *watch_sigwinch(void *data) {
	sigset_t winch;
	int sig;
	int master = ((int *)data)[0];
	int slave = ((int *)data)[1];

	sigemptyset(&winch);
	sigaddset(&winch, SIGWINCH);

	do {
		if (closing_time) break;

		// Get the new terminal size
		struct winsize w;
		if (ioctl(master, TIOCGWINSZ, &w) == -1) {
			continue;
		}

		// Set the new terminal size
		ioctl(slave, TIOCSWINSZ, &w);

	} while (sigwait(&winch, &sig) == 0);

	free(data);
	return NULL;
}

/**
 * watch_sigwinch_async
 *
 * After calling this function, if the application receives
 * SIGWINCH, the terminal window size will be read from 
 * "input" and set on "output".
 *
 * NOTE: This function blocks SIGWINCH and spawns a thread.
 * NOTE 2: This function must be called before any of the
 *         pump functions.
 *
 * Arguments
 * master   A file descriptor of the TTY window size to follow
 * slave    A file descriptor of the TTY window size which is
 *          to be set on SIGWINCH
 *
 * Return Value
 * on failure, -1 and errno will be set. In this case, no
 *      thread has been spawned and SIGWINCH will not be 
 *      blocked.
 * on success, 0
 */
int watch_sigwinch_async(int master, int slave) {
	pthread_t watcher;
	int *files = (int *) malloc(sizeof(int) * 2);
	if (files == NULL) {
		return -1;
	}

	// Block SIGWINCH so sigwait can later receive it
	sigset_t winch;
	sigemptyset(&winch);
	sigaddset(&winch, SIGWINCH);
	if (sigprocmask(SIG_BLOCK, &winch, NULL) == -1) {
		free(files);
		return -1;
	}

	// Initialize some variables, then start the thread
	closing_time = 0;
	files[0] = master;
	files[1] = slave;
	int ret = pthread_create(&watcher, NULL, &watch_sigwinch, files);
	if (ret != 0) {
		free(files);
		errno = ret;
		return -1;
	}

	return 0;
}

/**
 * watch_sigwinch_cleanup
 *
 * Cause the SIGWINCH watcher thread to terminate
 */
void watch_sigwinch_cleanup(void) {
	closing_time = 1;
	raise(SIGWINCH);
}

/**
 * pump_stdin_async
 *
 * Forward data from STDIN to the given FD
 * in a seperate thread
 */
void pump_stdin_async(int outfd) {
	// Put stdin into raw mode
	set_stdin_raw();

	// Pump data from stdin to the PTY
	pump_async(STDIN_FILENO, outfd);
}

/**
 * pump_stdout_blocking
 *
 * Forward data from the FD to STDOUT.
 * Returns when the remote end of the FD closes.
 *
 * Before returning, restores stdin settings.
 */
void pump_stdout_blocking(int infd) {
	// Pump data from stdout to PTY
	pump_ex(infd, STDOUT_FILENO, 0 /* Don't close output when done */);

	// Cleanup
	restore_stdin();
	watch_sigwinch_cleanup();
}