mouse bouncer

usb-pause.c

// SPDX-License-Identifier: GPL-2.0-or-later
// 
// looooosely based on usbip_unbind.c and sysfs_utils.c from the Linux source

// This C code is for replicating this kind of behavior from the shell:
//   sudo sh -c 'echo 8-1 > /sys/bus/usb/drivers/usb/unbind'
//   sleep 30
//   sudo sh -c 'echo 8-1 > /sys/bus/usb/drivers/usb/bind'

// I use that to bounce my wireless mouse to the receiver on another computer.

// Building this as an executable rather than a shell script means that I can
// give it root ownership and setuid so that I don't need to enter the root
// password, therefore I can bind it to a keyboard shortcut.


#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>


static const char usage_string[] =
    "usb-pause <id> [<seconds>]\n"
    "    <id> is bus and device in format such as \"8-1\"\n"
    "    <seconds> is number of seconds to pause; 30 if not specified\n";

void usage(void)
{
    printf("usage: %s", usage_string);
}

int write_sysfs(const char *attr_path, const char *new_value, size_t len)
{
    int fd;
    int length;

    fd = open(attr_path, O_WRONLY);
    if (fd < 0) {
        //fprintf(stderr, "error opening %s\n", attr_path);
        return -1;
    }

    length = write(fd, new_value, len);
    if (length < 0) {
        //fprintf(stderr, "error writing to %s\n", attr_path);
        close(fd);
        return -1;
    }

    close(fd);

    return 0;
}

int pause_device(char *id, int seconds)
{
    int rc;

    rc = write_sysfs("/sys/bus/usb/drivers/usb/unbind", id, strlen(id));
    if (rc < 0) {
        fprintf(stderr, "error pausing device %s\n", id);
        return -1;
    }

    printf("pausing device for %d seconds...\n", seconds);
    sleep(seconds);

    rc = write_sysfs("/sys/bus/usb/drivers/usb/bind", id, strlen(id));
    if (rc < 0) {
        fprintf(stderr, "error unpausing device %s\n", id);
        return -1;
    }

    printf("...done\n");

    return 0;
}

int main(int argc, char *argv[])
{
    int seconds = 30;

    if (argc < 2 || argc > 3) {
        usage();
        return -1;
    }

    if (argc == 3) {
        seconds = atoi(argv[2]);
    }

    return pause_device(argv[1], seconds);
}