How to control mouse movement in linux?

Question

I try to control the mouse in Linux. Xlib seems to works, but when I try to use it with OpenCV, it keeps returning:

Resource temporarily unavailable

So I decide to write "/dev/psaux". The code is as following:

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


int main() {
    unsigned char a[5]={0, 0xff, 0, 0x28, 0xff};
    int fp = open ("/dev/psaux", O_WRONLY);
    if(!fp)printf("open error:%s\n", strerror(errno));
    for(int i = 0; i < 10; i++)
        printf("write:%d\t\t%s\n", write(fp, a, 5), strerror(errno));
    close(fp);
    return 0;
}

Compile it with:

gcc  my_psaux.c -o my_psaux -std=gnu99 -g

Run and get

$sudo ./my_psaux 
write:5    Success
write:5    Success
write:5    Success
write:5    Success
write:5    Success
write:5    Success
write:5    Success
write:5    Success
write:5    Success
write:5    Success

However the mouse doesn't move. Then I open a new terminal, type in "sudo cat /dev/psaux" and run "my_psaux". But I just cat nothing. Nothing is written into "/dev/psaux" ?

Could anyone help me?

If this is not a good method to control the mouse, could anyone tell me another one?

Answer 1

The mouse is not a loopback/echo device. It's more like a terminal. Would you expect writing data to a terminal (which would appear on the screen) to make the same characters come back to you as input? The same applies to the mouse; the only point in writing to it is to send escape sequences that change its mode (e.g. the protocol used or the resolution).

If you want to "control" the mouse, you have to inject events some other way, or provide a fifo (named pipe) or pseudo-tty in place of /dev/psaux for the input system to read from. However this is probably a rather misguided way to do things...

If you explain why you need to control the mouse, perhaps we could offer you better alternative approaches to what you're trying to do.

Answer 2

Great thanks to @R.. for reminding me of some other ways instead of /dev/psaux

So I tried /dev/input/mouse* and /dev/input/event*

By using

cat /proc/bus/input/devices 

I get this:

I: Bus=0003 Vendor=0461 Product=4d81 Version=0111
N: Name="USB Optical Mouse"
P: Phys=usb-0000:00:1d.0-1/input0
S: Sysfs=/devices/pci0000:00/0000:00:1d.0/usb6/6-1/6-1:1.0/input/input10
U: Uniq=
H: Handlers=mouse2 event10 
B: EV=17
B: KEY=70000 0 0 0 0 0 0 0 0
B: REL=143
B: MSC=10

After testing, only /dev/input/event10 works. The code is as following:

#include <stdio.h>
#include <unistd.h>
#include <linux/input.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>

int main() {
  struct input_event event, event_end;

  int fd = open("/dev/input/event10", O_RDWR);
  if (fd < 0) {
    printf("Errro open mouse:%s\n", strerror(errno));
    return -1;
  }
  memset(&event, 0, sizeof(event));
  memset(&event, 0, sizeof(event_end));
  gettimeofday(&event.time, NULL);
  event.type = EV_REL;
  event.code = REL_X;
  event.value = 100;
  gettimeofday(&event_end.time, NULL);
  event_end.type = EV_SYN;
  event_end.code = SYN_REPORT;
  event_end.value = 0;
  for (int i=0; i<5; i++) {
    write(fd, &event, sizeof(event));// Move the mouse
    write(fd, &event_end, sizeof(event_end));// Show move
    sleep(1);// wait
  }
  close(fd);
  return 0;
}