Cannot make USBDEVFS_DISCSIGNAL work

[Alon Bar-Lev <alon.barlev@xxxxxxxxx>]

Hello,

I am trying to detect USB device removal using its file descriptor within
the /dev/bus/usb/999/999 filesystem.

I believe this is why the USBDEVFS_DISCSIGNAL ioctl is available.

But it looks like the poll never wakes up and the signal is never called.

I noticed some people who succeeded in making this work, but I cannot figure
out what is wrong.

I am using linux-2.6.28.

Can anyone help? Maybe there is a different way to achieve this task.

Thank you,
Alon.

---

#include <sys/ioctl.h>
#include <sys/poll.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <unistd.h>
#include <fcntl.h>
#include <linux/usbdevice_fs.h>

#define USB_DISCONNECT_SIGNAL (SIGRTMIN)

static void disconnect_action( int sig_num, siginfo_t *sinfo, void *pinfo)
{
	(void)sig_num;(void)sinfo;(void)pinfo;
	printf("SIGNAL!\n");
}

int main(int argc, char *argv[]) {
	struct sigaction act;
	struct usbdevfs_disconnectsignal ds;
	struct pollfd pfd;
	char *device;
	int fd;

	if (argc != 2) {
		printf("Usage: device\n");
		exit(1);
	}
	device = argv[1];

        if ((fd = open(device, O_RDWR)) == -1) {
		perror("open");
		exit(1);
	}

	if (sigaction(USB_DISCONNECT_SIGNAL, NULL, &act) == -1) {
		perror("sigaction");
		exit(1);
	}
	act.sa_sigaction = disconnect_action;
	act.sa_flags = SA_SIGINFO;
	if (sigaction(USB_DISCONNECT_SIGNAL, &act, NULL) == -1) {
		perror("sigaction");
		exit(1);
	}

	memset(&ds, 0, sizeof(ds));
	ds.signr = USB_DISCONNECT_SIGNAL;
	if (ioctl(fd, USBDEVFS_DISCSIGNAL, &ds) == -1) {
		perror("ioctl");
		exit(1);
	}

	pfd.fd = fd;
	pfd.events = POLLIN | POLLOUT;
	printf("Before poll\n");
	if (poll(&pfd, 1, -1) == -1) {
		perror("poll");
		exit(1);
	}
	printf("After poll\n");

	close(fd);
	return 0;
}

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