WIP: Use USB hot-plugging to detect devices as they come and go

... if only it was working

Change-Id: I6fddd62ce015dbf0151563e514a7bdf20ed01810

src/osmo-e1d.c

@@ -194,7 +194,7 @@ int main(int argc, char *argv[])
 	}
 
 	/* probe devices */
-	rv = e1_usb_probe(e1d);
+	rv = e1_usb_init(e1d);
 	if (rv != 0) {
 		LOGP(DE1D, LOGL_ERROR, "Failed to prove usb devices\n");
 	}

src/osmo-e1gen.c

@@ -422,7 +422,7 @@ int main(int argc, char **argv)
 	e1gen_init();
 
 	/* probe devices */
-	rv = e1_usb_probe(e1d);
+	rv = e1_usb_init(e1d);
 	if (rv != 0) {
 		LOGP(DE1D, LOGL_ERROR, "Failed to prove usb devices\n");
 	}

src/usb.c

@@ -960,12 +960,107 @@ next_interface:
 	return 0;
 }
 
-int
-e1_usb_probe(struct e1_daemon *e1d)
+static int
+_libusb_hotplug_cb(libusb_context *ctx, libusb_device *device, libusb_hotplug_event event, void *user_data)
 {
-	struct libusb_device **dev_list;
-	ssize_t n_dev;
-	int i, ret;
+	struct libusb_device_descriptor desc;
+	struct e1_daemon *e1d = user_data;
+	int ret;
+
+	switch (event) {
+	case LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED:
+		ret = libusb_get_device_descriptor(device, &desc);
+		if (ret)
+			break;
+
+		/* a bit  redundant as we register the call-back only for those two, but
+		 * in the future we might support more hardware and extend the checks here
+		 * and drop the matching in the callback registration */
+		if ((desc.idVendor != USB_VID) || (desc.idProduct != USB_PID))
+			break;
+
+		LOGP(DE1D, LOGL_NOTICE, "HOTPLUG: USB Device plugged in\n");
+		_e1_usb_open_device(e1d, device);
+		break;
+	case LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT:
+		LOGP(DE1D, LOGL_NOTICE, "HOTPLUG: USB Device removed\n");
+		/* TODO: iterate over list of interfaces, check for driver + usb-dev, ... */
+		break;
+	}
+
+	return 0;
+}
+
+/***********************************************************************
+ * BEGIN libosmocore <= 1.6.0 workaround
+ ***********************************************************************/
+
+#include <poll.h>
+
+static int _osmo_usb_fd_cb(struct osmo_fd *ofd, unsigned int what)
+{
+	libusb_context *luctx = ofd->data;
+
+	/* we assume that we're running Linux v2.6.27 with timerfd support here
+	 * and hence don't have to perform manual timeout handling.  See
+	 * "Notes on time-based events" at
+	 * http://libusb.sourceforge.net/api-1.0/group__libusb__poll.html */
+	struct timeval zero_tv = { 0, 0 };
+	libusb_handle_events_timeout(luctx, &zero_tv);
+
+	return 0;
+}
+
+static void _osmo_usb_added_cb(int fd, short events, void *user_data)
+{
+	struct osmo_fd *ofd = talloc_zero(OTC_GLOBAL, struct osmo_fd);
+	libusb_context *luctx = user_data;
+	unsigned int when = 0;
+	int rc;
+
+	LOGP(DLINP, LOGL_ERROR, "Adding fd=%u, events=0x%02x\n", fd, events);
+
+	if (events & POLLIN)
+		when |= OSMO_FD_READ;
+	if (events & POLLOUT)
+		when |= OSMO_FD_WRITE;
+
+	osmo_fd_setup(ofd, fd, when, _osmo_usb_fd_cb, luctx, 0);
+	rc = osmo_fd_register(ofd);
+	if (rc)
+		LOGP(DLINP, LOGL_ERROR, "osmo_fd_register() failed with rc=%d\n", rc);
+}
+
+/* work around a bug in all libosmocore versions <= 1.6.0 caused by misundertanding strange API
+ * requirements of libusb. */
+static void libosmocore_160_workaround(void)
+{
+	const struct libusb_pollfd **pfds;
+
+	/* get the initial file descriptors which were created even before during libusb_init() */
+	pfds = libusb_get_pollfds(g_usb);
+	if (pfds) {
+		const struct libusb_pollfd **pfds2 = pfds;
+		const struct libusb_pollfd *pfd;
+
+		/* synthesize 'add' call-backs. not sure why libusb doesn't do that by itself? */
+		for (pfd = *pfds2; pfd; pfd = *++pfds2) {
+			if (!osmo_fd_get_by_fd(pfd->fd))
+				_osmo_usb_added_cb(pfd->fd, pfd->events, g_usb);
+		}
+		libusb_free_pollfds(pfds);
+	}
+}
+
+/***********************************************************************
+ * END libosmocore <= 1.6.0 workaround
+ ***********************************************************************/
+
+int
+e1_usb_init(struct e1_daemon *e1d)
+{
+	int ret;
+	int events = LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED | LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT;
 
 	if (!g_usb) {
 		ret = osmo_libusb_init(&g_usb);
@@ -973,28 +1068,30 @@ e1_usb_probe(struct e1_daemon *e1d)
 			LOGP(DE1D, LOGL_ERROR, "Failed to initialize libusb\n");
 			return -EIO;
 		}
+		libosmocore_160_workaround();
 	}
 
-	n_dev = libusb_get_device_list(g_usb, &dev_list);
-	if (n_dev < 0) {
-		LOGP(DE1D, LOGL_ERROR, "Failed to list devices\n");
-		return -EIO;
+	if (libusb_has_capability(LIBUSB_CAP_HAS_HOTPLUG)) {
+		ret = libusb_hotplug_register_callback(g_usb, events, LIBUSB_HOTPLUG_ENUMERATE, LIBUSB_HOTPLUG_MATCH_ANY, LIBUSB_HOTPLUG_MATCH_ANY,
+							LIBUSB_HOTPLUG_MATCH_ANY, _libusb_hotplug_cb, e1d, NULL);
+		if (ret != LIBUSB_SUCCESS) {
+			LOGP(DE1D, LOGL_ERROR, "Failed to register USB hot plug call-back\n");
+			return -EIO;
+		}
+	} else {
+		/* no hot-plug capability, fall back to iterating devices once */
+		struct libusb_device **dev_list;
+		ssize_t n_dev, i;
+
+		n_dev = libusb_get_device_list(g_usb, &dev_list);
+		if (n_dev < 0) {
+			LOGP(DE1D, LOGL_ERROR, "Failed to list devices\n");
+			return -EIO;
+		}
+
+		for (i = 0; i < n_dev; i++)
+			_libusb_hotplug_cb(g_usb, dev_list[i], LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED, e1d);
 	}
 
-	for (i = 0; i < n_dev; i++) {
-		struct libusb_device_descriptor desc;
-
-		ret = libusb_get_device_descriptor(dev_list[i], &desc);
-		if (ret)
-			continue;
-
-		if ((desc.idVendor != USB_VID) || (desc.idProduct != USB_PID))
-			continue;
-
-		_e1_usb_open_device(e1d, dev_list[i]);
-	}
-
-	libusb_free_device_list(dev_list, 1);
-
 	return 0;
 }

src/usb.h

@@ -18,4 +18,4 @@ int e1_usb_ctrl_get_gpsdo_status(struct e1_intf *intf);
 
 int e1_usb_intf_gpsdo_state_string(char *buf, size_t len, const struct e1_intf *intf);
 
-int e1_usb_probe(struct e1_daemon *e1d);
+int e1_usb_init(struct e1_daemon *e1d);