hotplug.c

/* -*- Mode: C; indent-tabs-mode:t ; c-basic-offset:8 -*- */
/*
 * Hotplug functions for libusb
 * Copyright © 2012-2021 Nathan Hjelm <hjelmn@mac.com>
 * Copyright © 2012-2013 Peter Stuge <peter@stuge.se>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "libusbi.h"

/**
 * @defgroup libusb_hotplug Device hotplug event notification
 * This page details how to use the libusb hotplug interface, where available.
 *
 * Be mindful that not all platforms currently implement hotplug notification and
 * that you should first call on \ref libusb_has_capability() with parameter
 * \ref LIBUSB_CAP_HAS_HOTPLUG to confirm that hotplug support is available.
 *
 * \page libusb_hotplug Device hotplug event notification
 *
 * \section hotplug_intro Introduction
 *
 * Version 1.0.16, \ref LIBUSBX_API_VERSION >= 0x01000102, has added support
 * for hotplug events on <b>some</b> platforms (you should test if your platform
 * supports hotplug notification by calling \ref libusb_has_capability() with
 * parameter \ref LIBUSB_CAP_HAS_HOTPLUG).
 *
 * This interface allows you to request notification for the arrival and departure
 * of matching USB devices.
 *
 * To receive hotplug notification you register a callback by calling
 * \ref libusb_hotplug_register_callback(). This function will optionally return
 * a callback handle that can be passed to \ref libusb_hotplug_deregister_callback().
 *
 * A callback function must return an int (0 or 1) indicating whether the callback is
 * expecting additional events. Returning 0 will rearm the callback and 1 will cause
 * the callback to be deregistered. Note that when callbacks are called from
 * libusb_hotplug_register_callback() because of the \ref LIBUSB_HOTPLUG_ENUMERATE
 * flag, the callback return value is ignored. In other words, you cannot cause a
 * callback to be deregistered by returning 1 when it is called from
 * libusb_hotplug_register_callback().
 *
 * Callbacks for a particular context are automatically deregistered by libusb_exit().
 *
 * As of 1.0.16 there are two supported hotplug events:
 *  - LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED: A device has arrived and is ready to use
 *  - LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT: A device has left and is no longer available
 *
 * A hotplug event can listen for either or both of these events.
 *
 * Note: If you receive notification that a device has left and you have any
 * libusb_device_handles for the device it is up to you to call libusb_close()
 * on each device handle to free up any remaining resources associated with the device.
 * Once a device has left any libusb_device_handle associated with the device
 * are invalid and will remain so even if the device comes back.
 *
 * When handling a LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED event it is considered
 * safe to call any libusb function that takes a libusb_device. It also safe to
 * open a device and submit asynchronous transfers. However, most other functions
 * that take a libusb_device_handle are <b>not</b> safe to call. Examples of such
 * functions are any of the \ref libusb_syncio "synchronous API" functions or the blocking
 * functions that retrieve various \ref libusb_desc "USB descriptors". These functions must
 * be used outside of the context of the hotplug callback.
 *
 * When handling a LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT event the only safe function
 * is libusb_get_device_descriptor().
 *
 * The following code provides an example of the usage of the hotplug interface:
\code
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <libusb.h>

static int count = 0;

int hotplug_callback(struct libusb_context *ctx, struct libusb_device *dev,
                     libusb_hotplug_event event, void *user_data) {
  static libusb_device_handle *dev_handle = NULL;
  struct libusb_device_descriptor desc;
  int rc;

  (void)libusb_get_device_descriptor(dev, &desc);

  if (LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED == event) {
    rc = libusb_open(dev, &dev_handle);
    if (LIBUSB_SUCCESS != rc) {
      printf("Could not open USB device\n");
    }
  } else if (LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT == event) {
    if (dev_handle) {
      libusb_close(dev_handle);
      dev_handle = NULL;
    }
  } else {
    printf("Unhandled event %d\n", event);
  }
  count++;

  return 0;
}

int main (void) {
  libusb_hotplug_callback_handle callback_handle;
  int rc;

  libusb_init_context(NULL, NULL, 0);

  rc = libusb_hotplug_register_callback(NULL, LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED |
                                        LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT, 0, 0x045a, 0x5005,
                                        LIBUSB_HOTPLUG_MATCH_ANY, hotplug_callback, NULL,
                                        &callback_handle);
  if (LIBUSB_SUCCESS != rc) {
    printf("Error creating a hotplug callback\n");
    libusb_exit(NULL);
    return EXIT_FAILURE;
  }

  while (count < 2) {
    libusb_handle_events_completed(NULL, NULL);
    nanosleep(&(struct timespec){0, 10000000UL}, NULL);
  }

  libusb_hotplug_deregister_callback(NULL, callback_handle);
  libusb_exit(NULL);

  return 0;
}
\endcode
 */

#define VALID_HOTPLUG_EVENTS			\
	(LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED |	\
	 LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT)

#define VALID_HOTPLUG_FLAGS			\
	(LIBUSB_HOTPLUG_ENUMERATE)

void usbi_hotplug_init(struct libusb_context *ctx)
{
	/* check for hotplug support */
	if (!libusb_has_capability(LIBUSB_CAP_HAS_HOTPLUG))
		return;

	usbi_mutex_init(&ctx->hotplug_cbs_lock);
	list_init(&ctx->hotplug_cbs);
	ctx->next_hotplug_cb_handle = 1;
	usbi_atomic_store(&ctx->hotplug_ready, 1);
}

static void usbi_recursively_remove_parents(struct libusb_device *dev, struct libusb_device *next_dev)
{
	if (dev && dev->parent_dev) {
		if (usbi_atomic_load(&dev->parent_dev->refcnt) == 1) {
			/* The parent was processed before this device in the list and
			 * therefore has its ref count already decremented for its own ref.
			 * The only remaining counted ref comes from its remaining single child.
			 * It will thus be released when its child will be released. So we
			 * can remove it from the list. This is safe as parent_dev cannot be
			 * equal to next_dev given that we know at this point that it was
			 * previously seen in the list. */
			assert (dev->parent_dev != next_dev);
			if (dev->parent_dev->list.next && dev->parent_dev->list.prev) {
				list_del(&dev->parent_dev->list);
			}
		}

		usbi_recursively_remove_parents(dev->parent_dev, next_dev);
	}
}

void usbi_hotplug_exit(struct libusb_context *ctx)
{
	struct usbi_hotplug_callback *hotplug_cb, *next_cb;
	struct usbi_hotplug_message *msg;
	struct libusb_device *dev, *next_dev;

	/* check for hotplug support */
	if (!libusb_has_capability(LIBUSB_CAP_HAS_HOTPLUG))
		return;

	if (!usbi_atomic_load(&ctx->hotplug_ready))
		return;

	/* free all registered hotplug callbacks */
	for_each_hotplug_cb_safe(ctx, hotplug_cb, next_cb) {
		list_del(&hotplug_cb->list);
		free(hotplug_cb);
	}

	/* free all pending hotplug messages */
	while (!list_empty(&ctx->hotplug_msgs)) {
		msg = list_first_entry(&ctx->hotplug_msgs, struct usbi_hotplug_message, list);

		/* if the device left, the message holds a reference
		 * and we must drop it */
		if (msg->event == LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT)
			libusb_unref_device(msg->device);

		list_del(&msg->list);
		free(msg);
	}

	usbi_mutex_lock(&ctx->usb_devs_lock); /* hotplug thread might still be processing an already triggered event, possibly accessing this list as well */
	/* free all discovered devices */
	for_each_device_safe(ctx, dev, next_dev) {
		/* remove the device from the usb_devs list only if there are no
		 * references held, otherwise leave it on the list so that a
		 * warning message will be shown */
		if (usbi_atomic_load(&dev->refcnt) == 1) {
			list_del(&dev->list);
		}

		usbi_recursively_remove_parents(dev, next_dev);

		libusb_unref_device(dev);
	}
	usbi_mutex_unlock(&ctx->usb_devs_lock);

	usbi_mutex_destroy(&ctx->hotplug_cbs_lock);
}

static int usbi_hotplug_match_cb(struct libusb_device *dev,
	libusb_hotplug_event event, struct usbi_hotplug_callback *hotplug_cb)
{
	if (!(hotplug_cb->flags & event)) {
		return 0;
	}

	if ((hotplug_cb->flags & USBI_HOTPLUG_VENDOR_ID_VALID) &&
	    hotplug_cb->vendor_id != dev->device_descriptor.idVendor) {
		return 0;
	}

	if ((hotplug_cb->flags & USBI_HOTPLUG_PRODUCT_ID_VALID) &&
	    hotplug_cb->product_id != dev->device_descriptor.idProduct) {
		return 0;
	}

	if ((hotplug_cb->flags & USBI_HOTPLUG_DEV_CLASS_VALID) &&
	    hotplug_cb->dev_class != dev->device_descriptor.bDeviceClass) {
		return 0;
	}

	return hotplug_cb->cb(DEVICE_CTX(dev), dev, event, hotplug_cb->user_data);
}

void usbi_hotplug_notification(struct libusb_context *ctx, struct libusb_device *dev,
	libusb_hotplug_event event)
{
	struct usbi_hotplug_message *msg;
	unsigned int event_flags;

	/* Only generate a notification if hotplug is ready. This prevents hotplug
	 * notifications from being generated during initial enumeration or if the
	 * backend does not support hotplug. */
	if (!usbi_atomic_load(&ctx->hotplug_ready))
		return;

	msg = calloc(1, sizeof(*msg));
	if (!msg) {
		usbi_err(ctx, "error allocating hotplug message");
		return;
	}

	msg->event = event;
	msg->device = dev;

	/* Take the event data lock and add this message to the list.
	 * Only signal an event if there are no prior pending events. */
	usbi_mutex_lock(&ctx->event_data_lock);
	event_flags = ctx->event_flags;
	ctx->event_flags |= USBI_EVENT_HOTPLUG_MSG_PENDING;
	list_add_tail(&msg->list, &ctx->hotplug_msgs);
	if (!event_flags)
		usbi_signal_event(&ctx->event);
	usbi_mutex_unlock(&ctx->event_data_lock);
}

void usbi_hotplug_process(struct libusb_context *ctx, struct list_head *hotplug_msgs)
{
	struct usbi_hotplug_callback *hotplug_cb, *next_cb;
	struct usbi_hotplug_message *msg;
	int r;

	usbi_mutex_lock(&ctx->hotplug_cbs_lock);

	/* dispatch all pending hotplug messages */
	while (!list_empty(hotplug_msgs)) {
		msg = list_first_entry(hotplug_msgs, struct usbi_hotplug_message, list);

		for_each_hotplug_cb_safe(ctx, hotplug_cb, next_cb) {
			/* skip callbacks that have unregistered */
			if (hotplug_cb->flags & USBI_HOTPLUG_NEEDS_FREE)
				continue;

			usbi_mutex_unlock(&ctx->hotplug_cbs_lock);
			r = usbi_hotplug_match_cb(msg->device, msg->event, hotplug_cb);
			usbi_mutex_lock(&ctx->hotplug_cbs_lock);

			if (r) {
				list_del(&hotplug_cb->list);
				free(hotplug_cb);
			}
		}

		/* if the device left, the message holds a reference
		 * and we must drop it */
		if (msg->event == LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT)
			libusb_unref_device(msg->device);

		list_del(&msg->list);
		free(msg);
	}

	/* free any callbacks that have unregistered */
	for_each_hotplug_cb_safe(ctx, hotplug_cb, next_cb) {
		if (hotplug_cb->flags & USBI_HOTPLUG_NEEDS_FREE) {
			usbi_dbg(ctx, "freeing hotplug cb %p with handle %d",
				 (void *) hotplug_cb, hotplug_cb->handle);
			list_del(&hotplug_cb->list);
			free(hotplug_cb);
		}
	}

	usbi_mutex_unlock(&ctx->hotplug_cbs_lock);
}

int API_EXPORTED libusb_hotplug_register_callback(libusb_context *ctx,
	int events, int flags,
	int vendor_id, int product_id, int dev_class,
	libusb_hotplug_callback_fn cb_fn, void *user_data,
	libusb_hotplug_callback_handle *callback_handle)
{
	struct usbi_hotplug_callback *hotplug_cb;

	/* check for sane values */
	if (!events || (~VALID_HOTPLUG_EVENTS & events) ||
	    (~VALID_HOTPLUG_FLAGS & flags) ||
	    (LIBUSB_HOTPLUG_MATCH_ANY != vendor_id && (~0xffff & vendor_id)) ||
	    (LIBUSB_HOTPLUG_MATCH_ANY != product_id && (~0xffff & product_id)) ||
	    (LIBUSB_HOTPLUG_MATCH_ANY != dev_class && (~0xff & dev_class)) ||
	    !cb_fn) {
		return LIBUSB_ERROR_INVALID_PARAM;
	}

	/* check for hotplug support */
	if (!libusb_has_capability(LIBUSB_CAP_HAS_HOTPLUG))
		return LIBUSB_ERROR_NOT_SUPPORTED;

	ctx = usbi_get_context(ctx);

	hotplug_cb = calloc(1, sizeof(*hotplug_cb));
	if (!hotplug_cb)
		return LIBUSB_ERROR_NO_MEM;

	hotplug_cb->flags = (uint8_t)events;
	if (LIBUSB_HOTPLUG_MATCH_ANY != vendor_id) {
		hotplug_cb->flags |= USBI_HOTPLUG_VENDOR_ID_VALID;
		hotplug_cb->vendor_id = (uint16_t)vendor_id;
	}
	if (LIBUSB_HOTPLUG_MATCH_ANY != product_id) {
		hotplug_cb->flags |= USBI_HOTPLUG_PRODUCT_ID_VALID;
		hotplug_cb->product_id = (uint16_t)product_id;
	}
	if (LIBUSB_HOTPLUG_MATCH_ANY != dev_class) {
		hotplug_cb->flags |= USBI_HOTPLUG_DEV_CLASS_VALID;
		hotplug_cb->dev_class = (uint8_t)dev_class;
	}
	hotplug_cb->cb = cb_fn;
	hotplug_cb->user_data = user_data;

	usbi_mutex_lock(&ctx->hotplug_cbs_lock);

	/* protect the handle by the context hotplug lock */
	hotplug_cb->handle = ctx->next_hotplug_cb_handle++;

	/* handle the unlikely case of overflow */
	if (ctx->next_hotplug_cb_handle < 0)
		ctx->next_hotplug_cb_handle = 1;

	list_add(&hotplug_cb->list, &ctx->hotplug_cbs);

	usbi_mutex_unlock(&ctx->hotplug_cbs_lock);

	usbi_dbg(ctx, "new hotplug cb %p with handle %d",
		 (void *) hotplug_cb, hotplug_cb->handle);

	if ((flags & LIBUSB_HOTPLUG_ENUMERATE) && (events & LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED)) {
		ssize_t i, len;
		struct libusb_device **devs;

		len = libusb_get_device_list(ctx, &devs);
		if (len < 0) {
			libusb_hotplug_deregister_callback(ctx, hotplug_cb->handle);
			return (int)len;
		}

		for (i = 0; i < len; i++) {
			usbi_hotplug_match_cb(devs[i],
					LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED,
					hotplug_cb);
		}

		libusb_free_device_list(devs, 1);
	}

	if (callback_handle)
		*callback_handle = hotplug_cb->handle;

	return LIBUSB_SUCCESS;
}

void API_EXPORTED libusb_hotplug_deregister_callback(libusb_context *ctx,
	libusb_hotplug_callback_handle callback_handle)
{
	struct usbi_hotplug_callback *hotplug_cb;
	int deregistered = 0;

	/* check for hotplug support */
	if (!libusb_has_capability(LIBUSB_CAP_HAS_HOTPLUG))
		return;

	usbi_dbg(ctx, "deregister hotplug cb %d", callback_handle);

	ctx = usbi_get_context(ctx);

	usbi_mutex_lock(&ctx->hotplug_cbs_lock);
	for_each_hotplug_cb(ctx, hotplug_cb) {
		if (callback_handle == hotplug_cb->handle) {
			/* mark this callback for deregistration */
			hotplug_cb->flags |= USBI_HOTPLUG_NEEDS_FREE;
			deregistered = 1;
			break;
		}
	}
	usbi_mutex_unlock(&ctx->hotplug_cbs_lock);

	if (deregistered) {
		unsigned int event_flags;

		usbi_mutex_lock(&ctx->event_data_lock);
		event_flags = ctx->event_flags;
		ctx->event_flags |= USBI_EVENT_HOTPLUG_CB_DEREGISTERED;
		if (!event_flags)
			usbi_signal_event(&ctx->event);
		usbi_mutex_unlock(&ctx->event_data_lock);
	}
}

DEFAULT_VISIBILITY
void * LIBUSB_CALL libusb_hotplug_get_user_data(libusb_context *ctx,
	libusb_hotplug_callback_handle callback_handle)
{
	struct usbi_hotplug_callback *hotplug_cb;
	void *user_data = NULL;

	/* check for hotplug support */
	if (!libusb_has_capability(LIBUSB_CAP_HAS_HOTPLUG))
		return NULL;

	usbi_dbg(ctx, "get hotplug cb %d user data", callback_handle);

	ctx = usbi_get_context(ctx);

	usbi_mutex_lock(&ctx->hotplug_cbs_lock);
	for_each_hotplug_cb(ctx, hotplug_cb) {
		if (callback_handle == hotplug_cb->handle) {
			user_data = hotplug_cb->user_data;
			break;
		}
	}
	usbi_mutex_unlock(&ctx->hotplug_cbs_lock);

	return user_data;
}