hotplug: Add a hotplug_poll backend function

Apps which were written before hotplug support, may listen for hotplug events
on their own and call libusb_get_device_list on device addition.

In this case libusb_get_device_list will likely return a list without the new
device in there, as the hotplug event thread will still be busy enumerating
the device, which may take a while, or may not even have seen the event yet.

To avoid this add a new hotplug_poll backend function and make
libusb_get_device_list call a this before copying ctx->usb_devs to the user.

In this function the backend should ensure any pending hotplug events are
fully processed before returning.

This patch implements hotplug_poll for linux, it should probably be also
implemented for darwin.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/libusb/os/linux_netlink.c b/libusb/os/linux_netlink.c
index 7b1fdcd..3a68f69 100644
--- a/libusb/os/linux_netlink.c
+++ b/libusb/os/linux_netlink.c
@@ -241,3 +241,14 @@ static void *linux_netlink_event_thread_main(void *arg)
 
 	return NULL;
 }
+
+void linux_netlink_hotplug_poll(void)
+{
+	int r;
+
+	usbi_mutex_static_lock(&linux_hotplug_lock);
+	do {
+		r = linux_netlink_read_message();
+	} while (r == 0);
+	usbi_mutex_static_unlock(&linux_hotplug_lock);
+}