Re: [Libusb-devel] libusb-1.0 doesn't find usb devices

[Xiaofan C. <xia...@gm...>]

On Tue, Apr 7, 2009 at 6:47 PM, Richard <rk...@us...> wrote:
>> Supposedly libusb-1.0 will try /dev/bus/usb (sysfs)
>> first, it that fails, it will try /proc/bus/usb (usbfs).
>> So there might be a bug in the code. Maybe you
>> can enable debug and send out the log and hopefully
>> the developer can find the hidden bug.
>
>  Are there some instructions available how to do this?
> Thanks,
>

You can try call libusb_set_debug() after libusb_init() but
it does not seem to work right now (need to check further).

Or you can build libusb with the following.
./configure --enable-debug-log --prefix=/usr
make
sudo make install

This is the example output from the example lsusb.c output.

[mcuee@acerpc examples]$ ./lsusb
libusb:debug [libusb_init]
libusb:debug [find_usbfs_path] found usbfs at /dev/bus/usb
libusb:debug [op_init] found usb devices in sysfs
libusb:debug [usbi_add_pollfd] add fd 3 events 1
libusb:debug [libusb_init] created default context
libusb:debug [libusb_get_device_list]
libusb:debug [sysfs_scan_device] scan usb1
libusb:debug [sysfs_scan_device] sysfs descriptors available
libusb:debug [sysfs_scan_device] bus=1 dev=1
libusb:debug [enumerate_device] busnum 1 devaddr 1 session_id 257
libusb:debug [enumerate_device] allocating new device for 1/1 (session
257)
libusb:debug [sysfs_scan_device] scan usb2
libusb:debug [sysfs_scan_device] bus=2 dev=1
libusb:debug [enumerate_device] busnum 2 devaddr 1 session_id 513
libusb:debug [enumerate_device] allocating new device for 2/1 (session
513)
libusb:debug [sysfs_scan_device] scan 2-1
libusb:debug [sysfs_scan_device] bus=2 dev=2
libusb:debug [enumerate_device] busnum 2 devaddr 2 session_id 514
libusb:debug [enumerate_device] allocating new device for 2/2 (session
514)
libusb:debug [sysfs_scan_device] scan 2-3
libusb:debug [sysfs_scan_device] bus=2 dev=3
libusb:debug [enumerate_device] busnum 2 devaddr 3 session_id 515
libusb:debug [enumerate_device] allocating new device for 2/3 (session
515)
libusb:debug [sysfs_scan_device] scan 2-7
libusb:debug [sysfs_scan_device] bus=2 dev=4
libusb:debug [enumerate_device] busnum 2 devaddr 4 session_id 516
libusb:debug [enumerate_device] allocating new device for 2/4 (session
516)
libusb:debug [sysfs_scan_device] scan 2-8
libusb:debug [sysfs_scan_device] bus=2 dev=5
libusb:debug [enumerate_device] busnum 2 devaddr 5 session_id 517
libusb:debug [enumerate_device] allocating new device for 2/5 (session
517)
libusb:debug [libusb_get_device_descriptor]
1d6b:0002 (bus 1, device 1)
libusb:debug [libusb_get_device_descriptor]
1d6b:0001 (bus 2, device 1)
libusb:debug [libusb_get_device_descriptor]
058f:9360 (bus 2, device 2)
libusb:debug [libusb_get_device_descriptor]
046d:c054 (bus 2, device 3)
libusb:debug [libusb_get_device_descriptor]
04d8:0033 (bus 2, device 4)
libusb:debug [libusb_get_device_descriptor]
04d8:8001 (bus 2, device 5)
libusb:debug [libusb_unref_device] destroy device 1.1
libusb:debug [libusb_unref_device] destroy device 2.1
libusb:debug [libusb_unref_device] destroy device 2.2
libusb:debug [libusb_unref_device] destroy device 2.3
libusb:debug [libusb_unref_device] destroy device 2.4
libusb:debug [libusb_unref_device] destroy device 2.5
libusb:debug [libusb_exit]
libusb:debug [usbi_remove_pollfd] remove fd 3
libusb:debug [libusb_exit] freeing default context

The relevant code in linux_usbfs.c

static const char *find_usbfs_path(void)
{
	const char *path = "/dev/bus/usb";
	const char *ret = NULL;

	if (check_usb_vfs(path)) {
		ret = path;
	} else {
		path = "/proc/bus/usb";
		if (check_usb_vfs(path))
			ret = path;
	}

	usbi_dbg("found usbfs at %s", ret);
	return ret;
}

static int op_init(struct libusb_context *ctx)
{
	struct stat statbuf;
	int r;

	usbfs_path = find_usbfs_path();
	if (!usbfs_path) {
		usbi_err(ctx, "could not find usbfs");
		return LIBUSB_ERROR_OTHER;
	}

	r = stat(SYSFS_DEVICE_PATH, &statbuf);
	if (r == 0 && S_ISDIR(statbuf.st_mode)) {
		usbi_dbg("found usb devices in sysfs");
	} else {
		usbi_dbg("sysfs usb info not available");
		sysfs_has_descriptors = 0;
		sysfs_can_relate_devices = 0;
	}

	return 0;
}


Regards,
Xiaofan