usb_reset() behavior of libusb-0.1 and libusb-compat-0.1

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

I believe this is a document bug of libusb-0.1 API documentation
(libusb-compat-0.1 does not change the 0.1 API documentation)
that usb_reset() will not cause re-enumeration under most
cases for Linux (unless descriptor changes) and Darwin.

http://libusb.sourceforge.net/doc/function.usbreset.html
This old API document is probably not correct by saying it
will cause re-enumeration.

Ref:
http://libusb.6.n5.nabble.com/PATCH-make-libusb-reset-force-re-enumeration-on-Mac-td4499375.html

Actually if I look into the old libusb-0.1 codes, the Linux and
Darwin implementation will also not cause re-enumeration.

Is it possible to fix this?

Is it in early history of Linux (say 2.2 or 2.4 kernel), usb_reset
will indeed cause re-enumeration?

BTW, libusb-win32's usb_reset() will cause device re-enumeration
and it seems FreeBSD follows the 0.1 API document as well.

Regards,
Xiaofan


---------- Forwarded message ----------
From: Xiaofan Chen
Date: Sat, Dec 22, 2012 at 6:17 PM
Subject: Re: usb/173666: [USB, LIBUSB] usb_reset() behavior different
between GNU/Linux and FreeBSD
To: Hans Petter Selasky
Cc: freebsd-usb, "Wojciech A. Koszek"


On Fri, Dec 21, 2012 at 3:38 PM, Hans Petter Selasky <hse...@c2...> wrote:
> If you look in the old libusb-0.1 code you'll see something different I think.
> Could you check that?

Not much differences in reality. I believe it is a document bug for the
libusb-0.1.

Both old libusb-0.1 code and libusb-1.0 use the same IOCTL under Linux
and the behavior should be similar.

Please refer to the following code listing and take note even though
the name of the IOCTL is different but they are the same if you
look at the defines.

On the other hand, libusb-win32's usb_reset will cause re-enumeration.

>From libusb-0.1.12 source (linux.c)
int usb_reset(usb_dev_handle *dev)
{
  int ret;

  ret = ioctl(dev->fd, IOCTL_USB_RESET, NULL);
  if (ret)
     USB_ERROR_STR(-errno, "could not reset: %s", strerror(errno));

  return 0;
}

>From libusb.org libusb.git (libusb-1.0) souce:

static int op_reset_device(struct libusb_device_handle *handle)
{
        int fd = _device_handle_priv(handle)->fd;
        int i, r, ret = 0;

        /* Doing a device reset will cause the usbfs driver to get unbound
           from any interfaces it is bound to. By voluntarily unbinding
           the usbfs driver ourself, we stop the kernel from rebinding
           the interface after reset (which would end up with the interface
           getting bound to the in kernel driver if any). */
        for (i = 0; i < USB_MAXINTERFACES; i++) {
                if (handle->claimed_interfaces & (1L << i)) {
                        op_release_interface(handle, i);
                }
        }

        usbi_mutex_lock(&handle->lock);
        r = ioctl(fd, IOCTL_USBFS_RESET, NULL);
        if (r) {
                if (errno == ENODEV) {
                        ret = LIBUSB_ERROR_NOT_FOUND;
                        goto out;
                }

                usbi_err(HANDLE_CTX(handle),
                        "reset failed error %d errno %d", r, errno);
                ret = LIBUSB_ERROR_OTHER;
                goto out;
        }

        /* And re-claim any interfaces which were claimed before the reset */
        for (i = 0; i < USB_MAXINTERFACES; i++) {
                if (handle->claimed_interfaces & (1L << i)) {
                        r = op_claim_interface(handle, i);
                        if (r) {
                                usbi_warn(HANDLE_CTX(handle),
                                        "failed to re-claim interface
%d after reset", i);
                                handle->claimed_interfaces &= ~(1L << i);
                        }
                }
        }
out:
        usbi_mutex_unlock(&handle->lock);
        return ret;
}


--
Xiaofan