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Re: Mac OS real USB device support issue

From: Programmingkid
Subject: Re: Mac OS real USB device support issue
Date: Thu, 8 Apr 2021 15:43:43 -0400

> On Apr 8, 2021, at 7:05 AM, Gerd Hoffmann <gerd@kraxel.org> wrote:
>  Hi,
>>> Those might be a good place to start. IOKit provides the drivers and
>>> also the io registry which is probably where you can get if a driver
>>> is bound to a device and which one is it. How to dissociate the
>>> driver from the device though I don't know.
>> https://developer.apple.com/library/archive/documentation/DeviceDrivers/Conceptual/IOKitFundamentals/DeviceRemoval/DeviceRemoval.html
>> According to this article a driver has a stop() and detach() method
>> that is called by the IOKit to remove a device. I'm thinking QEMU can
>> be the one that calls these methods for a certain device.
> libusb should do that.  Interfaces exist already (see
> libusb_detach_kernel_driver & friends) because we have the very same
> problem on linux.
> take care,
>  Gerd

The questions that come to mind are:
- Does libusb_detach_kernel_driver() work on Mac OS?
- Is libusb_detach_kernel_driver() called on Mac OS in QEMU?

The only mention of this function in QEMU comes from host-libusb.c. 

After some tests I found out the function 
host-libusb.c:usb_host_detach_kernel() is being called on Mac OS 11.1. It never 
reaches the libusb_detach_kernel_driver() function. It stops at the continue 
statement. Here is the full function:

static void usb_host_detach_kernel(USBHostDevice *s)
    printf("usb_host_detach_kernel() called\n");
    struct libusb_config_descriptor *conf;
    int rc, i;

    rc = libusb_get_active_config_descriptor(s->dev, &conf);
    if (rc != 0) {
        printf("rc != 0 => %d\n", rc);
    for (i = 0; i < USB_MAX_INTERFACES; i++) {
        rc = libusb_kernel_driver_active(s->dh, i);
        usb_host_libusb_error("libusb_kernel_driver_active", rc);
        if (rc != 1) {
            if (rc == 0) {
                s->ifs[i].detached = true;
            printf("rc != 1 => %d\n", rc);
        trace_usb_host_detach_kernel(s->bus_num, s->addr, i);
        rc = libusb_detach_kernel_driver(s->dh, i);
        printf("libusb_detach_kernel_driver() called\n");
        usb_host_libusb_error("libusb_detach_kernel_driver", rc);
        s->ifs[i].detached = true;

Next to the continue statement in the loop is where my printf function says 
that rc is equal to 0. So it looks like libusb_kernel_driver_active() may have 
an issue since it sets the rc variable. Later on I will try to figure out what 
is happening here.

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