How to manually handle all plugged in USB devices to MacBook

Question

my problem is I want to manually handle how USB devices are handled when they are plugged in. I don't want the operating system to do anything with the plugged in USB devices other than notify me of their type and their ID when they are plugged in. From there I can then select the appropriate driver to apply to it, or manually do something with it with custom code.

I've read this about how MacOS handles USBs, and it says:

If you want your driver selected above others, all you need to do is add key value pairs for the device your driver is for which cause your driver to get a really high score. Usually it's enough to just put keys in for your vendor id/model. However, I think you can override the matching method (device drivers are written in a restricted set of C++) to give your driver a really high score.

I have also found these 3 libraries for getting notified about things in the USB drive:

I just am not sure if these libraries will interrupt all USB device handling by the operating system before anything occurs (before any device driver is selected automatically and applied). I would like for nothing to happen except for me to get access to the device and its type in one of the above libraries, but I'm not sure if they will do that.

I don't have much code yet other than this:

var usb = require('usb')
usb.getDeviceList()

But I imagine this would resolve the plugged in devices after the OS has already selected and applied a default driver to it. I want to do something like this:

usb.blockDefaultOSDeviceHandler()
usb.on('device:plugged_in', function(data){
  if (data.type == 'keyboard') {
    if (data.modelNumber == '123') {
      // allow
      usb.applyKeyboardDriver('abc', data.modelNumber)
      usb.on('keyboard:event', logKeyboardEvent)
    } else {
      throw new Error('Unrecognized device')
    }
  } 
})

I would hope that the library would interrupt all default behavior by the operating system so I can handle myself what should be done when a USB device is plugged in. A reason is because maybe the USB device is a keyboard and it automatically starts typing in some keys. I would like to know that it is a keyboard, and require a password and a specific driver I have pre-approved for it. Stuff like that.

I would like to get access to any newly plugged in USB device before the operating system applies its default handling rules. And then have the ability to write the code to manually handle what to do with each plugged in device.

If it's only possible in C, then knowing how to do it there would be good instead of node.js.

You may be shooting for something that node isn't built for. You're gonna need to go much deeper (think C). — basic
If it's only possible in C, then knowing how to do it there would be good instead of node.js. — user10869858
The person you quoted was talking about writing a driver (aka "kext"). You probably have to write a kernel-level USB driver to do this, so have you started and do you have any specific questions about how to make the driver work? If not, this is probably too broad. — David Grayson
Also, why do you even want to do this? Seems like you'd cripple your computer quite often by accidentally disabling your USB keyboard and mouse. Maybe there is a better solution that solves your actual problem, which you did not specify. — David Grayson

user10869858 user10869858 · Accepted Answer · 2019-01-10T03:57:07

The answer is in the Apple documentation on USB devices. Basically you want to override the probe function in a custom driver, have it return the highest score so as to override all other drivers, and implement the driver like normal. Here is some useful documentation on the driver selection and instantiation process.

Before a device—or any service provider—can be used, a driver for it must be found and loaded into the kernel. The I/O Kit defines a flexible, three-phase matching process that narrows a pool of candidate drivers down to one or more drivers. The final candidate (or, if multiple candidates, the m ost eligible one) is then loaded and given the first opportunity to manage the device or service provider.

...

Each device driver, considered as a loadable kernel extension (KEXT), must define one or more personalities that specify the kinds of devices it can support.

...

Because a driver can contain multiple matching dictionaries, each one defining a different personality for the driver, the same driver code can be loaded for different devices. For purposes of competition, the I/O Kit treats each personality as if it were a driver. If, in any single personality, all of the properties required by the family match, the driver’s code is loaded and given a chance to run for that device.

...

One common property of personalities is the probe score. A probe score is an integer that reflects how well-suited a driver is to drive a particular device. A driver may have an initial probe-score value in its personality and it may implement a probe function that allows it to modify this default value, based on its suitability to drive a device. As with other matching values, probe scores are specific to each family. That’s because once matching proceeds past the class-matching stage, only personalities from the same family compete. For more information on probe scores and what a driver does in the probe function, see Device Probing.

...

At boot time and at any time devices are added or removed, the process of driver matching occurs for each detected device (or other service provider). The process dynamically locates the most suitable driver in /System/Library/Extensions for the device or service.

...

As described in Driver Matching in the chapter Architectural Overview the matching process is triggered when a bus controller driver scans its bus and detects a new device attached to it. For each detected device the controller driver creates a nub. The I/O Kit then initiates the matching process and obtains the values from the device to use in matching (for example, examining the PCI registers). Once a suitable driver is found for the nub, the driver is registered and loaded. That driver, in turn, may create its own nub (possibly through behavior inherited from its family), which initiates the matching process to find a suitable driver.

...

The matching process proceeds as follows:

In the class matching step, the I/O Kit narrows the list of potential drivers by eliminating any drivers of the wrong class for the provider service (that is, the nub). For example, all driver objects that descend from a SCSI class can be ruled out when the search is for a USB driver.

In the passive matching step, the driver’s personality (specified in a driver’s XML information property list) is examined for properties specific to the provider’s family. For example, the personality might specify a particular vendor name.

In the active matching step, the driver’s probe function is called with reference to the nub it is being matched against. This function allows the driver to communicate with the device and verify that it can in fact drive it. The driver returns a probe score that reflects its ability to drive the device. See Device Probing for more information. During active matching, the I/O Kit loads and probes all candidate drivers, then sorts them in order of highest to lowest probe score.

...

The I/O Kit then chooses the remaining driver with the highest probe score and starts it. If the driver successfully starts, it is added to the I/O Registry and any remaining driver candidates are discarded. If it does not start successfully, the driver with the next highest probe score is started, and so on. If more than one driver is in the pool of possible candidates, the more generic driver typically loses out to the more specific driver if both claim to be able to drive the device.

...

The probe score is a signed 32-bit integer initialized to a value specified in the driver’s personality (or to zero if not explicitly initialized).

...

A driver, in its probe function, returns a driver object (IOService *) if the probe was successful and returns zero otherwise. The returned object is usually the driver itself, but the driver can return another driver that is more suited to the provider. The probe score is an in-out parameter, which probe can modify based on what it discovers about the device.

...

After all drivers have probed the device, the one with the highest probe score is attached and its startfunction, which must be implemented by all drivers, is invoked. The start function initializes the device hardware and prepares it for operation. If the driver succeeds in starting, it returns true; the remaining candidate driver instances are discarded and the driver that started successfully continues operating. If the driver cannot initialize the hardware it must leave the hardware in the state it was in when start was invoked and return false. The failing driver is then detached and discarded, and the candidate driver with the next highest probe score is given a chance to start.

This can't be done with Node.js unless (potentially) a C/C++ extension in node is used.

How to manually handle all plugged in USB devices to MacBook

1 Answers