Re: [Libusb-devel] Patch: libusb/os/linux_usbfs.c: Distingush between usbfs and other kernel mode drivers

[Peter S. <pe...@st...>]

Xiaofan Chen wrote:
> > It is really analogous to libusb0.sys in Windows.
> 
> Totally different. If I need to use libusb0.sys, then I need to
> attach it to the device (as a device driver or a filter).

Exactly the same! usbfs must be attached to the device (well, to the
interface) in order for libusb to work.

The only difference is that Linux includes a generic USB driver
(usbfs) already and Windows does not, and that when calling
libusb_claim_interface() on Linux the driver is bound to the
interface by the kernel. Windows binds the driver much more
statically.

drivers/usb/core/devio.c in Linux is the usbfs driver.

>From http://lxr.linux.no/#linux+v2.6.35.7/drivers/usb/core/devio.c#L471
/*
 * interface claims are made only at the request of user level code,
 * which can also release them (explicitly or by closing files).
 * they're also undone when devices disconnect.
 */


Here is the code that will be called as a result of libusb_claim_interface()
http://lxr.linux.no/#linux+v2.6.35.7/drivers/usb/core/devio.c#L528

Note the call to usb_driver_claim_interface(). That function is
defined here:
http://lxr.linux.no/#linux+v2.6.35.7/drivers/usb/core/driver.c#L408

Although it is not typically called by other drivers, the result of
the function is the same as when any other kernel driver binds to
any other device interface.


//Peter