Re: [Linux-usb-users] Re: USB API, ioctl's and libusb

[DervishD <lkml@dervishd.net>]

    Hi Alan :)
 * Alan Stern <stern@rowland.harvard.edu> dixit:
> >     BTW, and judging from the program I've read, there are lots of
> > operations that must be done using 'usb_control_msg', and libusb
> > implements that function with exactly the same interface as the
> > kernel. The only difference is that libusb uses ioctl and the kernel
> > implements the function using URB's. IMHO libusb doesn't provide a
> > cleaner API, the only advantage of libusb is portability. Anyway,
> > I've not used it enough to judge, I'm more concerned about kernel USB
> > interface, not libusb one.
> You don't seem to understand the difference between a kernel API and a
> user API.  Only code that is part of the kernel can use a kernel API, so
> only kernel drivers can use the "URB" interface.  By contrast, a user API
> can be used by regular programs, not part of the kernel.  libusb provides
> a user API.

    I thought that <linux/usb.h> provided a user API, not a kernel
one. In fact I thought that the functions provided throught that
header were syscalls. They are not, I've checked ;)

> So there's really no choice.  Unless you're writing a kernel module, your 
> program can't use URBs.  You can use libusb, or if you don't care about 
> portability you can use ioctl calls directly.  But you can't use URBs.

    OK, that's right. I really thought that there were syscalls
providing USB API for user space programs. That sounded less weird
when I first thought of it ;)) Thanks for the help :)))

    Raúl Núñez de Arenas Coronado

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