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ShengYi Hung
749318f2ae
FreeBSD's libusb has three components: libusb01, libusb10, and libusb20. libusb20 handles communication with character devices. We now requires a backend context for libusb20. The backend context contains contains the capsicumized usbctrl fd and usb directory (/dev/usb) fd so that the library user can enter the capiblity mode safely while using libusb. libusb10 is updated to support capabilities via a context option. Since libusb allows general read/write access, we preserve all possible capabilities when passing backend context to libusb20. It is the responsibility of the libusb user to call cap_enter() at an appropriate time. All base system tools using libusb and libusb20 have been updated to support Capsicum. Reviewed by: adrian, markj Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D51865
As I dug my own way through the documentation of libusb 2.0 that ships with FreeBSD 8+ as the OS'es own USB library API, I noticed there are only few code examples around under /usr/src (namely, usbconfig itself). The libusb20(3) man page is a starting point, but it's a reference manual, nothing less, nothing more. Using just a reference, it's not very easy to start writing your own code based on that. So I started writing my own examples, to "get a feeling" about how to use the library. I covered two typical scenarios which are common for a number of devices. The first one is called "bulk", and uses bulk output (host to device) and input transfers to talk to an USB device. The second one is called "control", and can use both control output and input transfers, as well as so-called interrupt transfers. The latter are used for data that are being reported frequently or repeatedly, like position updates from a pointing device (mouse). Despite of its name, the host has to poll devices for their interrupt transfers on each USB frame (i.e., each 1 ms). Recommended reading is the USB 3.0 specification (the older 2.0 one would do as well), to be found under http://www.usb.org/developers/docs/ as well as documents for individual USB device classes where appropriate. Feel free to be liberal in the licensing of these examples: while the beer-ware license mandates to keep the license notice, this only applies to modifications of the original examples itself. For copy&pasting (even a larger) piece of an example into your own work, I won't imply you have to reproduce the beer-ware license text there. Feel free to credit my name in your derived work if you want. Dresden, July 2012 Joerg Wunsch <[email protected]>