On 2013.03.18 10:32, Hans de Goede wrote: > Hmm, I'm not sure about claiming LIBUSB_CAP_HAS_HID_ACCESS in Linux, I > would rather not > actually, as on Linux there is no special hid code.
This is not what the capability is about. See below. > AFAIK the HID code > on Windows > allows accessing the device without doing driver swapping. Where as on > Linux, driver > swapping is still required. The fact that driver swapping is a lot > easier on Linux, > call libusb_detach_kernel_driver to detach usbhid, and the usbfs driver > will auto load > on claim-interface, does not change that it is still needed. Please understand what the caps are about. It's about answering the question: "Can libusbx, on its own, provide feature X". Nothing more. Nothing less. It doesn't matter if Windows does it without having to detach a driver and Linux requires a call to libusb_detach. Fact is, using libusbx, and libusbx alone (i.e. without having to perform additional actions outside of the library) on both the Linux and Windows platforms, libusbx should be able to communicate with an HID device. If we want to go with "but this is a different case because or detach", then the only thing you'll get is me adding an extra "LIBUSBX_HAS_HID_ACCESS_WITH_DETACH" cap set to true on Linux, which won't do our users any good. What we really want is tell our users whether libusbx has the capabilities to access and HID device on its own. That we need to invoke 12 libusbx calls before it can do or none is irrelevant. On Linux, libusbx _can_ access an HID device. Saying otherwise will be misleading. But to elaborate on that last point, please consider this scenario: We go with your proposal of setting the HID cap to false on Linux. Lo and behold, in a few months time, we have the following conversation on this mailing list "- Hey guys, I had to go overbudget and overdelay with my project for this, but just so you know, I produced an addon library that can combine libusbx and hidapi. The reason I did that is that, while I only need basic USB-like access from HID, HID access wasn't supported by libusbx on Linux, and I have to deliver a Windows+Linux USB application... - Huh, you know that libusbx _does_ provide HID access on Linux. You just need to call libusb_detach to be granted access - But libusb_has_capability() told me that HID access was not possible on Linux!!!" > To argue HID-access is supported under Linux would mean to argue that it > is supported under Darwin too. Or that it is supported under Windows by the current libusb (libusb, not libusbx), since all one has to do is replace the HID driver with WinUSB there. But as I explained above, the _BIG_ difference is that under Darwin you need to do something outside of libusbx (and likewise on Windows without native HID driver support from the backend). On Linux, you don't. If you want to pretend that differences between endo and exo don't matter, be my guest. > One can create a code-less kext (a darwin driver) and do a driver > swap of the official hid driver with that for a certain hid device, and > then access it through libusbx fine on Darwin. _OUTSIDE_ of libusbx. Again, the idea of caps is "Can libusbx, on its own, perform the following feature". If that answer is yes, as is the case for HID access on both Linux and Windows, then the caps _must_ be set to true. > So I would like to suggest to document that the capability is for > accessing HID devices > without detaching the OS native's HID driver, and that HID devices can > be accessed on > platforms without the capability too as long as the native driver is > detached (and > where necessary replaced with a generic libusb compatible driver). And > then only > claim the capability for windows. Sorry but I think that's going to be super conter-productive for our users. The capability is for accessing HID devices, period. Trying to get further than that is only going to confuse our users or worse, as exposed above, lead them to believe that HID access is not supported when using libusbx on Linux, which is plain wrong. This being said, I don't have a problem trying to make the documentation more comprehensive on the subject, but I'm also not going to delude myself into the belief that every single of our users is going to read the documentation meticulously to figure out what the actual story is on Linux. Better have them get a report that HID is supported on Linux, and then figure that they need to call detach(), than have a report that it isn't, and missing the part of the documentation that says that, well, it actually is. Regards, /Pete ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_d2d_mar _______________________________________________ libusbx-devel mailing list libusbx-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libusbx-devel
