Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> writes: > On Thu, Aug 25, 2016 at 07:14:52AM +0200, Rafał Miłecki wrote: >> >> Good question. I would like to extend this USB port trigger in the >> future by reacting to USB activity. This involves playing with URBs >> and I believe that at that point it'd be getting too much USB specific >> to /rule them all/. > > Oh that's never going to work, sorry. USB "activity" happens deep in > USB host controller hardware, not up at the kernel level at all. It's > just too fast, and would take up too much CPU to do it otherwise. Heck, > even old UHCI 1.1 USB controllers did this. > > USB "activity" happens all the time, look at a USB bus analyzer if you > want to see what goes on. Teasing out what is "real data" and what is > just "normal bus activity" is impossible at the kernel level, OK, I am going to play stupid again: Does this mean that usbmon is impossible? > and really > makes no sense at all (your led would just be "on" all the time.) I don't see how this is any different from e.g. the network activity triggers. FWIW, on my system "cat /sys/kernel/debug/usb/usbmon/0u" can be silent for long periods, and show a rush of lines whenever there is USB activity. I imagine that a LED triggered by a hook in a similar place would be useful on systems with LEDs for that sort of stuff. Bjørn -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
