Re: poll(2)ing or select(2)ing /dev/usb0

[Dirk GOUDERS <gouders_(_at_)_et_(_dot_)_bocholt_(_dot_)_fh-ge_(_dot_)_de>]

 > You cannot read data from /dev/usbN, only ioctls are possible on those 
 > devices.
 > 
 > See "/sys/dev/usb/usb.c" (usbpoll), if you got the source code installed.

Ah yes, thank you, now I understand why my programs behave like they do.

To me, it looks as if the manual page usb(4) is a little bit misleading:

<excerpt>
USB CONTROLLER INTERFACE
     Use the following to get access to the USB specific structures and
     defines.

     The /dev/usbN can be opened and a few operations can be performed on it.
     The poll(2) system call will say that I/O is possible on the controller
     device when a USB device has been connected or disconnected to the bus.

     The following ioctl(2) commands are supported on the controller device:
</excerpt>

I understood the text in the following way:

"If you want to know if a device has been connected/disconnected, then
 call poll(2) on /dev/usbN and if poll(2) says that descriptors are
 ready, perform one of the ioctl(2) command to find out what exactly
 happened."


Well, do I understand it right, that the only way to use poll(2) to
come to know if a device has been connected/disconnected to/from the
bus is to poll(2) /dev/usb (the event interface)?  And therefore on a
machine that runs usbd(8), no other process can use poll(2), to come to
know about such events, but has to do it somehow else?

Dirk
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