Re: definition of terms

Re: definition of terms

[David Brownell]

There's "function" too. "Physical device" is something I can pick
up, but when I plug it in it may do several things.  PCI cards
can integrate several functions (up to 8?) and USB devices
can have several "interfaces" (up to 255) or be parts of compound
devices (most software will ignore that last).  Examples (real):

    - Device:  Cardbus
        * Functions 1,2:  USB OHCI host controller
        * Function 3:  USB EHCI host controller
    - Device:  USB
        * Function 1: audio speaker
        * Function 2: three buttons
    - Compound USB device (integrates a hub):
        * Device 1: USB Hub (single function)
        * Device 2: USB Keyboard (single function)

Right now, /proc/bus/usb names devices, while /proc/bus/pci
names functions.  In an ideal world, we'd be consistent in those
two, and /proc/bus/pcmcia would also be consistent.  (Also in
an ideal world, /proc/bus/usb would expose stable names based
on topology, not unstable ones based on current addresses.)

We report hotplug events not in terms of "physical device"
as you said, or (device) function as I might prefer ... but in
the granularity used by those /proc/bus names.  Even in
kernels not configured with usbdevfs, and even though
multifunction USB devices should arguably get multiple
hotplug events.  (It'd work better that way on systems
that don't configure usbdevfs, too.)

Your definition needs to be less precise, if it's to be accurate.
More  general ... unless we change the code, which should
be a separate thread.

- Dave



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