On Wed, 8 Mar 2006, David Brownell wrote:
> > In this case it wouldn't make any difference, since all the altsettings
> > for a particular interface are supposed to have the same bInterfaceClass,
> > bInterfaceSubClass, and bInterfaceProtocol. Although I don't think the
> > USB spec actually says this anywhere..
>
> I'd have stopped at "wouldn't make any difference"; the kernel must make
> some initial choice, but userspace is free to revise it. Agreed it would
> be odd if altsettings had different class/subclass/protocol, but I don't
> see any good reason to make that illegal.
Agreed. And like I said before, this is only a heuristic.
> > The bMaxPower value could be different for different altsettings.
>
> Erm, no; that's a per-configuration thing, not a per-altsetting thing.
> It's checking the config descriptor, not the interface descriptor,
> for that particular concern.
Whoops, yes. I misread the code. All the more reason not to worry about
any but the first altsetting.
> > > > b) How do we know that there's actually anything _there_? The length of
> > > > that variable-sized array doesn't seem to have been stored anywhere
> > > > obvious by usb_parse_configuration() and choose_configuration() doesn't
> > > > check. What happens if the length was zero?
> > >
> > > I don't think it is allowed to be, as all USB devices have to have at
> > > least 1 interface.
>
> I think that's not true, and it would be worth verifying that it's not
> a no-interfaces device even if the USB spec required it. It's trivial
> to create device firmware that advertises no-interfaces, and those should
> never be able to make Linux hiccup (much less oops).
Ha! "should never be able" indeed. It turns out the code doesn't like it
if a configuration has no interfaces. How embarassing...
Andrew, if you tell us what's in your /proc/bus/usb/devices we'll see
whether that was the real problem. In any case, a patch follows.
Alan Stern
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
