HAL 0.1 release
Bryan W. Headley
bwheadley at earthlink.net
Sat Oct 11 00:30:14 EEST 2003
Joe Shaw wrote:
> On Fri, 2003-10-10 at 16:13, Bryan W. Headley wrote:
>>This is all sort of insane because not all digital cameras have
>>mountable memory cards. Some you have to go through the Exif tag library
>>to pull the pictures out.
> Yes. That's partly the point of the capabilities. Those specific
> cameras would only support "Camera" and not "Storage".
Hmm. Yes, but no. That thing I have with a lens on it which plugs into a
USB port contains two devices: a USB digital camera and a USB memory
card reader. It IS true that using the card reader as a generic card
reader is not very convenient, but...
>>On the other hand, let's consider my multi-function printer: it's a
>>printer, fax, copier, scanner, AND it has a slot to plug in those camera
>>memory cards. (And yes, it does let me mount the cards from there,
>>although the intent was more to have a 'camera printer')
> Not knowing really how those devices work with Linux currently, wouldn't
> that be handed by something like CUPS? ie, it's either available or
> not, right? Does this really fall into the realm of the HAL?
Okay, cups was told about the printer. It SHOULD HAVE been told about
the printer by Hal, but nevermind that... Sane knows there is a USB
scanner. The usb-storage kernel module knows that there's a memory card
in the slot. The point is, to the OS, it's several devices.
My printer may "look" like a printer to humans, but its other functions
are not sub-functions. Nor is the keyboard with the built-in hub a
keyboard: it is USB endpoint that has a hub, and into that hub there is
a keyboard which appears to be hardwired to it. And whatever else is
plugged into that hub -- maybe a mouse.
But I'm looking at it from an endpoint standpoint as I was trying to
ween folks away from thinking of sub-facilities: the OS cares about
When it's time to consider the hardware present when I plug in that
camera-looking thing, two pieces of hardware appeared: a camera and a
card reader (e.g., mountable hard disc). When I plug the printer-looking
thing, a printer, a scanner, a fax machine, a card reader and a copier
should be announced as separate pieces of hardware. With that
keyboard-looking thing, a hub with a keyboard connected to it (at least).
Which isn't to say that there isn't hardware that has sub-functions:
it's just not the way to deal with that camera.
(Thinking about it, what IS hardware with a sub-function? A network card
with a PXE boot eeprom on it? Accessible only at bootup?)
Who else likes ambiguous hardware? Well, my digital tablet has the same
behaviorial attributes of a mouse and a joystick; it accepts pressure
events so it may be a touchscreen... Oh, and there are macro keys, so
it's also a keyboard! And Linux Input system does get confused over the
mouse/joystick thing... :-)
____ .:. ____
Bryan W. Headley - bwheadley at earthlink.net
More information about the xdg