Re: evdev types

[Vojtech P. <vo...@su...>]

On Wed, Apr 17, 2002 at 09:56:05PM +1000, Brad Hards wrote:
> On Wed, 17 Apr 2002 18:21, Vojtech Pavlik wrote:
> <snip>
> > Not really a 2d bitfield, more like a bunch of 1d bitfields with uneven
> > lengths. You pass an argument selecting which one you want and you get
> > it. I think EVIOCGBIT is quite OK, because it doesn't really depend on
> > the data type ... it just copies a chunk of memory.
> >
> > What is probably the only wrong w/ the bit arrays is the way they're
> > passed through by /proc and hotplug support. And that can be fixed
> > without any major pain, because noone is using that on 64-bit systems
> > yet.
> OK, no issue on 2.4, correct?
> This was stuff you added in 2.5?
> 
> ><snip>
> > 	ioctl(fd, EVIOCGBIT(EV_KEY, sizeof(my_buffer)), buffer);
> Ah, I think I have it now. For 
> 
> ioctl(a, EVIOCGBIT(b, c), d)
> 
> a is the file descriptor for the event device you want
> 
> b is the type of descriptor bitfield to return
> 	0 for the type of descriptors that are used
> 	EV_KEY for the key bitfield
> 	EV_REL for the relative axes bitfield
> 	EV_ABS for the absolute axes bitfield
> 	EV_MSC for the miscellaneous bitfield (not used yet?)
> 	EV_LED for the bright lights bitfield
> 	EV_SND for the loud noises bitfield
> 	EV_REP for the repeat function bitfield (not used yet?)
> 	EV_FF for the force feedback bitfield
> 
> c is the maximum number of bits to return
> 	If the number of bits available is greater, then you get a warning message

Bytes.

> d is a pointer to the memory to put the bitfield

Yes.

> and the return value is the number of bits transfered (if it succeeds) or 
> -EFAULT if it fails. 

Bytes, again.

> The number of bits transferred is the lesser of c, and 
> the number of bits for that descriptor type (eg forb == 0, it is EV_MAX,  b 
> == EV_KEY, it is KEY_MAX; for b == EV_REL it is REL_MAX, and so on).
> 
> OK, my only question now is "how do you get the descriptor bitfield for 
> EV_RST?"

There is none. There are no bits for EV_RST, it's only one event in its
own class.

-- 
Vojtech Pavlik
SuSE Labs