[9fans] why is /dev/mousein exclusive use?

[9fans] why is /dev/mousein exclusive use?

[Richard Miller]

Is there a good reason to forbid multiple processes to open
the mousein device?  I can't think what trouble it could cause
(writes have to be atomic anyway because the driver will only
parse a complete input), and it makes it awkward to debug
a new mouse driver if a usb mouse is already (or has ever been)
connected.

Re: [9fans] why is /dev/mousein exclusive use?

[erik quanstrom]

On Mon Dec 10 11:37:12 EST 2012, 9fans@hamnavoe.com wrote:
> Is there a good reason to forbid multiple processes to open
> the mousein device?  I can't think what trouble it could cause
> (writes have to be atomic anyway because the driver will only
> parse a complete input), and it makes it awkward to debug
> a new mouse driver if a usb mouse is already (or has ever been)
> connected.

can't think of any.  one can already attach 2 mice to a pc,
one ps/2, and one usb.  it works fine.

- erik

Re: [9fans] why is /dev/mousein exclusive use?

[lucio]

> can't think of any.  one can already attach 2 mice to a pc,
> one ps/2, and one usb.  it works fine.

I second that, I've had a ps2 mouse and a serial trackball working
side by side.

++L

Re: [9fans] why is /dev/mousein exclusive use?

[Richard Miller]

No objections having been raised, I've submitted a patch
(mousein-non-exclusive) to remove this restriction.

Next, the same question about /dev/kbin - does that need to be
exclusive open?  I think not.  Slightly more complicated, because
kbin can receive a pair of inputs (escape + scancode) and pass them
one at a time to the kbd driver.  But that is already a potential bug,
not prevented by exclusive open - usbd can start driver processes for
two usb keyboards, multiplexing their inputs through one fd to kbin,
and on a multiprocessor the escapes might be incorrectly interleaved.

My proposal is to remove the exclusive open, and instead put a qlock
around the loop which sends codes from kbin to kbd.

Re: [9fans] why is /dev/mousein exclusive use?

[erik quanstrom]

> My proposal is to remove the exclusive open, and instead put a qlock
> around the loop which sends codes from kbin to kbd.

or, keep a small structure, perhaps in the channel to keep
track of these things.  there's also a limitation where the same
kbmap gets applied to all keyboards.

- erik

Re: [9fans] why is /dev/mousein exclusive use?

[Anthony Martin]

Richard Miller <9fans@hamnavoe.com> once said:
> Is there a good reason to forbid multiple processes to open
> the mousein device?  I can't think what trouble it could cause
> (writes have to be atomic anyway because the driver will only
> parse a complete input), and it makes it awkward to debug
> a new mouse driver if a usb mouse is already (or has ever been)
> connected.

IIRC, this restriction was removed in 9front.

  Anthony