Re: mousedev patch

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

On Mon, Jul 30, 2001 at 11:33:24AM -0700, Charles Duffy wrote:
> On Mon, Jul 30, 2001 at 09:19:53AM +0200, Vojtech Pavlik wrote:
> > On Sun, Jul 29, 2001 at 06:20:55PM -0700, Charles Duffy wrote:
> > > This will be less acute when a single interface is available which
> > > provides applications with all available information (such as
> > > James's suggestion of an evdev mixer which adds a field giving the
> > > minor number of the evdev device correspending with the source).
> > 
> > Do we really need an evdev mixer? Isn't it easier to just try to
> > open and read all the evdev devices?
> 
> No, it isn't.
> 
> There's quite a bit of software written (Qt/E, for one; Microwindows,
> for another) which already has a mouse-handling architecture which
> allows the mouse driver to open() a file, which is then returned by
> the driver; the framework select()s on that file (among other things),
> and calls the mouse event handler when select returns with the
> appropriate fd.

Unfortunately this probably won't help us with hotplugging.

> Writing evdev drivers for this software would mean not only writing a
> new driver module (a trivial task) but rearchitecting the framework to
> allow drivers to own (and pass to the core) multiple fds, and
> attempting to get these patches accepted by each of the projects in
> question.

Only if you want to use more than one mouse at a time.

> Furthermore, there's no means of detecting disconnection/reconnection
> -- another thing that an extended evdev mixer could (and, IMHO,
> /should/) report.

Disconnection is signalled by evdev by returning -ENODEV on read(). The
process will be woken up on disconnect.

> Assuming that all evdev devices support USB is
> faulty -- I personally have some that aren't (including some
> non-hot-pluggable devices which may be rmmod'd on entry to powersaving
> mode and re-insmod'd on restart; it's quite unuseful if applications
> can't detect new minor numbers and such as a result of such things).

How would you propose detecting new minor numbers? I'd suggest doing it
the same way as USB does with new devices - read /proc/input/devices for
an uptodate list, select() on the very same file to get notified of its
changes.

-- 
Vojtech Pavlik
SuSE Labs