[Qemu-devel] Re: Qemu does not pass pressed caps lock to client

[Paolo Bonzini <pbonzini@redhat.com>]

On 02/12/2010 12:09 PM, Shahar Havivi wrote:
> It's not true that SDL is not sending up event like the comment say,
>
> On Fedora 12 it behave like a toggle button, first press/release will send
> caps-down event second press/release send caps-up event
 >
> On Ubuntu 9.10 it work like any other key, i.e. pressing caps will generate two
> events down and up.

True.  To see why, start at 
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=317010 and 
http://archive.ubuntu.com/ubuntu/pool/main/libs/libsdl1.2/libsdl1.2_1.2.13-4ubuntu4.diff.gz 
-- it's a nice code reading exercise, so I'll suggest a possible 
solution before pointing out the reason for this behavior.  The solution 
would be to put hack after hack, i.e. something like this (untested):

     case 0x3a: /* caps lock */
         /* SDL will usually send only 2 events instead of 4, so we
            generate the missing ones.  However, on Debian/Ubuntu
            systems it may generate 4; in this case we have to discard
            the extra events.  On Debian/Ubuntu ev->key.keysym.mod
            will always be zero, but for other systems we need the
            complicated condition below.  */
	if ((ev->key.keysym.mod & KMOD_CAPS) ==
             (ev->type == SDL_KEYDOWN ? KMOD_CAPS : 0)) {
             kbd_put_keycode(keycode);
             kbd_put_keycode(keycode | 0x80);
         }
         return;
     case 0x45: /* num lock */
         /* Same as above.  */
	if ((ev->key.keysym.mod & KMOD_NUM) ==
             (ev->type == SDL_KEYDOWN ? KMOD_NUM : 0)) {
             kbd_put_keycode(keycode);
             kbd_put_keycode(keycode | 0x80);
         }
         return;

Now, the solution of the riddle.  The patch was correctly submitted as

+	SDL_UseLockKeys = getenv ("SDL_DISABLE_LOCK_KEYS") == NULL;

...

+	use_lock_keys = SDL_UseLockKeys;

...

+				if (!use_lock_keys)
+					break;

(i.e. by default do not change anything) but the maintainer apparently 
morphed it into

+	SDL_UseLockKeys = getenv("SDL_DISABLE_LOCK_KEYS");

...

+ 	use_lock_keys = ( SDL_UseLockKeys && *SDL_UseLockKeys );

...

+ 				if ( ! use_lock_keys )
+ 					break;

which changed the default and the meaning of SDL_DISABLE_LOCK_KEYS.

I initially thought about removing the caps lock/num lock hack 
altogether and add the following, however it would need SDL 1.2.14 
because SDL_NO_LOCK_KEYS support was added exactly two months after 
1.2.13 was released. :-( :-(

     /* There are two versions around of a Debian patch that changes the
        way Caps Lock and Num Lock are handled.  The first version
        by default sends only one of the KeyDown/KeyUp events, unless
        SDL_DISABLE_LOCK_KEYS is present in the environment.  The second
        version instead by default sends both events, unless
        SDL_DISABLE_LOCK_KEYS is present and not empty.  This version
        is the most commonly found (and a totally braindead idea).

        Upstream instead supports SDL_NO_LOCK_KEYS which, if set to 1,
        will generate all four events---which is what we want.  Luckily,
        there is a combination of environment variable that will satisfy
        all variant.  */

     putenv ("SDL_DISABLE_LOCK_KEYS", "");
     putenv ("SDL_NO_LOCK_KEYS", "1");

Yes, I love Debian.

Paolo