Description of problem: Configure a video wall. Try and run X11 on it and it aborts with Fatal server error: AddScreen/ScreenInit failed for driver 16 If it just skipped extra displays it couldnt cope with that wouldn't be too bad but it aborts the server instead which sucks 8) (Of course bumping X to 32 heads would be nice 8))
After discussing with XFree86 developers, increasing MAXSCREENS would break binary compatibility of the server<->module interface, and so can not be done until a major server version bump (ie: 5.0). Additionally, doing it as a customized build where bin compat doesn't matter will result in some amount of wasted resources do to fixed sized arrays that get allocated the size of MAXSCREENS, or some other similarly poorly implemented code. So for a short term hack, you can try increasing MAXSCREENS to 32 or whatever in xc/programs/Xserver/include/misc.h The protocol maximum is 256 screens, which is probably what the hard coded limit should be when the code is refactored to be dynamic for 5.0. Note also however, that someone mentioned that there might be somewhere in the server in which screens are manipulated via a 32bit integer bitmask or somesuch. If so, this would imply that going beyond 32 screens (possibly 31 if sign issues are present) would also break things. I haven't attempted to substantiate this last claim though. Closing as UPSTREAM, and linking to upstream bug report to track this for XFree86 5.0 et al. http://bugs.xfree86.org/cgi-bin/bugzilla/show_bug.cgi?id=235
Cleaning up UPSTREAM flagged bugs, moving this one to DEFERRED for long term tracking instead.
The MAXSCREENS problem has patches floating around which bypass this problem but change ABI incompatibly, so are unsuitable for any existing OS release. It's not possible to solve this issue without breaking ABI, so this will become an upstream change in a future X.Org major release. It might be in X11R7 later this year, but it hasn't been decided yet I don't think. A quick search of X.org bugzilla didn't yield a bug that is tracking this, but I know several developers have thought about it at least and discussed different solutions. The best place to track this is on xorg or to file an Xorg report to track it. Setting status to UPSTREAM.