Open letter to NetBSD about Mesa 13+

[David Shao <davshao%gmail.com@localhost>]

NetBSD developers need to make a couple of decisions about
implementing support for Mesa 13+.

As documented in PR kern/51786
(mesa 13.0.2 libdrm 2.4.74 Radeon needs kernel support, new ioctl or sysctl)
Mesa 13+ switched hardware detection to libdrm.  In libdrm
the work is now done by passing the file descriptor of the
equivalent of /dev/dri/card0 or whatever the device is and
then asking libdrm to fill in the pci video card information.

1) First decision: Provide either through sysctl or ioctls
this pci card information.  In the above PR, I ported
OpenBSD's use of an ioctl, but I changed it from re-using
an old ioctl to using a so-far unused ioctl number.
But FreeBSD and DragonFly already have the kernel provide
this information through sysctls.

After making this decision, patch libdrm somewhat similar
to what has been documented in PR pkg/51795
(x11/libdrm update xf86drm.c for mesa 13.0.2 needs negotiation)

NetBSD currently has a problem with dlopen, init-exec, and
non-trivial initializers.

See the discussion in the thread
(Workaround for NetBSD initial-exec and dlopen is not supported?)

https://mail-index.netbsd.org/pkgsrc-users/2015/08/25/msg022089.html

https://mail-index.netbsd.org/pkgsrc-users/2015/09/11/msg022183.html

Therefore there was a pkgsrc MesaLib 11 patch to initialize with 0 and
later in assembly generated code initialize
with a default array.

As further documented in PR pkg/51796
(graphics/MesaLib Update to 13.0.2 with glamor / egl somewhat working)
some change between Mesa 11 and Mesa 13 caused NetBSD's
patch to no longer compile.

2) Second decision:  Patch NetBSD so it can handle non-trivial
initializers to dlopen-ed init-exec, or try and figure out the
one change between Mesa 11 and Mesa 13 that broke the
patch, or brute force provide an initializing array.

I tried to revert various changes between Mesa 11 and 13
but never found a reversion that fixed compilation.  In the
above PR I submitted a brute force initializing array that
does not handle the case of debugging enabled.

Of course this is open source and doing nothing is an option.
It may be even easier to accept since apparently Intel
integrated graphics does not use the libdrm code path.
But if Mesa is ever upgraded to 13+, Radeon and perhaps
other pci graphics cards will lose even 2D exa acceleration.

This matter needs to be dealt with now.