7 Kernel Support for X

By default NetBSD 0.9C and higher include a kernel security feature that disable access to the /dev/mem device when in multi-users mode. But XFree86 servers can take advantage (or require) linear access to the display memory.

The P9000 and AGX servers require linear memory access, other accelerated servers can take advantage of it, but do not require it.

There are two ways to allow XFree86 to access linear memory:

1. Disable the kernel security feature by initializing the ``securelevel'' variable to -1 in /sys/kern/kern_sysctl.c, line 205 and building a new kernel. For more informations, see the comments in /usr/include/sys/systm.h.
2. Install the NetBSD aperture driver:
   1. add the following lines to the end of /etc/rc.local:

       KERNDIR=/usr/X11R6/lib/X11/kernel
       if [ -f ${KERNDIR}/ap.o ]; then
         modload -o ${KERNDIR}/ap -e ap -p ${KERNDIR}/apinstall ${KERNDIR}/ap.o
       fi
      

   2. On pre 1.0 versions of NetBSD modload does not execute post-install scripts. If you're running NetBSD 1.0 or later skip this. Else create the device manually: WARNING: be sure to understand what you'll do before proceeding
      1. find out what major device number will be allocated to you by modload. Modload allocates major numbers beginning at 29. So if ``ap'' is your only device driver module, it will have major number 29. If it's the third, it will be 31...
      2. goto the /dev directory and type: ``mknod xf86 c 29 0'' (replace 29 by the appropriate value if you load more than one device driver module.
   3. Reboot your system. XFree86 will auto-detect the aperture driver if available.

Caveat: the NetBSD aperture driver only allows one access at a time (so that the system is in the same security state once X is launched). This means that if you run multiple servers on multiples VT, only the first one will have linear memory access.

NetBSD 1.0 supports System V shared memory. If XFree86 3.1.1 detects this support in your kernel, it will support the MIT-SHM extension.

Under NetBSD 1.0, use the following to add shared memory support to your kernel:

To add support for system V shared memory to your kernel add the lines:

 # System V-like IPC
 options         SYSVMSG
 options         SYSVSEM
 options         SYSVSHM

to your kernel config file. Then from /sys/arch/i386/config, type:

 # rm -f ../compile/<KERNEL-NAME>/*
 # config <KERNEL-NAME>
 # cd ../compile/<KERNEL-NAME>
 # make depend 
 # make

Then install your new kernel and re-boot:

 # cp /netbsd /onetbsd
 # cp netbsd /
 # reboot