XF86(4) BSD Programmer's Manual XF86(4)
xf86 - XFree86 aperture driver
On alpha, amd64, cats, i386, macppc, and sparc64 the /dev/xf86 driver provides access to the memory and I/O ports of a VGA board and to the PCI configuration registers for use by the XFree86 X servers when running with a kernel security level > 0. The X servers require the use of this driver.
Access to the /dev/xf86 device is allowed when the sysctl variable machdep.allowaperture >= 1. This variable (which has a default value of 0) can only be manipulated when the security level is <= 0, so it should be set in /etc/sysctl.conf. The possible values for machdep.allowaperture are: 0 the aperture driver is disabled. Opening it returns EPERM. 1 the aperture driver allows access to standard VGA framebuffer and BIOS. Access to pci(4) configuration registers is also allowed. 2 in addition to allowing access to pci(4) configuration registers, the aperture driver allows access to the whole 1st megabyte of physical memory, permitting use of the int10 emulation in XFree86 4.0.x. Note that this can cause some security problems, since the process that has access to the aperture driver can also access part of the kernel memory. This mode is not supported on alpha or sparc64.
XF86_Accel(1), XF86_SVGA(1), options(4), pci(4), sysctl.conf(5), config(8), sysctl(8)
/dev/xf86 was introduced as a loadable kernel module for NetBSD 0.9c with XFree86 3.1. It was integrated as an in-kernel device on OpenBSD 2.3. It is required in order to allow access to I/O ports for all X servers since OpenBSD 2.4.
The aperture driver was written by Matthieu Herrb.
This driver allows access to all addresses above physmem. It should be restricted to the actual address range of the video memory. MirOS BSD #10-current February 20, 1998 1
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