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CentOS 7.0 - man page for vm86 (centos section 2)

VM86(2) 						     Linux Programmer's Manual							   VM86(2)

vm86old, vm86 - enter virtual 8086 mode
#include <sys/vm86.h> int vm86old(struct vm86_struct *info); int vm86(unsigned long fn, struct vm86plus_struct *v86);
The system call vm86() was introduced in Linux 0.97p2. In Linux 2.1.15 and 2.0.28 it was renamed to vm86old(), and a new vm86() was intro- duced. The definition of struct vm86_struct was changed in 1.1.8 and 1.1.9. These calls cause the process to enter VM86 mode (virtual-8086 in Intel literature), and are used by dosemu. VM86 mode is an emulation of real mode within a protected mode task.
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
EFAULT This return value is specific to i386 and indicates a problem with getting user-space data. ENOSYS This return value indicates the call is not implemented on the present architecture. EPERM Saved kernel stack exists. (This is a kernel sanity check; the saved stack should exist only within vm86 mode itself.)
This call is specific to Linux on 32-bit Intel processors, and should not be used in programs intended to be portable.
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at Linux 2009-02-20 VM86(2)