|| Linux Programmer's Manual
NAME iopl - change I/O privilege level
() changes the I/O privilege level of the calling process, as specified by the two least significant bits in
This call is necessary to allow 8514-compatible X servers to run under Linux. Since these X servers require access to all 65536 I/O ports, the
(2) call is not sufficient.
In addition to granting unrestricted I/O port access, running at a higher I/O privilege level also allows the process to disable interrupts. This will probably crash the system, and is not recommended.
Permissions are inherited by
The I/O privilege level for a normal process is 0.
This call is mostly for the i386 architecture. On many other architectures it does not exist or will always return an error.
RETURN VALUE On success, zero is returned. On error, -1 is returned, and
errno is set appropriately.
level is greater than 3.
This call is unimplemented.
The calling process has insufficient privilege to call
CAP_SYS_RAWIO capability is required to raise the I/O privilege level above its current value.
iopl() is Linux-specific and should not be used in programs that are intended to be portable.
NOTES Libc5 treats it as a system call and has a prototype in
<unistd.h>. Glibc1 does not have a prototype. Glibc2 has a prototype both in
<sys/io.h> and in
<sys/perm.h>. Avoid the latter, it is available on i386 only.
COLOPHON 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 http://www.kernel.org/doc/man-pages/.