Copyright 1993 Rickard E. Faith (email@example.com) Portions extracted from linux/kernel/ioport.c (no copyright notice). %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed un...
NAMEiopl - change I/O privilege level
int iopl(int level);
DESCRIPTIONiopl() changes the I/O privilege level of the calling process, as specified by the two least significant bits in level.
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 ioperm(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.
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 VALUEOn 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 iopl(); the CAP_SYS_RAWIO capability is required to raise the I/O privilege level above its current value.
CONFORMING TOiopl() is Linux-specific and should not be used in programs that are intended to be portable.
NOTESGlibc2 has a prototype both in <sys/io.h> and in <sys/perm.h>. Avoid the latter, it is available on i386 only.
Prior to Linux 3.7, on some architectures (such as i386), permissions were inherited by the child produced by fork(2) and were preserved across execve(2). This behavior was inadvertently changed in Linux 3.7, and won't be reinstated.