Manpage of IOPL
IOPLSection: Linux Programmer's Manual (2)
NAMEiopl - change I/O privilege 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.
RETURN VALUEOn success, zero is returned. On error, -1 is returned, and errnois set appropriately.
- levelis greater than 3.
- This call is unimplemented.
- The calling process has insufficient privilege to call iopl(); the CAP_SYS_RAWIOcapability 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 wereinherited 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.
SEE ALSOioperm(2), outb(2), capabilities(7)
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