iopl - change I/O privilege level
int iopl(int level);
() changes the I/O privilege level of the calling process, as
specified 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
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 fork(2)
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.
On success, zero is returned. On error, -1 is returned, and errno
- 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.
() is Linux-specific and should not be used in processes intended to
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
and in <sys/perm.h>
. Avoid the latter, it
is available on i386 only.
This page is part of release 3.44 of the Linux man-pages
description of the project, and information about reporting bugs, can be found