IOPL(2) Linux Programmer's Manual IOPL(2)
NAME
iopl - change I/O privilege level
SYNOPSIS
#include <sys/io.h>
int iopl(int level);
DESCRIPTION
iopl changes the I/O privilege level of the current process, as speci-
fied in(1,8) level.
This call is necessary to allow 8514-compatible X servers to run under
Linux. Since these X servers require access(2,5) to all 65536 I/O ports,
the ioperm call is not sufficient.
In addition to granting unrestricted I/O port access(2,5), running at a
higher I/O privilege level also allows the process to disable inter-
rupts. This will probably crash the system, and is not recommended.
Permissions are inherited by fork and exec.
The I/O privilege level for a normal process is 0.
This call is mostly for the i386 architecture. On many other architec-
tures it does not exist or will always return an error.
RETURN VALUE
On success, zero is returned. On error(8,n), -1 is returned, and errno is
set(7,n,1 builtins) appropriately.
ERRORS
EINVAL level is greater than 3.
ENOSYS This call is unimplemented.
EPERM The calling process has insufficient privilege to call iopl; the
CAP_SYS_RAWIO capability is required.
CONFORMING TO
iopl is Linux specific and should not be used in(1,8) processes intended to
be portable.
NOTES
Libc5 treats it as a system call and has a prototype in(1,8) <unistd.h>.
Glibc1 does not have a prototype. Glibc2 has a prototype both in(1,8)
<sys/io.h> and in(1,8) <sys/perm.h>. Avoid the latter, it is available on
i386 only.
SEE ALSO
ioperm(2), capabilities(7)
Linux 2.6.6 2004-05-27 IOPL(2)