iopl(2) -- Linux man page
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 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
ioperm
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 and exec.
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.
ERRORS
- EINVAL
-
level
is greater than 3.
- EPERM
-
The current user is not the super-user.
- ENOSYS
-
This call is unimplemented.
CONFORMING TO
iopl is Linux specific and should not be used in processes
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.
SEE ALSO
ioperm(2)
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