iopl()
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
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.
Permissions are inherited by
fork(2)
and
execve(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.
RETURN VALUE
On success, zero is returned.
On error, -1 is returned, and
errno
is set 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 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.
This page is part of release 3.14 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
