IOPL
Section: Linux Programmer's Manual (2)
Updated: 24 July 1993
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NAME
iopl - change I/O privilege level
SYNOPSIS
#include <unistd.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.
The I/O privilege level for a normal process is 0.
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.
NOTES FROM THE KERNEL SOURCE
iopl
has to be used when you want to access the I/O ports beyond the 0x3ff
range: to get the full 65536 ports bitmapped you'd need 8kB of
bitmaps/process, which is a bit excessive.
SEE ALSO
ioperm(2)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- NOTES FROM THE KERNEL SOURCE
-
- SEE ALSO
-
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