View Source: iopl(2) - Waikato Linux Users Group

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!!NAME
iopl - change I/O privilege level

!!SYNOPSIS
 __#include <sys/io.h>__

 __int iopl(int__ ''level''__);__
!!DESCRIPTION
iopl(2) 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(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 and exec.

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(2) 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.

!!CONFORMING TO
iopl(2) is Linux specific and should not be used in processes intended to be portable.

!!COMPATIBILITY
Under libc5, the prototype for __iopl__() was given 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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Last edited on Thursday, February 20, 2003 11:39:40 pm by PerryLorier

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