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RedHat 9 (Linux i386) - man page for iopl (redhat section 2)

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IOPL(2) 			    Linux Programmer's Manual				  IOPL(2)

       iopl - change I/O privilege level

       #include <sys/io.h>

       int iopl(int level);

       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.

       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

       EINVAL level is greater than 3.

       EPERM  The current user is not the super-user.

       iopl is Linux specific and should not be used in processes intended to be portable.

       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.


Linux 0.99.11				    1993-07-24					  IOPL(2)
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