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Manpages IOPLSection: Linux Programmer's Manual (2)Updated: 1993-07-24 Index Return to Main Contents NAMEiopl - change I/O privilege levelSYNOPSIS#include <sys/io.h>DESCRIPTIONiopl 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. RETURN VALUEOn success, zero is returned. On error, -1 is returned, and errno is set appropriately.ERRORS
NOTES FROM THE KERNEL SOURCEiopl 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 TOiopl is Linux specific and should not be used in processes intended to be portable.COMPATIBILITYUnder libc5, the prototype for iopl() was given in <unistd.h>.SEE ALSOioperm(2)
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