iopl(2) -- Linux man page
NAMEiopl - change I/O privilege level
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.
- level is greater than 3.
- The current user is not the super-user.
- This call is unimplemented.
CONFORMING TOiopl is Linux specific and should not be used in processes intended to be portable.
NOTESLibc5 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.