ioperm - set port input/output permissions
#include <unistd.h> /* for libc5 */
#include <sys/io.h> /* for glibc */
int ioperm(unsigned long from, unsigned long num, int
Ioperm sets the port access permission bits for the pro
cess for num bytes starting from port address from to the
value turn_on. The use of ioperm requires root privi
Only the first 0x3ff I/O ports can be specified in this
manner. For more ports, the iopl function must be used.
Permissions are not inherited on fork, but on exec they
are. This is useful for giving port access permissions to
On success, zero is returned. On error, -1 is returned,
and errno is set appropriately.
ioperm is Linux specific and should not be used in pro
grams 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.