ioperm - set port input/output permissions
/* for glibc */
int ioperm(unsigned long from, unsigned long num,
() sets the port access permission bits for the calling thread for
bits starting from port address from
. If turn_on
nonzero, then permission for the specified bits is enabled; otherwise it is
disabled. If turn_on
is nonzero, the calling thread must be privileged
Before Linux 2.6.8, only the first 0x3ff I/O ports could be specified in this
manner. For more ports, the iopl
(2) system call had to be used (with a
argument of 3). Since Linux 2.6.8, 65,536 I/O ports can be
Permissions are inherited by the child created by fork
(2) (but see
NOTES). Permissions are preserved across execve
(2); this is useful for
giving port access permissions to unprivileged programs.
This call is mostly for the i386 architecture. On many other architectures it
does not exist or will always return an error.
On success, zero is returned. On error, -1 is returned, and errno
- Invalid values for from or num.
- (on PowerPC) This call is not supported.
- Out of memory.
- The calling thread has insufficient privilege.
() is Linux-specific and should not be used in programs intended to
file shows the I/O ports that are currently allocated
on the system.
Before Linux 2.4, permissions were not inherited by a child created by
Glibc has an ioperm
() prototype both in <sys/io.h>
. Avoid the latter, it is available on i386 only.