IOPERM(2) Linux Programmer's Manual IOPERM(2)
ioperm - set port input/output permissions
#include <sys/io.h> /* for glibc */
int ioperm(unsigned long from, unsigned long num, int turn_on);
ioperm() sets the port access permission bits for the calling thread
for num bits starting from port address from. If turn_on is nonzero,
then permission for the specified bits is enabled; otherwise it is dis-
abled. 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 level argument of 3). Since Linux 2.6.8, 65,536 I/O ports can
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 architec-
tures it does not exist or will always return an error.
On success, zero is returned. On error, -1 is returned, and errno is
EINVAL Invalid values for from or num.
EIO (on PowerPC) This call is not supported.
ENOMEM Out of memory.
EPERM The calling thread has insufficient privilege.
ioperm() is Linux-specific and should not be used in programs intended
to be portable.
The /proc/ioports 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> and in <sys/perm.h>.
Avoid the latter, it is available on i386 only.
iopl(2), outb(2), capabilities(7)
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