ioperm

       #include <sys/io.h> /* for glibc */

       int ioperm(unsigned long from, unsigned long num, int turn_on);

DESCRIPTION
       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
       (CAP_SYS_RAWIO).

       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
       be specified.

       Permissions are not inherited by the child created by fork(2);  follow-
       ing  a  fork(2) the child must turn on those permissions that it needs.
       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.

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and  errno  is
       set appropriately.

ERRORS
       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.

CONFORMING TO
       ioperm()  is Linux-specific and should not be used in programs intended
       to be portable.

NOTES
       The /proc/ioports file shows the I/O ports that are currently allocated
       on the system.

       Glibc has an ioperm() prototype both in <sys/io.h> and in <sys/perm.h>.
       Avoid the latter, it is available on i386 only.

SEE ALSO
       iopl(2), outb(2), capabilities(7)

COLOPHON
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