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       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 turn_on);


       ioperm()  sets  the port access permission bits for the calling process
       for num bytes starting from port address from to the value turn_on.  If
       turn_on   is   nonzero,   the   calling   process  must  be  privileged

       Only the first 0x3ff I/O ports can be specified in  this  manner.   For
       more ports, the iopl(2) system call must be used.

       Permissions  are  not  inherited  by  the  child  created  by  fork(2).
       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  is
       set appropriately.


       EINVAL Invalid values for from or num.

       EIO    (on PowerPC) This call is not supported.

       ENOMEM Out of memory.

       EPERM  The calling process has insufficient privilege.


       ioperm()  is Linux-specific and should not be used in programs 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.


       iopl(2), capabilities(7)


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