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       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
       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 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);
       following  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
       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 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.

       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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