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 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 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.

   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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