NAME    [Toc]    [Back]

     io -- I/O privilege file

DESCRIPTION    [Toc]    [Back]

     The special file /dev/io is a controlled security hole that allows a
     process to gain I/O privileges (which are normally reserved for kernelinternal
 code).  Any process that holds a file descriptor on /dev/io open
     will get its IOPL bits in the flag register set, thus allowing it to perform
 direct I/O operations.  This can be useful in order to write userland
 programs that handle some hardware directly.	Note that even readonly
 access will grant the full I/O privileges.

     In addition to any file access permissions on /dev/io, the kernel
     enforces that only the super-user may open this device.

FILES    [Toc]    [Back]

     /dev/io

SEE ALSO    [Toc]    [Back]

     i386_get_ioperm(2), i386_set_ioperm(2), mem(4)

HISTORY    [Toc]    [Back]

     The io file appeared in FreeBSD 1.0.


FreeBSD 5.2.1			January 1, 1996 		 FreeBSD 5.2.1