io man page on DragonFly

io man page on DragonFly

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IO(4)		       BSD/i386 Kernel Interfaces Manual		 IO(4)

NAME
     io — I/O privilege file

DESCRIPTION
     The special file /dev/io is a controlled security hole that allows a
     process to gain I/O privileges (which are normally reserved for kernel-
     internal 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 per‐
     form direct I/O operations.  This can be useful in order to write user‐
     land programs that handle some hardware directly.	Note that even read-
     only 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
     /dev/io

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

HISTORY
     The io file appeared in FreeBSD 1.0.

BSD				January 1, 1996				   BSD

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