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NAMEio —
I/O privilege file
SYNOPSISdevice io
struct iodev_pio_req { u_int access; u_int port; u_int width; u_int val; }; DESCRIPTIONThe 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). This can be useful in order to write userland programs that handle some hardware directly.The usual operations on the device are to open it via the open(2) interface and to send I/O requests to the file descriptor using the ioctl(2) syscall. The
ioctl(2)
requests available for /dev/io are mostly platform
dependent, but there are also some in common between all of them. The
The access member specifies the type of operation requested. It may be:
Finally, the width member specifies the size of the operand to be read/written, expressed in bytes. In addition to any file access permissions on /dev/io, the kernel enforces that only the super-user may open this device. LEGACYThe /dev/io interface used to be very i386 specific and worked differently. The initial implementation simply raised the IOPL of the current thread when open(2) was called on the device. This behaviour is retained in the current implementation as legacy support for both i386 and amd64 architectures.SEE ALSOclose(2), i386_get_ioperm(2), i386_set_ioperm(2), ioctl(2), open(2), mem(4)HISTORYTheio file appeared in FreeBSD
1.0.
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