Standard C Library (libc, -lc)
() system call manipulates the
underlying device parameters of special files. In particular, many operating
characteristics of character special files (e.g. terminals) may be controlled
() requests. The argument
must be an open file descriptor.
The third argument to
traditionally named char *argp
. Most uses of
(), however, require the third
argument to be a caddr_t
has encoded in it whether the
argument is an “in” argument or “out” argument,
and the size of the argument argp
Macros and defines used in specifying an ioctl
are located in the file
Some generic ioctls are not implemented for all types of file descriptors. These
- Get the number of bytes that are immediately available for reading.
- Get the number of bytes in the descriptor's send queue. These bytes are
data which has been written to the descriptor but which are being held by
the kernel for further processing. The nature of the required processing
depends on the underlying device. For TCP sockets, these bytes have not
yet been acknowledged by the other side of the connection.
- Get the free space in the descriptor's send queue. This value is the size
of the send queue minus the number of bytes being held in the queue. Note:
while this value represents the number of bytes that may be added to the
queue, other resource limitations may cause a write not larger than the
send queue's space to be blocked. One such limitation would be a lack of
network buffers for a write to a network connection.
If an error has occurred, a value of -1 is returned and
is set to indicate the error.
() system call will fail if:
- The fd argument is not a valid
- The fd argument is not associated with a
character special device.
- The specified request does not apply to the kind of object that the
descriptor fd references.
- The request or
argp argument is not valid.
- The argp argument points outside the
process's allocated address space.
() function appeared in
Version 7 AT&T UNIX