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28 .\" @(#)ioctl.2 8.2 (Berkeley) 12/11/93
32 .Dd September 11, 2013
43 .Fn ioctl "int fd" "unsigned long request" ...
47 system call manipulates the underlying device parameters of special files.
48 In particular, many operating
49 characteristics of character special files (e.g.\& terminals)
50 may be controlled with
55 must be an open file descriptor.
59 is traditionally named
63 however, require the third argument to be a
71 has encoded in it whether the argument is an
76 argument, and the size of the argument
79 Macros and defines used in specifying an ioctl
81 are located in the file
84 Some generic ioctls are not implemented for all types of file
87 .Bl -tag -width "xxxxxx"
89 Get the number of bytes that are immediately available for reading.
91 Get the number of bytes in the descriptor's send queue.
92 These bytes are data which has been written to the descriptor but
93 which are being held by the kernel for further processing.
94 The nature of the required processing depends on the underlying device.
95 For TCP sockets, these bytes have not yet been acknowledged by the
96 other side of the connection.
98 Get the free space in the descriptor's send queue.
99 This value is the size of the send queue minus the number of bytes
100 being held in the queue.
101 Note: while this value represents the number of bytes that may be
102 added to the queue, other resource limitations may cause a write
103 not larger than the send queue's space to be blocked.
104 One such limitation would be a lack of network buffers for a write
105 to a network connection.
108 If an error has occurred, a value of -1 is returned and
110 is set to indicate the error.
121 is not a valid descriptor.
126 is not associated with a character
129 The specified request does not apply to the kind
130 of object that the descriptor
144 points outside the process's allocated address space.