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28 .Dd September 11, 2013
39 .Fn ioctl "int fd" "unsigned long request" ...
43 system call manipulates the underlying device parameters of special files.
44 In particular, many operating
45 characteristics of character special files (e.g.\& terminals)
46 may be controlled with
51 must be an open file descriptor.
55 is traditionally named
59 however, require the third argument to be a
67 has encoded in it whether the argument is an
72 argument, and the size of the argument
75 Macros and defines used in specifying an ioctl
77 are located in the file
80 Some generic ioctls are not implemented for all types of file
83 .Bl -tag -width "xxxxxx"
85 Get the number of bytes that are immediately available for reading.
87 Get the number of bytes in the descriptor's send queue.
88 These bytes are data which has been written to the descriptor but
89 which are being held by the kernel for further processing.
90 The nature of the required processing depends on the underlying device.
91 For TCP sockets, these bytes have not yet been acknowledged by the
92 other side of the connection.
94 Get the free space in the descriptor's send queue.
95 This value is the size of the send queue minus the number of bytes
96 being held in the queue.
97 Note: while this value represents the number of bytes that may be
98 added to the queue, other resource limitations may cause a write
99 not larger than the send queue's space to be blocked.
100 One such limitation would be a lack of network buffers for a write
101 to a network connection.
104 If an error has occurred, a value of -1 is returned and
106 is set to indicate the error.
117 is not a valid descriptor.
122 is not associated with a character
125 The specified request does not apply to the kind
126 of object that the descriptor
140 points outside the process's allocated address space.