17.4 File Operations
The next group of requests begin with
FIO and may apply to certain types of files, in addition
to sockets. We cover only the requests that apply to sockets (p.
553 of TCPv2). The following five requests all require that the
third argument to ioctl point to an integer:
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FIONBIO
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The nonblocking flag for the socket is cleared
or turned on, depending on whether the third argument to
ioctl points to a zero or nonzero value, respectively.
This request has the same effect as the O_NONBLOCK file
status flag, which can be set and cleared with the F_SETFL
command to the fcntl function.
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FIOASYNC
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The flag that governs the receipt of
asynchronous I/O signals (SIGIO) for the socket is cleared
or turned on, depending on whether the third argument to
ioctl points to a zero or nonzero value, respectively.
This flag has the same effect as the O_ASYNC file status
flag, which can be set and cleared with the F_SETFL
command to the fcntl function.
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FIONREAD
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Return in the integer pointed to by the third
argument to ioctl the number of bytes currently in the
socket receive buffer. This feature also works for files, pipes,
and terminals. We said more about this request in Section
14.7.
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FIOSETOWN
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Equivalent to SIOCSPGRP for a
socket.
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FIOGETOWN
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Equivalent to SIOCGPGRP for a
socket.
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