17.3 Socket Operations
Three ioctl requests are explicitly
used for sockets (pp. 551鈥?53 of TCPv2). All three require that the
third argument to ioctl be a pointer to an integer.
SIOCATMARK
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Return through the integer pointed to by the
third argument a nonzero value if the socket's read pointer is
currently at the out-of-band mark, or a zero value if the read
pointer is not at the out-of-band mark. We will describe
out-of-band data in more detail in Chapter 24. POSIX replaces this
request with the sockatmark function, and we will show an
implementation of this new function using ioctl in
Section 24.3.
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SIOCGPGRP
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Return through the integer pointed to by the
third argument either the process ID or the process group ID that
is set to receive the SIGIO or SIGURG signal for
this socket. This request is identical to an fcntl of
F_GETOWN, and we note in Figure 7.20 that
POSIX standardizes the fcntl.
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SIOCSPGRP
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Set either the process ID or process group ID to
receive the SIGIO or SIGURG signal for this
socket from the integer pointed to by the third argument. This
request is identical to an fcntl of F_SETOWN, and
we note in Figure 7.20 that
POSIX standardizes the fcntl.
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