If you set the O_ASYNC status flag on a file descriptor
(see section File Status Flags), a SIGIO signal is sent whenever
input or output becomes possible on that file descriptor. The process
or process group to receive the signal can be selected by using the
F_SETOWN command to the fcntl function. If the file
descriptor is a socket, this also selects the recipient of SIGURG
signals that are delivered when out-of-band data arrives on that socket;
see section Out-of-Band Data. (SIGURG is sent in any situation
where select would report the socket as having an "exceptional
condition". See section Waiting for Input or Output.)
If the file descriptor corresponds to a terminal device, then SIGIO
signals are sent to the foreground process group of the terminal.
See section Job Control.
The symbols in this section are defined in the header file `fcntl.h'.
fcntl, to
specify that it should get information about the process or process
group to which SIGIO signals are sent. (For a terminal, this is
actually the foreground process group ID, which you can get using
tcgetpgrp; see section Functions for Controlling Terminal Access.)
The return value is interpreted as a process ID; if negative, its absolute value is the process group ID.
The following errno error condition is defined for this command:
EBADF
fcntl, to
specify that it should set the process or process group to which
SIGIO signals are sent. This command requires a third argument
of type pid_t to be passed to fcntl, so that the form of
the call is:
fcntl (filedes, F_SETOWN, pid)
The pid argument should be a process ID. You can also pass a negative number whose absolute value is a process group ID.
The return value from fcntl with this command is @math{-1}
in case of error and some other value if successful. The following
errno error conditions are defined for this command:
EBADF
ESRCH
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