If you set the O_ASYNC status flag on a file descriptor
(see 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 Out-of-Band Data. (SIGURG is sent in any situation
where select would report the socket as having an “exceptional
condition”. See Waiting for I/O.)
If the file descriptor corresponds to a terminal device, then SIGIO
signals are sent to the foreground process group of the terminal.
See Job Control.
The symbols in this section are defined in the header file fcntl.h.
This macro is used as the command argument to
fcntl, to specify that it should get information about the process or process group to whichSIGIOsignals are sent. (For a terminal, this is actually the foreground process group ID, which you can get usingtcgetpgrp; see Terminal Access Functions.)The return value is interpreted as a process ID; if negative, its absolute value is the process group ID.
The following
errnoerror condition is defined for this command:
EBADF- The filedes argument is invalid.
This macro is used as the command argument to
fcntl, to specify that it should set the process or process group to whichSIGIOsignals are sent. This command requires a third argument of typepid_tto be passed tofcntl, 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
fcntlwith this command is -1 in case of error and some other value if successful. The followingerrnoerror conditions are defined for this command:
EBADF- The filedes argument is invalid.
ESRCH- There is no process or process group corresponding to pid.