The pipe2() system call allows control over the attributes of the file descriptors via the flags argument. Values for flags are constructed by a bitwise-inclusive OR of flags from the following list, defined in <fcntl.h>:
|Set the close-on-exec flag for the new file descriptors.
|Set the non-blocking flag for the ends of the pipe.
If the flags argument is 0, the behavior is identical to a call to pipe().
By convention, the first descriptor is normally used as the read end of the pipe, and the second is normally the write end, so that data written to fildes appears on (i.e., can be read from) fildes. This allows the output of one program to be sent to another program: the source's standard output is set up to be the write end of the pipe, and the sink's standard input is set up to be the read end of the pipe. The pipe itself persists until all its associated descriptors are closed.
A pipe that has had an end closed is considered widowed. Writing on such a pipe causes the writing process to receive a SIGPIPE signal. Widowing a pipe is the only way to deliver end-of-file to a reader: after the reader consumes any buffered data, reading a widowed pipe returns a zero count.
The bidirectional nature of this implementation of pipes is not portable to older systems, so it is recommended to use the convention for using the endpoints in the traditional manner when using a pipe in one direction.
|fildes argument points to an invalid memory location.
|Too many descriptors are active.
|The system file table is full.
|Not enough kernel memory to establish a pipe.
The pipe2() system call will also fail if:
|The flags argument is invalid.
Bidirectional pipes were first used on AT&T V.4 .
The pipe2() function appeared in FreeBSD 10.0 .
The pipe() function became a wrapper around pipe2() in FreeBSD 11.0 .
|December 1, 2017
|I have a natural revulsion to any operating system that shows so little planning as to have to named all of its commands after digestive noises (awk, grep, fsck, nroff).