FIFOs

•      A first-in, first-out (FIFO) file is a pipe that has a name in the filesystem. Any process can open or close the FIFO; the processes on either end of the pipe need not be related to each other.

•      FIFOs are also called named pipes.

•      You can make a FIFO using the “mkfifo” command. Specify the path to the FIFO on the command line. For example, create a FIFO in /tmp/fifo by invoking this command:

•      $ mkfifo /tmp/fifo

•      $ ls -l /tmp/fifo

prw-rw-rw-    1 samuel   users           0 Jan 16 14:04 /tmp/fifo

–     The first character of the output from ls is p, indicating that this file is actually a FIFO (named pipe).

Creating a FIFO

•      Create a FIFO programmatically using the mkfifo function.

•      Synopsis

#include <sys/types.h>

#include <sys/stat.h>

int mkfifo(const char *pathname, mode_t mode);

–     The first argument is the path at which to create the FIFO;

–     the second parameter specifies the pipe’s owner, group, and world permissions,

Accessing a FIFO

•      Access a FIFO just like an ordinary file.

•      To communicate through a FIFO, one program must open it for writing, and another program must open it for reading.

•      Either low-level I/O functions (open, write, read, close, and so on) or C library I/O functions (fopen, fprintf, fscanf, fclose, and so on) may be used.

•      For example, to write a buffer of data to a FIFO using low-level I/O routines, you could use this code:

int fd = open (fifo_path, O_WRONLY);

write (fd, data, data_length);

close (fd);

•      Bytes from each writer are written atomically up to a maximum size of PIPE_BUF (4KB on Linux)