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<H2><A NAME="SECTION00732000000000000000">6.3.2 Creating a FIFO</A></H2>
<P>
There are several ways of creating a named pipe. The first two can be done
directly from the shell.
<P>
<PRE> mknod MYFIFO p
mkfifo a=rw MYFIFO</PRE>
<P>
The above two commands perform identical operations, with one exception. The
mkfifo command provides a hook for altering the permissions on the FIFO file
directly after creation. With mknod, a quick call to the chmod command will
be necessary.
<P>
FIFO files can be quickly identified in a physical file system by the ``p''
indicator seen here in a long directory listing:
<P>
<PRE> $ ls -l MYFIFO
prw-r--r-- 1 root root 0 Dec 14 22:15 MYFIFO|</PRE>
<P>
Also notice the vertical bar (``pipe sign'') located directly after the file
name. Another great reason to run Linux, eh?
<P>
To create a FIFO in C, we can make use of the mknod() system call:
<P>
<P>
<HR><PRE> LIBRARY FUNCTION: mknod();
PROTOTYPE: int mknod( char *pathname, mode_t mode, dev_t dev);
RETURNS: 0 on success,
-1 on error: errno = EFAULT (pathname invalid)
EACCES (permission denied)
ENAMETOOLONG (pathname too long)
ENOENT (invalid pathname)
ENOTDIR (invalid pathname)
(see man page for mknod for others)
NOTES: Creates a filesystem node (file, device file, or FIFO)</PRE>
<HR>I will leave a more detailed discussion of mknod() to the man page, but let's
consider a simple example of FIFO creation from C:
<P>
<PRE> mknod("/tmp/MYFIFO", S_IFIFO|0666, 0);</PRE>
<P>
In this case, the file ``/tmp/MYFIFO'' is created as a FIFO file. The requested
permissions are ``0666'', although they are affected by the umask setting as
follows:
<P>
<PRE> final_umask = requested_permissions & ~original_umask</PRE>
<P>
A common trick is to use the umask() system call to temporarily zap the
umask value:
<P>
<PRE> umask(0);
mknod("/tmp/MYFIFO", S_IFIFO|0666, 0);</PRE>
<P>
In addition, the third argument to mknod() is ignored unless we are creating
a device file. In that instance, it should specify the major and minor
numbers of the device file.
<P>
<BR> <HR>
<P><ADDRESS>
<I>Converted on: <BR>
Fri Mar 29 14:43:04 EST 1996</I>
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