88 lines
3.0 KiB
HTML
88 lines
3.0 KiB
HTML
<!--
|
|
Copyright (c) 2014
|
|
The President and Fellows of Harvard College.
|
|
|
|
Redistribution and use in source and binary forms, with or without
|
|
modification, are permitted provided that the following conditions
|
|
are met:
|
|
1. Redistributions of source code must retain the above copyright
|
|
notice, this list of conditions and the following disclaimer.
|
|
2. Redistributions in binary form must reproduce the above copyright
|
|
notice, this list of conditions and the following disclaimer in the
|
|
documentation and/or other materials provided with the distribution.
|
|
3. Neither the name of the University nor the names of its contributors
|
|
may be used to endorse or promote products derived from this software
|
|
without specific prior written permission.
|
|
|
|
THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
|
|
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
|
|
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
SUCH DAMAGE.
|
|
-->
|
|
<html>
|
|
<head>
|
|
<title>semfs</title>
|
|
<link rel="stylesheet" type="text/css" media="all" href="../man.css">
|
|
</head>
|
|
<body bgcolor=#ffffff>
|
|
<h2 align=center>semfs</h2>
|
|
<h4 align=center>OS/161 Reference Manual</h4>
|
|
|
|
<h3>Name</h3>
|
|
<p>
|
|
semfs - semaphore filesystem
|
|
</p>
|
|
|
|
<h3>Synopsis</h3>
|
|
<p>
|
|
options semfs
|
|
</p>
|
|
|
|
<h3>Description</h3>
|
|
<p>
|
|
semfs is a simple "fake" (memory-only) file system that provides
|
|
synchronization facilities to userland in the form of counting
|
|
semaphores.
|
|
There is one semfs instance, called "sem:", which is created and
|
|
mounted during system boot.
|
|
</p>
|
|
|
|
<p>
|
|
Semaphores in semfs appear as files in "sem:". To create a semaphore,
|
|
open such a file using <tt>O_CREAT</tt>. To destroy it, remove it with
|
|
<tt>remove()</tt>.
|
|
</p>
|
|
|
|
<p>
|
|
To use the semaphore, write one byte to increase the semaphore count
|
|
by one (the "V" operation) and write one byte to decrease the
|
|
semaphore count by one (the "P" operation). The count will not
|
|
decrease below zero; attempts to do so will block until other
|
|
concurrent write operations raise the count again.
|
|
You can also set the count explicitly using <tt>ftruncate()</tt>; this
|
|
is useful for initializing a semaphore to a nonzero value. Note that
|
|
no data is actually transferred by the read and write calls; it is
|
|
acceptable to pass NULL as the data pointer.
|
|
</p>
|
|
|
|
<p>
|
|
You can create as many semaphores as you want (until memory runs out
|
|
or the directory reaches 2^32 entries); however, semfs does not
|
|
support subdirectories, hard links of semaphores, or renaming.
|
|
</p>
|
|
|
|
<h3>Files</h3>
|
|
<p>
|
|
<tt>sem:</tt>
|
|
</p>
|
|
|
|
</body>
|
|
</html>
|