177 lines
6.5 KiB
HTML
177 lines
6.5 KiB
HTML
<!--
|
|
Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009, 2013
|
|
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>open</title>
|
|
<link rel="stylesheet" type="text/css" media="all" href="../man.css">
|
|
</head>
|
|
<body bgcolor=#ffffff>
|
|
<h2 align=center>open</h2>
|
|
<h4 align=center>OS/161 Reference Manual</h4>
|
|
|
|
<h3>Name</h3>
|
|
<p>
|
|
open - open a file
|
|
</p>
|
|
|
|
<h3>Library</h3>
|
|
<p>
|
|
Standard C Library (libc, -lc)
|
|
</p>
|
|
|
|
<h3>Synopsis</h3>
|
|
<p>
|
|
<tt>#include <unistd.h></tt><br>
|
|
<tt>#include <fcntl.h></tt><br>
|
|
<br>
|
|
<tt>int</tt><br>
|
|
<tt>open(const char *</tt><em>filename</em><tt>,
|
|
int </tt><em>flags</em><tt>);</tt><br>
|
|
<tt>int</tt><br>
|
|
<tt>open(const char *</tt><em>filename</em><tt>, int </tt><em>flags</em><tt>,
|
|
mode_t </tt><em>mode</em><tt>);</tt><br>
|
|
</p>
|
|
|
|
<h3>Description</h3>
|
|
<p>
|
|
<tt>open</tt> opens the file, device, or other kernel object named by
|
|
the pathname <em>filename</em>. The <em>flags</em> argument specifies
|
|
how to open the file. The optional <em>mode</em> argument provides the
|
|
file permissions to use and is only meaningful in Unix, or if you
|
|
choose to implement Unix-style security later on. it can be ignored in
|
|
OS/161.
|
|
</p>
|
|
|
|
<p>
|
|
The flags argument should consist of one of
|
|
<table width=90%>
|
|
<tr><td width=5% rowspan=3> </td>
|
|
<td width=30%>O_RDONLY</td> <td>Open for reading only.</td></tr>
|
|
<tr><td>O_WRONLY</td> <td>Open for writing only.</td></tr>
|
|
<tr><td>O_RDWR</td> <td>Open for reading and writing.</td></tr>
|
|
</table>
|
|
</p>
|
|
|
|
<p>
|
|
It may also have any of the following flags OR'd in:
|
|
<table width=90%>
|
|
<tr><td width=5% rowspan=4> </td>
|
|
<td width=20%>O_CREAT</td>
|
|
<td>Create the file if it doesn't exist.</td></tr>
|
|
<tr><td>O_EXCL</td> <td>Fail if the file already exists.</td></tr>
|
|
<tr><td>O_TRUNC</td> <td>Truncate the file to length 0 upon open.</td></tr>
|
|
<tr><td>O_APPEND</td> <td>Open the file in append mode.</td></tr>
|
|
</table>
|
|
O_EXCL is only meaningful if O_CREAT is also used.
|
|
</p>
|
|
|
|
<p>
|
|
O_APPEND causes all writes to the file to occur at the end of file, no
|
|
matter what gets written to the file by whoever else, including
|
|
concurrently. (This functionality may be optional; consult your
|
|
course's assignments.)
|
|
</p>
|
|
|
|
<p>
|
|
<tt>open</tt> returns a file handle suitable for passing to
|
|
<A HREF=read.html>read</A>,
|
|
<A HREF=write.html>write</A>,
|
|
<A HREF=close.html>close</A>,
|
|
etc. This file handle must be greater than or equal to zero. Note
|
|
that file handles 0 (STDIN_FILENO), 1 (STDOUT_FILENO), and 2
|
|
(STDERR_FILENO) are used in special ways and are typically assumed by
|
|
user-level code to always be open.
|
|
</p>
|
|
|
|
<p>
|
|
If you are implementing symbolic links, there are some additional
|
|
points to take note of. If <em>filename</em> refers to a symbolic
|
|
link, that link does not point to an existing object, and O_CREAT is
|
|
specified, a new file is created <i>at the name the link points
|
|
to</i>. However, if in this case both O_CREAT and O_EXCL are
|
|
specified, <tt>open</tt> fails with EEXIST. These semantics are a
|
|
nuisance to implement but important for correct functioning.
|
|
</p>
|
|
|
|
<p>
|
|
<tt>open</tt> (like all system calls) should be atomic. It is
|
|
important for the handling of O_EXCL in the destination directory to
|
|
be atomic. Note, however, that in practice looking up directories that
|
|
contain <tt>..</tt> is usually not quite atomic.
|
|
</p>
|
|
|
|
<h3>Return Values</h3>
|
|
<p>
|
|
On success, <tt>open</tt> returns a nonnegative file handle. On error,
|
|
-1 is returned, and <A HREF=errno.html>errno</A> is set according to
|
|
the error encountered.
|
|
</p>
|
|
|
|
<h3>Errors</h3>
|
|
<p>
|
|
The following error codes should be returned under the conditions
|
|
given. Other error codes may be returned for other cases not
|
|
mentioned here.
|
|
|
|
<table width=90%>
|
|
<tr><td width=5% rowspan=15> </td>
|
|
<td width=10% valign=top>ENODEV</td>
|
|
<td>The device prefix of <em>filename</em> did
|
|
not exist.</td></tr>
|
|
<tr><td valign=top>ENOTDIR</td> <td>A non-final component of <em>filename</em>
|
|
was not a directory.</td></tr>
|
|
<tr><td valign=top>ENOENT</td> <td>A non-final component of <em>filename</em>
|
|
did not exist.</td></tr>
|
|
<tr><td valign=top>ENOENT</td> <td>The named file does not exist, and O_CREAT
|
|
was not specified.</td></tr>
|
|
<tr><td valign=top>EEXIST</td> <td>The named file exists, and O_EXCL was
|
|
specified.</td></tr>
|
|
<tr><td valign=top>EISDIR</td> <td>The named object is a directory, and it
|
|
was to be opened for writing.</td></tr>
|
|
<tr><td valign=top>EMFILE</td> <td>The process's file table was full, or a
|
|
process-specific limit on open files
|
|
was reached.</td></tr>
|
|
<tr><td valign=top>ENFILE</td> <td>The system file table is full, if such a
|
|
thing exists, or a system-wide limit
|
|
on open files was reached.</td></tr>
|
|
<tr><td valign=top>ENXIO</td> <td>The named object is a block device with no
|
|
filesystem mounted on it.</td></tr>
|
|
<tr><td valign=top>ENOSPC</td> <td>The file was to be created, and the
|
|
filesystem involved is full.</td></tr>
|
|
<tr><td valign=top>EINVAL</td> <td><em>flags</em> contained invalid
|
|
values.</td></tr>
|
|
<tr><td valign=top>EIO</td> <td>A hard I/O error occurred.</td></tr>
|
|
<tr><td valign=top>EFAULT</td> <td><em>filename</em> was an invalid
|
|
pointer.</td></tr>
|
|
</table>
|
|
</p>
|
|
|
|
</body>
|
|
</html>
|