syscalls_10.html

Linux系统调用

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<TITLE>Syscall specifications of Linux - creat</TITLE>
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<H2><A NAME="SEC10" HREF="syscalls_toc.html#SEC10" tppabs="http://personal.xfol.com/%7erezaie/syscall/syscalls_toc.html#SEC10">creat and open</A></H2>
<P>
<H3>SYNOPSIS</H3>
<P>
<CODE>int open(const char *<VAR>path</VAR>, int <VAR>flags</VAR>);</CODE>
<P>
<CODE>int open(const char *<VAR>path</VAR>, int <VAR>flags</VAR>, mode_t
<VAR>mode</VAR>);</CODE>
<P>
<CODE>int creat(const char *<VAR>path</VAR>, mode_t <VAR>mode</VAR>);</CODE>
<P>
<H3>PARAMETERS</H3>
<P>
<VAR>path</VAR>: [in] the path of the new file to create.
<P>
<VAR>mode</VAR>: [in] the new permission mask of the file. It is masked by
the <CODE>umask</CODE> value: <CODE>(mode &#38; ~umask)</CODE>.
<P>
<VAR>flags</VAR>: [in] flags (see description).
<P>
<H3>DESCRIPTION</H3>
<P>
<VAR>open</VAR> opens an file. The <VAR>flags</VAR> parameter must be one of the
following:
<P>
<DL COMPACT>
<DT><CODE>O_RDONLY</CODE>
<DD>the file is opened for reading.
<P>
<DT><CODE>O_WRONLY</CODE>
<DD>the file is opened for writing.
<P>
<DT><CODE>O_RDWR</CODE>
<DD>the file is opened for both reading and writing.
</DL>
<P>
The following values may be or'ed together and with one of the preceding
values:
<P>
<DL COMPACT>
<DT><CODE>O_CREAT</CODE>
<DD>create the file if it does not exist.
<P>
<DT><CODE>O_EXCL</CODE>
<DD>used with <CODE>O_CREAT</CODE>, if the file exists, the call fails. The test
for existence and the creation if the file does not exists is atomic
operation according to POSIX.1.
<P>
<DT><CODE>O_NOCTTY</CODE>
<DD>the file will not become the controly tty of the task even if the file
is a tty and the task does not have a controling terminal.
<P>
<DT><CODE>O_TRUNC</CODE>
<DD>if the file already exists, truncate its lenght to 0.
<P>
<DT><CODE>O_APPEND</CODE>
<DD>the file is opened for appending. The file pointer is always at the end
of the file.
<P>
<DT><CODE>O_NONBLOCK or O_NDELAY</CODE>
<DD>the calls manipulating the file never block.
<P>
<DT><CODE>O_SYNC</CODE>
<DD>the file buffers are always synchronized with the on disk file. The
write calls block until the data is completely written on disk. This is
not POSIX.1.
</DL>
 
<CODE>create</CODE> creates a new file. The new file is open for writing
only. If a file with the same path already existed, then it is trucated.
<P>
<H3>RETURN VALUE</H3>
<P>
On success, a file descriptor for the file is returned. This file
descriptor is the lowest numbered unused descriptor. On error, those
calls return -1, and errno is set to one of the following values.
<P>
<UL>
<LI><CODE>EISDIR</CODE>: the last component of the path is a directory.
<LI><CODE>ETXTBSY</CODE>: tried to create an already used executable.
<LI><CODE>EFAULT</CODE>, <CODE>EACCESS</CODE>, <CODE>ENAMETOOLONG</CODE>, <CODE>ENOENT</CODE>,
<CODE>ENOTDIR</CODE>, <CODE>EMFILE</CODE>, <CODE>ENFILE</CODE>, <CODE>ENOMEM</CODE>,
<CODE>EROFS</CODE>, <CODE>ELOOP</CODE>, <CODE>EEXIST</CODE> or <CODE>ENOSPC</CODE>.
</UL>
<P>
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