284 lines
5.7 KiB
HTML
284 lines
5.7 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of VMSPLICE</TITLE>
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</HEAD><BODY>
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<H1>VMSPLICE</H1>
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Section: Linux Programmer's Manual (2)<BR>Updated: 2019-03-06<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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vmsplice - splice user pages to/from a pipe
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>#define _GNU_SOURCE</B> /* See <A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A>(7) */
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<B>#include <<A HREF="file:///usr/include/fcntl.h">fcntl.h</A>></B>
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<B>#include <<A HREF="file:///usr/include/sys/uio.h">sys/uio.h</A>></B>
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<B>ssize_t vmsplice(int </B><I>fd</I><B>, const struct iovec *</B><I>iov</I><B>,</B>
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<B> unsigned long </B><I>nr_segs</I><B>, unsigned int </B><I>flags</I><B>);</B>
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</PRE>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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If
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<I>fd</I>
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is opened for writing, the
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<B>vmsplice</B>()
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system call maps
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<I>nr_segs</I>
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ranges of user memory described by
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<I>iov</I>
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into a pipe.
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If
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<I>fd</I>
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is opened for reading,
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the
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<B>vmsplice</B>()
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system call fills
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<I>nr_segs</I>
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ranges of user memory described by
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<I>iov</I>
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from a pipe.
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The file descriptor
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<I>fd</I>
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must refer to a pipe.
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<P>
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The pointer
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<I>iov</I>
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points to an array of
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<I>iovec</I>
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structures as defined in
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<I><<A HREF="file:///usr/include/sys/uio.h">sys/uio.h</A>></I>:
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<P>
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struct iovec {
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<BR> void *iov_base; /* Starting address */
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<BR> size_t iov_len; /* Number of bytes */
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};
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<P>
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The
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<I>flags</I>
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argument is a bit mask that is composed by ORing together
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zero or more of the following values:
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<DL COMPACT>
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<DT id="1"><B>SPLICE_F_MOVE</B>
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<DD>
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Unused for
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<B>vmsplice</B>();
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see
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<B><A HREF="/cgi-bin/man/man2html?2+splice">splice</A></B>(2).
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<DT id="2"><B>SPLICE_F_NONBLOCK</B>
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<DD>
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Do not block on I/O; see
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<B><A HREF="/cgi-bin/man/man2html?2+splice">splice</A></B>(2)
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for further details.
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<DT id="3"><B>SPLICE_F_MORE</B>
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<DD>
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Currently has no effect for
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<B>vmsplice</B>(),
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but may be implemented in the future; see
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<B><A HREF="/cgi-bin/man/man2html?2+splice">splice</A></B>(2).
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<DT id="4"><B>SPLICE_F_GIFT</B>
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<DD>
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The user pages are a gift to the kernel.
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The application may not modify this memory ever,
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otherwise the page cache and on-disk data may differ.
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Gifting pages to the kernel means that a subsequent
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<B><A HREF="/cgi-bin/man/man2html?2+splice">splice</A></B>(2)
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<B>SPLICE_F_MOVE</B>
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can successfully move the pages;
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if this flag is not specified, then a subsequent
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<B><A HREF="/cgi-bin/man/man2html?2+splice">splice</A></B>(2)
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<B>SPLICE_F_MOVE</B>
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must copy the pages.
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Data must also be properly page aligned, both in memory and length.
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</DL>
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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Upon successful completion,
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<B>vmsplice</B>()
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returns the number of bytes transferred to the pipe.
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On error,
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<B>vmsplice</B>()
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returns -1 and
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<I>errno</I>
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is set to indicate the error.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<DL COMPACT>
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<DT id="5"><B>EAGAIN</B>
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<DD>
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<B>SPLICE_F_NONBLOCK</B>
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was specified in
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<I>flags</I>,
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and the operation would block.
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<DT id="6"><B>EBADF</B>
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<DD>
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<I>fd</I>
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either not valid, or doesn't refer to a pipe.
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<DT id="7"><B>EINVAL</B>
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<DD>
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<I>nr_segs</I>
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is greater than
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<B>IOV_MAX</B>;
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or memory not aligned if
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<B>SPLICE_F_GIFT</B>
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set.
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<DT id="8"><B>ENOMEM</B>
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<DD>
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Out of memory.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>VERSIONS</H2>
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The
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<B>vmsplice</B>()
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system call first appeared in Linux 2.6.17;
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library support was added to glibc in version 2.5.
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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This system call is Linux-specific.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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<B>vmsplice</B>()
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follows the other vectorized read/write type functions when it comes to
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limitations on the number of segments being passed in.
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This limit is
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<B>IOV_MAX</B>
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as defined in
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<I><<A HREF="file:///usr/include/limits.h">limits.h</A>></I>.
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Currently,
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this limit is 1024.
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<P>
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<B>vmsplice</B>()
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really supports true splicing only from user memory to a pipe.
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In the opposite direction, it actually just copies the data to userspace.
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But this makes the interface nice and symmetric and enables people to build on
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<B>vmsplice</B>()
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with room for future improvement in performance.
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<A NAME="lbAJ"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+splice">splice</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+tee">tee</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?7+pipe">pipe</A></B>(7)
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<A NAME="lbAK"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="9"><A HREF="#lbAB">NAME</A><DD>
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<DT id="10"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="11"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="12"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="13"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="14"><A HREF="#lbAG">VERSIONS</A><DD>
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<DT id="15"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="16"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="17"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="18"><A HREF="#lbAK">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:35 GMT, March 31, 2021
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</BODY>
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</HTML>
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