327 lines
6.8 KiB
HTML
327 lines
6.8 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 MPOOL</TITLE>
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</HEAD><BODY>
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<H1>MPOOL</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2017-09-15<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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mpool - shared memory buffer pool
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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>#include <<A HREF="file:///usr/include/db.h">db.h</A>></B>
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<B>#include <<A HREF="file:///usr/include/mpool.h">mpool.h</A>></B>
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<B>MPOOL *mpool_open(DBT *</B><I>key</I><B>, int </B><I>fd</I><B>, pgno_t </B><I>pagesize</I><B>, pgno_t </B><I>maxcache</I><B>);</B>
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<B>void mpool_filter(MPOOL *</B><I>mp</I><B>, void (*pgin)(void *, pgno_t, void *),</B>
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<B> void (*</B><I>pgout</I><B>)(void *, pgno_t, void *),</B>
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<B> void *</B><I>pgcookie</I><B>);</B>
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<B>void *mpool_new(MPOOL *</B><I>mp</I><B>, pgno_t *</B><I>pgnoaddr</I><B>);</B>
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<B>void *mpool_get(MPOOL *</B><I>mp</I><B>, pgno_t </B><I>pgno</I><B>, unsigned int </B><I>flags</I><B>);</B>
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<B>int mpool_put(MPOOL *</B><I>mp</I><B>, void *</B><I>pgaddr</I><B>, unsigned int </B><I>flags</I><B>);</B>
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<B>int mpool_sync(MPOOL *</B><I>mp</I><B>);</B>
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<B>int mpool_close(MPOOL *</B><I>mp</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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<I>Note well</I>:
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This page documents interfaces provided in glibc up until version 2.1.
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Since version 2.2, glibc no longer provides these interfaces.
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Probably, you are looking for the APIs provided by the
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<I>libdb</I>
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library instead.
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<P>
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<I>Mpool</I>
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is the library interface intended to provide page oriented buffer management
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of files.
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The buffers may be shared between processes.
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<P>
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The function
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<B>mpool_open</B>()
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initializes a memory pool.
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The
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<I>key</I>
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argument is the byte string used to negotiate between multiple
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processes wishing to share buffers.
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If the file buffers are mapped in shared memory, all processes using
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the same key will share the buffers.
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If
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<I>key</I>
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is NULL, the buffers are mapped into private memory.
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The
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<I>fd</I>
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argument is a file descriptor for the underlying file, which must be seekable.
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If
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<I>key</I>
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is non-NULL and matches a file already being mapped, the
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<I>fd</I>
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argument is ignored.
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<P>
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The
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<I>pagesize</I>
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argument is the size, in bytes, of the pages into which the file is broken up.
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The
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<I>maxcache</I>
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argument is the maximum number of pages from the underlying file to cache
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at any one time.
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This value is not relative to the number of processes which share a file's
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buffers, but will be the largest value specified by any of the processes
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sharing the file.
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<P>
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The
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<B>mpool_filter</B>()
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function is intended to make transparent input and output processing of the
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pages possible.
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If the
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<I>pgin</I>
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function is specified, it is called each time a buffer is read into the memory
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pool from the backing file.
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If the
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<I>pgout</I>
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function is specified, it is called each time a buffer is written into the
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backing file.
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Both functions are called with the
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<I>pgcookie</I>
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pointer, the page number and a pointer to the page to being read or written.
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<P>
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The function
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<B>mpool_new</B>()
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takes an
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<I>MPOOL</I>
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pointer and an address as arguments.
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If a new page can be allocated, a pointer to the page is returned and
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the page number is stored into the
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<I>pgnoaddr</I>
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address.
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Otherwise, NULL is returned and
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<I>errno</I>
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is set.
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<P>
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The function
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<B>mpool_get</B>()
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takes an
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<I>MPOOL</I>
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pointer and a page number as arguments.
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If the page exists, a pointer to the page is returned.
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Otherwise, NULL is returned and
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<I>errno</I>
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is set.
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The
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<I>flags</I>
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argument is not currently used.
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<P>
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The function
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<B>mpool_put</B>()
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unpins the page referenced by
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<I>pgaddr</I>.
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<I>pgaddr</I>
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must be an address previously returned by
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<B>mpool_get</B>()
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or
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<B>mpool_new</B>().
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The flag value is specified by ORing
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any of the following values:
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<DL COMPACT>
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<DT id="1"><B>MPOOL_DIRTY</B>
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<DD>
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The page has been modified and needs to be written to the backing file.
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</DL>
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<P>
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<B>mpool_put</B>()
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returns 0 on success and -1 if an error occurs.
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<P>
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The function
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<B>mpool_sync</B>()
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writes all modified pages associated with the
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<I>MPOOL</I>
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pointer to the
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backing file.
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<B>mpool_sync</B>()
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returns 0 on success and -1 if an error occurs.
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<P>
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The
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<B>mpool_close</B>()
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function free's up any allocated memory associated with the memory pool
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cookie.
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Modified pages are
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<B>not</B>
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written to the backing file.
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<B>mpool_close</B>()
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returns 0 on success and -1 if an error occurs.
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<A NAME="lbAE"> </A>
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<H2>ERRORS</H2>
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The
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<B>mpool_open</B>()
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function may fail and set
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<I>errno</I>
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for any of the errors specified for the library routine
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<B><A HREF="/cgi-bin/man/man2html?3+malloc">malloc</A></B>(3).
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<P>
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The
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<B>mpool_get</B>()
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function may fail and set
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<I>errno</I>
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for the following:
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<DL COMPACT>
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<DT id="2"><B>EINVAL</B>
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<DD>
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The requested record doesn't exist.
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</DL>
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<P>
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The
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<B>mpool_new</B>()
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and
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<B>mpool_get</B>()
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functions may fail and set
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<I>errno</I>
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for any of the errors specified for the library routines
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<B><A HREF="/cgi-bin/man/man2html?2+read">read</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+write">write</A></B>(2),
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and
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<B><A HREF="/cgi-bin/man/man2html?3+malloc">malloc</A></B>(3).
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<P>
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The
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<B>mpool_sync</B>()
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function may fail and set
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<I>errno</I>
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for any of the errors specified for the library routine
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<B><A HREF="/cgi-bin/man/man2html?2+write">write</A></B>(2).
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<P>
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The
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<B>mpool_close</B>()
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function may fail and set
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<I>errno</I>
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for any of the errors specified for the library routine
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<B><A HREF="/cgi-bin/man/man2html?3+free">free</A></B>(3).
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<A NAME="lbAF"> </A>
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<H2>CONFORMING TO</H2>
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Not in POSIX.1.
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Present on the BSDs.
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<A NAME="lbAG"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?3+btree">btree</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+dbopen">dbopen</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+hash">hash</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+recno">recno</A></B>(3)
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<A NAME="lbAH"> </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="3"><A HREF="#lbAB">NAME</A><DD>
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<DT id="4"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="5"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="6"><A HREF="#lbAE">ERRORS</A><DD>
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<DT id="7"><A HREF="#lbAF">CONFORMING TO</A><DD>
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<DT id="8"><A HREF="#lbAG">SEE ALSO</A><DD>
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<DT id="9"><A HREF="#lbAH">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: 00:05:48 GMT, March 31, 2021
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</BODY>
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</HTML>
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