Adding upstream version 3.45.1.upstream/3.45.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
author: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-04-13 14:07:11 +0000
committer: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-04-13 14:07:11 +0000
commit: 63847496f14c813a5d80efd5b7de0f1294ffe1e3 (patch)
tree: 01c7571c7c762ceee70638549a99834fdd7c411b /www/cksumvfs.html
parent: Initial commit. (diff)
download: sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.tar.xz
sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.zip
1 files changed, 314 insertions, 0 deletions
diff --git a/www/cksumvfs.html b/www/cksumvfs.html
new file mode 100644
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--- /dev/null
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+<!DOCTYPE html>
+<html><head>
+<meta name="viewport" content="width=device-width, initial-scale=1.0">
+<meta http-equiv="content-type" content="text/html; charset=UTF-8">
+<link href="sqlite.css" rel="stylesheet">
+<title>The Checksum VFS Shim</title>
+<!-- path= -->
+</head>
+<body>
+<div class=nosearch>
+<a href="index.html">
+<img class="logo" src="images/sqlite370_banner.gif" alt="SQLite" border="0">
+</a>
+<div><!-- IE hack to prevent disappearing logo --></div>
+<div class="tagline desktoponly">
+Small. Fast. Reliable.<br>Choose any three.
+</div>
+<div class="menu mainmenu">
+<ul>
+<li><a href="index.html">Home</a>
+<li class='mobileonly'><a href="javascript:void(0)" onclick='toggle_div("submenu")'>Menu</a>
+<li class='wideonly'><a href='about.html'>About</a>
+<li class='desktoponly'><a href="docs.html">Documentation</a>
+<li class='desktoponly'><a href="download.html">Download</a>
+<li class='wideonly'><a href='copyright.html'>License</a>
+<li class='desktoponly'><a href="support.html">Support</a>
+<li class='desktoponly'><a href="prosupport.html">Purchase</a>
+<li class='search' id='search_menubutton'>
+<a href="javascript:void(0)" onclick='toggle_search()'>Search</a>
+</ul>
+</div>
+<div class="menu submenu" id="submenu">
+<ul>
+<li><a href='about.html'>About</a>
+<li><a href='docs.html'>Documentation</a>
+<li><a href='download.html'>Download</a>
+<li><a href='support.html'>Support</a>
+<li><a href='prosupport.html'>Purchase</a>
+</ul>
+</div>
+<div class="searchmenu" id="searchmenu">
+<form method="GET" action="search">
+<select name="s" id="searchtype">
+<option value="d">Search Documentation</option>
+<option value="c">Search Changelog</option>
+</select>
+<input type="text" name="q" id="searchbox" value="">
+<input type="submit" value="Go">
+</form>
+</div>
+</div>
+<script>
+function toggle_div(nm) {
+var w = document.getElementById(nm);
+if( w.style.display=="block" ){
+w.style.display = "none";
+}else{
+w.style.display = "block";
+}
+}
+function toggle_search() {
+var w = document.getElementById("searchmenu");
+if( w.style.display=="block" ){
+w.style.display = "none";
+} else {
+w.style.display = "block";
+setTimeout(function(){
+document.getElementById("searchbox").focus()
+}, 30);
+}
+}
+function div_off(nm){document.getElementById(nm).style.display="none";}
+window.onbeforeunload = function(e){div_off("submenu");}
+/* Disable the Search feature if we are not operating from CGI, since */
+/* Search is accomplished using CGI and will not work without it. */
+if( !location.origin || !location.origin.match || !location.origin.match(/http/) ){
+document.getElementById("search_menubutton").style.display = "none";
+}
+/* Used by the Hide/Show button beside syntax diagrams, to toggle the */
+function hideorshow(btn,obj){
+var x = document.getElementById(obj);
+var b = document.getElementById(btn);
+if( x.style.display!='none' ){
+x.style.display = 'none';
+b.innerHTML='show';
+}else{
+x.style.display = '';
+b.innerHTML='hide';
+}
+return false;
+}
+var antiRobot = 0;
+function antiRobotGo(){
+if( antiRobot!=3 ) return;
+antiRobot = 7;
+var j = document.getElementById("mtimelink");
+if(j && j.hasAttribute("data-href")) j.href=j.getAttribute("data-href");
+}
+function antiRobotDefense(){
+document.body.onmousedown=function(){
+antiRobot |= 2;
+antiRobotGo();
+document.body.onmousedown=null;
+}
+document.body.onmousemove=function(){
+antiRobot |= 2;
+antiRobotGo();
+document.body.onmousemove=null;
+}
+setTimeout(function(){
+antiRobot |= 1;
+antiRobotGo();
+}, 100)
+antiRobotGo();
+}
+antiRobotDefense();
+</script>
+<div class=fancy>
+<div class=nosearch>
+<div class="fancy_title">
+The Checksum VFS Shim
+</div>
+<div class="fancy_toc">
+<a onclick="toggle_toc()">
+<span class="fancy_toc_mark" id="toc_mk">&#x25ba;</span>
+Table Of Contents
+</a>
+<div id="toc_sub"><div class="fancy-toc1"><a href="#overview">1. Overview</a></div>
+<div class="fancy-toc1"><a href="#compiling">2. Compiling</a></div>
+<div class="fancy-toc1"><a href="#loading">3. Loading</a></div>
+<div class="fancy-toc1"><a href="#usage">4. Usage</a></div>
+<div class="fancy-toc1"><a href="#verification_of_checksums">5. Verification Of Checksums</a></div>
+<div class="fancy-toc1"><a href="#controlling_checksum_verification">6. Controlling Checksum Verification</a></div>
+</div>
+</div>
+<script>
+function toggle_toc(){
+var sub = document.getElementById("toc_sub")
+var mk = document.getElementById("toc_mk")
+if( sub.style.display!="block" ){
+sub.style.display = "block";
+mk.innerHTML = "&#x25bc;";
+} else {
+sub.style.display = "none";
+mk.innerHTML = "&#x25ba;";
+}
+}
+</script>
+</div>
+
+
+
+
+
+<h1 id="overview"><span>1. </span>Overview</h1>
+
+<p>The checksum VFS extension is a <a href="vfs.html#shim">VFS shim</a> that adds an 8-byte
+checksum to the end of every page in an SQLite database.  The checksum
+is added as each page is written and verified as each page is read.
+The checksum is intended to help detect database corruption caused by
+random bit-flips in the mass storage device.
+
+</p><p>The checksum VFS extension requires 
+SQLite version 3.32.0 (2020-05-22) or later.  It will not
+work with earlier versions of SQLite.
+
+</p><h1 id="compiling"><span>2. </span>Compiling</h1>
+
+<p>The checksum VFS module is a <a href="loadext.html">loadable extension</a>.  It is not
+included in the <a href="amalgamation.html">amalgamation</a>.  It must be added to SQLite
+either at compile-time or at run-time.  The source code to
+the checksum VFS module is in the
+<a href="https://sqlite.org/src/file/ext/misc/cksumvfs.c">ext/misc/cksumvfs.c</a>
+source file in the
+<a href="https://sqlite.org/src">SQLite source tree</a>.
+
+</p><p>To build the checksum VFS module into a run-time loadable
+extension, use commands similar to the following:
+
+</p><ul>
+<li>(linux) &rarr; <tt>gcc -fPIC -shared cksumvfs.c -o cksumvfs.so</tt>
+</li><li>(mac) &rarr; <tt>clang -fPIC -dynamiclib cksumvfs.c -o cksumvfs.dylib</tt>
+</li><li>(windows) &rarr; <tt>cl cksumvfs.c -link -dll -out:cksumvfs.dll</tt>
+</li></ul>
+
+<p>You may want to add additional compiler options, of course,
+according to the needs of your project.
+
+</p><p>To statically link this extension with your product,
+compile it like any other C-language module but add the
+"-DSQLITE_CKSUMVFS_STATIC" option so that this module knows that
+it is being statically linked rather than dynamically linked.
+
+</p><h1 id="loading"><span>3. </span>Loading</h1>
+
+<p>To load this extension as a shared library, you first have to
+bring up a dummy SQLite database connection to use as the argument
+to the <a href="c3ref/load_extension.html">sqlite3_load_extension()</a> API call.  Then you invoke the
+<a href="c3ref/load_extension.html">sqlite3_load_extension()</a> API and shutdown the dummy database
+connection.  All subsequent database connections that are opened
+will include this extension.  For example:
+
+</p><div class="codeblock"><pre>sqlite3 *db;
+sqlite3_open(":memory:", &db);
+sqlite3_load_extension(db, "./cksumvfs");
+sqlite3_close(db);
+</pre></div>
+
+<p>If this extension is compiled with -DSQLITE_CKSUMVFS_STATIC and
+statically linked against the application, initialize it using
+a single API call as follows:
+
+</p><div class="codeblock"><pre>sqlite3_cksumvfs_init();
+</pre></div>
+
+<p>Cksumvfs is a <a href="vfs.html#shim">VFS shim</a>. When loaded, "cksmvfs" becomes the new
+default VFS, and it uses the prior default VFS as the next VFS
+down in the stack.  This is normally what you want.  However, in
+complex situations where multiple VFS shims are being loaded,
+it might be important to ensure that cksumvfs is loaded in the
+correct order so that it sequences itself into the default VFS
+Shim stack in the right order.
+
+</p><h1 id="usage"><span>4. </span>Usage</h1>
+
+<p>Open database connections using the <a href="c3ref/open.html">sqlite3_open()</a> or 
+<a href="c3ref/open.html">sqlite3_open_v2()</a> interfaces, as normal.  Ordinary database files
+(without a checksum) will operate normally.  Databases with 
+checksums will return an SQLITE_IOERR_DATA error if a page is
+encountered that contains an invalid checksum.
+
+</p><p>Checksumming only works on databases that have a <a href="fileformat2.html#resbyte">reserve bytes</a>
+value of exactly 8.  The default value for reserve-bytes is 0.
+Hence, newly created database files will omit the checksum by
+default.  To create a database that includes a checksum, change
+the reserve-bytes value to 8 by running code similar to this:
+
+</p><div class="codeblock"><pre>int n = 8;
+sqlite3_file_control(db, 0, SQLITE_FCNTL_RESERVE_BYTES, &n);
+</pre></div>
+
+<p>If you do this immediately after creating a new database file,
+before anything else has been written into the file, then that
+might be all that you need to do.  Otherwise, the API call
+above should be followed by:
+
+</p><div class="codeblock"><pre>sqlite3_exec(db, "VACUUM", 0, 0, 0);
+</pre></div>
+
+<p>It never hurts to run the VACUUM, even if you don't need it.
+If the database is in WAL mode, you should shutdown and
+reopen all database connections before continuing.
+
+</p><p>From the CLI, use the ".filectrl reserve_bytes 8" command, 
+followed by "VACUUM;".
+
+</p><p>Note that SQLite allows the number of reserve-bytes to be
+increased but not decreased.  So if a database file already
+has a reserve-bytes value greater than 8, there is no way to
+activate checksumming on that database, other than to dump
+and restore the database file.  Note also that other extensions
+might also make use of the reserve-bytes.  Checksumming will
+be incompatible with those other extensions.
+
+</p><h1 id="verification_of_checksums"><span>5. </span>Verification Of Checksums</h1>
+
+<p>If any checksum is incorrect, the "PRAGMA quick_check" command
+will find it.  To verify that checksums are actually enabled
+and running, use SQL like the following:
+
+</p><div class="codeblock"><pre>SELECT count(*), verify_checksum(data)
+  FROM sqlite_dbpage
+ GROUP BY 2;
+</pre></div>
+
+<p>There are three possible outputs from the verify_checksum()
+function: 1, 0, and NULL.  1 is returned if the checksum is
+correct.  0 is returned if the checksum is incorrect.  NULL
+is returned if the page is unreadable.  If checksumming is
+enabled, the read will fail if the checksum is wrong, so the
+usual result from verify_checksum() on a bad checksum is NULL.
+
+</p><p>If everything is OK, the query above should return a single
+row where the second column is 1.  Any other result indicates
+either that there is a checksum error, or checksum validation
+is disabled.
+
+</p><h1 id="controlling_checksum_verification"><span>6. </span>Controlling Checksum Verification</h1>
+
+<p>The cksumvfs extension implements a new PRAGMA statement that can
+be used to disable, re-enable, or query the status of checksum
+verification:
+
+</p><div class="codeblock"><pre>PRAGMA checksum_verification;          -- query status
+PRAGMA checksum_verification=OFF;      -- disable verification
+PRAGMA checksum_verification=ON;       -- re-enable verification
+</pre></div>
+
+<p>The "checksum_verification" pragma will return "1" (true) or "0"
+(false) if checksum verification is enabled or disabled, respectively.
+"Verification" in this context means the feature that causes
+SQLITE_IOERR_DATA errors if a checksum mismatch is detected while
+reading.  Checksums are always kept up-to-date as long as the
+<a href="fileformat2.html#resbyte">reserve bytes</a> value of the database is 8, regardless of the setting
+of this pragma.  Checksum verification can be disabled (for example)
+to do forensic analysis of a database that has previously reported
+a checksum error.
+
+</p><p>The "checksum_verification" pragma will always respond with "0" if
+the database file does not have a <a href="fileformat2.html#resbyte">reserve bytes</a> value of 8.  The
+pragma will return no rows at all if the cksumvfs extension is
+not loaded.
+</p><p align="center"><small><i>This page last modified on  <a href="https://sqlite.org/docsrc/honeypot" id="mtimelink"  data-href="https://sqlite.org/docsrc/finfo/pages/cksumvfs.in?m=c9b2514ff0">2022-01-08 05:02:57</a> UTC </small></i></p>
+
author	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-04-13 14:07:11 +0000
committer	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-04-13 14:07:11 +0000
commit	63847496f14c813a5d80efd5b7de0f1294ffe1e3 (patch)
tree	01c7571c7c762ceee70638549a99834fdd7c411b /www/cksumvfs.html
parent	Initial commit. (diff)
download	sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.tar.xz sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.zip