[sql] Import reference version of SQLite 3.17..

third_party/sqlite/sqlite-src-3170000/src/test_multiplex.c

+/*
+** 2010 October 28
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+*************************************************************************
+**
+** This file contains a VFS "shim" - a layer that sits in between the
+** pager and the real VFS - that breaks up a very large database file
+** into two or more smaller files on disk.  This is useful, for example,
+** in order to support large, multi-gigabyte databases on older filesystems
+** that limit the maximum file size to 2 GiB.
+**
+** USAGE:
+**
+** Compile this source file and link it with your application.  Then
+** at start-time, invoke the following procedure:
+**
+**   int sqlite3_multiplex_initialize(
+**      const char *zOrigVfsName,    // The underlying real VFS
+**      int makeDefault              // True to make multiplex the default VFS
+**   );
+**
+** The procedure call above will create and register a new VFS shim named
+** "multiplex".  The multiplex VFS will use the VFS named by zOrigVfsName to
+** do the actual disk I/O.  (The zOrigVfsName parameter may be NULL, in 
+** which case the default VFS at the moment sqlite3_multiplex_initialize()
+** is called will be used as the underlying real VFS.)  
+**
+** If the makeDefault parameter is TRUE then multiplex becomes the new
+** default VFS.  Otherwise, you can use the multiplex VFS by specifying
+** "multiplex" as the 4th parameter to sqlite3_open_v2() or by employing
+** URI filenames and adding "vfs=multiplex" as a parameter to the filename
+** URI.
+**
+** The multiplex VFS allows databases up to 32 GiB in size.  But it splits
+** the files up into smaller pieces, so that they will work even on 
+** filesystems that do not support large files.  The default chunk size
+** is 2147418112 bytes (which is 64KiB less than 2GiB) but this can be
+** changed at compile-time by defining the SQLITE_MULTIPLEX_CHUNK_SIZE
+** macro.  Use the "chunksize=NNNN" query parameter with a URI filename
+** in order to select an alternative chunk size for individual connections
+** at run-time.
+*/
+#include "sqlite3.h"
+#include <string.h>
+#include <assert.h>
+#include <stdlib.h>
+#include "test_multiplex.h"
+
+#ifndef SQLITE_CORE
+  #define SQLITE_CORE 1  /* Disable the API redefinition in sqlite3ext.h */
+#endif
+#include "sqlite3ext.h"
+
+/* 
+** These should be defined to be the same as the values in 
+** sqliteInt.h.  They are defined separately here so that
+** the multiplex VFS shim can be built as a loadable 
+** module.
+*/
+#define UNUSED_PARAMETER(x) (void)(x)
+#define MAX_PAGE_SIZE       0x10000
+#define DEFAULT_SECTOR_SIZE 0x1000
+
+/* Maximum chunk number */
+#define MX_CHUNK_NUMBER 299
+
+/* First chunk for rollback journal files */
+#define SQLITE_MULTIPLEX_JOURNAL_8_3_OFFSET 400
+#define SQLITE_MULTIPLEX_WAL_8_3_OFFSET 700
+
+
+/************************ Shim Definitions ******************************/
+
+#ifndef SQLITE_MULTIPLEX_VFS_NAME
+# define SQLITE_MULTIPLEX_VFS_NAME "multiplex"
+#endif
+
+/* This is the limit on the chunk size.  It may be changed by calling
+** the xFileControl() interface.  It will be rounded up to a 
+** multiple of MAX_PAGE_SIZE.  We default it here to 2GiB less 64KiB.
+*/
+#ifndef SQLITE_MULTIPLEX_CHUNK_SIZE
+# define SQLITE_MULTIPLEX_CHUNK_SIZE 2147418112
+#endif
+
+/* This used to be the default limit on number of chunks, but
+** it is no longer enforced. There is currently no limit to the
+** number of chunks.
+**
+** May be changed by calling the xFileControl() interface.
+*/
+#ifndef SQLITE_MULTIPLEX_MAX_CHUNKS
+# define SQLITE_MULTIPLEX_MAX_CHUNKS 12
+#endif
+
+/************************ Object Definitions ******************************/
+
+/* Forward declaration of all object types */
+typedef struct multiplexGroup multiplexGroup;
+typedef struct multiplexConn multiplexConn;
+
+/*
+** A "multiplex group" is a collection of files that collectively
+** makeup a single SQLite DB file.  This allows the size of the DB
+** to exceed the limits imposed by the file system.
+**
+** There is an instance of the following object for each defined multiplex
+** group.
+*/
+struct multiplexGroup {
+  struct multiplexReal {           /* For each chunk */
+    sqlite3_file *p;                  /* Handle for the chunk */
+    char *z;                          /* Name of this chunk */
+  } *aReal;                        /* list of all chunks */
+  int nReal;                       /* Number of chunks */
+  char *zName;                     /* Base filename of this group */
+  int nName;                       /* Length of base filename */
+  int flags;                       /* Flags used for original opening */
+  unsigned int szChunk;            /* Chunk size used for this group */
+  unsigned char bEnabled;          /* TRUE to use Multiplex VFS for this file */
+  unsigned char bTruncate;         /* TRUE to enable truncation of databases */
+};
+
+/*
+** An instance of the following object represents each open connection
+** to a file that is multiplex'ed.  This object is a 
+** subclass of sqlite3_file.  The sqlite3_file object for the underlying
+** VFS is appended to this structure.
+*/
+struct multiplexConn {
+  sqlite3_file base;              /* Base class - must be first */
+  multiplexGroup *pGroup;         /* The underlying group of files */
+};
+
+/************************* Global Variables **********************************/
+/*
+** All global variables used by this file are containing within the following
+** gMultiplex structure.
+*/
+static struct {
+  /* The pOrigVfs is the real, original underlying VFS implementation.
+  ** Most operations pass-through to the real VFS.  This value is read-only
+  ** during operation.  It is only modified at start-time and thus does not
+  ** require a mutex.
+  */
+  sqlite3_vfs *pOrigVfs;
+
+  /* The sThisVfs is the VFS structure used by this shim.  It is initialized
+  ** at start-time and thus does not require a mutex
+  */
+  sqlite3_vfs sThisVfs;
+
+  /* The sIoMethods defines the methods used by sqlite3_file objects 
+  ** associated with this shim.  It is initialized at start-time and does
+  ** not require a mutex.
+  **
+  ** When the underlying VFS is called to open a file, it might return 
+  ** either a version 1 or a version 2 sqlite3_file object.  This shim
+  ** has to create a wrapper sqlite3_file of the same version.  Hence
+  ** there are two I/O method structures, one for version 1 and the other
+  ** for version 2.
+  */
+  sqlite3_io_methods sIoMethodsV1;
+  sqlite3_io_methods sIoMethodsV2;
+
+  /* True when this shim has been initialized.
+  */
+  int isInitialized;
+} gMultiplex;
+
+/************************* Utility Routines *********************************/
+/*
+** Compute a string length that is limited to what can be stored in
+** lower 30 bits of a 32-bit signed integer.
+**
+** The value returned will never be negative.  Nor will it ever be greater
+** than the actual length of the string.  For very long strings (greater
+** than 1GiB) the value returned might be less than the true string length.
+*/
+static int multiplexStrlen30(const char *z){
+  const char *z2 = z;
+  if( z==0 ) return 0;
+  while( *z2 ){ z2++; }
+  return 0x3fffffff & (int)(z2 - z);
+}
+
+/*
+** Generate the file-name for chunk iChunk of the group with base name
+** zBase. The file-name is written to buffer zOut before returning. Buffer
+** zOut must be allocated by the caller so that it is at least (nBase+5)
+** bytes in size, where nBase is the length of zBase, not including the
+** nul-terminator.
+**
+** If iChunk is 0 (or 400 - the number for the first journal file chunk),
+** the output is a copy of the input string. Otherwise, if 
+** SQLITE_ENABLE_8_3_NAMES is not defined or the input buffer does not contain
+** a "." character, then the output is a copy of the input string with the 
+** three-digit zero-padded decimal representation if iChunk appended to it. 
+** For example:
+**
+**   zBase="test.db", iChunk=4  ->  zOut="test.db004"
+**
+** Or, if SQLITE_ENABLE_8_3_NAMES is defined and the input buffer contains
+** a "." character, then everything after the "." is replaced by the 
+** three-digit representation of iChunk.
+**
+**   zBase="test.db", iChunk=4  ->  zOut="test.004"
+**
+** The output buffer string is terminated by 2 0x00 bytes. This makes it safe
+** to pass to sqlite3_uri_parameter() and similar.
+*/
+static void multiplexFilename(
+  const char *zBase,              /* Filename for chunk 0 */
+  int nBase,                      /* Size of zBase in bytes (without \0) */
+  int flags,                      /* Flags used to open file */
+  int iChunk,                     /* Chunk to generate filename for */
+  char *zOut                      /* Buffer to write generated name to */
+){
+  int n = nBase;
+  memcpy(zOut, zBase, n+1);
+  if( iChunk!=0 && iChunk<=MX_CHUNK_NUMBER ){
+#ifdef SQLITE_ENABLE_8_3_NAMES
+    int i;
+    for(i=n-1; i>0 && i>=n-4 && zOut[i]!='.'; i--){}
+    if( i>=n-4 ) n = i+1;
+    if( flags & SQLITE_OPEN_MAIN_JOURNAL ){
+      /* The extensions on overflow files for main databases are 001, 002,
+      ** 003 and so forth.  To avoid name collisions, add 400 to the 
+      ** extensions of journal files so that they are 401, 402, 403, ....
+      */
+      iChunk += SQLITE_MULTIPLEX_JOURNAL_8_3_OFFSET;
+    }else if( flags & SQLITE_OPEN_WAL ){
+      /* To avoid name collisions, add 700 to the 
+      ** extensions of WAL files so that they are 701, 702, 703, ....
+      */
+      iChunk += SQLITE_MULTIPLEX_WAL_8_3_OFFSET;
+    }
+#endif
+    sqlite3_snprintf(4,&zOut[n],"%03d",iChunk);
+    n += 3;
+  }
+
+  assert( zOut[n]=='\0' );
+  zOut[n+1] = '\0';
+}
+
+/* Compute the filename for the iChunk-th chunk
+*/
+static int multiplexSubFilename(multiplexGroup *pGroup, int iChunk){
+  if( iChunk>=pGroup->nReal ){
+    struct multiplexReal *p;
+    p = sqlite3_realloc64(pGroup->aReal, (iChunk+1)*sizeof(*p));
+    if( p==0 ){
+      return SQLITE_NOMEM;
+    }
+    memset(&p[pGroup->nReal], 0, sizeof(p[0])*(iChunk+1-pGroup->nReal));
+    pGroup->aReal = p;
+    pGroup->nReal = iChunk+1;
+  }
+  if( pGroup->zName && pGroup->aReal[iChunk].z==0 ){
+    char *z;
+    int n = pGroup->nName;
+    pGroup->aReal[iChunk].z = z = sqlite3_malloc64( n+5 );
+    if( z==0 ){
+      return SQLITE_NOMEM;
+    }
+    multiplexFilename(pGroup->zName, pGroup->nName, pGroup->flags, iChunk, z);
+  }
+  return SQLITE_OK;
+}
+
+/* Translate an sqlite3_file* that is really a multiplexGroup* into
+** the sqlite3_file* for the underlying original VFS.
+**
+** For chunk 0, the pGroup->flags determines whether or not a new file
+** is created if it does not already exist.  For chunks 1 and higher, the
+** file is created only if createFlag is 1.
+*/
+static sqlite3_file *multiplexSubOpen(
+  multiplexGroup *pGroup,    /* The multiplexor group */
+  int iChunk,                /* Which chunk to open.  0==original file */
+  int *rc,                   /* Result code in and out */
+  int *pOutFlags,            /* Output flags */
+  int createFlag             /* True to create if iChunk>0 */
+){
+  sqlite3_file *pSubOpen = 0;
+  sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;        /* Real VFS */
+
+#ifdef SQLITE_ENABLE_8_3_NAMES
+  /* If JOURNAL_8_3_OFFSET is set to (say) 400, then any overflow files are 
+  ** part of a database journal are named db.401, db.402, and so on. A 
+  ** database may therefore not grow to larger than 400 chunks. Attempting
+  ** to open chunk 401 indicates the database is full. */
+  if( iChunk>=SQLITE_MULTIPLEX_JOURNAL_8_3_OFFSET ){
+    sqlite3_log(SQLITE_FULL, "multiplexed chunk overflow: %s", pGroup->zName);
+    *rc = SQLITE_FULL;
+    return 0;
+  }
+#endif
+
+  *rc = multiplexSubFilename(pGroup, iChunk);
+  if( (*rc)==SQLITE_OK && (pSubOpen = pGroup->aReal[iChunk].p)==0 ){
+    int flags, bExists;
+    flags = pGroup->flags;
+    if( createFlag ){
+      flags |= SQLITE_OPEN_CREATE;
+    }else if( iChunk==0 ){
+      /* Fall through */
+    }else if( pGroup->aReal[iChunk].z==0 ){
+      return 0;
+    }else{
+      *rc = pOrigVfs->xAccess(pOrigVfs, pGroup->aReal[iChunk].z,
+                              SQLITE_ACCESS_EXISTS, &bExists);
+     if( *rc || !bExists ){
+        if( *rc ){
+          sqlite3_log(*rc, "multiplexor.xAccess failure on %s",
+                      pGroup->aReal[iChunk].z);
+        }
+        return 0;
+      }
+      flags &= ~SQLITE_OPEN_CREATE;
+    }
+    pSubOpen = sqlite3_malloc64( pOrigVfs->szOsFile );
+    if( pSubOpen==0 ){
+      *rc = SQLITE_IOERR_NOMEM;
+      return 0;
+    }
+    pGroup->aReal[iChunk].p = pSubOpen;
+    *rc = pOrigVfs->xOpen(pOrigVfs, pGroup->aReal[iChunk].z, pSubOpen,
+                          flags, pOutFlags);
+    if( (*rc)!=SQLITE_OK ){
+      sqlite3_log(*rc, "multiplexor.xOpen failure on %s",
+                  pGroup->aReal[iChunk].z);
+      sqlite3_free(pSubOpen);
+      pGroup->aReal[iChunk].p = 0;
+      return 0;
+    }
+  }
+  return pSubOpen;
+}
+
+/*
+** Return the size, in bytes, of chunk number iChunk.  If that chunk
+** does not exist, then return 0.  This function does not distingish between
+** non-existant files and zero-length files.
+*/
+static sqlite3_int64 multiplexSubSize(
+  multiplexGroup *pGroup,    /* The multiplexor group */
+  int iChunk,                /* Which chunk to open.  0==original file */
+  int *rc                    /* Result code in and out */
+){
+  sqlite3_file *pSub;
+  sqlite3_int64 sz = 0;
+
+  if( *rc ) return 0;
+  pSub = multiplexSubOpen(pGroup, iChunk, rc, NULL, 0);
+  if( pSub==0 ) return 0;
+  *rc = pSub->pMethods->xFileSize(pSub, &sz);
+  return sz;
+}    
+
+/*
+** This is the implementation of the multiplex_control() SQL function.
+*/
+static void multiplexControlFunc(
+  sqlite3_context *context,
+  int argc,
+  sqlite3_value **argv
+){
+  int rc = SQLITE_OK;
+  sqlite3 *db = sqlite3_context_db_handle(context);
+  int op = 0;
+  int iVal;
+
+  if( !db || argc!=2 ){ 
+    rc = SQLITE_ERROR; 
+  }else{
+    /* extract params */
+    op = sqlite3_value_int(argv[0]);
+    iVal = sqlite3_value_int(argv[1]);
+    /* map function op to file_control op */
+    switch( op ){
+      case 1: 
+        op = MULTIPLEX_CTRL_ENABLE; 
+        break;
+      case 2: 
+        op = MULTIPLEX_CTRL_SET_CHUNK_SIZE; 
+        break;
+      case 3: 
+        op = MULTIPLEX_CTRL_SET_MAX_CHUNKS; 
+        break;
+      default:
+        rc = SQLITE_NOTFOUND;
+        break;
+    }
+  }
+  if( rc==SQLITE_OK ){
+    rc = sqlite3_file_control(db, 0, op, &iVal);
+  }
+  sqlite3_result_error_code(context, rc);
+}
+
+/*
+** This is the entry point to register the auto-extension for the 
+** multiplex_control() function.
+*/
+static int multiplexFuncInit(
+  sqlite3 *db, 
+  char **pzErrMsg, 
+  const sqlite3_api_routines *pApi
+){
+  int rc;
+  rc = sqlite3_create_function(db, "multiplex_control", 2, SQLITE_ANY, 
+      0, multiplexControlFunc, 0, 0);
+  return rc;
+}
+
+/*
+** Close a single sub-file in the connection group.
+*/
+static void multiplexSubClose(
+  multiplexGroup *pGroup,
+  int iChunk,
+  sqlite3_vfs *pOrigVfs
+){
+  sqlite3_file *pSubOpen = pGroup->aReal[iChunk].p;
+  if( pSubOpen ){
+    pSubOpen->pMethods->xClose(pSubOpen);
+    if( pOrigVfs && pGroup->aReal[iChunk].z ){
+      pOrigVfs->xDelete(pOrigVfs, pGroup->aReal[iChunk].z, 0);
+    }
+    sqlite3_free(pGroup->aReal[iChunk].p);
+  }
+  sqlite3_free(pGroup->aReal[iChunk].z);
+  memset(&pGroup->aReal[iChunk], 0, sizeof(pGroup->aReal[iChunk]));
+}
+
+/*
+** Deallocate memory held by a multiplexGroup
+*/
+static void multiplexFreeComponents(multiplexGroup *pGroup){
+  int i;
+  for(i=0; i<pGroup->nReal; i++){ multiplexSubClose(pGroup, i, 0); }
+  sqlite3_free(pGroup->aReal);
+  pGroup->aReal = 0;
+  pGroup->nReal = 0;
+}
+
+
+/************************* VFS Method Wrappers *****************************/
+
+/*
+** This is the xOpen method used for the "multiplex" VFS.
+**
+** Most of the work is done by the underlying original VFS.  This method
+** simply links the new file into the appropriate multiplex group if it is a
+** file that needs to be tracked.
+*/
+static int multiplexOpen(
+  sqlite3_vfs *pVfs,         /* The multiplex VFS */
+  const char *zName,         /* Name of file to be opened */
+  sqlite3_file *pConn,       /* Fill in this file descriptor */
+  int flags,                 /* Flags to control the opening */
+  int *pOutFlags             /* Flags showing results of opening */
+){
+  int rc = SQLITE_OK;                  /* Result code */
+  multiplexConn *pMultiplexOpen;       /* The new multiplex file descriptor */
+  multiplexGroup *pGroup = 0;          /* Corresponding multiplexGroup object */
+  sqlite3_file *pSubOpen = 0;                    /* Real file descriptor */
+  sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
+  int nName = 0;
+  int sz = 0;
+  char *zToFree = 0;
+
+  UNUSED_PARAMETER(pVfs);
+  memset(pConn, 0, pVfs->szOsFile);
+  assert( zName || (flags & SQLITE_OPEN_DELETEONCLOSE) );
+
+  /* We need to create a group structure and manage
+  ** access to this group of files.
+  */
+  pMultiplexOpen = (multiplexConn*)pConn;
+
+  if( rc==SQLITE_OK ){
+    /* allocate space for group */
+    nName = zName ? multiplexStrlen30(zName) : 0;
+    sz = sizeof(multiplexGroup)                             /* multiplexGroup */
+       + nName + 1;                                         /* zName */
+    pGroup = sqlite3_malloc64( sz );
+    if( pGroup==0 ){
+      rc = SQLITE_NOMEM;
+    }
+  }
+
+  if( rc==SQLITE_OK ){
+    const char *zUri = (flags & SQLITE_OPEN_URI) ? zName : 0;
+    /* assign pointers to extra space allocated */
+    memset(pGroup, 0, sz);
+    pMultiplexOpen->pGroup = pGroup;
+    pGroup->bEnabled = (unsigned char)-1;
+    pGroup->bTruncate = (unsigned char)sqlite3_uri_boolean(zUri, "truncate", 
+                                   (flags & SQLITE_OPEN_MAIN_DB)==0);
+    pGroup->szChunk = (int)sqlite3_uri_int64(zUri, "chunksize",
+                                        SQLITE_MULTIPLEX_CHUNK_SIZE);
+    pGroup->szChunk = (pGroup->szChunk+0xffff)&~0xffff;
+    if( zName ){
+      char *p = (char *)&pGroup[1];
+      pGroup->zName = p;
+      memcpy(pGroup->zName, zName, nName+1);
+      pGroup->nName = nName;
+    }
+    if( pGroup->bEnabled ){
+      /* Make sure that the chunksize is such that the pending byte does not
+      ** falls at the end of a chunk.  A region of up to 64K following
+      ** the pending byte is never written, so if the pending byte occurs
+      ** near the end of a chunk, that chunk will be too small. */
+#ifndef SQLITE_OMIT_WSD
+      extern int sqlite3PendingByte;
+#else
+      int sqlite3PendingByte = 0x40000000;
+#endif
+      while( (sqlite3PendingByte % pGroup->szChunk)>=(pGroup->szChunk-65536) ){
+        pGroup->szChunk += 65536;
+      }
+    }
+    pGroup->flags = flags;
+    rc = multiplexSubFilename(pGroup, 1);
+    if( rc==SQLITE_OK ){
+      pSubOpen = multiplexSubOpen(pGroup, 0, &rc, pOutFlags, 0);
+      if( pSubOpen==0 && rc==SQLITE_OK ) rc = SQLITE_CANTOPEN;
+    }
+    if( rc==SQLITE_OK ){
+      sqlite3_int64 sz64;
+
+      rc = pSubOpen->pMethods->xFileSize(pSubOpen, &sz64);
+      if( rc==SQLITE_OK && zName ){
+        int bExists;
+        if( flags & SQLITE_OPEN_MASTER_JOURNAL ){
+          pGroup->bEnabled = 0;
+        }else
+        if( sz64==0 ){
+          if( flags & SQLITE_OPEN_MAIN_JOURNAL ){
+            /* If opening a main journal file and the first chunk is zero
+            ** bytes in size, delete any subsequent chunks from the 
+            ** file-system. */
+            int iChunk = 1;
+            do {
+              rc = pOrigVfs->xAccess(pOrigVfs, 
+                  pGroup->aReal[iChunk].z, SQLITE_ACCESS_EXISTS, &bExists
+              );
+              if( rc==SQLITE_OK && bExists ){
+                rc = pOrigVfs->xDelete(pOrigVfs, pGroup->aReal[iChunk].z, 0);
+                if( rc==SQLITE_OK ){
+                  rc = multiplexSubFilename(pGroup, ++iChunk);
+                }
+              }
+            }while( rc==SQLITE_OK && bExists );
+          }
+        }else{
+          /* If the first overflow file exists and if the size of the main file
+          ** is different from the chunk size, that means the chunk size is set
+          ** set incorrectly.  So fix it.
+          **
+          ** Or, if the first overflow file does not exist and the main file is
+          ** larger than the chunk size, that means the chunk size is too small.
+          ** But we have no way of determining the intended chunk size, so 
+          ** just disable the multiplexor all togethre.
+          */
+          rc = pOrigVfs->xAccess(pOrigVfs, pGroup->aReal[1].z,
+              SQLITE_ACCESS_EXISTS, &bExists);
+          bExists = multiplexSubSize(pGroup, 1, &rc)>0;
+          if( rc==SQLITE_OK && bExists && sz64==(sz64&0xffff0000) && sz64>0
+              && sz64!=pGroup->szChunk ){
+            pGroup->szChunk = (int)sz64;
+          }else if( rc==SQLITE_OK && !bExists && sz64>pGroup->szChunk ){
+            pGroup->bEnabled = 0;
+          }
+        }
+      }
+    }
+
+    if( rc==SQLITE_OK ){
+      if( pSubOpen->pMethods->iVersion==1 ){
+        pMultiplexOpen->base.pMethods = &gMultiplex.sIoMethodsV1;
+      }else{
+        pMultiplexOpen->base.pMethods = &gMultiplex.sIoMethodsV2;
+      }
+    }else{
+      multiplexFreeComponents(pGroup);
+      sqlite3_free(pGroup);
+    }
+  }
+  sqlite3_free(zToFree);
+  return rc;
+}
+
+/*
+** This is the xDelete method used for the "multiplex" VFS.
+** It attempts to delete the filename specified.
+*/
+static int multiplexDelete(
+  sqlite3_vfs *pVfs,         /* The multiplex VFS */
+  const char *zName,         /* Name of file to delete */
+  int syncDir
+){
+  int rc;
+  sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
+  rc = pOrigVfs->xDelete(pOrigVfs, zName, syncDir);
+  if( rc==SQLITE_OK ){
+    /* If the main chunk was deleted successfully, also delete any subsequent
+    ** chunks - starting with the last (highest numbered). 
+    */
+    int nName = (int)strlen(zName);
+    char *z;
+    z = sqlite3_malloc64(nName + 5);
+    if( z==0 ){
+      rc = SQLITE_IOERR_NOMEM;
+    }else{
+      int iChunk = 0;
+      int bExists;
+      do{
+        multiplexFilename(zName, nName, SQLITE_OPEN_MAIN_JOURNAL, ++iChunk, z);
+        rc = pOrigVfs->xAccess(pOrigVfs, z, SQLITE_ACCESS_EXISTS, &bExists);
+      }while( rc==SQLITE_OK && bExists );
+      while( rc==SQLITE_OK && iChunk>1 ){
+        multiplexFilename(zName, nName, SQLITE_OPEN_MAIN_JOURNAL, --iChunk, z);
+        rc = pOrigVfs->xDelete(pOrigVfs, z, syncDir);
+      }
+      if( rc==SQLITE_OK ){
+        iChunk = 0;
+        do{
+          multiplexFilename(zName, nName, SQLITE_OPEN_WAL, ++iChunk, z);
+          rc = pOrigVfs->xAccess(pOrigVfs, z, SQLITE_ACCESS_EXISTS, &bExists);
+        }while( rc==SQLITE_OK && bExists );
+        while( rc==SQLITE_OK && iChunk>1 ){
+          multiplexFilename(zName, nName, SQLITE_OPEN_WAL, --iChunk, z);
+          rc = pOrigVfs->xDelete(pOrigVfs, z, syncDir);
+        }
+      }
+    }
+    sqlite3_free(z);
+  }
+  return rc;
+}
+
+static int multiplexAccess(sqlite3_vfs *a, const char *b, int c, int *d){
+  return gMultiplex.pOrigVfs->xAccess(gMultiplex.pOrigVfs, b, c, d);
+}
+static int multiplexFullPathname(sqlite3_vfs *a, const char *b, int c, char *d){
+  return gMultiplex.pOrigVfs->xFullPathname(gMultiplex.pOrigVfs, b, c, d);
+}
+static void *multiplexDlOpen(sqlite3_vfs *a, const char *b){
+  return gMultiplex.pOrigVfs->xDlOpen(gMultiplex.pOrigVfs, b);
+}
+static void multiplexDlError(sqlite3_vfs *a, int b, char *c){
+  gMultiplex.pOrigVfs->xDlError(gMultiplex.pOrigVfs, b, c);
+}
+static void (*multiplexDlSym(sqlite3_vfs *a, void *b, const char *c))(void){
+  return gMultiplex.pOrigVfs->xDlSym(gMultiplex.pOrigVfs, b, c);
+}
+static void multiplexDlClose(sqlite3_vfs *a, void *b){
+  gMultiplex.pOrigVfs->xDlClose(gMultiplex.pOrigVfs, b);
+}
+static int multiplexRandomness(sqlite3_vfs *a, int b, char *c){
+  return gMultiplex.pOrigVfs->xRandomness(gMultiplex.pOrigVfs, b, c);
+}
+static int multiplexSleep(sqlite3_vfs *a, int b){
+  return gMultiplex.pOrigVfs->xSleep(gMultiplex.pOrigVfs, b);
+}
+static int multiplexCurrentTime(sqlite3_vfs *a, double *b){
+  return gMultiplex.pOrigVfs->xCurrentTime(gMultiplex.pOrigVfs, b);
+}
+static int multiplexGetLastError(sqlite3_vfs *a, int b, char *c){
+  if( gMultiplex.pOrigVfs->xGetLastError ){
+    return gMultiplex.pOrigVfs->xGetLastError(gMultiplex.pOrigVfs, b, c);
+  }else{
+    return 0;
+  }
+}
+static int multiplexCurrentTimeInt64(sqlite3_vfs *a, sqlite3_int64 *b){
+  return gMultiplex.pOrigVfs->xCurrentTimeInt64(gMultiplex.pOrigVfs, b);
+}
+
+/************************ I/O Method Wrappers *******************************/
+
+/* xClose requests get passed through to the original VFS.
+** We loop over all open chunk handles and close them.
+** The group structure for this file is unlinked from 
+** our list of groups and freed.
+*/
+static int multiplexClose(sqlite3_file *pConn){
+  multiplexConn *p = (multiplexConn*)pConn;
+  multiplexGroup *pGroup = p->pGroup;
+  int rc = SQLITE_OK;
+  multiplexFreeComponents(pGroup);
+  sqlite3_free(pGroup);
+  return rc;
+}
+
+/* Pass xRead requests thru to the original VFS after
+** determining the correct chunk to operate on.
+** Break up reads across chunk boundaries.
+*/
+static int multiplexRead(
+  sqlite3_file *pConn,
+  void *pBuf,
+  int iAmt,
+  sqlite3_int64 iOfst
+){
+  multiplexConn *p = (multiplexConn*)pConn;
+  multiplexGroup *pGroup = p->pGroup;
+  int rc = SQLITE_OK;
+  if( !pGroup->bEnabled ){
+    sqlite3_file *pSubOpen = multiplexSubOpen(pGroup, 0, &rc, NULL, 0);
+    if( pSubOpen==0 ){
+      rc = SQLITE_IOERR_READ;
+    }else{
+      rc = pSubOpen->pMethods->xRead(pSubOpen, pBuf, iAmt, iOfst);
+    }
+  }else{
+    while( iAmt > 0 ){
+      int i = (int)(iOfst / pGroup->szChunk);
+      sqlite3_file *pSubOpen;
+      pSubOpen = multiplexSubOpen(pGroup, i, &rc, NULL, 1);
+      if( pSubOpen ){
+        int extra = ((int)(iOfst % pGroup->szChunk) + iAmt) - pGroup->szChunk;
+        if( extra<0 ) extra = 0;
+        iAmt -= extra;
+        rc = pSubOpen->pMethods->xRead(pSubOpen, pBuf, iAmt,
+                                       iOfst % pGroup->szChunk);
+        if( rc!=SQLITE_OK ) break;
+        pBuf = (char *)pBuf + iAmt;
+        iOfst += iAmt;
+        iAmt = extra;
+      }else{
+        rc = SQLITE_IOERR_READ;
+        break;
+      }
+    }
+  }
+
+  return rc;
+}
+
+/* Pass xWrite requests thru to the original VFS after
+** determining the correct chunk to operate on.
+** Break up writes across chunk boundaries.
+*/
+static int multiplexWrite(
+  sqlite3_file *pConn,
+  const void *pBuf,
+  int iAmt,
+  sqlite3_int64 iOfst
+){
+  multiplexConn *p = (multiplexConn*)pConn;
+  multiplexGroup *pGroup = p->pGroup;
+  int rc = SQLITE_OK;
+  if( !pGroup->bEnabled ){
+    sqlite3_file *pSubOpen = multiplexSubOpen(pGroup, 0, &rc, NULL, 0);
+    if( pSubOpen==0 ){
+      rc = SQLITE_IOERR_WRITE;
+    }else{
+      rc = pSubOpen->pMethods->xWrite(pSubOpen, pBuf, iAmt, iOfst);
+    }
+  }else{
+    while( rc==SQLITE_OK && iAmt>0 ){
+      int i = (int)(iOfst / pGroup->szChunk);
+      sqlite3_file *pSubOpen = multiplexSubOpen(pGroup, i, &rc, NULL, 1);
+      if( pSubOpen ){
+        int extra = ((int)(iOfst % pGroup->szChunk) + iAmt) -
+                    pGroup->szChunk;
+        if( extra<0 ) extra = 0;
+        iAmt -= extra;
+        rc = pSubOpen->pMethods->xWrite(pSubOpen, pBuf, iAmt,
+                                        iOfst % pGroup->szChunk);
+        pBuf = (char *)pBuf + iAmt;
+        iOfst += iAmt;
+        iAmt = extra;
+      }
+    }
+  }
+  return rc;
+}
+
+/* Pass xTruncate requests thru to the original VFS after
+** determining the correct chunk to operate on.  Delete any
+** chunks above the truncate mark.
+*/
+static int multiplexTruncate(sqlite3_file *pConn, sqlite3_int64 size){
+  multiplexConn *p = (multiplexConn*)pConn;
+  multiplexGroup *pGroup = p->pGroup;
+  int rc = SQLITE_OK;
+  if( !pGroup->bEnabled ){
+    sqlite3_file *pSubOpen = multiplexSubOpen(pGroup, 0, &rc, NULL, 0);
+    if( pSubOpen==0 ){
+      rc = SQLITE_IOERR_TRUNCATE;
+    }else{
+      rc = pSubOpen->pMethods->xTruncate(pSubOpen, size);
+    }
+  }else{
+    int i;
+    int iBaseGroup = (int)(size / pGroup->szChunk);
+    sqlite3_file *pSubOpen;
+    sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
+    /* delete the chunks above the truncate limit */
+    for(i = pGroup->nReal-1; i>iBaseGroup && rc==SQLITE_OK; i--){
+      if( pGroup->bTruncate ){
+        multiplexSubClose(pGroup, i, pOrigVfs);
+      }else{
+        pSubOpen = multiplexSubOpen(pGroup, i, &rc, 0, 0);
+        if( pSubOpen ){
+          rc = pSubOpen->pMethods->xTruncate(pSubOpen, 0);
+        }
+      }
+    }
+    if( rc==SQLITE_OK ){
+      pSubOpen = multiplexSubOpen(pGroup, iBaseGroup, &rc, 0, 0);
+      if( pSubOpen ){
+        rc = pSubOpen->pMethods->xTruncate(pSubOpen, size % pGroup->szChunk);
+      }
+    }
+    if( rc ) rc = SQLITE_IOERR_TRUNCATE;
+  }
+  return rc;
+}
+
+/* Pass xSync requests through to the original VFS without change
+*/
+static int multiplexSync(sqlite3_file *pConn, int flags){
+  multiplexConn *p = (multiplexConn*)pConn;
+  multiplexGroup *pGroup = p->pGroup;
+  int rc = SQLITE_OK;
+  int i;
+  for(i=0; i<pGroup->nReal; i++){
+    sqlite3_file *pSubOpen = pGroup->aReal[i].p;
+    if( pSubOpen ){
+      int rc2 = pSubOpen->pMethods->xSync(pSubOpen, flags);
+      if( rc2!=SQLITE_OK ) rc = rc2;
+    }
+  }
+  return rc;
+}
+
+/* Pass xFileSize requests through to the original VFS.
+** Aggregate the size of all the chunks before returning.
+*/
+static int multiplexFileSize(sqlite3_file *pConn, sqlite3_int64 *pSize){
+  multiplexConn *p = (multiplexConn*)pConn;
+  multiplexGroup *pGroup = p->pGroup;
+  int rc = SQLITE_OK;
+  int i;
+  if( !pGroup->bEnabled ){
+    sqlite3_file *pSubOpen = multiplexSubOpen(pGroup, 0, &rc, NULL, 0);
+    if( pSubOpen==0 ){
+      rc = SQLITE_IOERR_FSTAT;
+    }else{
+      rc = pSubOpen->pMethods->xFileSize(pSubOpen, pSize);
+    }
+  }else{
+    *pSize = 0;
+    for(i=0; rc==SQLITE_OK; i++){
+      sqlite3_int64 sz = multiplexSubSize(pGroup, i, &rc);
+      if( sz==0 ) break;
+      *pSize = i*(sqlite3_int64)pGroup->szChunk + sz;
+    }
+  }
+  return rc;
+}
+
+/* Pass xLock requests through to the original VFS unchanged.
+*/
+static int multiplexLock(sqlite3_file *pConn, int lock){
+  multiplexConn *p = (multiplexConn*)pConn;
+  int rc;
+  sqlite3_file *pSubOpen = multiplexSubOpen(p->pGroup, 0, &rc, NULL, 0);
+  if( pSubOpen ){
+    return pSubOpen->pMethods->xLock(pSubOpen, lock);
+  }
+  return SQLITE_BUSY;
+}
+
+/* Pass xUnlock requests through to the original VFS unchanged.
+*/
+static int multiplexUnlock(sqlite3_file *pConn, int lock){
+  multiplexConn *p = (multiplexConn*)pConn;
+  int rc;
+  sqlite3_file *pSubOpen = multiplexSubOpen(p->pGroup, 0, &rc, NULL, 0);
+  if( pSubOpen ){
+    return pSubOpen->pMethods->xUnlock(pSubOpen, lock);
+  }
+  return SQLITE_IOERR_UNLOCK;
+}
+
+/* Pass xCheckReservedLock requests through to the original VFS unchanged.
+*/
+static int multiplexCheckReservedLock(sqlite3_file *pConn, int *pResOut){
+  multiplexConn *p = (multiplexConn*)pConn;
+  int rc;
+  sqlite3_file *pSubOpen = multiplexSubOpen(p->pGroup, 0, &rc, NULL, 0);
+  if( pSubOpen ){
+    return pSubOpen->pMethods->xCheckReservedLock(pSubOpen, pResOut);
+  }
+  return SQLITE_IOERR_CHECKRESERVEDLOCK;
+}
+
+/* Pass xFileControl requests through to the original VFS unchanged,
+** except for any MULTIPLEX_CTRL_* requests here.
+*/
+static int multiplexFileControl(sqlite3_file *pConn, int op, void *pArg){
+  multiplexConn *p = (multiplexConn*)pConn;
+  multiplexGroup *pGroup = p->pGroup;
+  int rc = SQLITE_ERROR;
+  sqlite3_file *pSubOpen;
+
+  if( !gMultiplex.isInitialized ) return SQLITE_MISUSE;
+  switch( op ){
+    case MULTIPLEX_CTRL_ENABLE:
+      if( pArg ) {
+        int bEnabled = *(int *)pArg;
+        pGroup->bEnabled = (unsigned char)bEnabled;
+        rc = SQLITE_OK;
+      }
+      break;
+    case MULTIPLEX_CTRL_SET_CHUNK_SIZE:
+      if( pArg ) {
+        unsigned int szChunk = *(unsigned*)pArg;
+        if( szChunk<1 ){
+          rc = SQLITE_MISUSE;
+        }else{
+          /* Round up to nearest multiple of MAX_PAGE_SIZE. */
+          szChunk = (szChunk + (MAX_PAGE_SIZE-1));
+          szChunk &= ~(MAX_PAGE_SIZE-1);
+          pGroup->szChunk = szChunk;
+          rc = SQLITE_OK;
+        }
+      }
+      break;
+    case MULTIPLEX_CTRL_SET_MAX_CHUNKS:
+      rc = SQLITE_OK;
+      break;
+    case SQLITE_FCNTL_SIZE_HINT:
+    case SQLITE_FCNTL_CHUNK_SIZE:
+      /* no-op these */
+      rc = SQLITE_OK;
+      break;
+    case SQLITE_FCNTL_PRAGMA: {
+      char **aFcntl = (char**)pArg;
+      /*
+      ** EVIDENCE-OF: R-29875-31678 The argument to the SQLITE_FCNTL_PRAGMA
+      ** file control is an array of pointers to strings (char**) in which the
+      ** second element of the array is the name of the pragma and the third
+      ** element is the argument to the pragma or NULL if the pragma has no
+      ** argument.
+      */
+      if( aFcntl[1] && sqlite3_stricmp(aFcntl[1],"multiplex_truncate")==0 ){
+        if( aFcntl[2] && aFcntl[2][0] ){
+          if( sqlite3_stricmp(aFcntl[2], "on")==0
+           || sqlite3_stricmp(aFcntl[2], "1")==0 ){
+            pGroup->bTruncate = 1;
+          }else
+          if( sqlite3_stricmp(aFcntl[2], "off")==0
+           || sqlite3_stricmp(aFcntl[2], "0")==0 ){
+            pGroup->bTruncate = 0;
+          }
+        }
+        /* EVIDENCE-OF: R-27806-26076 The handler for an SQLITE_FCNTL_PRAGMA
+        ** file control can optionally make the first element of the char**
+        ** argument point to a string obtained from sqlite3_mprintf() or the
+        ** equivalent and that string will become the result of the pragma
+        ** or the error message if the pragma fails.
+        */
+        aFcntl[0] = sqlite3_mprintf(pGroup->bTruncate ? "on" : "off");
+        rc = SQLITE_OK;
+        break;
+      }
+      /* If the multiplexor does not handle the pragma, pass it through
+      ** into the default case. */
+    }
+    default:
+      pSubOpen = multiplexSubOpen(pGroup, 0, &rc, NULL, 0);
+      if( pSubOpen ){
+        rc = pSubOpen->pMethods->xFileControl(pSubOpen, op, pArg);
+        if( op==SQLITE_FCNTL_VFSNAME && rc==SQLITE_OK ){
+         *(char**)pArg = sqlite3_mprintf("multiplex/%z", *(char**)pArg);
+        }
+      }
+      break;
+  }
+  return rc;
+}
+
+/* Pass xSectorSize requests through to the original VFS unchanged.
+*/
+static int multiplexSectorSize(sqlite3_file *pConn){
+  multiplexConn *p = (multiplexConn*)pConn;
+  int rc;
+  sqlite3_file *pSubOpen = multiplexSubOpen(p->pGroup, 0, &rc, NULL, 0);
+  if( pSubOpen && pSubOpen->pMethods->xSectorSize ){
+    return pSubOpen->pMethods->xSectorSize(pSubOpen);
+  }
+  return DEFAULT_SECTOR_SIZE;
+}
+
+/* Pass xDeviceCharacteristics requests through to the original VFS unchanged.
+*/
+static int multiplexDeviceCharacteristics(sqlite3_file *pConn){
+  multiplexConn *p = (multiplexConn*)pConn;
+  int rc;
+  sqlite3_file *pSubOpen = multiplexSubOpen(p->pGroup, 0, &rc, NULL, 0);
+  if( pSubOpen ){
+    return pSubOpen->pMethods->xDeviceCharacteristics(pSubOpen);
+  }
+  return 0;
+}
+
+/* Pass xShmMap requests through to the original VFS unchanged.
+*/
+static int multiplexShmMap(
+  sqlite3_file *pConn,            /* Handle open on database file */
+  int iRegion,                    /* Region to retrieve */
+  int szRegion,                   /* Size of regions */
+  int bExtend,                    /* True to extend file if necessary */
+  void volatile **pp              /* OUT: Mapped memory */
+){
+  multiplexConn *p = (multiplexConn*)pConn;
+  int rc;
+  sqlite3_file *pSubOpen = multiplexSubOpen(p->pGroup, 0, &rc, NULL, 0);
+  if( pSubOpen ){
+    return pSubOpen->pMethods->xShmMap(pSubOpen, iRegion, szRegion, bExtend,pp);
+  }
+  return SQLITE_IOERR;
+}
+
+/* Pass xShmLock requests through to the original VFS unchanged.
+*/
+static int multiplexShmLock(
+  sqlite3_file *pConn,       /* Database file holding the shared memory */
+  int ofst,                  /* First lock to acquire or release */
+  int n,                     /* Number of locks to acquire or release */
+  int flags                  /* What to do with the lock */
+){
+  multiplexConn *p = (multiplexConn*)pConn;
+  int rc;
+  sqlite3_file *pSubOpen = multiplexSubOpen(p->pGroup, 0, &rc, NULL, 0);
+  if( pSubOpen ){
+    return pSubOpen->pMethods->xShmLock(pSubOpen, ofst, n, flags);
+  }
+  return SQLITE_BUSY;
+}
+
+/* Pass xShmBarrier requests through to the original VFS unchanged.
+*/
+static void multiplexShmBarrier(sqlite3_file *pConn){
+  multiplexConn *p = (multiplexConn*)pConn;
+  int rc;
+  sqlite3_file *pSubOpen = multiplexSubOpen(p->pGroup, 0, &rc, NULL, 0);
+  if( pSubOpen ){
+    pSubOpen->pMethods->xShmBarrier(pSubOpen);
+  }
+}
+
+/* Pass xShmUnmap requests through to the original VFS unchanged.
+*/
+static int multiplexShmUnmap(sqlite3_file *pConn, int deleteFlag){
+  multiplexConn *p = (multiplexConn*)pConn;
+  int rc;
+  sqlite3_file *pSubOpen = multiplexSubOpen(p->pGroup, 0, &rc, NULL, 0);
+  if( pSubOpen ){
+    return pSubOpen->pMethods->xShmUnmap(pSubOpen, deleteFlag);
+  }
+  return SQLITE_OK;
+}
+
+/************************** Public Interfaces *****************************/
+/*
+** CAPI: Initialize the multiplex VFS shim - sqlite3_multiplex_initialize()
+**
+** Use the VFS named zOrigVfsName as the VFS that does the actual work.  
+** Use the default if zOrigVfsName==NULL.  
+**
+** The multiplex VFS shim is named "multiplex".  It will become the default
+** VFS if makeDefault is non-zero.
+**
+** THIS ROUTINE IS NOT THREADSAFE.  Call this routine exactly once
+** during start-up.
+*/
+int sqlite3_multiplex_initialize(const char *zOrigVfsName, int makeDefault){
+  sqlite3_vfs *pOrigVfs;
+  if( gMultiplex.isInitialized ) return SQLITE_MISUSE;
+  pOrigVfs = sqlite3_vfs_find(zOrigVfsName);
+  if( pOrigVfs==0 ) return SQLITE_ERROR;
+  assert( pOrigVfs!=&gMultiplex.sThisVfs );
+  gMultiplex.isInitialized = 1;
+  gMultiplex.pOrigVfs = pOrigVfs;
+  gMultiplex.sThisVfs = *pOrigVfs;
+  gMultiplex.sThisVfs.szOsFile += sizeof(multiplexConn);
+  gMultiplex.sThisVfs.zName = SQLITE_MULTIPLEX_VFS_NAME;
+  gMultiplex.sThisVfs.xOpen = multiplexOpen;
+  gMultiplex.sThisVfs.xDelete = multiplexDelete;
+  gMultiplex.sThisVfs.xAccess = multiplexAccess;
+  gMultiplex.sThisVfs.xFullPathname = multiplexFullPathname;
+  gMultiplex.sThisVfs.xDlOpen = multiplexDlOpen;
+  gMultiplex.sThisVfs.xDlError = multiplexDlError;
+  gMultiplex.sThisVfs.xDlSym = multiplexDlSym;
+  gMultiplex.sThisVfs.xDlClose = multiplexDlClose;
+  gMultiplex.sThisVfs.xRandomness = multiplexRandomness;
+  gMultiplex.sThisVfs.xSleep = multiplexSleep;
+  gMultiplex.sThisVfs.xCurrentTime = multiplexCurrentTime;
+  gMultiplex.sThisVfs.xGetLastError = multiplexGetLastError;
+  gMultiplex.sThisVfs.xCurrentTimeInt64 = multiplexCurrentTimeInt64;
+
+  gMultiplex.sIoMethodsV1.iVersion = 1;
+  gMultiplex.sIoMethodsV1.xClose = multiplexClose;
+  gMultiplex.sIoMethodsV1.xRead = multiplexRead;
+  gMultiplex.sIoMethodsV1.xWrite = multiplexWrite;
+  gMultiplex.sIoMethodsV1.xTruncate = multiplexTruncate;
+  gMultiplex.sIoMethodsV1.xSync = multiplexSync;
+  gMultiplex.sIoMethodsV1.xFileSize = multiplexFileSize;
+  gMultiplex.sIoMethodsV1.xLock = multiplexLock;
+  gMultiplex.sIoMethodsV1.xUnlock = multiplexUnlock;
+  gMultiplex.sIoMethodsV1.xCheckReservedLock = multiplexCheckReservedLock;
+  gMultiplex.sIoMethodsV1.xFileControl = multiplexFileControl;
+  gMultiplex.sIoMethodsV1.xSectorSize = multiplexSectorSize;
+  gMultiplex.sIoMethodsV1.xDeviceCharacteristics =
+                                            multiplexDeviceCharacteristics;
+  gMultiplex.sIoMethodsV2 = gMultiplex.sIoMethodsV1;
+  gMultiplex.sIoMethodsV2.iVersion = 2;
+  gMultiplex.sIoMethodsV2.xShmMap = multiplexShmMap;
+  gMultiplex.sIoMethodsV2.xShmLock = multiplexShmLock;
+  gMultiplex.sIoMethodsV2.xShmBarrier = multiplexShmBarrier;
+  gMultiplex.sIoMethodsV2.xShmUnmap = multiplexShmUnmap;
+  sqlite3_vfs_register(&gMultiplex.sThisVfs, makeDefault);
+
+  sqlite3_auto_extension((void(*)(void))multiplexFuncInit);
+
+  return SQLITE_OK;
+}
+
+/*
+** CAPI: Shutdown the multiplex system - sqlite3_multiplex_shutdown()
+**
+** All SQLite database connections must be closed before calling this
+** routine.
+**
+** THIS ROUTINE IS NOT THREADSAFE.  Call this routine exactly once while
+** shutting down in order to free all remaining multiplex groups.
+*/
+int sqlite3_multiplex_shutdown(int eForce){
+  int rc = SQLITE_OK;
+  if( gMultiplex.isInitialized==0 ) return SQLITE_MISUSE;
+  gMultiplex.isInitialized = 0;
+  sqlite3_vfs_unregister(&gMultiplex.sThisVfs);
+  memset(&gMultiplex, 0, sizeof(gMultiplex));
+  return rc;
+}
+
+/***************************** Test Code ***********************************/
+#ifdef SQLITE_TEST
+#if defined(INCLUDE_SQLITE_TCL_H)
+#  include "sqlite_tcl.h"
+#else
+#  include "tcl.h"
+#  ifndef SQLITE_TCLAPI
+#    define SQLITE_TCLAPI
+#  endif
+#endif
+extern const char *sqlite3ErrName(int);
+
+
+/*
+** tclcmd: sqlite3_multiplex_initialize NAME MAKEDEFAULT
+*/
+static int SQLITE_TCLAPI test_multiplex_initialize(
+  void * clientData,
+  Tcl_Interp *interp,
+  int objc,
+  Tcl_Obj *CONST objv[]
+){
+  const char *zName;              /* Name of new multiplex VFS */
+  int makeDefault;                /* True to make the new VFS the default */
+  int rc;                         /* Value returned by multiplex_initialize() */
+
+  UNUSED_PARAMETER(clientData);
+
+  /* Process arguments */
+  if( objc!=3 ){
+    Tcl_WrongNumArgs(interp, 1, objv, "NAME MAKEDEFAULT");
+    return TCL_ERROR;
+  }
+  zName = Tcl_GetString(objv[1]);
+  if( Tcl_GetBooleanFromObj(interp, objv[2], &makeDefault) ) return TCL_ERROR;
+  if( zName[0]=='\0' ) zName = 0;
+
+  /* Call sqlite3_multiplex_initialize() */
+  rc = sqlite3_multiplex_initialize(zName, makeDefault);
+  Tcl_SetResult(interp, (char *)sqlite3ErrName(rc), TCL_STATIC);
+
+  return TCL_OK;
+}
+
+/*
+** tclcmd: sqlite3_multiplex_shutdown
+*/
+static int SQLITE_TCLAPI test_multiplex_shutdown(
+  void * clientData,
+  Tcl_Interp *interp,
+  int objc,
+  Tcl_Obj *CONST objv[]
+){
+  int rc;                         /* Value returned by multiplex_shutdown() */
+
+  UNUSED_PARAMETER(clientData);
+
+  if( objc==2 && strcmp(Tcl_GetString(objv[1]),"-force")!=0 ){
+    objc = 3;
+  }
+  if( (objc!=1 && objc!=2) ){
+    Tcl_WrongNumArgs(interp, 1, objv, "?-force?");
+    return TCL_ERROR;
+  }
+
+  /* Call sqlite3_multiplex_shutdown() */
+  rc = sqlite3_multiplex_shutdown(objc==2);
+  Tcl_SetResult(interp, (char *)sqlite3ErrName(rc), TCL_STATIC);
+
+  return TCL_OK;
+}
+
+/*
+** Tclcmd: test_multiplex_control HANDLE DBNAME SUB-COMMAND ?INT-VALUE?
+*/
+static int SQLITE_TCLAPI test_multiplex_control(
+  ClientData cd,
+  Tcl_Interp *interp,
+  int objc,
+  Tcl_Obj *CONST objv[]
+){
+  int rc;                         /* Return code from file_control() */
+  int idx;                        /* Index in aSub[] */
+  Tcl_CmdInfo cmdInfo;            /* Command info structure for HANDLE */
+  sqlite3 *db;                    /* Underlying db handle for HANDLE */
+  int iValue = 0;
+  void *pArg = 0;
+
+  struct SubCommand {
+    const char *zName;
+    int op;
+    int argtype;
+  } aSub[] = {
+    { "enable",       MULTIPLEX_CTRL_ENABLE,           1 },
+    { "chunk_size",   MULTIPLEX_CTRL_SET_CHUNK_SIZE,   1 },
+    { "max_chunks",   MULTIPLEX_CTRL_SET_MAX_CHUNKS,   1 },
+    { 0, 0, 0 }
+  };
+
+  if( objc!=5 ){
+    Tcl_WrongNumArgs(interp, 1, objv, "HANDLE DBNAME SUB-COMMAND INT-VALUE");
+    return TCL_ERROR;
+  }
+
+  if( 0==Tcl_GetCommandInfo(interp, Tcl_GetString(objv[1]), &cmdInfo) ){
+    Tcl_AppendResult(interp, "expected database handle, got \"", 0);
+    Tcl_AppendResult(interp, Tcl_GetString(objv[1]), "\"", 0);
+    return TCL_ERROR;
+  }else{
+    db = *(sqlite3 **)cmdInfo.objClientData;
+  }
+
+  rc = Tcl_GetIndexFromObjStruct(
+      interp, objv[3], aSub, sizeof(aSub[0]), "sub-command", 0, &idx
+  );
+  if( rc!=TCL_OK ) return rc;
+
+  switch( aSub[idx].argtype ){
+    case 1:
+      if( Tcl_GetIntFromObj(interp, objv[4], &iValue) ){
+        return TCL_ERROR;
+      }
+      pArg = (void *)&iValue;
+      break;
+    default:
+      Tcl_WrongNumArgs(interp, 4, objv, "SUB-COMMAND");
+      return TCL_ERROR;
+  }
+
+  rc = sqlite3_file_control(db, Tcl_GetString(objv[2]), aSub[idx].op, pArg);
+  Tcl_SetResult(interp, (char *)sqlite3ErrName(rc), TCL_STATIC);
+  return (rc==SQLITE_OK) ? TCL_OK : TCL_ERROR;
+}
+
+/*
+** This routine registers the custom TCL commands defined in this
+** module.  This should be the only procedure visible from outside
+** of this module.
+*/
+int Sqlitemultiplex_Init(Tcl_Interp *interp){
+  static struct {
+     char *zName;
+     Tcl_ObjCmdProc *xProc;
+  } aCmd[] = {
+    { "sqlite3_multiplex_initialize", test_multiplex_initialize },
+    { "sqlite3_multiplex_shutdown", test_multiplex_shutdown },
+    { "sqlite3_multiplex_control", test_multiplex_control },
+  };
+  int i;
+
+  for(i=0; i<sizeof(aCmd)/sizeof(aCmd[0]); i++){
+    Tcl_CreateObjCommand(interp, aCmd[i].zName, aCmd[i].xProc, 0, 0);
+  }
+
+  return TCL_OK;
+}
+#endif