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third_party/sqlite/src/src/test_multiplex.c

Index: third_party/sqlite/src/src/test_multiplex.c
diff --git a/third_party/sqlite/src/src/test_multiplex.c b/third_party/sqlite/src/src/test_multiplex.c
new file mode 100644
index 0000000000000000000000000000000000000000..d8a7db86e1d4f568b3cd745b38eba105636e58dd
--- /dev/null
+++ b/third_party/sqlite/src/src/test_multiplex.c
@@ -0,0 +1,1179 @@
+/*
+** 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.
+**
+** This particular shim enforces a multiplex system on DB files.  
+** This shim shards/partitions a single DB file into smaller 
+** "chunks" such that the total DB file size may exceed the maximum
+** file size of the underlying file system.
+**
+*/
+#include "sqlite3.h"
+#include <string.h>
+#include <assert.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 seperately 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
+
+/*
+** For a build without mutexes, no-op the mutex calls.
+*/
+#if defined(SQLITE_THREADSAFE) && SQLITE_THREADSAFE==0
+#define sqlite3_mutex_alloc(X)    ((sqlite3_mutex*)8)
+#define sqlite3_mutex_free(X)
+#define sqlite3_mutex_enter(X)
+#define sqlite3_mutex_try(X)      SQLITE_OK
+#define sqlite3_mutex_leave(X)
+#define sqlite3_mutex_held(X)     ((void)(X),1)
+#define sqlite3_mutex_notheld(X)  ((void)(X),1)
+#endif /* SQLITE_THREADSAFE==0 */
+
+
+/************************ Shim Definitions ******************************/
+
+#define SQLITE_MULTIPLEX_VFS_NAME "multiplex"
+
+/* 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 1GB.
+*/
+#define SQLITE_MULTIPLEX_CHUNK_SIZE (MAX_PAGE_SIZE*16384)
+
+/* Default limit on number of chunks.  Care should be taken
+** so that values for chunks numbers fit in the SQLITE_MULTIPLEX_EXT_FMT
+** format specifier. It may be changed by calling
+** the xFileControl() interface.
+*/
+#define SQLITE_MULTIPLEX_MAX_CHUNKS 32
+
+/* If SQLITE_MULTIPLEX_EXT_OVWR is defined, the 
+** last SQLITE_MULTIPLEX_EXT_SZ characters of the 
+** filename will be overwritten, otherwise, the 
+** multiplex extension is simply appended to the filename.
+** Ex.  (undefined) test.db -> test.db01
+**      (defined)   test.db -> test.01
+** Chunk 0 does not have a modified extension.
+*/
+#define SQLITE_MULTIPLEX_EXT_FMT    "%02d"
+#define SQLITE_MULTIPLEX_EXT_SZ     2
+
+/************************ 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 {
+  sqlite3_file **pReal;            /* Handles to each chunk */
+  char *bOpen;                     /* array of bools - 0 if chunk not opened */
+  char *zName;                     /* Base filename of this group */
+  int nName;                       /* Length of base filename */
+  int flags;                       /* Flags used for original opening */
+  int nChunkSize;                  /* Chunk size used for this group */
+  int nMaxChunks;                  /* Max number of chunks for this group */
+  int bEnabled;                    /* TRUE to use Multiplex VFS for this file */
+  multiplexGroup *pNext, *pPrev;   /* Doubly linked list of all group objects */
+};
+
+/*
+** 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;
+
+  /* For run-time access any of the other global data structures in this
+  ** shim, the following mutex must be held.
+  */
+  sqlite3_mutex *pMutex;
+
+  /* List of multiplexGroup objects.
+  */
+  multiplexGroup *pGroups;
+
+  /* Storage for temp file names.  Allocated during 
+  ** initialization to the max pathname of the underlying VFS.
+  */
+  char *zName;
+
+} gMultiplex;
+
+/************************* Utility Routines *********************************/
+/*
+** Acquire and release the mutex used to serialize access to the
+** list of multiplexGroups.
+*/
+static void multiplexEnter(void){ sqlite3_mutex_enter(gMultiplex.pMutex); }
+static void multiplexLeave(void){ sqlite3_mutex_leave(gMultiplex.pMutex); }
+
+/*
+** 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.
+*/
+int multiplexStrlen30(const char *z){
+  const char *z2 = z;
+  if( z==0 ) return 0;
+  while( *z2 ){ z2++; }
+  return 0x3fffffff & (int)(z2 - z);
+}
+
+/* Translate an sqlite3_file* that is really a multiplexGroup* into
+** the sqlite3_file* for the underlying original VFS.
+*/
+static sqlite3_file *multiplexSubOpen(multiplexConn *pConn, int iChunk, int *rc, int *pOutFlags){
+  multiplexGroup *pGroup = pConn->pGroup;
+  sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;        /* Real VFS */
+  if( iChunk<pGroup->nMaxChunks ){
+    sqlite3_file *pSubOpen = pGroup->pReal[iChunk];    /* Real file descriptor */
+    if( !pGroup->bOpen[iChunk] ){
+      memcpy(gMultiplex.zName, pGroup->zName, pGroup->nName+1);
+      if( iChunk ){
+#ifdef SQLITE_MULTIPLEX_EXT_OVWR
+        sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, gMultiplex.zName+pGroup->nName-SQLITE_MULTIPLEX_EXT_SZ, SQLITE_MULTIPLEX_EXT_FMT, iChunk);
+#else
+        sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, gMultiplex.zName+pGroup->nName, SQLITE_MULTIPLEX_EXT_FMT, iChunk);
+#endif
+      }
+      *rc = pOrigVfs->xOpen(pOrigVfs, gMultiplex.zName, pSubOpen, pGroup->flags, pOutFlags);
+      if( *rc==SQLITE_OK ){
+        pGroup->bOpen[iChunk] = -1;
+        return pSubOpen;
+      }
+      return NULL;
+    }
+    *rc = SQLITE_OK;
+    return pSubOpen;
+  }
+  *rc = SQLITE_FULL;
+  return NULL;
+}
+
+/*
+** 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;
+  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;
+}
+
+/************************* 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;                                        /* Result code */
+  multiplexConn *pMultiplexOpen;                 /* The new multiplex file descriptor */
+  multiplexGroup *pGroup;                        /* Corresponding multiplexGroup object */
+  sqlite3_file *pSubOpen;                        /* Real file descriptor */
+  sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
+  int nName = multiplexStrlen30(zName);
+  int i;
+  int sz;
+
+  UNUSED_PARAMETER(pVfs);
+
+  /* We need to create a group structure and manage
+  ** access to this group of files.
+  */
+  multiplexEnter();
+  pMultiplexOpen = (multiplexConn*)pConn;
+  /* allocate space for group */
+  sz = sizeof(multiplexGroup)                                /* multiplexGroup */
+     + (sizeof(sqlite3_file *)*SQLITE_MULTIPLEX_MAX_CHUNKS)  /* pReal[] */
+     + (pOrigVfs->szOsFile*SQLITE_MULTIPLEX_MAX_CHUNKS)      /* *pReal */
+     + SQLITE_MULTIPLEX_MAX_CHUNKS                           /* bOpen[] */
+     + nName + 1;                                            /* zName */
+#ifndef SQLITE_MULTIPLEX_EXT_OVWR
+  sz += SQLITE_MULTIPLEX_EXT_SZ;
+  assert(nName+SQLITE_MULTIPLEX_EXT_SZ < pOrigVfs->mxPathname);
+#else
+  assert(nName >= SQLITE_MULTIPLEX_EXT_SZ);
+  assert(nName < pOrigVfs->mxPathname);
+#endif
+  pGroup = sqlite3_malloc( sz );
+  if( pGroup==0 ){
+    rc=SQLITE_NOMEM;
+  }else{
+    /* assign pointers to extra space allocated */
+    char *p = (char *)&pGroup[1];
+    pMultiplexOpen->pGroup = pGroup;
+    memset(pGroup, 0, sz);
+    pGroup->bEnabled = -1;
+    pGroup->nChunkSize = SQLITE_MULTIPLEX_CHUNK_SIZE;
+    pGroup->nMaxChunks = SQLITE_MULTIPLEX_MAX_CHUNKS;
+    pGroup->pReal = (sqlite3_file **)p;
+    p += (sizeof(sqlite3_file *)*pGroup->nMaxChunks);
+    for(i=0; i<pGroup->nMaxChunks; i++){
+      pGroup->pReal[i] = (sqlite3_file *)p;
+      p += pOrigVfs->szOsFile;
+    }
+    /* bOpen[] vals should all be zero from memset above */
+    pGroup->bOpen = p;
+    p += pGroup->nMaxChunks;
+    pGroup->zName = p;
+    /* save off base filename, name length, and original open flags  */
+    memcpy(pGroup->zName, zName, nName+1);
+    pGroup->nName = nName;
+    pGroup->flags = flags;
+    pSubOpen = multiplexSubOpen(pMultiplexOpen, 0, &rc, pOutFlags);
+    if( pSubOpen ){
+      /* if this file is already larger than chunk size, disable 
+      ** the multiplex feature.
+      */
+      sqlite3_int64 sz;
+      int rc2 = pSubOpen->pMethods->xFileSize(pSubOpen, &sz);
+      if( (rc2==SQLITE_OK) && (sz>pGroup->nChunkSize) ){
+        pGroup->bEnabled = 0;
+      }
+      if( pSubOpen->pMethods->iVersion==1 ){
+        pMultiplexOpen->base.pMethods = &gMultiplex.sIoMethodsV1;
+      }else{
+        pMultiplexOpen->base.pMethods = &gMultiplex.sIoMethodsV2;
+      }
+      /* place this group at the head of our list */
+      pGroup->pNext = gMultiplex.pGroups;
+      if( gMultiplex.pGroups ) gMultiplex.pGroups->pPrev = pGroup;
+      gMultiplex.pGroups = pGroup;
+    }else{
+      sqlite3_free(pGroup);
+    }
+  }
+  multiplexLeave();
+  return rc;
+}
+
+/*
+** This is the xDelete method used for the "multiplex" VFS.
+** It attempts to delete the filename specified, as well
+** as additional files with the SQLITE_MULTIPLEX_EXT_FMT extension.
+*/
+static int multiplexDelete(
+  sqlite3_vfs *pVfs,         /* The multiplex VFS */
+  const char *zName,         /* Name of file to delete */
+  int syncDir
+){
+  sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
+  int rc = SQLITE_OK;
+  int nName = multiplexStrlen30(zName);
+  int i;
+
+  UNUSED_PARAMETER(pVfs);
+
+  multiplexEnter();
+  memcpy(gMultiplex.zName, zName, nName+1);
+  for(i=0; i<SQLITE_MULTIPLEX_MAX_CHUNKS; i++){
+    int rc2;
+    int exists = 0;
+    if( i ){
+#ifdef SQLITE_MULTIPLEX_EXT_OVWR
+        sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, 
+            gMultiplex.zName+nName-SQLITE_MULTIPLEX_EXT_SZ, 
+            SQLITE_MULTIPLEX_EXT_FMT, i);
+#else
+        sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, 
+            gMultiplex.zName+nName, 
+            SQLITE_MULTIPLEX_EXT_FMT, i);
+#endif
+    }
+    rc2 = pOrigVfs->xAccess(pOrigVfs, gMultiplex.zName, 
+        SQLITE_ACCESS_EXISTS, &exists);
+    if( rc2==SQLITE_OK && exists){
+      /* if it exists, delete it */
+      rc2 = pOrigVfs->xDelete(pOrigVfs, gMultiplex.zName, syncDir);
+      if( rc2!=SQLITE_OK ) rc = rc2;
+    }else{
+      /* stop at first "gap" */
+      break;
+    }
+  }
+  multiplexLeave();
+  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){
+  return gMultiplex.pOrigVfs->xGetLastError(gMultiplex.pOrigVfs, b, c);
+}
+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;
+  int i;
+  multiplexEnter();
+  /* close any open handles */
+  for(i=0; i<pGroup->nMaxChunks; i++){
+    if( pGroup->bOpen[i] ){
+      sqlite3_file *pSubOpen = pGroup->pReal[i];
+      int rc2 = pSubOpen->pMethods->xClose(pSubOpen);
+      if( rc2!=SQLITE_OK ) rc = rc2;
+      pGroup->bOpen[i] = 0;
+    }
+  }
+  /* remove from linked list */
+  if( pGroup->pNext ) pGroup->pNext->pPrev = pGroup->pPrev;
+  if( pGroup->pPrev ){
+    pGroup->pPrev->pNext = pGroup->pNext;
+  }else{
+    gMultiplex.pGroups = pGroup->pNext;
+  }
+  sqlite3_free(pGroup);
+  multiplexLeave();
+  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;
+  multiplexEnter();
+  if( !pGroup->bEnabled ){
+    sqlite3_file *pSubOpen = multiplexSubOpen(p, 0, &rc, NULL);
+    rc = ( !pSubOpen ) ? SQLITE_IOERR_READ : pSubOpen->pMethods->xRead(pSubOpen, pBuf, iAmt, iOfst);
+  }else{
+    while( iAmt > 0 ){
+      int i = (int)(iOfst / pGroup->nChunkSize);
+      sqlite3_file *pSubOpen = multiplexSubOpen(p, i, &rc, NULL);
+      if( pSubOpen ){
+        int extra = ((int)(iOfst % pGroup->nChunkSize) + iAmt) - pGroup->nChunkSize;
+        if( extra<0 ) extra = 0;
+        iAmt -= extra;
+        rc = pSubOpen->pMethods->xRead(pSubOpen, pBuf, iAmt, iOfst % pGroup->nChunkSize);
+        if( rc!=SQLITE_OK ) break;
+        pBuf = (char *)pBuf + iAmt;
+        iOfst += iAmt;
+        iAmt = extra;
+      }else{
+        rc = SQLITE_IOERR_READ;
+        break;
+      }
+    }
+  }
+  multiplexLeave();
+  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;
+  multiplexEnter();
+  if( !pGroup->bEnabled ){
+    sqlite3_file *pSubOpen = multiplexSubOpen(p, 0, &rc, NULL);
+    rc = ( !pSubOpen ) ? SQLITE_IOERR_WRITE : pSubOpen->pMethods->xWrite(pSubOpen, pBuf, iAmt, iOfst);
+  }else{
+    while( iAmt > 0 ){
+      int i = (int)(iOfst / pGroup->nChunkSize);
+      sqlite3_file *pSubOpen = multiplexSubOpen(p, i, &rc, NULL);
+      if( pSubOpen ){
+        int extra = ((int)(iOfst % pGroup->nChunkSize) + iAmt) - pGroup->nChunkSize;
+        if( extra<0 ) extra = 0;
+        iAmt -= extra;
+        rc = pSubOpen->pMethods->xWrite(pSubOpen, pBuf, iAmt, iOfst % pGroup->nChunkSize);
+        if( rc!=SQLITE_OK ) break;
+        pBuf = (char *)pBuf + iAmt;
+        iOfst += iAmt;
+        iAmt = extra;
+      }else{
+        rc = SQLITE_IOERR_WRITE;
+        break;
+      }
+    }
+  }
+  multiplexLeave();
+  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;
+  multiplexEnter();
+  if( !pGroup->bEnabled ){
+    sqlite3_file *pSubOpen = multiplexSubOpen(p, 0, &rc, NULL);
+    rc = ( !pSubOpen ) ? SQLITE_IOERR_TRUNCATE : pSubOpen->pMethods->xTruncate(pSubOpen, size);
+  }else{
+    int rc2;
+    int i;
+    sqlite3_file *pSubOpen;
+    sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
+    memcpy(gMultiplex.zName, pGroup->zName, pGroup->nName+1);
+    /* delete the chunks above the truncate limit */
+    for(i=(int)(size / pGroup->nChunkSize)+1; i<pGroup->nMaxChunks; i++){
+      /* close any open chunks before deleting them */
+      if( pGroup->bOpen[i] ){
+        pSubOpen = pGroup->pReal[i];
+        rc2 = pSubOpen->pMethods->xClose(pSubOpen);
+        if( rc2!=SQLITE_OK ) rc = SQLITE_IOERR_TRUNCATE;
+        pGroup->bOpen[i] = 0;
+      }
+#ifdef SQLITE_MULTIPLEX_EXT_OVWR
+      sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, 
+          gMultiplex.zName+pGroup->nName-SQLITE_MULTIPLEX_EXT_SZ, 
+          SQLITE_MULTIPLEX_EXT_FMT, i);
+#else
+      sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, 
+          gMultiplex.zName+pGroup->nName, 
+          SQLITE_MULTIPLEX_EXT_FMT, i);
+#endif
+      rc2 = pOrigVfs->xDelete(pOrigVfs, gMultiplex.zName, 0);
+      if( rc2!=SQLITE_OK ) rc = SQLITE_IOERR_TRUNCATE;
+    }
+    pSubOpen = multiplexSubOpen(p, (int)(size / pGroup->nChunkSize), &rc2, NULL);
+    if( pSubOpen ){
+      rc2 = pSubOpen->pMethods->xTruncate(pSubOpen, size % pGroup->nChunkSize);
+      if( rc2!=SQLITE_OK ) rc = rc2;
+    }else{
+      rc = SQLITE_IOERR_TRUNCATE;
+    }
+  }
+  multiplexLeave();
+  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;
+  multiplexEnter();
+  for(i=0; i<pGroup->nMaxChunks; i++){
+    /* if we don't have it open, we don't need to sync it */
+    if( pGroup->bOpen[i] ){
+      sqlite3_file *pSubOpen = pGroup->pReal[i];
+      int rc2 = pSubOpen->pMethods->xSync(pSubOpen, flags);
+      if( rc2!=SQLITE_OK ) rc = rc2;
+    }
+  }
+  multiplexLeave();
+  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 rc2;
+  int i;
+  multiplexEnter();
+  if( !pGroup->bEnabled ){
+    sqlite3_file *pSubOpen = multiplexSubOpen(p, 0, &rc, NULL);
+    rc = ( !pSubOpen ) ? SQLITE_IOERR_FSTAT : pSubOpen->pMethods->xFileSize(pSubOpen, pSize);
+  }else{
+    *pSize = 0;
+    for(i=0; i<pGroup->nMaxChunks; i++){
+      sqlite3_file *pSubOpen = NULL;
+      /* if not opened already, check to see if the chunk exists */
+      if( pGroup->bOpen[i] ){
+        pSubOpen = pGroup->pReal[i];
+      }else{
+        sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
+        int exists = 0;
+        memcpy(gMultiplex.zName, pGroup->zName, pGroup->nName+1);
+        if( i ){
+#ifdef SQLITE_MULTIPLEX_EXT_OVWR
+          sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, 
+              gMultiplex.zName+pGroup->nName-SQLITE_MULTIPLEX_EXT_SZ, 
+              SQLITE_MULTIPLEX_EXT_FMT, i);
+#else
+          sqlite3_snprintf(SQLITE_MULTIPLEX_EXT_SZ+1, 
+              gMultiplex.zName+pGroup->nName, 
+              SQLITE_MULTIPLEX_EXT_FMT, i);
+#endif
+        }
+        rc2 = pOrigVfs->xAccess(pOrigVfs, gMultiplex.zName, 
+            SQLITE_ACCESS_EXISTS, &exists);
+        if( rc2==SQLITE_OK && exists){
+          /* if it exists, open it */
+          pSubOpen = multiplexSubOpen(p, i, &rc, NULL);
+        }else{
+          /* stop at first "gap" */
+          break;
+        }
+      }
+      if( pSubOpen ){
+        sqlite3_int64 sz;
+        rc2 = pSubOpen->pMethods->xFileSize(pSubOpen, &sz);
+        if( rc2!=SQLITE_OK ){
+          rc = rc2;
+        }else{
+          if( sz>pGroup->nChunkSize ){
+            rc = SQLITE_IOERR_FSTAT;
+          }
+          *pSize += sz;
+        }
+      }else{
+        break;
+      }
+    }
+  }
+  multiplexLeave();
+  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, 0, &rc, NULL);
+  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, 0, &rc, NULL);
+  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, 0, &rc, NULL);
+  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 = bEnabled;
+        rc = SQLITE_OK;
+      }
+      break;
+    case MULTIPLEX_CTRL_SET_CHUNK_SIZE:
+      if( pArg ) {
+        int nChunkSize = *(int *)pArg;
+        if( nChunkSize<1 ){
+          rc = SQLITE_MISUSE;
+        }else{
+          /* Round up to nearest multiple of MAX_PAGE_SIZE. */
+          nChunkSize = (nChunkSize + (MAX_PAGE_SIZE-1));
+          nChunkSize &= ~(MAX_PAGE_SIZE-1);
+          pGroup->nChunkSize = nChunkSize;
+          rc = SQLITE_OK;
+        }
+      }
+      break;
+    case MULTIPLEX_CTRL_SET_MAX_CHUNKS:
+      if( pArg ) {
+        int nMaxChunks = *(int *)pArg;
+        if(( nMaxChunks<1 ) || ( nMaxChunks>SQLITE_MULTIPLEX_MAX_CHUNKS )){
+          rc = SQLITE_MISUSE;
+        }else{
+          pGroup->nMaxChunks = nMaxChunks;
+          rc = SQLITE_OK;
+        }
+      }
+      break;
+    case SQLITE_FCNTL_SIZE_HINT:
+    case SQLITE_FCNTL_CHUNK_SIZE:
+      /* no-op these */
+      rc = SQLITE_OK;
+      break;
+    default:
+      pSubOpen = multiplexSubOpen(p, 0, &rc, NULL);
+      if( pSubOpen ){
+        rc = pSubOpen->pMethods->xFileControl(pSubOpen, op, 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, 0, &rc, NULL);
+  if( pSubOpen ){
+    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, 0, &rc, NULL);
+  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, 0, &rc, NULL);
+  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, 0, &rc, NULL);
+  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, 0, &rc, NULL);
+  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, 0, &rc, NULL);
+  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.pMutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
+  if( !gMultiplex.pMutex ){
+    return SQLITE_NOMEM;
+  }
+  gMultiplex.zName = sqlite3_malloc(pOrigVfs->mxPathname);
+  if( !gMultiplex.zName ){
+    sqlite3_mutex_free(gMultiplex.pMutex);
+    return SQLITE_NOMEM;
+  }
+  gMultiplex.pGroups = NULL;
+  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*)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(void){
+  if( gMultiplex.isInitialized==0 ) return SQLITE_MISUSE;
+  if( gMultiplex.pGroups ) return SQLITE_MISUSE;
+  gMultiplex.isInitialized = 0;
+  sqlite3_free(gMultiplex.zName);
+  sqlite3_mutex_free(gMultiplex.pMutex);
+  sqlite3_vfs_unregister(&gMultiplex.sThisVfs);
+  memset(&gMultiplex, 0, sizeof(gMultiplex));
+  return SQLITE_OK;
+}
+
+/***************************** Test Code ***********************************/
+#ifdef SQLITE_TEST
+#include <tcl.h>
+extern const char *sqlite3TestErrorName(int);
+
+
+/*
+** tclcmd: sqlite3_multiplex_initialize NAME MAKEDEFAULT
+*/
+static int 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 *)sqlite3TestErrorName(rc), TCL_STATIC);
+
+  return TCL_OK;
+}
+
+/*
+** tclcmd: sqlite3_multiplex_shutdown
+*/
+static int 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!=1 ){
+    Tcl_WrongNumArgs(interp, 1, objv, "");
+    return TCL_ERROR;
+  }
+
+  /* Call sqlite3_multiplex_shutdown() */
+  rc = sqlite3_multiplex_shutdown();
+  Tcl_SetResult(interp, (char *)sqlite3TestErrorName(rc), TCL_STATIC);
+
+  return TCL_OK;
+}
+
+/*
+** tclcmd:  sqlite3_multiplex_dump
+*/
+static int test_multiplex_dump(
+  void * clientData,
+  Tcl_Interp *interp,
+  int objc,
+  Tcl_Obj *CONST objv[]
+){
+  Tcl_Obj *pResult;
+  Tcl_Obj *pGroupTerm;
+  multiplexGroup *pGroup;
+  int i;
+  int nChunks = 0;
+
+  UNUSED_PARAMETER(clientData);
+  UNUSED_PARAMETER(objc);
+  UNUSED_PARAMETER(objv);
+
+  pResult = Tcl_NewObj();
+  multiplexEnter();
+  for(pGroup=gMultiplex.pGroups; pGroup; pGroup=pGroup->pNext){
+    pGroupTerm = Tcl_NewObj();
+
+    pGroup->zName[pGroup->nName] = '\0';
+    Tcl_ListObjAppendElement(interp, pGroupTerm,
+          Tcl_NewStringObj(pGroup->zName, -1));
+    Tcl_ListObjAppendElement(interp, pGroupTerm,
+          Tcl_NewIntObj(pGroup->nName));
+    Tcl_ListObjAppendElement(interp, pGroupTerm,
+          Tcl_NewIntObj(pGroup->flags));
+
+    /* count number of chunks with open handles */
+    for(i=0; i<pGroup->nMaxChunks; i++){
+      if( pGroup->bOpen[i] ) nChunks++;
+    }
+    Tcl_ListObjAppendElement(interp, pGroupTerm,
+          Tcl_NewIntObj(nChunks));
+
+    Tcl_ListObjAppendElement(interp, pGroupTerm,
+          Tcl_NewIntObj(pGroup->nChunkSize));
+    Tcl_ListObjAppendElement(interp, pGroupTerm,
+          Tcl_NewIntObj(pGroup->nMaxChunks));
+
+    Tcl_ListObjAppendElement(interp, pResult, pGroupTerm);
+  }
+  multiplexLeave();
+  Tcl_SetObjResult(interp, pResult);
+  return TCL_OK;
+}
+
+/*
+** Tclcmd: test_multiplex_control HANDLE DBNAME SUB-COMMAND ?INT-VALUE?
+*/
+static int 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 *)sqlite3TestErrorName(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_dump", test_multiplex_dump },
+    { "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