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 */
  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
................................................................................
*/
static int multiplexStrlen30(const char *z){
  const char *z2 = z;
  if( z==0 ) return 0;
  while( *z2 ){ z2++; }
  return 0x3fffffff & (int)(z2 - z);
}


































/* Compute the filename for the iChunk-th chunk
*/
static int multiplexSubFilename(multiplexGroup *pGroup, int iChunk){
  if( iChunk>=pGroup->nReal ){
    struct multiplexReal *p;
    p = sqlite3_realloc(pGroup->aReal, (iChunk+1)*sizeof(*p));
................................................................................
  if( pGroup->zName && pGroup->aReal[iChunk].z==0 ){
    char *z;
    int n = pGroup->nName;
    pGroup->aReal[iChunk].z = z = sqlite3_malloc( n+4 );
    if( z==0 ){
      return SQLITE_NOMEM;
    }
    memcpy(z, pGroup->zName, n+1);
    if( iChunk>0 ){
#ifdef SQLITE_ENABLE_8_3_NAMES
      int i;
      for(i=n-1; i>0 && i>=n-4 && z[i]!='.'; i--){}
      if( i>=n-4 ) n = i+1;
      if( pGroup->flags & (SQLITE_OPEN_MAIN_JOURNAL|SQLITE_OPEN_TEMP_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;
      }
#endif
      sqlite3_snprintf(4,&z[n],"%03d",iChunk);
    }
  }
  return SQLITE_OK;
}

/* Translate an sqlite3_file* that is really a multiplexGroup* into
** the sqlite3_file* for the underlying original VFS.




*/
static sqlite3_file *multiplexSubOpen(
  multiplexGroup *pGroup,
  int iChunk,
  int *rc,


  int *pOutFlags

){
  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 
................................................................................
    *rc = SQLITE_FULL;
    return 0;
  }
#endif

  *rc = multiplexSubFilename(pGroup, iChunk);
  if( (*rc)==SQLITE_OK && (pSubOpen = pGroup->aReal[iChunk].p)==0 ){















    pSubOpen = sqlite3_malloc( pOrigVfs->szOsFile );
    if( pSubOpen==0 ){
      *rc = SQLITE_NOMEM;
      return 0;
    }
    pGroup->aReal[iChunk].p = pSubOpen;
    *rc = pOrigVfs->xOpen(pOrigVfs, pGroup->aReal[iChunk].z, pSubOpen,
                          pGroup->flags, pOutFlags);
    if( *rc!=SQLITE_OK ){
      sqlite3_free(pSubOpen);
      pGroup->aReal[iChunk].p = 0;
      return 0;
    }
  }
  return pSubOpen;
}




















/*
** This is the implementation of the multiplex_control() SQL function.
*/
static void multiplexControlFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
................................................................................
  multiplexGroup *pGroup,
  int iChunk,
  sqlite3_vfs *pOrigVfs
){
  sqlite3_file *pSubOpen = pGroup->aReal[iChunk].p;
  if( pSubOpen ){
    pSubOpen->pMethods->xClose(pSubOpen);

    if( pOrigVfs ) 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]));
}

/*
................................................................................
  }

  if( rc==SQLITE_OK ){
    /* assign pointers to extra space allocated */
    memset(pGroup, 0, sz);
    pMultiplexOpen->pGroup = pGroup;
    pGroup->bEnabled = -1;

    pGroup->szChunk = SQLITE_MULTIPLEX_CHUNK_SIZE;

    if( zName ){
      char *p = (char *)&pGroup[1];
      if( flags & SQLITE_OPEN_URI ){
        const char *zChunkSize;
        zChunkSize = sqlite3_uri_parameter(zName, "chunksize");
................................................................................
          if( n>0 ){
            pGroup->szChunk = (n+0xffff)&~0xffff;
          }else{
            /* A zero or negative chunksize disabled the multiplexor */
            pGroup->bEnabled = 0;
          }
        }

      }
      pGroup->zName = p;
      memcpy(pGroup->zName, zName, nName+1);
      pGroup->nName = nName;










    }
    pGroup->flags = flags;
    rc = multiplexSubFilename(pGroup, 1);
    if( rc==SQLITE_OK ){
      pSubOpen = multiplexSubOpen(pGroup, 0, &rc, pOutFlags);

    }
    if( pSubOpen ){
      int exists, rc2, rc3;
      sqlite3_int64 sz;

      rc2 = pSubOpen->pMethods->xFileSize(pSubOpen, &sz);
      if( rc2==SQLITE_OK && zName ){




















        /* 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.
        */
        rc3 = pOrigVfs->xAccess(pOrigVfs, pGroup->aReal[1].z,
            SQLITE_ACCESS_EXISTS, &exists);

        if( rc3==SQLITE_OK && exists && sz==(sz&0xffff0000) && sz>0
            && sz!=pGroup->szChunk ){
          pGroup->szChunk = sz;
        }else if( rc3==SQLITE_OK && !exists && sz>pGroup->szChunk ){
          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;
................................................................................
** 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
){

  sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
  return pOrigVfs->xDelete(pOrigVfs, zName, syncDir);
























}

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);
................................................................................
  sqlite3_int64 iOfst
){
  multiplexConn *p = (multiplexConn*)pConn;
  multiplexGroup *pGroup = p->pGroup;
  int rc = SQLITE_OK;
  multiplexEnter();
  if( !pGroup->bEnabled ){
    sqlite3_file *pSubOpen = multiplexSubOpen(pGroup, 0, &rc, NULL);
    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 = multiplexSubOpen(pGroup, i, &rc, NULL);
      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;
................................................................................
  sqlite3_int64 iOfst
){
  multiplexConn *p = (multiplexConn*)pConn;
  multiplexGroup *pGroup = p->pGroup;
  int rc = SQLITE_OK;
  multiplexEnter();
  if( !pGroup->bEnabled ){
    sqlite3_file *pSubOpen = multiplexSubOpen(pGroup, 0, &rc, NULL);
    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);
      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);
................................................................................
*/
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(pGroup, 0, &rc, NULL);
    if( pSubOpen==0 ){
      rc = SQLITE_IOERR_TRUNCATE;
    }else{
      rc = pSubOpen->pMethods->xTruncate(pSubOpen, size);
    }
  }else if( (pGroup->flags & SQLITE_OPEN_MAIN_DB)==0 ){
    int rc2;
    int i;

    sqlite3_file *pSubOpen;
    sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
    /* delete the chunks above the truncate limit */
    for(i=(int)(size / pGroup->szChunk)+1; i<pGroup->nReal; i++){

      multiplexSubClose(pGroup, i, pOrigVfs);




    }



    pSubOpen = multiplexSubOpen(pGroup, (int)(size/pGroup->szChunk), &rc2,0);
    if( pSubOpen ){
      rc2 = pSubOpen->pMethods->xTruncate(pSubOpen, size % pGroup->szChunk);
      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 multiplexFileSize(sqlite3_file *pConn, sqlite3_int64 *pSize){
  multiplexConn *p = (multiplexConn*)pConn;
  multiplexGroup *pGroup = p->pGroup;
  int rc = SQLITE_OK;
  int i;
  multiplexEnter();
  if( !pGroup->bEnabled ){
    sqlite3_file *pSubOpen = multiplexSubOpen(pGroup, 0, &rc, NULL);
    if( pSubOpen==0 ){
      rc = SQLITE_IOERR_FSTAT;
    }else{
      rc = pSubOpen->pMethods->xFileSize(pSubOpen, pSize);
    }
  }else{
    sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;
    *pSize = 0;
    for(i=0; rc==SQLITE_OK; i++){
      sqlite3_file *pSubOpen = 0;
      int exists = 0;
      rc = multiplexSubFilename(pGroup, i);
      if( rc!=SQLITE_OK ) break;
      if( pGroup->nReal>i && pGroup->aReal[i].p!=0 ){
        exists = 1;
      }else if( (pGroup->flags & SQLITE_OPEN_DELETEONCLOSE)==0 ){
        const char *zReal = pGroup->aReal[i].z;
        rc = pOrigVfs->xAccess(pOrigVfs, zReal, SQLITE_ACCESS_EXISTS, &exists);
      }
      if( exists==0 ){
        /* stop at first "gap" or IO error. */

        break;
      }
      if( rc==SQLITE_OK ){
        pSubOpen = multiplexSubOpen(pGroup, i, &rc, NULL);
      }
      assert( pSubOpen || rc!=SQLITE_OK );
      if( rc==SQLITE_OK ){
        sqlite3_int64 sz = 0;
        rc = pSubOpen->pMethods->xFileSize(pSubOpen, &sz);
        if( rc==SQLITE_OK && sz>pGroup->szChunk ){
          rc = SQLITE_IOERR_FSTAT;
        }
        *pSize += sz;
      }
    }
  }
  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->pGroup, 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->pGroup, 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->pGroup, 0, &rc, NULL);
  if( pSubOpen ){
    return pSubOpen->pMethods->xCheckReservedLock(pSubOpen, pResOut);
  }
  return SQLITE_IOERR_CHECKRESERVEDLOCK;
}

/* Pass xFileControl requests through to the original VFS unchanged,
................................................................................
      break;
    case SQLITE_FCNTL_SIZE_HINT:
    case SQLITE_FCNTL_CHUNK_SIZE:
      /* no-op these */
      rc = SQLITE_OK;
      break;
    default:
      pSubOpen = multiplexSubOpen(pGroup, 0, &rc, NULL);
      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;
................................................................................
}

/* 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);
  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);
  if( pSubOpen ){
    return pSubOpen->pMethods->xDeviceCharacteristics(pSubOpen);
  }
  return 0;
}

/* Pass xShmMap requests through to the original VFS unchanged.
................................................................................
  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);
  if( pSubOpen ){
    return pSubOpen->pMethods->xShmMap(pSubOpen, iRegion, szRegion, bExtend,pp);
  }
  return SQLITE_IOERR;
}

/* Pass xShmLock requests through to the original VFS unchanged.
................................................................................
  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);
  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);
  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);
  if( pSubOpen ){
    return pSubOpen->pMethods->xShmUnmap(pSubOpen, deleteFlag);
  }
  return SQLITE_OK;
}

/************************** Public Interfaces *****************************/

    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 */
  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
................................................................................
*/
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+4)
** bytes in size, where nBase is the length of zBase, not including the
** nul-terminator.
*/
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 */
){
  memcpy(zOut, zBase, nBase+1);
  if( iChunk!=0 && iChunk!=SQLITE_MULTIPLEX_JOURNAL_8_3_OFFSET ){
    int n = nBase;
#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;
    }
#endif
    sqlite3_snprintf(4,&zOut[n],"%03d",iChunk);
  }
}

/* Compute the filename for the iChunk-th chunk
*/
static int multiplexSubFilename(multiplexGroup *pGroup, int iChunk){
  if( iChunk>=pGroup->nReal ){
    struct multiplexReal *p;
    p = sqlite3_realloc(pGroup->aReal, (iChunk+1)*sizeof(*p));
................................................................................
  if( pGroup->zName && pGroup->aReal[iChunk].z==0 ){
    char *z;
    int n = pGroup->nName;
    pGroup->aReal[iChunk].z = z = sqlite3_malloc( n+4 );
    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 
................................................................................
    *rc = SQLITE_FULL;
    return 0;
  }
#endif

  *rc = multiplexSubFilename(pGroup, iChunk);
  if( (*rc)==SQLITE_OK && (pSubOpen = pGroup->aReal[iChunk].p)==0 ){
    int flags, bExists;
    createFlag = (pGroup->flags & SQLITE_OPEN_CREATE)!=0;
    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 ) return 0;
      flags &= ~SQLITE_OPEN_CREATE;
    }
    pSubOpen = sqlite3_malloc( 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_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;

  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
................................................................................
  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]));
}

/*
................................................................................
  }

  if( rc==SQLITE_OK ){
    /* assign pointers to extra space allocated */
    memset(pGroup, 0, sz);
    pMultiplexOpen->pGroup = pGroup;
    pGroup->bEnabled = -1;
    pGroup->bTruncate = (flags & SQLITE_OPEN_MAIN_DB)==0;
    pGroup->szChunk = SQLITE_MULTIPLEX_CHUNK_SIZE;

    if( zName ){
      char *p = (char *)&pGroup[1];
      if( flags & SQLITE_OPEN_URI ){
        const char *zChunkSize;
        zChunkSize = sqlite3_uri_parameter(zName, "chunksize");
................................................................................
          if( n>0 ){
            pGroup->szChunk = (n+0xffff)&~0xffff;
          }else{
            /* A zero or negative chunksize disabled the multiplexor */
            pGroup->bEnabled = 0;
          }
        }
        if( sqlite3_uri_parameter(zName, "truncate") ) pGroup->bTruncate = 1;
      }
      pGroup->zName = p;
      memcpy(pGroup->zName, zName, nName+1);
      pGroup->nName = nName;
    }
    if( pGroup->bEnabled ){
      /* Make sure that the chunksize is not such that the pending byte
      ** 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. */
      extern int sqlite3PendingByte;
      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 sz;

      rc = pSubOpen->pMethods->xFileSize(pSubOpen, &sz);
      if( rc==SQLITE_OK && zName ){
        int bExists;
        if( sz==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  && sz==(sz&0xffff0000) && sz>0
              && sz!=pGroup->szChunk ){
            pGroup->szChunk = sz;
          }else if( rc==SQLITE_OK && !bExists && sz>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;
      }
      /* place this group at the head of our list */
      pGroup->pNext = gMultiplex.pGroups;
................................................................................
** 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 = strlen(zName);
    char *z;
    z = sqlite3_malloc(nName + 4);
    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);
      }
    }
    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);
................................................................................
  sqlite3_int64 iOfst
){
  multiplexConn *p = (multiplexConn*)pConn;
  multiplexGroup *pGroup = p->pGroup;
  int rc = SQLITE_OK;
  multiplexEnter();
  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 = 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;
................................................................................
  sqlite3_int64 iOfst
){
  multiplexConn *p = (multiplexConn*)pConn;
  multiplexGroup *pGroup = p->pGroup;
  int rc = SQLITE_OK;
  multiplexEnter();
  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);
................................................................................
*/
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(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;
  }
  multiplexLeave();
  return rc;
}

/* Pass xSync requests through to the original VFS without change
*/
................................................................................
static int multiplexFileSize(sqlite3_file *pConn, sqlite3_int64 *pSize){
  multiplexConn *p = (multiplexConn*)pConn;
  multiplexGroup *pGroup = p->pGroup;
  int rc = SQLITE_OK;
  int i;
  multiplexEnter();
  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;






    }
  }
  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->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,
................................................................................
      break;
    case SQLITE_FCNTL_SIZE_HINT:
    case SQLITE_FCNTL_CHUNK_SIZE:
      /* no-op these */
      rc = SQLITE_OK;
      break;
    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;
................................................................................
}

/* 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.
................................................................................
  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.
................................................................................
  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 *****************************/

** do the suffix shortening regardless of URI parameter.
**
** Examples:
**
**     test.db-journal    =>   test.nal
**     test.db-wal        =>   test.wal
**     test.db-shm        =>   test.shm

*/
void sqlite3FileSuffix3(const char *zBaseFilename, char *z){
#if SQLITE_ENABLE_8_3_NAMES<2
  const char *zOk;
  zOk = sqlite3_uri_parameter(zBaseFilename, "8_3_names");
  if( zOk && sqlite3GetBoolean(zOk) )
#endif

** do the suffix shortening regardless of URI parameter.
**
** Examples:
**
**     test.db-journal    =>   test.nal
**     test.db-wal        =>   test.wal
**     test.db-shm        =>   test.shm
**     test.db-mj7f3319fa =>   test.9fa
*/
void sqlite3FileSuffix3(const char *zBaseFilename, char *z){
#if SQLITE_ENABLE_8_3_NAMES<2
  const char *zOk;
  zOk = sqlite3_uri_parameter(zBaseFilename, "8_3_names");
  if( zOk && sqlite3GetBoolean(zOk) )
#endif

    sqlite3_vfs *pVfs = db->pVfs;
    int needSync = 0;
    char *zMaster = 0;   /* File-name for the master journal */
    char const *zMainFile = sqlite3BtreeGetFilename(db->aDb[0].pBt);
    sqlite3_file *pMaster = 0;
    i64 offset = 0;
    int res;



    /* Select a master journal file name */



    do {
      u32 iRandom;
      sqlite3DbFree(db, zMaster);
      sqlite3_randomness(sizeof(iRandom), &iRandom);
      zMaster = sqlite3MPrintf(db, "%s-mj%08X", zMainFile, iRandom&0x7fffffff);
      if( !zMaster ){
        return SQLITE_NOMEM;




      }






      sqlite3FileSuffix3(zMainFile, zMaster);
      rc = sqlite3OsAccess(pVfs, zMaster, SQLITE_ACCESS_EXISTS, &res);
    }while( rc==SQLITE_OK && res );
    if( rc==SQLITE_OK ){
      /* Open the master journal. */
      rc = sqlite3OsOpenMalloc(pVfs, zMaster, &pMaster, 
          SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|

    sqlite3_vfs *pVfs = db->pVfs;
    int needSync = 0;
    char *zMaster = 0;   /* File-name for the master journal */
    char const *zMainFile = sqlite3BtreeGetFilename(db->aDb[0].pBt);
    sqlite3_file *pMaster = 0;
    i64 offset = 0;
    int res;
    int retryCount = 0;
    int nMainFile;

    /* Select a master journal file name */
    nMainFile = sqlite3Strlen30(zMainFile);
    zMaster = sqlite3MPrintf(db, "%s-mjXXXXXX9XX", zMainFile);
    if( zMaster==0 ) return SQLITE_NOMEM;
    do {
      u32 iRandom;





      if( retryCount++>100 ){
        sqlite3_log(SQLITE_FULL, "cannot find unique master-journal");
        sqlite3OsDelete(pVfs, zMaster, 0);
        break;
      }
      sqlite3_randomness(sizeof(iRandom), &iRandom);
      sqlite3_snprintf(13, &zMaster[nMainFile], "-mj%06X9%02X",
                               (iRandom>>8)&0xffffff, iRandom&0xff);
      /* The antipenultimate character of the master journal name must
      ** be "9" to avoid name collisions when using 8+3 filenames. */
      assert( zMaster[sqlite3Strlen30(zMaster)-3]=='9' );
      sqlite3FileSuffix3(zMainFile, zMaster);
      rc = sqlite3OsAccess(pVfs, zMaster, SQLITE_ACCESS_EXISTS, &res);
    }while( rc==SQLITE_OK && res );
    if( rc==SQLITE_OK ){
      /* Open the master journal. */
      rc = sqlite3OsOpenMalloc(pVfs, zMaster, &pMaster, 
          SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|