lsm_file *fdDb;                 /* Database file */
  lsm_file *fdLog;                /* Log file */
  int szSector;                   /* Database file sector size */

  /* If this is a compressed database, a pointer to the compression methods.
  ** For an uncompressed database, a NULL pointer.  */
  lsm_compress *pCompress;
  u8 *aBuffer;                    /* Buffer to compress into */

  int nBuffer;                    /* Allocated size of aBuffer[] in bytes */

  /* mmap() mode things */
  int bUseMmap;                   /* True to use mmap() to access db file */
  void *pMap;                     /* Current mapping of database file */
  i64 nMap;                       /* Bytes mapped at pMap */
  Page *pFree;
................................................................................
      pPg = pNext;
    }

    if( pFS->fdDb ) lsmEnvClose(pFS->pEnv, pFS->fdDb );
    if( pFS->fdLog ) lsmEnvClose(pFS->pEnv, pFS->fdLog );
    lsmFree(pEnv, pFS->pLsmFile);
    lsmFree(pEnv, pFS->apHash);
    lsmFree(pEnv, pFS->aBuffer);

    lsmFree(pEnv, pFS);
  }
}

void lsmFsDeferClose(FileSystem *pFS, LsmFile **pp){
  LsmFile *p = pFS->pLsmFile;
  assert( p->pNext==0 );
................................................................................
  }

  rc = fsBlockNext(pFS, fsPageToBlock(pFS, iOff), &iBlk);
  *piRes = fsFirstPageOnBlock(pFS, iBlk) + iAdd - (iEob - iOff + 1);
  return rc;
}

static int fsAllocateBuffer(FileSystem *pFS){


  assert( pFS->pCompress );



  if( pFS->aBuffer==0 ){

    pFS->nBuffer = pFS->pCompress->xBound(pFS->pCompress->pCtx, pFS->nPagesize);
    if( pFS->nBuffer<(pFS->szSector+6) ){
      pFS->nBuffer = pFS->szSector+6;
    }




    pFS->aBuffer = lsmMalloc(pFS->pEnv, LSM_MAX(pFS->nBuffer, pFS->nPagesize));
    if( pFS->aBuffer==0 ) return LSM_NOMEM_BKPT;
  }

  return LSM_OK;
}

/*
** This function is only called in compressed database mode. It reads and
** uncompresses the compressed data for page pPg from the database and
** populates the pPg->aData[] buffer and pPg->nCompress field.
................................................................................
  lsm_compress *p = pFS->pCompress;
  i64 iOff = pPg->iPg;
  u8 aSz[3];
  int rc;

  assert( p && pPg->nCompress==0 );

  if( fsAllocateBuffer(pFS) ) return LSM_NOMEM;

  rc = fsReadData(pFS, iOff, aSz, sizeof(aSz));

  if( rc==LSM_OK ){
    int bFree;
    if( aSz[0] & 0x80 ){
      pPg->nCompress = (int)getRecordSize(aSz, &bFree);
................................................................................
      }
    }else{
      rc = fsAddOffset(pFS, iOff, 3, &iOff);
      if( rc==LSM_OK ){
        if( pPg->nCompress>pFS->nBuffer ){
          rc = LSM_CORRUPT_BKPT;
        }else{
          rc = fsReadData(pFS, iOff, pFS->aBuffer, pPg->nCompress);
        }
        if( rc==LSM_OK ){
          int n = pFS->nPagesize;
          rc = p->xUncompress(p->pCtx, 
              (char *)pPg->aData, &n, 
              (const char *)pFS->aBuffer, pPg->nCompress
              );
          if( rc==LSM_OK && n!=pPg->nData ){
            rc = LSM_CORRUPT_BKPT;
          }
        }
      }
    }
  }
................................................................................
**
** If buffer pFS->aBuffer[] has not been allocated then this function
** allocates it. If this fails, LSM_NOMEM is returned. Otherwise, LSM_OK.
*/
static int fsCompressIntoBuffer(FileSystem *pFS, Page *pPg){
  lsm_compress *p = pFS->pCompress;

  if( fsAllocateBuffer(pFS) ) return LSM_NOMEM;
  assert( pPg->nData==pFS->nPagesize );

  pPg->nCompress = pFS->nBuffer;
  return p->xCompress(p->pCtx, 
      (char *)pFS->aBuffer, &pPg->nCompress, 
      (const char *)pPg->aData, pPg->nData
  );
}

/*
** If the page passed as an argument is dirty, update the database file
** (or mapping of the database file) with its current contents and mark
................................................................................
      rc = fsCompressIntoBuffer(pFS, pPg);

      /* Serialize the compressed size into buffer aSz[] */
      putRecordSize(aSz, pPg->nCompress, 0);

      /* Write the serialized page record into the database file. */
      pPg->iPg = fsAppendData(pFS, pPg->pSeg, aSz, sizeof(aSz), &rc);
      fsAppendData(pFS, pPg->pSeg, pFS->aBuffer, pPg->nCompress, &rc);
      fsAppendData(pFS, pPg->pSeg, aSz, sizeof(aSz), &rc);

      /* Now that it has a page number, insert the page into the hash table */
      iHash = fsHashKey(pFS->nHash, pPg->iPg);
      pPg->pHashNext = pFS->apHash[iHash];
      pFS->apHash[iHash] = pPg;

................................................................................
    assert( nPad>=0 );

    if( nPad>=6 ){
      pSeg->nSize += nPad;
      nPad -= 6;
      putRecordSize(aSz, nPad, 1);
      fsAppendData(pFS, pSeg, aSz, sizeof(aSz), &rc);
      memset(pFS->aBuffer, 0, nPad);
      fsAppendData(pFS, pSeg, pFS->aBuffer, nPad, &rc);
      fsAppendData(pFS, pSeg, aSz, sizeof(aSz), &rc);
    }else if( nPad>0 ){
      u8 aBuf[5] = {0,0,0,0,0};
      aBuf[0] = (u8)nPad;
      aBuf[nPad-1] = (u8)nPad;
      fsAppendData(pFS, pSeg, aBuf, nPad, &rc);
    }

  lsm_file *fdDb;                 /* Database file */
  lsm_file *fdLog;                /* Log file */
  int szSector;                   /* Database file sector size */

  /* If this is a compressed database, a pointer to the compression methods.
  ** For an uncompressed database, a NULL pointer.  */
  lsm_compress *pCompress;
  u8 *aIBuffer;                   /* Buffer to compress to */
  u8 *aOBuffer;                   /* Buffer to uncompress from */
  int nBuffer;                    /* Allocated size of aBuffer[] in bytes */

  /* mmap() mode things */
  int bUseMmap;                   /* True to use mmap() to access db file */
  void *pMap;                     /* Current mapping of database file */
  i64 nMap;                       /* Bytes mapped at pMap */
  Page *pFree;
................................................................................
      pPg = pNext;
    }

    if( pFS->fdDb ) lsmEnvClose(pFS->pEnv, pFS->fdDb );
    if( pFS->fdLog ) lsmEnvClose(pFS->pEnv, pFS->fdLog );
    lsmFree(pEnv, pFS->pLsmFile);
    lsmFree(pEnv, pFS->apHash);
    lsmFree(pEnv, pFS->aIBuffer);
    lsmFree(pEnv, pFS->aOBuffer);
    lsmFree(pEnv, pFS);
  }
}

void lsmFsDeferClose(FileSystem *pFS, LsmFile **pp){
  LsmFile *p = pFS->pLsmFile;
  assert( p->pNext==0 );
................................................................................
  }

  rc = fsBlockNext(pFS, fsPageToBlock(pFS, iOff), &iBlk);
  *piRes = fsFirstPageOnBlock(pFS, iBlk) + iAdd - (iEob - iOff + 1);
  return rc;
}

static int fsAllocateBuffer(FileSystem *pFS, int bWrite){
  u8 **pp;                        /* Pointer to either aIBuffer or aOBuffer */

  assert( pFS->pCompress );

  /* If neither buffer has been allocated, figure out how large they
  ** should be. Store this value in FileSystem.nBuffer.  */
  if( pFS->nBuffer==0 ){
    assert( pFS->aIBuffer==0 && pFS->aOBuffer==0 );
    pFS->nBuffer = pFS->pCompress->xBound(pFS->pCompress->pCtx, pFS->nPagesize);
    if( pFS->nBuffer<(pFS->szSector+6) ){
      pFS->nBuffer = pFS->szSector+6;
    }
  }

  pp = (bWrite ? &pFS->aOBuffer : &pFS->aIBuffer);
  if( *pp==0 ){
    *pp = lsmMalloc(pFS->pEnv, LSM_MAX(pFS->nBuffer, pFS->nPagesize));
    if( *pp==0 ) return LSM_NOMEM_BKPT;
  }

  return LSM_OK;
}

/*
** This function is only called in compressed database mode. It reads and
** uncompresses the compressed data for page pPg from the database and
** populates the pPg->aData[] buffer and pPg->nCompress field.
................................................................................
  lsm_compress *p = pFS->pCompress;
  i64 iOff = pPg->iPg;
  u8 aSz[3];
  int rc;

  assert( p && pPg->nCompress==0 );

  if( fsAllocateBuffer(pFS, 0) ) return LSM_NOMEM;

  rc = fsReadData(pFS, iOff, aSz, sizeof(aSz));

  if( rc==LSM_OK ){
    int bFree;
    if( aSz[0] & 0x80 ){
      pPg->nCompress = (int)getRecordSize(aSz, &bFree);
................................................................................
      }
    }else{
      rc = fsAddOffset(pFS, iOff, 3, &iOff);
      if( rc==LSM_OK ){
        if( pPg->nCompress>pFS->nBuffer ){
          rc = LSM_CORRUPT_BKPT;
        }else{
          rc = fsReadData(pFS, iOff, pFS->aIBuffer, pPg->nCompress);
        }
        if( rc==LSM_OK ){
          int n = pFS->nPagesize;
          rc = p->xUncompress(p->pCtx, 
              (char *)pPg->aData, &n, 
              (const char *)pFS->aIBuffer, pPg->nCompress
          );
          if( rc==LSM_OK && n!=pPg->nData ){
            rc = LSM_CORRUPT_BKPT;
          }
        }
      }
    }
  }
................................................................................
**
** If buffer pFS->aBuffer[] has not been allocated then this function
** allocates it. If this fails, LSM_NOMEM is returned. Otherwise, LSM_OK.
*/
static int fsCompressIntoBuffer(FileSystem *pFS, Page *pPg){
  lsm_compress *p = pFS->pCompress;

  if( fsAllocateBuffer(pFS, 1) ) return LSM_NOMEM;
  assert( pPg->nData==pFS->nPagesize );

  pPg->nCompress = pFS->nBuffer;
  return p->xCompress(p->pCtx, 
      (char *)pFS->aOBuffer, &pPg->nCompress, 
      (const char *)pPg->aData, pPg->nData
  );
}

/*
** If the page passed as an argument is dirty, update the database file
** (or mapping of the database file) with its current contents and mark
................................................................................
      rc = fsCompressIntoBuffer(pFS, pPg);

      /* Serialize the compressed size into buffer aSz[] */
      putRecordSize(aSz, pPg->nCompress, 0);

      /* Write the serialized page record into the database file. */
      pPg->iPg = fsAppendData(pFS, pPg->pSeg, aSz, sizeof(aSz), &rc);
      fsAppendData(pFS, pPg->pSeg, pFS->aOBuffer, pPg->nCompress, &rc);
      fsAppendData(pFS, pPg->pSeg, aSz, sizeof(aSz), &rc);

      /* Now that it has a page number, insert the page into the hash table */
      iHash = fsHashKey(pFS->nHash, pPg->iPg);
      pPg->pHashNext = pFS->apHash[iHash];
      pFS->apHash[iHash] = pPg;

................................................................................
    assert( nPad>=0 );

    if( nPad>=6 ){
      pSeg->nSize += nPad;
      nPad -= 6;
      putRecordSize(aSz, nPad, 1);
      fsAppendData(pFS, pSeg, aSz, sizeof(aSz), &rc);
      memset(pFS->aOBuffer, 0, nPad);
      fsAppendData(pFS, pSeg, pFS->aOBuffer, nPad, &rc);
      fsAppendData(pFS, pSeg, aSz, sizeof(aSz), &rc);
    }else if( nPad>0 ){
      u8 aBuf[5] = {0,0,0,0,0};
      aBuf[0] = (u8)nPad;
      aBuf[nPad-1] = (u8)nPad;
      fsAppendData(pFS, pSeg, aBuf, nPad, &rc);
    }