#define LSM_DFLT_USE_LOG            1

/* Initial values for log file checksums. These are only used if the 
** database file does not contain a valid checkpoint.  */
#define LSM_CKSUM0_INIT 42
#define LSM_CKSUM1_INIT 42



/* "mmap" mode is currently only used in environments with 64-bit address 
** spaces. The following macro is used to test for this.  */
#define LSM_IS_64_BIT (sizeof(void*)==8)

#define LSM_AUTOWORK_QUANT 32

typedef struct Database Database;

#define LSM_LOCK_WRITER       4
#define LSM_LOCK_WORKER       5
#define LSM_LOCK_CHECKPOINTER 6
#define LSM_LOCK_ROTRANS      7
#define LSM_LOCK_READER(i)    ((i) + LSM_LOCK_ROTRANS + 1)
#define LSM_LOCK_RWCLIENT(i)  ((i) + LSM_LOCK_READER(LSM_LOCK_NREADER))

#define LSM_N_LOCK LSM_LOCK_RWCLIENT(LSM_LOCK_NRWCLIENT)

/*
** Meta-page size and usable size.
*/
#define LSM_META_PAGE_SIZE 4096

#define LSM_META_RW_PAGE_SIZE (LSM_META_PAGE_SIZE - LSM_N_LOCK)

/*
** Hard limit on the number of free-list entries that may be stored in 
** a checkpoint (the remainder are stored as a system record in the LSM).
** See also LSM_CONFIG_MAX_FREELIST.
*/
#define LSM_MAX_FREELIST_ENTRIES 24

** checkpoint.
*/
static int ckptChecksumOk(u32 *aCkpt){
  u32 nCkpt = aCkpt[CKPT_HDR_NCKPT];
  u32 cksum1;
  u32 cksum2;

  if( nCkpt<CKPT_HDR_NCKPT || nCkpt>(LSM_META_RW_PAGE_SIZE)/sizeof(u32) ){
    return 0;
  }
  ckptChecksum(aCkpt, nCkpt, &cksum1, &cksum2);
  return (cksum1==aCkpt[nCkpt-2] && cksum2==aCkpt[nCkpt-1]);
}

/*
** Attempt to load a checkpoint from meta page iMeta.
**

int lsmCheckpointLoad(lsm_db *pDb, int *piRead){
  int nRem = LSM_ATTEMPTS_BEFORE_PROTOCOL;
  ShmHeader *pShm = pDb->pShmhdr;
  while( (nRem--)>0 ){
    int nInt;

    nInt = pShm->aSnap1[CKPT_HDR_NCKPT];
    if( nInt<=(LSM_META_RW_PAGE_SIZE / sizeof(u32)) ){
      memcpy(pDb->aSnapshot, pShm->aSnap1, nInt*sizeof(u32));
      if( ckptChecksumOk(pDb->aSnapshot) ){
        if( piRead ) *piRead = 1;
        return LSM_OK;
      }
    }

    nInt = pShm->aSnap2[CKPT_HDR_NCKPT];
    if( nInt<=(LSM_META_RW_PAGE_SIZE / sizeof(u32)) ){
      memcpy(pDb->aSnapshot, pShm->aSnap2, nInt*sizeof(u32));
      if( ckptChecksumOk(pDb->aSnapshot) ){
        if( piRead ) *piRead = 2;
        return LSM_OK;
      }
    }

  int rc;

  pSnap->iId++;
  rc = ckptExportSnapshot(pDb, bFlush, pSnap->iId, 1, &p, &n);
  if( rc!=LSM_OK ) return rc;
  assert( ckptChecksumOk((u32 *)p) );

  assert( n<=LSM_META_RW_PAGE_SIZE );
  memcpy(pShm->aSnap2, p, n);
  lsmShmBarrier(pDb);
  memcpy(pShm->aSnap1, p, n);
  lsmFree(pDb->pEnv, p);

  assert( lsmFsIntegrityCheck(pDb) );
  return LSM_OK;

    rc = lsmFsMetaPageGet(pDb->pFS, 0, iMeta, &pPg);
    if( rc==LSM_OK ){
      int nCkpt;
      int nData;
      u8 *aData; 

      aData = lsmFsMetaPageData(pPg, &nData);
      assert( nData==LSM_META_RW_PAGE_SIZE );
      nCkpt = lsmGetU32(&aData[CKPT_HDR_NCKPT*sizeof(u32)]);
      if( nCkpt<(LSM_META_RW_PAGE_SIZE/sizeof(u32)) ){
        u32 *aCopy = lsmMallocRc(pDb->pEnv, sizeof(u32) * nCkpt, &rc);
        if( aCopy ){
          memcpy(aCopy, aData, nCkpt*sizeof(u32));
          ckptChangeEndianness(aCopy, nCkpt);
          if( ckptChecksumOk(aCopy) ){
            if( piId ) *piId = lsmCheckpointId(aCopy, 0);
            if( piLog ) *piLog = (lsmCheckpointLogOffset(aCopy) >> 1);

*/
struct FileSystem {
  lsm_db *pDb;                    /* Database handle that owns this object */
  lsm_env *pEnv;                  /* Environment pointer */
  char *zDb;                      /* Database file name */
  char *zLog;                     /* Database file name */
  int nMetasize;                  /* Size of meta pages in bytes */
  int nMetaRwSize;                /* Read/written size of meta pages in bytes */
  int nPagesize;                  /* Database page-size in bytes */
  int nBlocksize;                 /* Database block-size in bytes */

  /* r/w file descriptors for both files. */
  LsmFile *pLsmFile;              /* Used after lsm_close() to link into list */
  lsm_file *fdDb;                 /* Database file */
  lsm_file *fdLog;                /* Log file */

  pFS = (FileSystem *)lsmMallocZeroRc(pDb->pEnv, nByte, &rc);
  if( pFS ){
    LsmFile *pLsmFile;
    pFS->zDb = (char *)&pFS[1];
    pFS->zLog = &pFS->zDb[nDb+1];
    pFS->nPagesize = LSM_DFLT_PAGE_SIZE;
    pFS->nBlocksize = LSM_DFLT_BLOCK_SIZE;
    pFS->nMetasize = LSM_META_PAGE_SIZE;
    pFS->nMetaRwSize = LSM_META_RW_PAGE_SIZE;
    pFS->pDb = pDb;
    pFS->pEnv = pDb->pEnv;

    /* Make a copy of the database and log file names. */
    memcpy(pFS->zDb, zDb, nDb+1);
    memcpy(pFS->zLog, zDb, nDb);
    memcpy(&pFS->zLog[nDb], "-log", 5);

    i64 iOff = (iPg-1) * pFS->nMetasize;
    if( pFS->nMapLimit>0 ){
      fsGrowMapping(pFS, 2*pFS->nMetasize, &rc);
      pPg->aData = (u8 *)(pFS->pMap) + iOff;
    }else{
      pPg->aData = lsmMallocRc(pFS->pEnv, pFS->nMetasize, &rc);
      if( rc==LSM_OK && bWrite==0 ){
        rc = lsmEnvRead(
            pFS->pEnv, pFS->fdDb, iOff, pPg->aData, pFS->nMetaRwSize
        );
      }
#ifndef NDEBUG
      /* pPg->aData causes an uninitialized access via a downstreadm write().
         After discussion on this list, this memory should not, for performance
         reasons, be memset. However, tracking down "real" misuse is more
         difficult with this "false" positive, so it is set when NDEBUG.
      */

  int rc = LSM_OK;
  if( pPg ){
    FileSystem *pFS = pPg->pFS;

    if( pFS->nMapLimit==0 ){
      if( pPg->bWrite ){
        i64 iOff = (pPg->iPg==2 ? pFS->nMetasize : 0);
        int nWrite = pFS->nMetaRwSize;
        rc = lsmEnvWrite(pFS->pEnv, pFS->fdDb, iOff, pPg->aData, nWrite);
      }
      lsmFree(pFS->pEnv, pPg->aData);
    }

    lsmFree(pFS->pEnv, pPg);
  }
  return rc;
}

/*
** Return a pointer to a buffer containing the data associated with the
** meta-page passed as the first argument. If parameter pnData is not NULL,
** set *pnData to the size of the meta-page in bytes before returning.
*/
u8 *lsmFsMetaPageData(MetaPage *pPg, int *pnData){
  if( pnData ) *pnData = pPg->pFS->nMetaRwSize;
  return pPg->aData;
}

/*
** Return true if page is currently writable. This is used in assert() 
** statements only.
*/