SQLite

  ** occur if a file is updated without also updating the transaction
  ** counter.  This test is made to avoid new problems similar to the
  ** one described by ticket #3584. 
  */
  unsigned char transCntrChng;   /* True if the transaction counter changed */
  unsigned char dbUpdate;        /* True if any part of database file changed */
  unsigned char inNormalWrite;   /* True if in a normal write operation */
  sqlite3_int64 mmapSize;        /* Size of xMremap() */
  void *pMapRegion;              /* Area memory mapped */
#endif
#ifdef SQLITE_TEST
  /* In test mode, increase the size of this structure a bit so that 
  ** it is larger than the struct CrashFile defined in test6.c.
  */
  char aPadding[32];
#endif

  void *pBuf, 
  int amt,
  sqlite3_int64 offset
){
  unixFile *pFile = (unixFile *)id;
  int got;
  assert( id );
  assert( offset>=pFile->mmapSize );  /* Never read from the mmapped region */

  /* If this is a database file (not a journal, master-journal or temp
  ** file), the bytes in the locking range should never be read or written. */
#if 0
  assert( pFile->pUnused==0
       || offset>=PENDING_BYTE+512
       || offset+amt<=PENDING_BYTE 

  int amt,
  sqlite3_int64 offset 
){
  unixFile *pFile = (unixFile*)id;
  int wrote = 0;
  assert( id );
  assert( amt>0 );
  assert( offset>=pFile->mmapSize );   /* Never write into the mmapped region */

  /* If this is a database file (not a journal, master-journal or temp
  ** file), the bytes in the locking range should never be read or written. */
#if 0
  assert( pFile->pUnused==0
       || offset>=PENDING_BYTE+512
       || offset+amt<=PENDING_BYTE 

  unixFile *p = (unixFile *)fd;   /* The underlying database file */
  int rc = SQLITE_OK;             /* Return code */
  void *pNew = 0;                 /* New mapping */
  i64 nNewRnd;                    /* nNew rounded up */
  i64 nOldRnd;                    /* nOld rounded up */

  assert( iOff==0 );
  assert( p->mmapSize==nOld );
  assert( p->pMapRegion==0 || p->pMapRegion==(*ppMap) );

  /* If the SQLITE_MREMAP_EXTEND flag is set, then the size of the requested 
  ** mapping (nNew bytes) may be greater than the size of the database file.
  ** If this is the case, extend the file on disk using ftruncate().  */
  assert( nNew>0 || (flags & SQLITE_MREMAP_EXTEND)==0 );
  if( flags & SQLITE_MREMAP_EXTEND ){
    struct stat statbuf;          /* Low-level file information */

  nNewRnd = ROUNDUP(nNew, 4096*1);
  nOldRnd = ROUNDUP(nOld, 4096*1);
#endif

  /* On OSX or Linux, reuse the old mapping if it is the right size. */
#if defined(__APPLE__) || defined(__linux__)
  if( nNewRnd==nOldRnd ){
    VVA_ONLY( p->mmapSize = nNew; )
    return SQLITE_OK;
  }
#endif

  /* If we get this far, unmap any old mapping. */
  if( nOldRnd!=0 ){
    void *pOld = *ppMap;
    munmap(pOld, nOldRnd);
    VVA_ONLY( p->mmapSize = 0; p->pMapRegion = 0; );
  }

  /* And, if required, use mmap() to create a new mapping. */
  if( nNewRnd>0 ){
    int flags = PROT_READ;
    if( (p->ctrlFlags & UNIXFILE_RDONLY)==0 ) flags |= PROT_WRITE;
    pNew = mmap(0, nNewRnd, flags, MAP_SHARED, p->h, iOff);
    if( pNew==MAP_FAILED ){
      pNew = 0;
      VVA_ONLY( p->mmapSize = 0; p->pMapRegion = 0; )
      rc = SQLITE_IOERR_MREMAP;
    }else{
      VVA_ONLY( p->mmapSize = nNew; p->pMapRegion = pNew; )
    }
  }

  *ppMap = pNew;
  return rc;
}

  assert( zFilename!=0 || (ctrlFlags & UNIXFILE_NOLOCK)!=0 );

  OSTRACE(("OPEN    %-3d %s\n", h, zFilename));
  pNew->h = h;
  pNew->pVfs = pVfs;
  pNew->zPath = zFilename;
  pNew->ctrlFlags = (u8)ctrlFlags;
  VVA_ONLY( pNew->mmapSize = 0; )
  if( sqlite3_uri_boolean(((ctrlFlags & UNIXFILE_URI) ? zFilename : 0),
                           "psow", SQLITE_POWERSAFE_OVERWRITE) ){
    pNew->ctrlFlags |= UNIXFILE_PSOW;
  }
  if( strcmp(pVfs->zName,"unix-excl")==0 ){
    pNew->ctrlFlags |= UNIXFILE_EXCL;
  }