SQLite

#define MX_CELL(pBt) ((pBt->pageSize-8)/6)

/* Forward declarations */
typedef struct MemPage MemPage;
typedef struct BtLock BtLock;
typedef struct CellInfo CellInfo;

















/*
** Page type flags.  An ORed combination of these flags appear as the
** first byte of on-disk image of every BTree page.
*/
#define PTF_INTKEY    0x01
#define PTF_ZERODATA  0x02
#define PTF_LEAFDATA  0x04

      
      /* Check to see if the shm file is already opened for this pFile */
      if( j==2 ){
        unixEnterMutex(); /* Because pFile->pInode is shared across threads */
        unixShmNode *pShmNode = pFile->pInode->pShmNode;
        if( pShmNode && !pShmNode->isReadonly ){
          struct stat sStat;
          sqlite3_mutex_enter(pShmNode->pShmMutex);
          
          if( pShmNode->hShm>=0 && !osFstat(pShmNode->hShm, &sStat) ){
            unsigned long size = (sStat.st_size<4) ? sStat.st_size : 4;
            if( size>0 ){
              bzero(pShmNode->apRegion[0], size);
              sqlite3_mutex_leave(pShmNode->pShmMutex);
              unixLeaveMutex();
              continue;
            }
          }
          sqlite3_mutex_leave(pShmNode->pShmMutex);
        }
        unixLeaveMutex();
      }
      jLen = strlcpy(&jPath[zLen], extensions[j], 9);
      if( jLen < 9 ){
        int jflags = (j<2) ? O_TRUNC : O_RDWR;
        int jfd = open(jPath, jflags);

  }
  if( nLock==0 && isWal!=0 ){
    /* lookup the file descriptor for the shared memory file if we have it open
    ** in this process */
    unixEnterMutex(); /* Because pFile->pInode is shared across threads */
    unixShmNode *pShmNode = pFile->pInode->pShmNode;
    if( pShmNode ){
      sqlite3_mutex_enter(pShmNode->pShmMutex);
      
      hShm = pShmNode->hShm;
      if( hShm >= 0){
        if( unixIsLocked(pid, hShm, F_RDLCK, SHM_RECOVER, 1, "WAL-RECOVERY") ||
           unixIsLocked(pid, hShm, F_RDLCK, SHM_WRITE, 1, "WAL-WRITE") ){
          nLock = 1;
        }
      }
      
      sqlite3_mutex_leave(pShmNode->pShmMutex);
    } 
    
    if( hShm<0 ){
      /* the shared memory file isn't open in this process space, open our
      ** own FD */
      char zShm[MAXPATHLEN];
      

#if defined(SQLITE_SYSTEM_MALLOC) \
  + defined(SQLITE_WIN32_MALLOC) \
  + defined(SQLITE_ZERO_MALLOC) \
  + defined(SQLITE_MEMDEBUG)==0
# define SQLITE_SYSTEM_MALLOC 1
#endif

/*
** This is a magic string that appears at the beginning of every
** SQLite database in order to identify the file as a real database.
**
** You can change this value at compile-time by specifying a
** -DSQLITE_FILE_HEADER="..." on the compiler command-line.  The
** header must be exactly 16 bytes including the zero-terminator so
** the string itself should be 15 characters long.  If you change
** the header, then your custom library will not be able to read 
** databases generated by the standard tools and the standard tools
** will not be able to read databases created by your custom library.
*/
#ifndef SQLITE_FILE_HEADER /* 123456789 123456 */
#  define SQLITE_FILE_HEADER "SQLite format 3"
#endif

/*
** If SQLITE_MALLOC_SOFT_LIMIT is not zero, then try to keep the
** sizes of memory allocations below this value where possible.
*/
#if !defined(SQLITE_MALLOC_SOFT_LIMIT)
# define SQLITE_MALLOC_SOFT_LIMIT 1024
#endif