SQLite

#define SQLITE_LOCKED_SHAREDCACHE      (SQLITE_LOCKED |  (1<<8))
#define SQLITE_BUSY_RECOVERY           (SQLITE_BUSY   |  (1<<8))
#define SQLITE_BUSY_SNAPSHOT           (SQLITE_BUSY   |  (2<<8))
#define SQLITE_CANTOPEN_NOTEMPDIR      (SQLITE_CANTOPEN | (1<<8))
#define SQLITE_CANTOPEN_ISDIR          (SQLITE_CANTOPEN | (2<<8))
#define SQLITE_CANTOPEN_FULLPATH       (SQLITE_CANTOPEN | (3<<8))
#define SQLITE_CANTOPEN_CONVPATH       (SQLITE_CANTOPEN | (4<<8))

#define SQLITE_CORRUPT_VTAB            (SQLITE_CORRUPT | (1<<8))
#define SQLITE_READONLY_RECOVERY       (SQLITE_READONLY | (1<<8))
#define SQLITE_READONLY_CANTLOCK       (SQLITE_READONLY | (2<<8))
#define SQLITE_READONLY_ROLLBACK       (SQLITE_READONLY | (3<<8))
#define SQLITE_READONLY_DBMOVED        (SQLITE_READONLY | (4<<8))
#define SQLITE_ABORT_ROLLBACK          (SQLITE_ABORT | (2<<8))
#define SQLITE_CONSTRAINT_CHECK        (SQLITE_CONSTRAINT | (1<<8))

** The [SQLITE_FCNTL_ROLLBACK_ATOMIC_WRITE] opcode causes all write
** operations since the previous successful call to 
** [SQLITE_FCNTL_BEGIN_ATOMIC_WRITE] to be rolled back.
** ^This file control takes the file descriptor out of batch write mode
** so that all subsequent write operations are independent.
** ^SQLite will never invoke SQLITE_FCNTL_ROLLBACK_ATOMIC_WRITE without
** a prior successful call to [SQLITE_FCNTL_BEGIN_ATOMIC_WRITE].
**
** <li>[[SQLITE_FCNTL_READ_SHM]]
** The [SQLITE_FCNTL_READ_SHM] opcode may be used to read data from 
** the shared-memory region used by wal mode if the previous call
** to the xShmMap method returned SQLITE_READONLY_CANTLOCK. The argument
** must point to an instance of a structure declared as:
** <blockquote><pre>
**   struct ReadShmArg { void *pBuf; int nBuf };
** </pre></blockquote>)^
** Before returning, this operation allocates a buffer large enough for
** the entire shared-memory using sqlite3_malloc() and populates it with
** a copy thereof. ReadShmArg.pBuf is set to point to the buffer, and
** ReadShmArg to its size in bytes. It is the responsibility of the caller
** to eventually free the buffer using sqlite3_free().
** </ul>
*/
#define SQLITE_FCNTL_LOCKSTATE               1
#define SQLITE_FCNTL_GET_LOCKPROXYFILE       2
#define SQLITE_FCNTL_SET_LOCKPROXYFILE       3
#define SQLITE_FCNTL_LAST_ERRNO              4
#define SQLITE_FCNTL_SIZE_HINT               5

  }

  if( !useWal ){
    rc = walIndexReadHdr(pWal, pChanged);
    if( rc==SQLITE_READONLY_CANTLOCK ){
      /* This is a readonly_shm connection and there are no other connections
      ** to the database. So the *-shm file may not be accessed using mmap.
      ** Try to open an "unlocked" transaction - one that loads the *-shm
      ** file into memory using read() - instead.  */
      assert( pWal->nWiData>0 && pWal->apWiData[0]==0 );
      assert( pWal->readOnly & WAL_SHM_RDONLY );
      return walBeginUnlocked(pWal, pChanged);
    }
    if( rc==SQLITE_BUSY ){
      /* If there is not a recovery running in another thread or process
      ** then convert BUSY errors to WAL_RETRY.  If recovery is known to