*/
static void robust_close(unixFile *pFile, int h, int lineno){
  if( osClose(h) ){
    unixLogErrorAtLine(SQLITE_IOERR_CLOSE, "close",
                       pFile ? pFile->zPath : 0, lineno);
  }
}









/*
** Close all file descriptors accumuated in the unixInodeInfo->pUnused list.
*/ 
static void closePendingFds(unixFile *pFile){
  unixInodeInfo *pInode = pFile->pInode;
  UnixUnusedFd *p;
................................................................................

  /* Get low-level information about the file that we can used to
  ** create a unique name for the file.
  */
  fd = pFile->h;
  rc = osFstat(fd, &statbuf);
  if( rc!=0 ){
    pFile->lastErrno = errno;
#ifdef EOVERFLOW
    if( pFile->lastErrno==EOVERFLOW ) return SQLITE_NOLFS;
#endif
    return SQLITE_IOERR;
  }

#ifdef __APPLE__
................................................................................
  ** in the header of every SQLite database.  In this way, if there
  ** is a race condition such that another thread has already populated
  ** the first page of the database, no damage is done.
  */
  if( statbuf.st_size==0 && (pFile->fsFlags & SQLITE_FSFLAGS_IS_MSDOS)!=0 ){
    do{ rc = osWrite(fd, "S", 1); }while( rc<0 && errno==EINTR );
    if( rc!=1 ){
      pFile->lastErrno = errno;
      return SQLITE_IOERR;
    }
    rc = osFstat(fd, &statbuf);
    if( rc!=0 ){
      pFile->lastErrno = errno;
      return SQLITE_IOERR;
    }
  }
#endif

  memset(&fileId, 0, sizeof(fileId));
  fileId.dev = statbuf.st_dev;
................................................................................
    struct flock lock;
    lock.l_whence = SEEK_SET;
    lock.l_start = RESERVED_BYTE;
    lock.l_len = 1;
    lock.l_type = F_WRLCK;
    if( osFcntl(pFile->h, F_GETLK, &lock) ){
      rc = SQLITE_IOERR_CHECKRESERVEDLOCK;
      pFile->lastErrno = errno;
    } else if( lock.l_type!=F_UNLCK ){
      reserved = 1;
    }
  }
#endif
  
  unixLeaveMutex();
................................................................................
  ){
    lock.l_type = (eFileLock==SHARED_LOCK?F_RDLCK:F_WRLCK);
    lock.l_start = PENDING_BYTE;
    if( unixFileLock(pFile, &lock) ){
      tErrno = errno;
      rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
      if( rc!=SQLITE_BUSY ){
        pFile->lastErrno = tErrno;
      }
      goto end_lock;
    }
  }


  /* If control gets to this point, then actually go ahead and make
................................................................................
      /* This could happen with a network mount */
      tErrno = errno;
      rc = SQLITE_IOERR_UNLOCK; 
    }

    if( rc ){
      if( rc!=SQLITE_BUSY ){
        pFile->lastErrno = tErrno;
      }
      goto end_lock;
    }else{
      pFile->eFileLock = SHARED_LOCK;
      pInode->nLock++;
      pInode->nShared = 1;
    }
................................................................................
      lock.l_len = SHARED_SIZE;
    }

    if( unixFileLock(pFile, &lock) ){
      tErrno = errno;
      rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
      if( rc!=SQLITE_BUSY ){
        pFile->lastErrno = tErrno;
      }
    }
  }
  

#ifdef SQLITE_DEBUG
  /* Set up the transaction-counter change checking flags when
................................................................................
    ** write lock until the rest is covered by a read lock:
    **  1:   [WWWWW]
    **  2:   [....W]
    **  3:   [RRRRW]
    **  4:   [RRRR.]
    */
    if( eFileLock==SHARED_LOCK ){


#if !defined(__APPLE__) || !SQLITE_ENABLE_LOCKING_STYLE
      (void)handleNFSUnlock;
      assert( handleNFSUnlock==0 );
#endif
#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
      if( handleNFSUnlock ){
        int tErrno;               /* Error code from system call errors */
        off_t divSize = SHARED_SIZE - 1;
        
        lock.l_type = F_UNLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = SHARED_FIRST;
        lock.l_len = divSize;
        if( unixFileLock(pFile, &lock)==(-1) ){
          tErrno = errno;
          rc = SQLITE_IOERR_UNLOCK;
          if( IS_LOCK_ERROR(rc) ){
            pFile->lastErrno = tErrno;
          }
          goto end_unlock;
        }
        lock.l_type = F_RDLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = SHARED_FIRST;
        lock.l_len = divSize;
        if( unixFileLock(pFile, &lock)==(-1) ){
          tErrno = errno;
          rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_RDLOCK);
          if( IS_LOCK_ERROR(rc) ){
            pFile->lastErrno = tErrno;
          }
          goto end_unlock;
        }
        lock.l_type = F_UNLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = SHARED_FIRST+divSize;
        lock.l_len = SHARED_SIZE-divSize;
        if( unixFileLock(pFile, &lock)==(-1) ){
          tErrno = errno;
          rc = SQLITE_IOERR_UNLOCK;
          if( IS_LOCK_ERROR(rc) ){
            pFile->lastErrno = tErrno;
          }
          goto end_unlock;
        }
      }else
#endif /* defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE */
      {
        lock.l_type = F_RDLCK;
................................................................................
          /* In theory, the call to unixFileLock() cannot fail because another
          ** process is holding an incompatible lock. If it does, this 
          ** indicates that the other process is not following the locking
          ** protocol. If this happens, return SQLITE_IOERR_RDLOCK. Returning
          ** SQLITE_BUSY would confuse the upper layer (in practice it causes 
          ** an assert to fail). */ 
          rc = SQLITE_IOERR_RDLOCK;
          pFile->lastErrno = errno;
          goto end_unlock;
        }
      }
    }
    lock.l_type = F_UNLCK;
    lock.l_whence = SEEK_SET;
    lock.l_start = PENDING_BYTE;
    lock.l_len = 2L;  assert( PENDING_BYTE+1==RESERVED_BYTE );
    if( unixFileLock(pFile, &lock)==0 ){
      pInode->eFileLock = SHARED_LOCK;
    }else{
      rc = SQLITE_IOERR_UNLOCK;
      pFile->lastErrno = errno;
      goto end_unlock;
    }
  }
  if( eFileLock==NO_LOCK ){
    /* Decrement the shared lock counter.  Release the lock using an
    ** OS call only when all threads in this same process have released
    ** the lock.
................................................................................
      lock.l_type = F_UNLCK;
      lock.l_whence = SEEK_SET;
      lock.l_start = lock.l_len = 0L;
      if( unixFileLock(pFile, &lock)==0 ){
        pInode->eFileLock = NO_LOCK;
      }else{
        rc = SQLITE_IOERR_UNLOCK;
        pFile->lastErrno = errno;
        pInode->eFileLock = NO_LOCK;
        pFile->eFileLock = NO_LOCK;
      }
    }

    /* Decrement the count of locks against this same file.  When the
    ** count reaches zero, close any other file descriptors whose close
................................................................................
    /* failed to open/create the lock directory */
    int tErrno = errno;
    if( EEXIST == tErrno ){
      rc = SQLITE_BUSY;
    } else {
      rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
      if( IS_LOCK_ERROR(rc) ){
        pFile->lastErrno = tErrno;
      }
    }
    return rc;
  } 
  
  /* got it, set the type and return ok */
  pFile->eFileLock = eFileLock;
................................................................................
  if( rc<0 ){
    int tErrno = errno;
    rc = 0;
    if( ENOENT != tErrno ){
      rc = SQLITE_IOERR_UNLOCK;
    }
    if( IS_LOCK_ERROR(rc) ){
      pFile->lastErrno = tErrno;
    }
    return rc; 
  }
  pFile->eFileLock = NO_LOCK;
  return SQLITE_OK;
}

................................................................................
      /* got the lock, unlock it */
      lrc = robust_flock(pFile->h, LOCK_UN);
      if ( lrc ) {
        int tErrno = errno;
        /* unlock failed with an error */
        lrc = SQLITE_IOERR_UNLOCK; 
        if( IS_LOCK_ERROR(lrc) ){
          pFile->lastErrno = tErrno;
          rc = lrc;
        }
      }
    } else {
      int tErrno = errno;
      reserved = 1;
      /* someone else might have it reserved */
      lrc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK); 
      if( IS_LOCK_ERROR(lrc) ){
        pFile->lastErrno = tErrno;
        rc = lrc;
      }
    }
  }
  OSTRACE(("TEST WR-LOCK %d %d %d (flock)\n", pFile->h, rc, reserved));

#ifdef SQLITE_IGNORE_FLOCK_LOCK_ERRORS
................................................................................
  /* grab an exclusive lock */
  
  if (robust_flock(pFile->h, LOCK_EX | LOCK_NB)) {
    int tErrno = errno;
    /* didn't get, must be busy */
    rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
    if( IS_LOCK_ERROR(rc) ){
      pFile->lastErrno = tErrno;
    }
  } else {
    /* got it, set the type and return ok */
    pFile->eFileLock = eFileLock;
  }
  OSTRACE(("LOCK    %d %s %s (flock)\n", pFile->h, azFileLock(eFileLock), 
           rc==SQLITE_OK ? "ok" : "failed"));
................................................................................
  if( !reserved ){
    sem_t *pSem = pFile->pInode->pSem;

    if( sem_trywait(pSem)==-1 ){
      int tErrno = errno;
      if( EAGAIN != tErrno ){
        rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_CHECKRESERVEDLOCK);
        pFile->lastErrno = tErrno;
      } else {
        /* someone else has the lock when we are in NO_LOCK */
        reserved = (pFile->eFileLock < SHARED_LOCK);
      }
    }else{
      /* we could have it if we want it */
      sem_post(pSem);
................................................................................
  }
  
  /* no, really unlock. */
  if ( sem_post(pSem)==-1 ) {
    int rc, tErrno = errno;
    rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_UNLOCK);
    if( IS_LOCK_ERROR(rc) ){
      pFile->lastErrno = tErrno;
    }
    return rc; 
  }
  pFile->eFileLock = NO_LOCK;
  return SQLITE_OK;
}

................................................................................
#ifdef SQLITE_IGNORE_AFP_LOCK_ERRORS
    rc = SQLITE_BUSY;
#else
    rc = sqliteErrorFromPosixError(tErrno,
                    setLockFlag ? SQLITE_IOERR_LOCK : SQLITE_IOERR_UNLOCK);
#endif /* SQLITE_IGNORE_AFP_LOCK_ERRORS */
    if( IS_LOCK_ERROR(rc) ){
      pFile->lastErrno = tErrno;
    }
    return rc;
  } else {
    return SQLITE_OK;
  }
}

................................................................................
    if( IS_LOCK_ERROR(lrc1) ){
      lrc1Errno = pFile->lastErrno;
    }
    /* Drop the temporary PENDING lock */
    lrc2 = afpSetLock(context->dbPath, pFile, PENDING_BYTE, 1, 0);
    
    if( IS_LOCK_ERROR(lrc1) ) {
      pFile->lastErrno = lrc1Errno;
      rc = lrc1;
      goto afp_end_lock;
    } else if( IS_LOCK_ERROR(lrc2) ){
      rc = lrc2;
      goto afp_end_lock;
    } else if( lrc1 != SQLITE_OK ) {
      rc = lrc1;
................................................................................
    got = osPread64(id->h, pBuf, cnt, offset);
    SimulateIOError( got = -1 );
#else
    newOffset = lseek(id->h, offset, SEEK_SET);
    SimulateIOError( newOffset-- );
    if( newOffset!=offset ){
      if( newOffset == -1 ){
        ((unixFile*)id)->lastErrno = errno;
      }else{
        ((unixFile*)id)->lastErrno = 0;
      }
      return -1;
    }
    got = osRead(id->h, pBuf, cnt);
#endif
    if( got==cnt ) break;
    if( got<0 ){
      if( errno==EINTR ){ got = 1; continue; }
      prior = 0;
      ((unixFile*)id)->lastErrno = errno;
      break;
    }else if( got>0 ){
      cnt -= got;
      offset += got;
      prior += got;
      pBuf = (void*)(got + (char*)pBuf);
    }
................................................................................
  got = seekAndRead(pFile, offset, pBuf, amt);
  if( got==amt ){
    return SQLITE_OK;
  }else if( got<0 ){
    /* lastErrno set by seekAndRead */
    return SQLITE_IOERR_READ;
  }else{
    pFile->lastErrno = 0; /* not a system error */
    /* Unread parts of the buffer must be zero-filled */
    memset(&((char*)pBuf)[got], 0, amt-got);
    return SQLITE_IOERR_SHORT_READ;
  }
}

/*
................................................................................
  SimulateDiskfullError(( wrote=0, amt=1 ));

  if( amt>0 ){
    if( wrote<0 && pFile->lastErrno!=ENOSPC ){
      /* lastErrno set by seekAndWrite */
      return SQLITE_IOERR_WRITE;
    }else{
      pFile->lastErrno = 0; /* not a system error */
      return SQLITE_FULL;
    }
  }

  return SQLITE_OK;
}

................................................................................
  SimulateDiskfullError( return SQLITE_FULL );

  assert( pFile );
  OSTRACE(("SYNC    %-3d\n", pFile->h));
  rc = full_fsync(pFile->h, isFullsync, isDataOnly);
  SimulateIOError( rc=1 );
  if( rc ){
    pFile->lastErrno = errno;
    return unixLogError(SQLITE_IOERR_FSYNC, "full_fsync", pFile->zPath);
  }

  /* Also fsync the directory containing the file if the DIRSYNC flag
  ** is set.  This is a one-time occurrence.  Many systems (examples: AIX)
  ** are unable to fsync a directory, so ignore errors on the fsync.
  */
................................................................................
  */
  if( pFile->szChunk>0 ){
    nByte = ((nByte + pFile->szChunk - 1)/pFile->szChunk) * pFile->szChunk;
  }

  rc = robust_ftruncate(pFile->h, nByte);
  if( rc ){
    pFile->lastErrno = errno;
    return unixLogError(SQLITE_IOERR_TRUNCATE, "ftruncate", pFile->zPath);
  }else{
#ifdef SQLITE_DEBUG
    /* If we are doing a normal write to a database file (as opposed to
    ** doing a hot-journal rollback or a write to some file other than a
    ** normal database file) and we truncate the file to zero length,
    ** that effectively updates the change counter.  This might happen
................................................................................
static int unixFileSize(sqlite3_file *id, i64 *pSize){
  int rc;
  struct stat buf;
  assert( id );
  rc = osFstat(((unixFile*)id)->h, &buf);
  SimulateIOError( rc=1 );
  if( rc!=0 ){
    ((unixFile*)id)->lastErrno = errno;
    return SQLITE_IOERR_FSTAT;
  }
  *pSize = buf.st_size;

  /* When opening a zero-size database, the findInodeInfo() procedure
  ** writes a single byte into that file in order to work around a bug
  ** in the OS-X msdos filesystem.  In order to avoid problems with upper
................................................................................
** nBytes or larger, this routine is a no-op.
*/
static int fcntlSizeHint(unixFile *pFile, i64 nByte){
  if( pFile->szChunk>0 ){
    i64 nSize;                    /* Required file size */
    struct stat buf;              /* Used to hold return values of fstat() */
   
    if( osFstat(pFile->h, &buf) ) return SQLITE_IOERR_FSTAT;



    nSize = ((nByte+pFile->szChunk-1) / pFile->szChunk) * pFile->szChunk;
    if( nSize>(i64)buf.st_size ){

#if defined(HAVE_POSIX_FALLOCATE) && HAVE_POSIX_FALLOCATE
      /* The code below is handling the return value of osFallocate() 
      ** correctly. posix_fallocate() is defined to "returns zero on success, 
................................................................................
  }

#if SQLITE_MAX_MMAP_SIZE>0
  if( pFile->mmapSizeMax>0 && nByte>pFile->mmapSize ){
    int rc;
    if( pFile->szChunk<=0 ){
      if( robust_ftruncate(pFile->h, nByte) ){
        pFile->lastErrno = errno;
        return unixLogError(SQLITE_IOERR_TRUNCATE, "ftruncate", pFile->zPath);
      }
    }

    rc = unixMapfile(pFile, nByte);
    return rc;
  }
................................................................................
static int unixFileControl(sqlite3_file *id, int op, void *pArg){
  unixFile *pFile = (unixFile*)id;
  switch( op ){
    case SQLITE_FCNTL_LOCKSTATE: {
      *(int*)pArg = pFile->eFileLock;
      return SQLITE_OK;
    }
    case SQLITE_LAST_ERRNO: {
      *(int*)pArg = pFile->lastErrno;
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_CHUNK_SIZE: {
      pFile->szChunk = *(int *)pArg;
      return SQLITE_OK;
    }
................................................................................
    */
    case SQLITE_FCNTL_DB_UNCHANGED: {
      ((unixFile*)id)->dbUpdate = 0;
      return SQLITE_OK;
    }
#endif
#if SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__)
    case SQLITE_SET_LOCKPROXYFILE:
    case SQLITE_GET_LOCKPROXYFILE: {
      return proxyFileControl(id,op,pArg);
    }
#endif /* SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__) */
  }
  return SQLITE_NOTFOUND;
}

................................................................................
  ** one if present. Create a new one if necessary.
  */
  unixEnterMutex();
  pInode = pDbFd->pInode;
  pShmNode = pInode->pShmNode;
  if( pShmNode==0 ){
    struct stat sStat;                 /* fstat() info for database file */




    /* Call fstat() to figure out the permissions on the database file. If
    ** a new *-shm file is created, an attempt will be made to create it
    ** with the same permissions.
    */
    if( osFstat(pDbFd->h, &sStat) && pInode->bProcessLock==0 ){
      rc = SQLITE_IOERR_FSTAT;
      goto shm_open_err;
    }

#ifdef SQLITE_SHM_DIRECTORY
    nShmFilename = sizeof(SQLITE_SHM_DIRECTORY) + 31;
#else
    nShmFilename = 6 + (int)strlen(pDbFd->zPath);
#endif
    pShmNode = sqlite3_malloc( sizeof(*pShmNode) + nShmFilename );
    if( pShmNode==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }
    memset(pShmNode, 0, sizeof(*pShmNode)+nShmFilename);
    zShmFilename = pShmNode->zFilename = (char*)&pShmNode[1];
#ifdef SQLITE_SHM_DIRECTORY
    sqlite3_snprintf(nShmFilename, zShmFilename, 
                     SQLITE_SHM_DIRECTORY "/sqlite-shm-%x-%x",
                     (u32)sStat.st_ino, (u32)sStat.st_dev);
#else
    sqlite3_snprintf(nShmFilename, zShmFilename, "%s-shm", pDbFd->zPath);
    sqlite3FileSuffix3(pDbFd->zPath, zShmFilename);
#endif
    pShmNode->h = -1;
    pDbFd->pInode->pShmNode = pShmNode;
    pShmNode->pInode = pDbFd->pInode;
    pShmNode->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pShmNode->mutex==0 ){
................................................................................

  /* If pShmNode->nRef has reached 0, then close the underlying
  ** shared-memory file, too */
  unixEnterMutex();
  assert( pShmNode->nRef>0 );
  pShmNode->nRef--;
  if( pShmNode->nRef==0 ){
    if( deleteFlag && pShmNode->h>=0 ) osUnlink(pShmNode->zFilename);


    unixShmPurge(pDbFd);
  }
  unixLeaveMutex();

  return SQLITE_OK;
}

................................................................................
        pNew->pInode->aSemName[0] = '\0';
      }
    }
    unixLeaveMutex();
  }
#endif
  
  pNew->lastErrno = 0;
#if OS_VXWORKS
  if( rc!=SQLITE_OK ){
    if( h>=0 ) robust_close(pNew, h, __LINE__);
    h = -1;
    osUnlink(zFilename);
    pNew->ctrlFlags |= UNIXFILE_DELETE;
  }
................................................................................
#endif

  noLock = eType!=SQLITE_OPEN_MAIN_DB;

  
#if defined(__APPLE__) || SQLITE_ENABLE_LOCKING_STYLE
  if( fstatfs(fd, &fsInfo) == -1 ){
    ((unixFile*)pFile)->lastErrno = errno;
    robust_close(p, fd, __LINE__);
    return SQLITE_IOERR_ACCESS;
  }
  if (0 == strncmp("msdos", fsInfo.f_fstypename, 5)) {
    ((unixFile*)pFile)->fsFlags |= SQLITE_FSFLAGS_IS_MSDOS;
  }



#endif

  /* Set up appropriate ctrlFlags */
  if( isDelete )                ctrlFlags |= UNIXFILE_DELETE;
  if( isReadonly )              ctrlFlags |= UNIXFILE_RDONLY;
  if( noLock )                  ctrlFlags |= UNIXFILE_NOLOCK;
  if( syncDir )                 ctrlFlags |= UNIXFILE_DIRSYNC;
................................................................................
        /* In theory, the close(fd) call is sub-optimal. If the file opened
        ** with fd is a database file, and there are other connections open
        ** on that file that are currently holding advisory locks on it,
        ** then the call to close() will cancel those locks. In practice,
        ** we're assuming that statfs() doesn't fail very often. At least
        ** not while other file descriptors opened by the same process on
        ** the same file are working.  */
        p->lastErrno = errno;
        robust_close(p, fd, __LINE__);
        rc = SQLITE_IOERR_ACCESS;
        goto open_finished;
      }
      useProxy = !(fsInfo.f_flags&MNT_LOCAL);
    }
    if( useProxy ){
................................................................................
**
**
** Using proxy locks
** -----------------
**
** C APIs
**
**  sqlite3_file_control(db, dbname, SQLITE_SET_LOCKPROXYFILE,
**                       <proxy_path> | ":auto:");
**  sqlite3_file_control(db, dbname, SQLITE_GET_LOCKPROXYFILE, &<proxy_path>);

**
**
** SQL pragmas
**
**  PRAGMA [database.]lock_proxy_file=<proxy_path> | :auto:
**  PRAGMA [database.]lock_proxy_file
**
................................................................................
**       lock proxy files, only used when LOCKPROXYDIR is not set.
**    
**    
** As mentioned above, when compiled with SQLITE_PREFER_PROXY_LOCKING,
** setting the environment variable SQLITE_FORCE_PROXY_LOCKING to 1 will
** force proxy locking to be used for every database file opened, and 0
** will force automatic proxy locking to be disabled for all database
** files (explicitly calling the SQLITE_SET_LOCKPROXYFILE pragma or
** sqlite_file_control API is not affected by SQLITE_FORCE_PROXY_LOCKING).
*/

/*
** Proxy locking is only available on MacOSX 
*/
#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
................................................................................
struct proxyLockingContext {
  unixFile *conchFile;         /* Open conch file */
  char *conchFilePath;         /* Name of the conch file */
  unixFile *lockProxy;         /* Open proxy lock file */
  char *lockProxyPath;         /* Name of the proxy lock file */
  char *dbPath;                /* Name of the open file */
  int conchHeld;               /* 1 if the conch is held, -1 if lockless */

  void *oldLockingContext;     /* Original lockingcontext to restore on close */
  sqlite3_io_methods const *pOldMethod;     /* Original I/O methods for close */
};

/* 
** The proxy lock file path for the database at dbPath is written into lPath, 
** which must point to valid, writable memory large enough for a maxLen length
................................................................................

/* get the host ID via gethostuuid(), pHostID must point to PROXY_HOSTIDLEN 
** bytes of writable memory.
*/
static int proxyGetHostID(unsigned char *pHostID, int *pError){
  assert(PROXY_HOSTIDLEN == sizeof(uuid_t));
  memset(pHostID, 0, PROXY_HOSTIDLEN);
#if defined(__MAX_OS_X_VERSION_MIN_REQUIRED)\
               && __MAC_OS_X_VERSION_MIN_REQUIRED<1050
  {
    static const struct timespec timeout = {1, 0}; /* 1 sec timeout */
    if( gethostuuid(pHostID, &timeout) ){
      int err = errno;
      if( pError ){
        *pError = err;
      }
      return SQLITE_IOERR;
    }
................................................................................
       * 1st try: get the mod time of the conch, wait 0.5s and try again. 
       * 2nd try: fail if the mod time changed or host id is different, wait 
       *           10 sec and try again
       * 3rd try: break the lock unless the mod time has changed.
       */
      struct stat buf;
      if( osFstat(conchFile->h, &buf) ){
        pFile->lastErrno = errno;
        return SQLITE_IOERR_LOCK;
      }
      
      if( nTries==1 ){
        conchModTime = buf.st_mtimespec;
        usleep(500000); /* wait 0.5 sec and try the lock again*/
        continue;  
................................................................................
        return SQLITE_BUSY;
      }
      
      if( nTries==2 ){  
        char tBuf[PROXY_MAXCONCHLEN];
        int len = osPread(conchFile->h, tBuf, PROXY_MAXCONCHLEN, 0);
        if( len<0 ){
          pFile->lastErrno = errno;
          return SQLITE_IOERR_LOCK;
        }
        if( len>PROXY_PATHINDEX && tBuf[0]==(char)PROXY_CONCHVERSION){
          /* don't break the lock if the host id doesn't match */
          if( 0!=memcmp(&tBuf[PROXY_HEADERLEN], myHostID, PROXY_HOSTIDLEN) ){
            return SQLITE_BUSY;
          }
................................................................................
    int forceNewLockPath = 0;
    
    OSTRACE(("TAKECONCH  %d for %s pid=%d\n", conchFile->h,
             (pCtx->lockProxyPath ? pCtx->lockProxyPath : ":auto:"), getpid()));

    rc = proxyGetHostID(myHostID, &pError);
    if( (rc&0xff)==SQLITE_IOERR ){
      pFile->lastErrno = pError;
      goto end_takeconch;
    }
    rc = proxyConchLock(pFile, myHostID, SHARED_LOCK);
    if( rc!=SQLITE_OK ){
      goto end_takeconch;
    }
    /* read the existing conch file */
    readLen = seekAndRead((unixFile*)conchFile, 0, readBuf, PROXY_MAXCONCHLEN);
    if( readLen<0 ){
      /* I/O error: lastErrno set by seekAndRead */
      pFile->lastErrno = conchFile->lastErrno;
      rc = SQLITE_IOERR_READ;
      goto end_takeconch;
    }else if( readLen<=(PROXY_HEADERLEN+PROXY_HOSTIDLEN) || 
             readBuf[0]!=(char)PROXY_CONCHVERSION ){
      /* a short read or version format mismatch means we need to create a new 
      ** conch file. 
      */
................................................................................
          /* We are trying for an exclusive lock but another thread in this
           ** same process is still holding a shared lock. */
          rc = SQLITE_BUSY;
        } else {          
          rc = proxyConchLock(pFile, myHostID, EXCLUSIVE_LOCK);
        }
      }else{
        rc = conchFile->pMethod->xLock((sqlite3_file*)conchFile, EXCLUSIVE_LOCK);
      }
      if( rc==SQLITE_OK ){
        char writeBuffer[PROXY_MAXCONCHLEN];
        int writeSize = 0;
        
        writeBuffer[0] = (char)PROXY_CONCHVERSION;
        memcpy(&writeBuffer[PROXY_HEADERLEN], myHostID, PROXY_HOSTIDLEN);
        if( pCtx->lockProxyPath!=NULL ){
          strlcpy(&writeBuffer[PROXY_PATHINDEX], pCtx->lockProxyPath, MAXPATHLEN);

        }else{
          strlcpy(&writeBuffer[PROXY_PATHINDEX], tempLockPath, MAXPATHLEN);
        }
        writeSize = PROXY_PATHINDEX + strlen(&writeBuffer[PROXY_PATHINDEX]);
        robust_ftruncate(conchFile->h, writeSize);
        rc = unixWrite((sqlite3_file *)conchFile, writeBuffer, writeSize, 0);
        fsync(conchFile->h);
................................................................................
*/
static int proxyGetDbPathForUnixFile(unixFile *pFile, char *dbPath){
#if defined(__APPLE__)
  if( pFile->pMethod == &afpIoMethods ){
    /* afp style keeps a reference to the db path in the filePath field 
    ** of the struct */
    assert( (int)strlen((char*)pFile->lockingContext)<=MAXPATHLEN );
    strlcpy(dbPath, ((afpLockingContext *)pFile->lockingContext)->dbPath, MAXPATHLEN);

  } else
#endif
  if( pFile->pMethod == &dotlockIoMethods ){
    /* dot lock style uses the locking context to store the dot lock
    ** file path */
    int len = strlen((char *)pFile->lockingContext) - strlen(DOTLOCK_SUFFIX);
    memcpy(dbPath, (char *)pFile->lockingContext, len + 1);
................................................................................

/*
** This routine handles sqlite3_file_control() calls that are specific
** to proxy locking.
*/
static int proxyFileControl(sqlite3_file *id, int op, void *pArg){
  switch( op ){
    case SQLITE_GET_LOCKPROXYFILE: {
      unixFile *pFile = (unixFile*)id;
      if( pFile->pMethod == &proxyIoMethods ){
        proxyLockingContext *pCtx = (proxyLockingContext*)pFile->lockingContext;
        proxyTakeConch(pFile);
        if( pCtx->lockProxyPath ){
          *(const char **)pArg = pCtx->lockProxyPath;
        }else{
................................................................................
          *(const char **)pArg = ":auto: (not held)";
        }
      } else {
        *(const char **)pArg = NULL;
      }
      return SQLITE_OK;
    }
    case SQLITE_SET_LOCKPROXYFILE: {
      unixFile *pFile = (unixFile*)id;
      int rc = SQLITE_OK;
      int isProxyStyle = (pFile->pMethod == &proxyIoMethods);
      if( pArg==NULL || (const char *)pArg==0 ){
        if( isProxyStyle ){
          /* turn off proxy locking - not supported */



          rc = SQLITE_ERROR /*SQLITE_PROTOCOL? SQLITE_MISUSE?*/;
        }else{
          /* turn off proxy locking - already off - NOOP */
          rc = SQLITE_OK;
        }
      }else{
        const char *proxyPath = (const char *)pArg;

*/
static void robust_close(unixFile *pFile, int h, int lineno){
  if( osClose(h) ){
    unixLogErrorAtLine(SQLITE_IOERR_CLOSE, "close",
                       pFile ? pFile->zPath : 0, lineno);
  }
}

/*
** Set the pFile->lastErrno.  Do this in a subroutine as that provides a convenient
** place to set a breakpoint.
*/
static void storeLastErrno(unixFile *pFile, int error){
  pFile->lastErrno = error;
}

/*
** Close all file descriptors accumuated in the unixInodeInfo->pUnused list.
*/ 
static void closePendingFds(unixFile *pFile){
  unixInodeInfo *pInode = pFile->pInode;
  UnixUnusedFd *p;
................................................................................

  /* Get low-level information about the file that we can used to
  ** create a unique name for the file.
  */
  fd = pFile->h;
  rc = osFstat(fd, &statbuf);
  if( rc!=0 ){
    storeLastErrno(pFile, errno);
#ifdef EOVERFLOW
    if( pFile->lastErrno==EOVERFLOW ) return SQLITE_NOLFS;
#endif
    return SQLITE_IOERR;
  }

#ifdef __APPLE__
................................................................................
  ** in the header of every SQLite database.  In this way, if there
  ** is a race condition such that another thread has already populated
  ** the first page of the database, no damage is done.
  */
  if( statbuf.st_size==0 && (pFile->fsFlags & SQLITE_FSFLAGS_IS_MSDOS)!=0 ){
    do{ rc = osWrite(fd, "S", 1); }while( rc<0 && errno==EINTR );
    if( rc!=1 ){
      storeLastErrno(pFile, errno);
      return SQLITE_IOERR;
    }
    rc = osFstat(fd, &statbuf);
    if( rc!=0 ){
      storeLastErrno(pFile, errno);
      return SQLITE_IOERR;
    }
  }
#endif

  memset(&fileId, 0, sizeof(fileId));
  fileId.dev = statbuf.st_dev;
................................................................................
    struct flock lock;
    lock.l_whence = SEEK_SET;
    lock.l_start = RESERVED_BYTE;
    lock.l_len = 1;
    lock.l_type = F_WRLCK;
    if( osFcntl(pFile->h, F_GETLK, &lock) ){
      rc = SQLITE_IOERR_CHECKRESERVEDLOCK;
      storeLastErrno(pFile, errno);
    } else if( lock.l_type!=F_UNLCK ){
      reserved = 1;
    }
  }
#endif
  
  unixLeaveMutex();
................................................................................
  ){
    lock.l_type = (eFileLock==SHARED_LOCK?F_RDLCK:F_WRLCK);
    lock.l_start = PENDING_BYTE;
    if( unixFileLock(pFile, &lock) ){
      tErrno = errno;
      rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
      if( rc!=SQLITE_BUSY ){
        storeLastErrno(pFile, tErrno);
      }
      goto end_lock;
    }
  }


  /* If control gets to this point, then actually go ahead and make
................................................................................
      /* This could happen with a network mount */
      tErrno = errno;
      rc = SQLITE_IOERR_UNLOCK; 
    }

    if( rc ){
      if( rc!=SQLITE_BUSY ){
        storeLastErrno(pFile, tErrno);
      }
      goto end_lock;
    }else{
      pFile->eFileLock = SHARED_LOCK;
      pInode->nLock++;
      pInode->nShared = 1;
    }
................................................................................
      lock.l_len = SHARED_SIZE;
    }

    if( unixFileLock(pFile, &lock) ){
      tErrno = errno;
      rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
      if( rc!=SQLITE_BUSY ){
        storeLastErrno(pFile, tErrno);
      }
    }
  }
  

#ifdef SQLITE_DEBUG
  /* Set up the transaction-counter change checking flags when
................................................................................
    ** write lock until the rest is covered by a read lock:
    **  1:   [WWWWW]
    **  2:   [....W]
    **  3:   [RRRRW]
    **  4:   [RRRR.]
    */
    if( eFileLock==SHARED_LOCK ){
      int tErrno;               /* Error code from system call errors */

#if !defined(__APPLE__) || !SQLITE_ENABLE_LOCKING_STYLE
      (void)handleNFSUnlock;
      assert( handleNFSUnlock==0 );
#endif
#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
      if( handleNFSUnlock ){

        off_t divSize = SHARED_SIZE - 1;
        
        lock.l_type = F_UNLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = SHARED_FIRST;
        lock.l_len = divSize;
        if( unixFileLock(pFile, &lock)==(-1) ){
          tErrno = errno;
          rc = SQLITE_IOERR_UNLOCK;
          if( IS_LOCK_ERROR(rc) ){
            storeLastErrno(pFile, tErrno);
          }
          goto end_unlock;
        }
        lock.l_type = F_RDLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = SHARED_FIRST;
        lock.l_len = divSize;
        if( unixFileLock(pFile, &lock)==(-1) ){
          tErrno = errno;
          rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_RDLOCK);
          if( IS_LOCK_ERROR(rc) ){
            storeLastErrno(pFile, tErrno);
          }
          goto end_unlock;
        }
        lock.l_type = F_UNLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = SHARED_FIRST+divSize;
        lock.l_len = SHARED_SIZE-divSize;
        if( unixFileLock(pFile, &lock)==(-1) ){
          tErrno = errno;
          rc = SQLITE_IOERR_UNLOCK;
          if( IS_LOCK_ERROR(rc) ){
            storeLastErrno(pFile, tErrno);
          }
          goto end_unlock;
        }
      }else
#endif /* defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE */
      {
        lock.l_type = F_RDLCK;
................................................................................
          /* In theory, the call to unixFileLock() cannot fail because another
          ** process is holding an incompatible lock. If it does, this 
          ** indicates that the other process is not following the locking
          ** protocol. If this happens, return SQLITE_IOERR_RDLOCK. Returning
          ** SQLITE_BUSY would confuse the upper layer (in practice it causes 
          ** an assert to fail). */ 
          rc = SQLITE_IOERR_RDLOCK;
          storeLastErrno(pFile, errno);
          goto end_unlock;
        }
      }
    }
    lock.l_type = F_UNLCK;
    lock.l_whence = SEEK_SET;
    lock.l_start = PENDING_BYTE;
    lock.l_len = 2L;  assert( PENDING_BYTE+1==RESERVED_BYTE );
    if( unixFileLock(pFile, &lock)==0 ){
      pInode->eFileLock = SHARED_LOCK;
    }else{
      rc = SQLITE_IOERR_UNLOCK;
      storeLastErrno(pFile, errno);
      goto end_unlock;
    }
  }
  if( eFileLock==NO_LOCK ){
    /* Decrement the shared lock counter.  Release the lock using an
    ** OS call only when all threads in this same process have released
    ** the lock.
................................................................................
      lock.l_type = F_UNLCK;
      lock.l_whence = SEEK_SET;
      lock.l_start = lock.l_len = 0L;
      if( unixFileLock(pFile, &lock)==0 ){
        pInode->eFileLock = NO_LOCK;
      }else{
        rc = SQLITE_IOERR_UNLOCK;
        storeLastErrno(pFile, errno);
        pInode->eFileLock = NO_LOCK;
        pFile->eFileLock = NO_LOCK;
      }
    }

    /* Decrement the count of locks against this same file.  When the
    ** count reaches zero, close any other file descriptors whose close
................................................................................
    /* failed to open/create the lock directory */
    int tErrno = errno;
    if( EEXIST == tErrno ){
      rc = SQLITE_BUSY;
    } else {
      rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
      if( IS_LOCK_ERROR(rc) ){
        storeLastErrno(pFile, tErrno);
      }
    }
    return rc;
  } 
  
  /* got it, set the type and return ok */
  pFile->eFileLock = eFileLock;
................................................................................
  if( rc<0 ){
    int tErrno = errno;
    rc = 0;
    if( ENOENT != tErrno ){
      rc = SQLITE_IOERR_UNLOCK;
    }
    if( IS_LOCK_ERROR(rc) ){
      storeLastErrno(pFile, tErrno);
    }
    return rc; 
  }
  pFile->eFileLock = NO_LOCK;
  return SQLITE_OK;
}

................................................................................
      /* got the lock, unlock it */
      lrc = robust_flock(pFile->h, LOCK_UN);
      if ( lrc ) {
        int tErrno = errno;
        /* unlock failed with an error */
        lrc = SQLITE_IOERR_UNLOCK; 
        if( IS_LOCK_ERROR(lrc) ){
          storeLastErrno(pFile, tErrno);
          rc = lrc;
        }
      }
    } else {
      int tErrno = errno;
      reserved = 1;
      /* someone else might have it reserved */
      lrc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK); 
      if( IS_LOCK_ERROR(lrc) ){
        storeLastErrno(pFile, tErrno);
        rc = lrc;
      }
    }
  }
  OSTRACE(("TEST WR-LOCK %d %d %d (flock)\n", pFile->h, rc, reserved));

#ifdef SQLITE_IGNORE_FLOCK_LOCK_ERRORS
................................................................................
  /* grab an exclusive lock */
  
  if (robust_flock(pFile->h, LOCK_EX | LOCK_NB)) {
    int tErrno = errno;
    /* didn't get, must be busy */
    rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
    if( IS_LOCK_ERROR(rc) ){
      storeLastErrno(pFile, tErrno);
    }
  } else {
    /* got it, set the type and return ok */
    pFile->eFileLock = eFileLock;
  }
  OSTRACE(("LOCK    %d %s %s (flock)\n", pFile->h, azFileLock(eFileLock), 
           rc==SQLITE_OK ? "ok" : "failed"));
................................................................................
  if( !reserved ){
    sem_t *pSem = pFile->pInode->pSem;

    if( sem_trywait(pSem)==-1 ){
      int tErrno = errno;
      if( EAGAIN != tErrno ){
        rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_CHECKRESERVEDLOCK);
        storeLastErrno(pFile, tErrno);
      } else {
        /* someone else has the lock when we are in NO_LOCK */
        reserved = (pFile->eFileLock < SHARED_LOCK);
      }
    }else{
      /* we could have it if we want it */
      sem_post(pSem);
................................................................................
  }
  
  /* no, really unlock. */
  if ( sem_post(pSem)==-1 ) {
    int rc, tErrno = errno;
    rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_UNLOCK);
    if( IS_LOCK_ERROR(rc) ){
      storeLastErrno(pFile, tErrno);
    }
    return rc; 
  }
  pFile->eFileLock = NO_LOCK;
  return SQLITE_OK;
}

................................................................................
#ifdef SQLITE_IGNORE_AFP_LOCK_ERRORS
    rc = SQLITE_BUSY;
#else
    rc = sqliteErrorFromPosixError(tErrno,
                    setLockFlag ? SQLITE_IOERR_LOCK : SQLITE_IOERR_UNLOCK);
#endif /* SQLITE_IGNORE_AFP_LOCK_ERRORS */
    if( IS_LOCK_ERROR(rc) ){
      storeLastErrno(pFile, tErrno);
    }
    return rc;
  } else {
    return SQLITE_OK;
  }
}

................................................................................
    if( IS_LOCK_ERROR(lrc1) ){
      lrc1Errno = pFile->lastErrno;
    }
    /* Drop the temporary PENDING lock */
    lrc2 = afpSetLock(context->dbPath, pFile, PENDING_BYTE, 1, 0);
    
    if( IS_LOCK_ERROR(lrc1) ) {
      storeLastErrno(pFile, lrc1Errno);
      rc = lrc1;
      goto afp_end_lock;
    } else if( IS_LOCK_ERROR(lrc2) ){
      rc = lrc2;
      goto afp_end_lock;
    } else if( lrc1 != SQLITE_OK ) {
      rc = lrc1;
................................................................................
    got = osPread64(id->h, pBuf, cnt, offset);
    SimulateIOError( got = -1 );
#else
    newOffset = lseek(id->h, offset, SEEK_SET);
    SimulateIOError( newOffset-- );
    if( newOffset!=offset ){
      if( newOffset == -1 ){
        storeLastErrno((unixFile*)id, errno);
      }else{
        storeLastErrno((unixFile*)id, 0);
      }
      return -1;
    }
    got = osRead(id->h, pBuf, cnt);
#endif
    if( got==cnt ) break;
    if( got<0 ){
      if( errno==EINTR ){ got = 1; continue; }
      prior = 0;
      storeLastErrno((unixFile*)id,  errno);
      break;
    }else if( got>0 ){
      cnt -= got;
      offset += got;
      prior += got;
      pBuf = (void*)(got + (char*)pBuf);
    }
................................................................................
  got = seekAndRead(pFile, offset, pBuf, amt);
  if( got==amt ){
    return SQLITE_OK;
  }else if( got<0 ){
    /* lastErrno set by seekAndRead */
    return SQLITE_IOERR_READ;
  }else{
    storeLastErrno(pFile, 0);   /* not a system error */
    /* Unread parts of the buffer must be zero-filled */
    memset(&((char*)pBuf)[got], 0, amt-got);
    return SQLITE_IOERR_SHORT_READ;
  }
}

/*
................................................................................
  SimulateDiskfullError(( wrote=0, amt=1 ));

  if( amt>0 ){
    if( wrote<0 && pFile->lastErrno!=ENOSPC ){
      /* lastErrno set by seekAndWrite */
      return SQLITE_IOERR_WRITE;
    }else{
      storeLastErrno(pFile, 0); /* not a system error */
      return SQLITE_FULL;
    }
  }

  return SQLITE_OK;
}

................................................................................
  SimulateDiskfullError( return SQLITE_FULL );

  assert( pFile );
  OSTRACE(("SYNC    %-3d\n", pFile->h));
  rc = full_fsync(pFile->h, isFullsync, isDataOnly);
  SimulateIOError( rc=1 );
  if( rc ){
    storeLastErrno(pFile, errno);
    return unixLogError(SQLITE_IOERR_FSYNC, "full_fsync", pFile->zPath);
  }

  /* Also fsync the directory containing the file if the DIRSYNC flag
  ** is set.  This is a one-time occurrence.  Many systems (examples: AIX)
  ** are unable to fsync a directory, so ignore errors on the fsync.
  */
................................................................................
  */
  if( pFile->szChunk>0 ){
    nByte = ((nByte + pFile->szChunk - 1)/pFile->szChunk) * pFile->szChunk;
  }

  rc = robust_ftruncate(pFile->h, nByte);
  if( rc ){
    storeLastErrno(pFile, errno);
    return unixLogError(SQLITE_IOERR_TRUNCATE, "ftruncate", pFile->zPath);
  }else{
#ifdef SQLITE_DEBUG
    /* If we are doing a normal write to a database file (as opposed to
    ** doing a hot-journal rollback or a write to some file other than a
    ** normal database file) and we truncate the file to zero length,
    ** that effectively updates the change counter.  This might happen
................................................................................
static int unixFileSize(sqlite3_file *id, i64 *pSize){
  int rc;
  struct stat buf;
  assert( id );
  rc = osFstat(((unixFile*)id)->h, &buf);
  SimulateIOError( rc=1 );
  if( rc!=0 ){
    storeLastErrno((unixFile*)id, errno);
    return SQLITE_IOERR_FSTAT;
  }
  *pSize = buf.st_size;

  /* When opening a zero-size database, the findInodeInfo() procedure
  ** writes a single byte into that file in order to work around a bug
  ** in the OS-X msdos filesystem.  In order to avoid problems with upper
................................................................................
** nBytes or larger, this routine is a no-op.
*/
static int fcntlSizeHint(unixFile *pFile, i64 nByte){
  if( pFile->szChunk>0 ){
    i64 nSize;                    /* Required file size */
    struct stat buf;              /* Used to hold return values of fstat() */
   
    if( osFstat(pFile->h, &buf) ){
      return SQLITE_IOERR_FSTAT;
    }

    nSize = ((nByte+pFile->szChunk-1) / pFile->szChunk) * pFile->szChunk;
    if( nSize>(i64)buf.st_size ){

#if defined(HAVE_POSIX_FALLOCATE) && HAVE_POSIX_FALLOCATE
      /* The code below is handling the return value of osFallocate() 
      ** correctly. posix_fallocate() is defined to "returns zero on success, 
................................................................................
  }

#if SQLITE_MAX_MMAP_SIZE>0
  if( pFile->mmapSizeMax>0 && nByte>pFile->mmapSize ){
    int rc;
    if( pFile->szChunk<=0 ){
      if( robust_ftruncate(pFile->h, nByte) ){
        storeLastErrno(pFile, errno);
        return unixLogError(SQLITE_IOERR_TRUNCATE, "ftruncate", pFile->zPath);
      }
    }

    rc = unixMapfile(pFile, nByte);
    return rc;
  }
................................................................................
static int unixFileControl(sqlite3_file *id, int op, void *pArg){
  unixFile *pFile = (unixFile*)id;
  switch( op ){
    case SQLITE_FCNTL_LOCKSTATE: {
      *(int*)pArg = pFile->eFileLock;
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_LAST_ERRNO: {
      *(int*)pArg = pFile->lastErrno;
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_CHUNK_SIZE: {
      pFile->szChunk = *(int *)pArg;
      return SQLITE_OK;
    }
................................................................................
    */
    case SQLITE_FCNTL_DB_UNCHANGED: {
      ((unixFile*)id)->dbUpdate = 0;
      return SQLITE_OK;
    }
#endif
#if SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__)
    case SQLITE_FCNTL_SET_LOCKPROXYFILE:
    case SQLITE_FCNTL_GET_LOCKPROXYFILE: {
      return proxyFileControl(id,op,pArg);
    }
#endif /* SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__) */
  }
  return SQLITE_NOTFOUND;
}

................................................................................
  ** one if present. Create a new one if necessary.
  */
  unixEnterMutex();
  pInode = pDbFd->pInode;
  pShmNode = pInode->pShmNode;
  if( pShmNode==0 ){
    struct stat sStat;                 /* fstat() info for database file */
#ifndef SQLITE_SHM_DIRECTORY
    const char *zBasePath = pDbFd->zPath;
#endif

    /* Call fstat() to figure out the permissions on the database file. If
    ** a new *-shm file is created, an attempt will be made to create it
    ** with the same permissions.
    */
    if( osFstat(pDbFd->h, &sStat) && pInode->bProcessLock==0 ){
      rc = SQLITE_IOERR_FSTAT;
      goto shm_open_err;
    }

#ifdef SQLITE_SHM_DIRECTORY
    nShmFilename = sizeof(SQLITE_SHM_DIRECTORY) + 31;
#else
    nShmFilename = 6 + (int)strlen(zBasePath);
#endif
    pShmNode = sqlite3_malloc( sizeof(*pShmNode) + nShmFilename );
    if( pShmNode==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }
    memset(pShmNode, 0, sizeof(*pShmNode)+nShmFilename);
    zShmFilename = pShmNode->zFilename = (char*)&pShmNode[1];
#ifdef SQLITE_SHM_DIRECTORY
    sqlite3_snprintf(nShmFilename, zShmFilename, 
                     SQLITE_SHM_DIRECTORY "/sqlite-shm-%x-%x",
                     (u32)sStat.st_ino, (u32)sStat.st_dev);
#else
    sqlite3_snprintf(nShmFilename, zShmFilename, "%s-shm", zBasePath);
    sqlite3FileSuffix3(pDbFd->zPath, zShmFilename);
#endif
    pShmNode->h = -1;
    pDbFd->pInode->pShmNode = pShmNode;
    pShmNode->pInode = pDbFd->pInode;
    pShmNode->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pShmNode->mutex==0 ){
................................................................................

  /* If pShmNode->nRef has reached 0, then close the underlying
  ** shared-memory file, too */
  unixEnterMutex();
  assert( pShmNode->nRef>0 );
  pShmNode->nRef--;
  if( pShmNode->nRef==0 ){
    if( deleteFlag && pShmNode->h>=0 ){
      osUnlink(pShmNode->zFilename);
    }
    unixShmPurge(pDbFd);
  }
  unixLeaveMutex();

  return SQLITE_OK;
}

................................................................................
        pNew->pInode->aSemName[0] = '\0';
      }
    }
    unixLeaveMutex();
  }
#endif
  
  storeLastErrno(pNew, 0);
#if OS_VXWORKS
  if( rc!=SQLITE_OK ){
    if( h>=0 ) robust_close(pNew, h, __LINE__);
    h = -1;
    osUnlink(zFilename);
    pNew->ctrlFlags |= UNIXFILE_DELETE;
  }
................................................................................
#endif

  noLock = eType!=SQLITE_OPEN_MAIN_DB;

  
#if defined(__APPLE__) || SQLITE_ENABLE_LOCKING_STYLE
  if( fstatfs(fd, &fsInfo) == -1 ){
    storeLastErrno(p, errno);
    robust_close(p, fd, __LINE__);
    return SQLITE_IOERR_ACCESS;
  }
  if (0 == strncmp("msdos", fsInfo.f_fstypename, 5)) {
    ((unixFile*)pFile)->fsFlags |= SQLITE_FSFLAGS_IS_MSDOS;
  }
  if (0 == strncmp("exfat", fsInfo.f_fstypename, 5)) {
    ((unixFile*)pFile)->fsFlags |= SQLITE_FSFLAGS_IS_MSDOS;
  }
#endif

  /* Set up appropriate ctrlFlags */
  if( isDelete )                ctrlFlags |= UNIXFILE_DELETE;
  if( isReadonly )              ctrlFlags |= UNIXFILE_RDONLY;
  if( noLock )                  ctrlFlags |= UNIXFILE_NOLOCK;
  if( syncDir )                 ctrlFlags |= UNIXFILE_DIRSYNC;
................................................................................
        /* In theory, the close(fd) call is sub-optimal. If the file opened
        ** with fd is a database file, and there are other connections open
        ** on that file that are currently holding advisory locks on it,
        ** then the call to close() will cancel those locks. In practice,
        ** we're assuming that statfs() doesn't fail very often. At least
        ** not while other file descriptors opened by the same process on
        ** the same file are working.  */
        storeLastErrno(p, errno);
        robust_close(p, fd, __LINE__);
        rc = SQLITE_IOERR_ACCESS;
        goto open_finished;
      }
      useProxy = !(fsInfo.f_flags&MNT_LOCAL);
    }
    if( useProxy ){
................................................................................
**
**
** Using proxy locks
** -----------------
**
** C APIs
**
**  sqlite3_file_control(db, dbname, SQLITE_FCNTL_SET_LOCKPROXYFILE,
**                       <proxy_path> | ":auto:");
**  sqlite3_file_control(db, dbname, SQLITE_FCNTL_GET_LOCKPROXYFILE,
**                       &<proxy_path>);
**
**
** SQL pragmas
**
**  PRAGMA [database.]lock_proxy_file=<proxy_path> | :auto:
**  PRAGMA [database.]lock_proxy_file
**
................................................................................
**       lock proxy files, only used when LOCKPROXYDIR is not set.
**    
**    
** As mentioned above, when compiled with SQLITE_PREFER_PROXY_LOCKING,
** setting the environment variable SQLITE_FORCE_PROXY_LOCKING to 1 will
** force proxy locking to be used for every database file opened, and 0
** will force automatic proxy locking to be disabled for all database
** files (explicitly calling the SQLITE_FCNTL_SET_LOCKPROXYFILE pragma or
** sqlite_file_control API is not affected by SQLITE_FORCE_PROXY_LOCKING).
*/

/*
** Proxy locking is only available on MacOSX 
*/
#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
................................................................................
struct proxyLockingContext {
  unixFile *conchFile;         /* Open conch file */
  char *conchFilePath;         /* Name of the conch file */
  unixFile *lockProxy;         /* Open proxy lock file */
  char *lockProxyPath;         /* Name of the proxy lock file */
  char *dbPath;                /* Name of the open file */
  int conchHeld;               /* 1 if the conch is held, -1 if lockless */
  int nFails;                  /* Number of conch taking failures */
  void *oldLockingContext;     /* Original lockingcontext to restore on close */
  sqlite3_io_methods const *pOldMethod;     /* Original I/O methods for close */
};

/* 
** The proxy lock file path for the database at dbPath is written into lPath, 
** which must point to valid, writable memory large enough for a maxLen length
................................................................................

/* get the host ID via gethostuuid(), pHostID must point to PROXY_HOSTIDLEN 
** bytes of writable memory.
*/
static int proxyGetHostID(unsigned char *pHostID, int *pError){
  assert(PROXY_HOSTIDLEN == sizeof(uuid_t));
  memset(pHostID, 0, PROXY_HOSTIDLEN);
# if defined(__APPLE__) && ((__MAC_OS_X_VERSION_MIN_REQUIRED > 1050) || \
                            (__IPHONE_OS_VERSION_MIN_REQUIRED > 2000))
  {
    struct timespec timeout = {1, 0}; /* 1 sec timeout */
    if( gethostuuid(pHostID, &timeout) ){
      int err = errno;
      if( pError ){
        *pError = err;
      }
      return SQLITE_IOERR;
    }
................................................................................
       * 1st try: get the mod time of the conch, wait 0.5s and try again. 
       * 2nd try: fail if the mod time changed or host id is different, wait 
       *           10 sec and try again
       * 3rd try: break the lock unless the mod time has changed.
       */
      struct stat buf;
      if( osFstat(conchFile->h, &buf) ){
        storeLastErrno(pFile, errno);
        return SQLITE_IOERR_LOCK;
      }
      
      if( nTries==1 ){
        conchModTime = buf.st_mtimespec;
        usleep(500000); /* wait 0.5 sec and try the lock again*/
        continue;  
................................................................................
        return SQLITE_BUSY;
      }
      
      if( nTries==2 ){  
        char tBuf[PROXY_MAXCONCHLEN];
        int len = osPread(conchFile->h, tBuf, PROXY_MAXCONCHLEN, 0);
        if( len<0 ){
          storeLastErrno(pFile, errno);
          return SQLITE_IOERR_LOCK;
        }
        if( len>PROXY_PATHINDEX && tBuf[0]==(char)PROXY_CONCHVERSION){
          /* don't break the lock if the host id doesn't match */
          if( 0!=memcmp(&tBuf[PROXY_HEADERLEN], myHostID, PROXY_HOSTIDLEN) ){
            return SQLITE_BUSY;
          }
................................................................................
    int forceNewLockPath = 0;
    
    OSTRACE(("TAKECONCH  %d for %s pid=%d\n", conchFile->h,
             (pCtx->lockProxyPath ? pCtx->lockProxyPath : ":auto:"), getpid()));

    rc = proxyGetHostID(myHostID, &pError);
    if( (rc&0xff)==SQLITE_IOERR ){
      storeLastErrno(pFile, pError);
      goto end_takeconch;
    }
    rc = proxyConchLock(pFile, myHostID, SHARED_LOCK);
    if( rc!=SQLITE_OK ){
      goto end_takeconch;
    }
    /* read the existing conch file */
    readLen = seekAndRead((unixFile*)conchFile, 0, readBuf, PROXY_MAXCONCHLEN);
    if( readLen<0 ){
      /* I/O error: lastErrno set by seekAndRead */
      storeLastErrno(pFile, conchFile->lastErrno);
      rc = SQLITE_IOERR_READ;
      goto end_takeconch;
    }else if( readLen<=(PROXY_HEADERLEN+PROXY_HOSTIDLEN) || 
             readBuf[0]!=(char)PROXY_CONCHVERSION ){
      /* a short read or version format mismatch means we need to create a new 
      ** conch file. 
      */
................................................................................
          /* We are trying for an exclusive lock but another thread in this
           ** same process is still holding a shared lock. */
          rc = SQLITE_BUSY;
        } else {          
          rc = proxyConchLock(pFile, myHostID, EXCLUSIVE_LOCK);
        }
      }else{
        rc = proxyConchLock(pFile, myHostID, EXCLUSIVE_LOCK);
      }
      if( rc==SQLITE_OK ){
        char writeBuffer[PROXY_MAXCONCHLEN];
        int writeSize = 0;
        
        writeBuffer[0] = (char)PROXY_CONCHVERSION;
        memcpy(&writeBuffer[PROXY_HEADERLEN], myHostID, PROXY_HOSTIDLEN);
        if( pCtx->lockProxyPath!=NULL ){
          strlcpy(&writeBuffer[PROXY_PATHINDEX], pCtx->lockProxyPath,
                  MAXPATHLEN);
        }else{
          strlcpy(&writeBuffer[PROXY_PATHINDEX], tempLockPath, MAXPATHLEN);
        }
        writeSize = PROXY_PATHINDEX + strlen(&writeBuffer[PROXY_PATHINDEX]);
        robust_ftruncate(conchFile->h, writeSize);
        rc = unixWrite((sqlite3_file *)conchFile, writeBuffer, writeSize, 0);
        fsync(conchFile->h);
................................................................................
*/
static int proxyGetDbPathForUnixFile(unixFile *pFile, char *dbPath){
#if defined(__APPLE__)
  if( pFile->pMethod == &afpIoMethods ){
    /* afp style keeps a reference to the db path in the filePath field 
    ** of the struct */
    assert( (int)strlen((char*)pFile->lockingContext)<=MAXPATHLEN );
    strlcpy(dbPath, ((afpLockingContext *)pFile->lockingContext)->dbPath,
            MAXPATHLEN);
  } else
#endif
  if( pFile->pMethod == &dotlockIoMethods ){
    /* dot lock style uses the locking context to store the dot lock
    ** file path */
    int len = strlen((char *)pFile->lockingContext) - strlen(DOTLOCK_SUFFIX);
    memcpy(dbPath, (char *)pFile->lockingContext, len + 1);
................................................................................

/*
** This routine handles sqlite3_file_control() calls that are specific
** to proxy locking.
*/
static int proxyFileControl(sqlite3_file *id, int op, void *pArg){
  switch( op ){
    case SQLITE_FCNTL_GET_LOCKPROXYFILE: {
      unixFile *pFile = (unixFile*)id;
      if( pFile->pMethod == &proxyIoMethods ){
        proxyLockingContext *pCtx = (proxyLockingContext*)pFile->lockingContext;
        proxyTakeConch(pFile);
        if( pCtx->lockProxyPath ){
          *(const char **)pArg = pCtx->lockProxyPath;
        }else{
................................................................................
          *(const char **)pArg = ":auto: (not held)";
        }
      } else {
        *(const char **)pArg = NULL;
      }
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_SET_LOCKPROXYFILE: {
      unixFile *pFile = (unixFile*)id;
      int rc = SQLITE_OK;
      int isProxyStyle = (pFile->pMethod == &proxyIoMethods);
      if( pArg==NULL || (const char *)pArg==0 ){
        if( isProxyStyle ){
          /* turn off proxy locking - not supported.  If support is added for
          ** switching proxy locking mode off then it will need to fail if
          ** the journal mode is WAL mode. 
          */
          rc = SQLITE_ERROR /*SQLITE_PROTOCOL? SQLITE_MISUSE?*/;
        }else{
          /* turn off proxy locking - already off - NOOP */
          rc = SQLITE_OK;
        }
      }else{
        const char *proxyPath = (const char *)pArg;