嗯，把每天看过的源码记录下来。希望最终能有个好结果 不要漫无目的的看下去..

今天看了有minix系统的mini_send,mini_receive,mini_notify

感觉系统对标志位的操作(bit operation) 实在很厉害..配合宏定义和magic numbers;

dst_ptr->p_rts_flags & (RECEIVING | SENDING)) == RECEIVING

注意这这种使用方法..

以及十分严格的检测机制（死锁）等.

不仅十分节约空间 且十分明了.

/*===========================================================================*
 *				mini_send				     * 
 *===========================================================================*/
PRIVATE int mini_send(caller_ptr, dst, m_ptr, flags)
register struct proc *caller_ptr;	/* who is trying to send a message? */
int dst;				/* to whom is message being sent? */
message *m_ptr;				/* pointer to message buffer */
unsigned flags;				/* system call flags */
{
/* Send a message from 'caller_ptr' to 'dst'. If 'dst' is blocked waiting
 * for this message, copy the message to it and unblock 'dst'. If 'dst' is
 * not waiting at all, or is waiting for another source, queue 'caller_ptr'.
 */
  register struct proc *dst_ptr = proc_addr(dst);
  register struct proc **xpp;
  register struct proc *xp;
/*Check for deadlock by 'caller_ptr' and 'dest' sending to each other. */
xp = dst_ptr;
while(xp->p_rts_flags & SENDING){		 /* check while sending */
	xp = proc_addr(xp->p_sendto);		 /* get xp's destination */
	if(xp == caller_ptr) return(ELOCKED);/*deadlock if cyclic */
}
  /* Check if 'dst' is blocked waiting for this message. The destination's 
   * SENDING flag may be set when its SENDREC call blocked while sending.  
   */															 		  /* SUNUS NOTE*/
  if ( (dst_ptr->p_rts_flags & (RECEIVING | SENDING)) == RECEIVING && /* make sure that  SENDING flag is 0*/
       (dst_ptr->p_getfrom == ANY || dst_ptr->p_getfrom == caller_ptr->p_nr)) {
	/* Destination is indeed waiting for this message. */
	CopyMess(caller_ptr->p_nr, caller_ptr, m_ptr, dst_ptr,
		 dst_ptr->p_messbuf);
	if ((dst_ptr->p_rts_flags &= ~RECEIVING) == 0) enqueue(dst_ptr);
  } else if ( ! (flags & NON_BLOCKING)) {
	/* Destination is not waiting.  Block and dequeue caller. */
	caller_ptr->p_messbuf = m_ptr;
	if (caller_ptr->p_rts_flags == 0) dequeue(caller_ptr);
	caller_ptr->p_rts_flags |= SENDING;
	caller_ptr->p_sendto = dst;

	/* Process is now blocked.  Put in on the destination's queue. */
	xpp = &dst_ptr->p_caller_q;		/* find end of list */
	while (*xpp != NIL_PROC) xpp = &(*xpp)->p_q_link;	
	*xpp = caller_ptr;			/* add caller to end */
	caller_ptr->p_q_link = NIL_PROC;	/* mark new end of list */
  } else {
	return(ENOTREADY);
  }
  return(OK);
}

/*===========================================================================*
 *				mini_receive				     * 
 *===========================================================================*/
PRIVATE int mini_receive(caller_ptr, src, m_ptr, flags)
register struct proc *caller_ptr;	/* process trying to get message */
int src;				/* which message source is wanted */
message *m_ptr;				/* pointer to message buffer */
unsigned flags;				/* system call flags */
{
/* A process or task wants to get a message.  If a message is already queued,
 * acquire it and deblock the sender.  If no message from the desired source
 * is available block the caller, unless the flags don't allow blocking.  
 */
  register struct proc **xpp;
  register struct notification **ntf_q_pp;
  message m;
  int bit_nr;
  sys_map_t *map;
  bitchunk_t *chunk;
  int i, src_id, src_proc_nr;

  /* Check to see if a message from desired source is already available.
   * The caller's SENDING flag may be set if SENDREC couldn't send. If it is
   * set, the process should be blocked.
   */
  if (!(caller_ptr->p_rts_flags & SENDING)) {

    /* Check if there are pending notifications, except for SENDREC. */
    if (! (priv(caller_ptr)->s_flags & SENDREC_BUSY)) {

        map = &priv(caller_ptr)->s_notify_pending;
        for (chunk=&map->chunk[0]; chunk<&map->chunk[NR_SYS_CHUNKS]; chunk++) {

            /* Find a pending notification from the requested source. */ 
            if (! *chunk) continue; 			/* no bits in chunk */
            for (i=0; ! (*chunk & (1<<i)); ++i) {} 	/* look up the bit */
            src_id = (chunk - &map->chunk[0]) * BITCHUNK_BITS + i;
            if (src_id >= NR_SYS_PROCS) break;		/* out of range */
            src_proc_nr = id_to_nr(src_id);		/* get source proc */
#if DEBUG_ENABLE_IPC_WARNINGS
	    if(src_proc_nr == NONE) {
		kprintf("mini_receive: sending notify from NONE\n");
	    }
#endif
            if (src!=ANY && src!=src_proc_nr) continue;	/* source not ok */
            *chunk &= ~(1 << i);			/* no longer pending */

            /* Found a suitable source, deliver the notification message. */
	    BuildMess(&m, src_proc_nr, caller_ptr);	/* assemble message */
            CopyMess(src_proc_nr, proc_addr(HARDWARE), &m, caller_ptr, m_ptr);
            return(OK);					/* report success */
        }
    }

    /* Check caller queue. Use pointer pointers to keep code simple. */
    xpp = &caller_ptr->p_caller_q;
    while (*xpp != NIL_PROC) {
        if (src == ANY || src == proc_nr(*xpp)) {
	    /* Found acceptable message. Copy it and update status. */
	    CopyMess((*xpp)->p_nr, *xpp, (*xpp)->p_messbuf, caller_ptr, m_ptr);
            if (((*xpp)->p_rts_flags &= ~SENDING) == 0) enqueue(*xpp);
            *xpp = (*xpp)->p_q_link;		/* remove from queue */
            return(OK);				/* report success */
	}
	xpp = &(*xpp)->p_q_link;		/* proceed to next */
    }
  }

  /* No suitable message is available or the caller couldn't send in SENDREC. 
   * Block the process trying to receive, unless the flags tell otherwise.
   */
  if ( ! (flags & NON_BLOCKING)) {
      caller_ptr->p_getfrom = src;		
      caller_ptr->p_messbuf = m_ptr;
      if (caller_ptr->p_rts_flags == 0) dequeue(caller_ptr);
      caller_ptr->p_rts_flags |= RECEIVING;		
      return(OK);
  } else {
      return(ENOTREADY);
  }
}

/*===========================================================================*
 *				mini_notify				     * 
 *===========================================================================*/
PRIVATE int mini_notify(caller_ptr, dst)
register struct proc *caller_ptr;	/* sender of the notification */
int dst;				/* which process to notify */
{
  register struct proc *dst_ptr = proc_addr(dst);
  int src_id;				/* source id for late delivery */
  message m;				/* the notification message */

  /* Check to see if target is blocked waiting for this message. A process 
   * can be both sending and receiving during a SENDREC system call.
   */
  if ((dst_ptr->p_rts_flags & (RECEIVING|SENDING)) == RECEIVING && /* Make sure  SENDING bit == 0*/
      ! (priv(dst_ptr)->s_flags & SENDREC_BUSY) &&
      (dst_ptr->p_getfrom == ANY || dst_ptr->p_getfrom == caller_ptr->p_nr)) {

      /* Destination is indeed waiting for a message. Assemble a notification 
       * message and deliver it. Copy from pseudo-source HARDWARE, since the
       * message is in the kernel's address space.
       */ 
      BuildMess(&m, proc_nr(caller_ptr), dst_ptr);
      CopyMess(proc_nr(caller_ptr), proc_addr(HARDWARE), &m, 
          dst_ptr, dst_ptr->p_messbuf);
      dst_ptr->p_rts_flags &= ~RECEIVING;	/* deblock destination */
      if (dst_ptr->p_rts_flags == 0) enqueue(dst_ptr);
      return(OK);
  } 

  /* Destination is not ready to receive the notification. Add it to the 
   * bit map with pending notifications. Note the indirectness: the system id 
   * instead of the process number is used in the pending bit map.
   */ 
  src_id = priv(caller_ptr)->s_id;
  set_sys_bit(priv(dst_ptr)->s_notify_pending, src_id); 
  return(OK);
}

希望有一起学习minix的同学联系我 大家一起进步～