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Given a pointer to a queue (q) and an error
number (err), the send_error()
routine sends an M_ERROR type
message to the stream head.
If a message cannot be allocated, NULL
is returned, indicating an allocation failure (line 8). Otherwise, the message
type is set to M_ERROR (line
10). Line 11 increments the write pointer (bp->b_wptr)
by the size (one byte) of the data in the message.
A message must be sent up the read side of the stream to arrive at
the stream head. To determine whether q points to
a read queue or to a write queue, the q->q_flag member
is tested to see if QREADR is
set (line 13). If it is not set, q points to a write
queue, and in line 14 the RD(9F) function
is used to find the corresponding read queue. In line 15, the putnext(9F)
function is used to send the message upstream, returning 1
if successful.
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1 send_error(q,err)
2 queue_t *q;
3 unsigned char err;
4 {
5 mblk_t *bp;
6
7 if ((bp = allocb(1, BPRI_HI)) == NULL) /* allocate msg. block */
8 return(0);
9
10 bp->b_datap->db_type = M_ERROR; /* set msg type to M_ERROR */
11 *bp->b_wptr++ = err; /* increment write pointer */
12
13 if (!(q->q_flag & QREADR)) /* if not read queue */
14 q = RD(q); /* get read queue */
15 putnext(q,bp); /* send message upstream */
16 return(1);
17 }
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