copyb

- copy a message block

Synopsis

#include <sys/stream.h>

mblk_t *copyb(mblk_t *bp);

Interface Level

Architecture independent level 1 (DDI/DKI).

Parameters

bp

Pointer to the message block from which data is copied.

Description

The copyb() function allocates a new message block, and copies into it the data from the block that bp denotes. The new block will be at least as large as the block being copied. copyb() uses the b_rptr and b_wptr members of bp to determine how many bytes to copy.

Return Values

If successful, copyb() returns a pointer to the newly allocated message block containing the copied data. Otherwise, it returns a NULL pointer.

Context

The copyb() function can be called from user, interrupt, or kernel context.

Examples

Example 1 Using copyb

For each message in the list, test to see if the downstream queue is full with the canputnext(9F) function (line 21). If it is not full, use copyb to copy a header message block, and dupmsg(9F) to duplicate the data to be retransmitted. If either operation fails, reschedule a timeout at the next valid interval.

Update the new header block with the correct destination address (line 34), link the message to it (line 35), and send it downstream (line 36). At the end of the list, reschedule this routine.

 1  struct retrans {
 2        mblk_t             *r_mp;
 3        int                r_address;
 4        queue_t            *r_outq;
 5        struct retrans     *r_next;
 6  };
 7  
 8  struct protoheader {
       …
 9     int                    h_address;
       …
10  };
11
12  mblk_t *header;
13
14  void
15  retransmit(struct retrans *ret)
16  {
17       mblk_t *bp, *mp;
18       struct protoheader *php;
19
20       while (ret) {
21         if (!canputnext(ret->r_outq)) {   /* no room */
22                ret = ret->r_next;
23                continue;
24         }
25         bp = copyb(header);               /* copy header msg. block */
26         if (bp == NULL)
27               break;
28         mp = dupmsg(ret->r_mp);           /* duplicate data */
29         if (mp == NULL) {                 /* if unsuccessful */
30              freeb(bp);                   /* free the block */
31              break;
32         }
33         php = (struct protoheader *)bp->b_rptr;
34         php->h_address = ret->r_address;   /* new header */
35         bp->bp_cont = mp;                  /* link the message */
36         putnext(ret->r_outq, bp);          /* send downstream */
37         ret = ret->r_next;
38       }
39       /* reschedule */
40       (void) timeout(retransmit, (caddr_t)ret, RETRANS_TIME);
41  }

See Also

allocb(9F), canputnext(9F), dupmsg(9F)

Writing Device Drivers

STREAMS Programming Guide