copyb(9F)

NAME

     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

     copyb() 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  allo-
     cated  message block containing the copied data.  Otherwise,
     it returns a NULL pointer.

CONTEXT

     copyb() can be called from user or interrupt 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