copyb(9F)						   Kernel Functions for Drivers 						 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 allocated 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

SunOS 5.10							    07 Nov 1996 							 copyb(9F)