NAME

pullupmsg - concatenate bytes in a message

SYNOPSIS

#include <sys/stream.h>
int pullupmsg(mblk_t *mp, ssize_t len);

INTERFACE LEVEL

Architecture independent level 1 (DDI/DKI).

PARAMETERS

Pointer to the message whose blocks are to be concatenated. mblk_t is an instance of the msgb(9S) structure.

len

Number of bytes to concatenate.

DESCRIPTION

The pullupmsg() function tries to combine multiple data blocks into a single block. pullupmsg() concatenates and aligns the first len data bytes of the message pointed to by mp. If len equals -1, all data are concatenated. If len bytes of the same message type cannot be found, pullupmsg() fails and returns 0.

RETURN VALUES

On success, 1 is returned; on failure, 0 is returned.

CONTEXT

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

EXAMPLES

Example 1 Using pullupmsg()

This is a driver write srv(9E) (service) routine for a device that does not support scatter/gather DMA. For all M_DATA messages, the data will be transferred to the device with DMA. First, try to pull up the message into one message block with the pullupmsg() function (line 12). If successful, the transfer can be accomplished in one DMA job. Otherwise, it must be done one message block at a time (lines 19-22). After the data has been transferred to the device, free the message and continue processing messages on the queue.



 1 xxxwsrv(q)


 2    queue_t *q;


 3 {


 4	    mblk_t *mp;


 5	    mblk_t *tmp;


 6	    caddr_t dma_addr;


 7     ssize_t dma_len;


 8


 9	    while ((mp = getq(q)) != NULL) {
10	            switch (mp->b_datap->db_type) {
11             case M_DATA:
12	                   if (pullupmsg(mp, -1)) {
13                            dma_addr = vtop(mp->b_rptr);
14	                           dma_len = mp->b_wptr - mp->b_rptr;
15	                           xxx_do_dma(dma_addr, dma_len);
16	                           freemsg(mp);
17	                           break;
18	                   }
19	                   for (tmp = mp; tmp; tmp = tmp->b_cont) {
20                            dma_addr = vtop(tmp->b_rptr);
21                            dma_len = tmp->b_wptr - tmp->b_rptr;
22                            xxx_do_dma(dma_addr, dma_len);
23                    }
24	                   freemsg(mp);
25	                   break;
	            ...
26		        }
27	    }
28 }

NOTES

The pullupmsg() function is not included in the DKI and will be removed from the system in a future release. Device driver writers are strongly encouraged to use msgpullup(9F) instead of pullupmsg().