illumos: manual page: copyb.9f

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

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 }