esbbcall(9F) Kernel Functions for Drivers esbbcall(9F)NAME
esbbcall - call function when buffer is available
SYNOPSIS
#include <sys/stream.h>
bufcall_id_t esbbcall(uint_t pri, void (*func)(void *arg), void (arg));
INTERFACE LEVEL
Architecture independent level 1 (DDI/DKI).
PARAMETERS
pri Priority of allocation request (to be used by allocb(9F) function, called by esbbcall())
func Function to be called when buffer becomes available.
arg Argument to func.
DESCRIPTION
esbbcall(), like bufcall(9F), serves as a timeout(9F) call of indeterminate length. If esballoc(9F) is unable to allocate a message and
data block header to go with its externally supplied data buffer, esbbcall() can be used to schedule the routine func, to be called with
the argument arg when a buffer becomes available. func may be a routine that calls esballoc(9F) or it may be another kernel function.
RETURN VALUES
On success, a bufcall IDis returned. On failure, 0 is returned. The value returned from a successful call should be saved for possible
future use with unbufcall() should it become necessary to cancel the esbbcall() request (as at driver close time).
CONTEXT
esbbcall() can be called from user or interrupt context.
SEE ALSO allocb(9F), bufcall(9F), esballoc(9F), timeout(9F), datab(9S), unbufcall(9F)
Writing Device Drivers STREAMS Programming Guide
SunOS 5.10 18 Feb 98 esbbcall(9F)
Check Out this Related Man Page
bufcall(9F) Kernel Functions for Drivers bufcall(9F)NAME
bufcall - call a function when a buffer becomes available
SYNOPSIS
#include <sys/types.h>
#include <sys/stream.h>
bufcall_id_t bufcall(size_t size, uint_t pri, void (*func)(void *arg), void *arg);
INTERFACE LEVEL
Architecture independent level 1 (DDI/DKI).
PARAMETERS
size Number of bytes required for the buffer.
pri Priority of the allocb(9F) allocation request (not used).
func Function or driver routine to be called when a buffer becomes available.
arg Argument to the function to be called when a buffer becomes available.
DESCRIPTION
bufcall() serves as a timeout(9F) call of indeterminate length. When a buffer allocation request fails, bufcall() can be used to schedule
the routine func, to be called with the argument arg when a buffer becomes available. func may call allocb() or it may do something else.
RETURN VALUES
If successful, bufcall() returns a bufcall ID that can be used in a call to unbufcall() to cancel the request. If the bufcall() scheduling
fails, func is never called and 0 is returned.
CONTEXT
bufcall() can be called from user or interrupt context.
EXAMPLES
Example 1: Calling a function when a buffer becomes available:
The purpose of this srv(9E) service routine is to add a header to all M_DATA messages. Service routines must process all messages on their
queues before returning, or arrange to be rescheduled
While there are messages to be processed (line 13), check to see if it is a high priority message or a normal priority message that can be
sent on (line 14). Normal priority message that cannot be sent are put back on the message queue (line 34). If the message was a high pri-
ority one, or if it was normal priority and canputnext(9F) succeeded, then send all but M_DATA messages to the next module with putnext(9F)
(line 16).
For M_DATA messages, try to allocate a buffer large enough to hold the header (line 18). If no such buffer is available, the service rou-
tine must be rescheduled for a time when a buffer is available. The original message is put back on the queue (line 20) and bufcall (line
21) is used to attempt the rescheduling. It will succeed if the rescheduling succeeds, indicating that qenable will be called subsequently
with the argument q once a buffer of the specified size (sizeof (struct hdr)) becomes available. If it does, qenable(9F) will put q on the
list of queues to have their service routines called. If bufcall() fails, timeout(9F) (line 22) is used to try again in about a half sec-
ond.
If the buffer allocation was successful, initialize the header (lines 25-28), make the message type M_PROTO (line 29), link the M_DATA mes-
sage to it (line 30), and pass it on (line 31).
Note that this example ignores the bookkeeping needed to handle bufcall() and timeout(9F) cancellation for ones that are still outstanding
at close time.
1 struct hdr {
2 unsigned int h_size;
3 int h_version;
4 };
5
6 void xxxsrv(q)
7 queue_t *q;
8 {
9 mblk_t *bp;
10 mblk_t *mp;
11 struct hdr *hp;
12
13 while ((mp = getq(q)) != NULL) { /* get next message */
14 if (mp->b_datap->db_type >= QPCTL || /* if high priority */
canputnext(q)) { /* normal & can be passed */
15 if (mp->b_datap->db_type != M_DATA)
16 putnext(q, mp); /* send all but M_DATA */
17 else {
18 bp = allocb(sizeof(struct hdr), BPRI_LO);
19 if (bp == NULL) { /* if unsuccessful */
20 putbq(q, mp); /* put it back */
21 if (!bufcall(sizeof(struct hdr), BPRI_LO,
qenable, q)) /* try to reschedule */
22 timeout(qenable, q, drv_usectohz(500000));
23 return(0);
24 }
25 hp = (struct hdr *)bp->b_wptr;
26 hp->h_size = msgdsize(mp); /* initialize header */
27 hp->h_version = 1;
28 bp->b_wptr += sizeof(struct hdr);
29 bp->b_datap->db_type = M_PROTO; /* make M_PROTO */
30 bp->b_cont = mp; /* link it */
31 putnext(q, bp); /* pass it on */
32 }
33 } else { /* normal priority, canputnext failed */
34 putbq(q, mp); /* put back on the message queue */
35 return(0);
36 }
37 }
return(0);
38 }
SEE ALSO srv(9E), allocb(9F), canputnext(9F), esballoc(9F), esbbcall(9F), putnext(9F), qenable(9F), testb(9F), timeout(9F), unbufcall(9F)
Writing Device Drivers
STREAMS Programming Guide
WARNINGS
Even when func is called by bufcall(), allocb(9F) can fail if another module or driver had allocated the memory before func was able to
call allocb(9F).
SunOS 5.10 13 Feb 1998 bufcall(9F)