mkiocb(9F) Kernel Functions for Drivers mkiocb(9F)NAMEmkiocb - allocates a STREAMS ioctl block for M_IOCTL messages in the
kernel.
SYNOPSIS
#include <sys/stream.h>
mblk_t *mkiocb(uint_t command);
INTERFACE LEVEL
Solaris DDI specific (Solaris DDI).
PARAMETERS
command ioctl command for the ioc_cmd field.
DESCRIPTION
STREAMS modules or drivers might need to issue an ioctl to a lower mod‐
ule or driver. The mkiocb() function tries to allocate (using
allocb(9F)) a STREAMS M_IOCTL message block (iocblk(9S)). Buffer allo‐
cation fails only when the system is out of memory. If no buffer is
available, the qbufcall(9F) function can help a module recover from an
allocation failure.
The mkiocb function returns a mblk_t structure which is large enough to
hold any of the ioctl messages (iocblk(9S), copyreq(9S) or copy‐
resp(9S)), and has the following special properties:
b_wptr Set to b_rptr + sizeof(struct iocblk).
b_cont Set to NULL..
b_datap->db_type Set to M_IOCTL.
The fields in the iocblk structure are initialized as follows:
ioc_cmd Set to the command value passed in.
ioc_id Set to a unique identifier.
ioc_cr Set to point to a credential structure encoding the maxi‐
mum system privilege and which does not need to be freed
in any fashion.
ioc_count Set to 0.
ioc_rval Set to 0.
ioc_error Set to 0.
ioc_flags Set to IOC_NATIVE to reflect that this is native to the
running kernel.
RETURN VALUES
Upon success, the mkiocb() function returns a pointer to the allocated
mblk_t of type M_IOCTL.
On failure, it returns a null pointer.
CONTEXT
The mkiocb() function can be called from user, interrupt, or kernel
context.
EXAMPLES
Example 1 M_IOCTL Allocation
The first example shows an M_IOCTL allocation with the ioctl command
TEST_CMD. If the iocblk(9S) cannot be allocated, NULL is returned,
indicating an allocation failure (line 5). In line 11, the putnext(9F)
function is used to send the message downstream.
1 test_function(queue_t *q, test_info_t *testinfo)
2 {
3 mblk_t *mp;
4
5 if ((mp = mkiocb(TEST_CMD)) == NULL)
6 return (0);
7
8 /* save off ioctl ID value */
9 testinfo->xx_iocid = ((struct iocblk *)mp->b_rptr)->ioc_id;
10
11 putnext(q, mp); /* send message downstream */
12 return (1);
13 }
Example 2 The ioctl ID Value
During the read service routine, the ioctl ID value for M_IOCACK or
M_IOCNAK should equal the ioctl that was previously sent by this module
before processing.
1 test_lrsrv(queue_t *q)
2 {
3 ...
4
5 switch (DB_TYPE(mp)) {
6 case M_IOCACK:
7 case M_IOCNAK:
8 /* Does this match the ioctl that this module sent */
9 ioc = (struct iocblk*)mp->b_rptr;
10 if (ioc->ioc_id == testinfo->xx_iocid) {
11 /* matches, so process the message */
12 ...
13 freemsg(mp);
14 }
15 break;
16 }
17 ...
18 }
Example 3 An iocblk Allocation Which Fails
The next example shows an iocblk allocation which fails. Since the open
routine is in user context, the caller may block using qbufcall(9F)
until memory is available.
1 test_open(queue_t *q, dev_t devp, int oflag, int sflag,
cred_t *credp)
2 {
3 while ((mp = mkiocb(TEST_IOCTL)) == NULL) {
4 int id;
5
6 id = qbufcall(q, sizeof (union ioctypes), BPRI_HI,
7 dummy_callback, 0);
8 /* Handle interrupts */
9 if (!qwait_sig(q)) {
10 qunbufcall(q, id);
11 return (EINTR);
12 }
13 }
14 putnext(q, mp);
15 }
SEE ALSOallocb(9F), putnext(9F), qbufcall(9F), qwait_sig(9F), copyreq(9S),
copyresp(9S), iocblk(9S)
Writing Device Drivers
STREAMS Programming Guide
WARNINGS
It is the module's responsibility to remember the ID value of the
M_IOCTL that was allocated. This will ensure proper cleanup and ID
matching when the M_IOCACK or M_IOCNAK is received.
SunOS 5.11 16 Jan 2006 mkiocb(9F)
