Tribblix: manual page: ddi_soft

DDI_SOFT_STATE(9F) Kernel Functions for Drivers DDI_SOFT_STATE(9F)

NAME

ddi_soft_state, ddi_get_soft_state, ddi_soft_state_fini,
ddi_soft_state_free, ddi_soft_state_init, ddi_soft_state_zalloc -
driver soft state utility routines

SYNOPSIS

#include <sys/ddi.h>
#include <sys/sunddi.h>

void *ddi_get_soft_state(void *state, int item);

void ddi_soft_state_fini(void **state_p);

void ddi_soft_state_free(void *state, int item);

int ddi_soft_state_init(void **state_p, size_t size, size_t n_items);

int ddi_soft_state_zalloc(void *state, int item);

INTERFACE LEVEL

illumos DDI specific (illumos DDI).

PARAMETERS

state_p
Address of the opaque state pointer which will be
initialized by ddi_soft_state_init() to point to
implementation dependent data.

size
Size of the item which will be allocated by subsequent
calls to ddi_soft_state_zalloc().

n_items
A hint of the number of items which will be preallocated;
zero is allowed.

state
An opaque pointer to implementation-dependent data that
describes the soft state.

item
The item number for the state structure; usually the
instance number of the associated devinfo node.

DESCRIPTION

Most device drivers maintain state information with each instance of
the device they control; for example, a soft copy of a device control
register, a mutex that must be held while accessing a piece of
hardware, a partition table, or a unit structure. These utility
routines are intended to help device drivers manage the space used by
the driver to hold such state information.

For example, if the driver holds the state of each instance in a
single state structure, these routines can be used to dynamically
allocate and deallocate a separate structure for each instance of the
driver as the instance is attached and detached.

To use the routines, the driver writer needs to declare a state
pointer, state_p, which the implementation uses as a place to hang a
set of per-driver structures; everything else is managed by these
routines.

The routine ddi_soft_state_init() is usually called in the driver's
_init(9E) routine to initialize the state pointer, set the size of
the soft state structure, and to allow the driver to pre-allocate a
given number of such structures if required.

The routine ddi_soft_state_zalloc() is usually called in the driver's
attach(9E) routine. The routine is passed an item number which is
used to refer to the structure in subsequent calls to
ddi_get_soft_state() and ddi_soft_state_free(). The item number is
usually just the instance number of the devinfo node, obtained with
ddi_get_instance(9F). The routine attempts to allocate space for the
new structure, and if the space allocation was successful,
DDI_SUCCESS is returned to the caller. Returned memory is zeroed.

A pointer to the space previously allocated for a soft state
structure can be obtained by calling ddi_get_soft_state() with the
appropriate item number.

The space used by a given soft state structure can be returned to the
system using ddi_soft_state_free(). This routine is usually called
from the driver's detach(9E) entry point.

The space used by all the soft state structures allocated on a given
state pointer, together with the housekeeping information used by the
implementation can be returned to the system using
ddi_soft_state_fini(). This routine can be called from the driver's
_fini(9E) routine.

The ddi_soft_state_zalloc(), ddi_soft_state_free() and
ddi_get_soft_state() routines coordinate access to the underlying
data structures in an MT-safe fashion, thus no additional locks
should be necessary.

RETURN VALUES

ddi_get_soft_state()

NULL
The requested state structure was not allocated at the
time of the call.

pointer
The pointer to the state structure.

ddi_soft_state_init()

0
The allocation was successful.

EINVAL
Either the size parameter was zero, or the state_p
parameter was invalid.

ddi_soft_state_zalloc()

DDI_SUCCESS
The allocation was successful.

DDI_FAILURE
The routine failed to allocate the storage required;
either the state parameter was invalid, the item
number was negative, or an attempt was made to
allocate an item number that was already allocated.

CONTEXT

The ddi_soft_state_init() and ddi_soft_state_alloc() functions can be
called from user or kernel context only, since they may internally
call kmem_zalloc(9F) with the KM_SLEEP flag.

The ddi_soft_state_fini(), ddi_soft_state_free() and
ddi_get_soft_state() routines can be called from any driver context.

EXAMPLES

Example 1: Creating and Removing Data Structures

The following example shows how the routines described above can be
used in terms of the driver entry points of a character-only driver.
The example concentrates on the portions of the code that deal with
creating and removing the driver's data structures.

typedef struct {
volatile caddr_t *csr; /* device registers */
kmutex_t csr_mutex; /* protects 'csr' field */
unsigned int state;
dev_info_t *dip; /* back pointer to devinfo */
} devstate_t;
static void *statep;

int
_init(void)
{
int error;

error = ddi_soft_state_init(&statep, sizeof (devstate_t), 0);
if (error != 0)
return (error);
if ((error = mod_install(&modlinkage)) != 0)
ddi_soft_state_fini(&statep);
return (error);
}

int
_fini(void)
{
int error;

if ((error = mod_remove(&modlinkage)) != 0)
return (error);
ddi_soft_state_fini(&statep);
return (0);
}

static int
xxattach(dev_info_t *dip, ddi_attach_cmd_t cmd)
{
int instance;
devstate_t *softc;

switch (cmd) {
case DDI_ATTACH:
instance = ddi_get_instance(dip);
if (ddi_soft_state_zalloc(statep, instance) != DDI_SUCCESS)
return (DDI_FAILURE);
softc = ddi_get_soft_state(statep, instance);
softc->dip = dip;
...
return (DDI_SUCCESS);
default:
return (DDI_FAILURE);
}
}

static int
xxdetach(dev_info_t *dip, ddi_detach_cmd_t cmd)
{
int instance;

switch (cmd) {

case DDI_DETACH:
instance = ddi_get_instance(dip);
...
ddi_soft_state_free(statep, instance);
return (DDI_SUCCESS);

default:
return (DDI_FAILURE);
}
}

static int
xxopen(dev_t *devp, int flag, int otyp, cred_t *cred_p)
{
devstate_t *softc;
int instance;

instance = getminor(*devp);
if ((softc = ddi_get_soft_state(statep, instance)) == NULL)
return (ENXIO);
...
softc->state |= XX_IN_USE;
...
return (0);
}

WARNINGS

There is no attempt to validate the item parameter given to
ddi_soft_state_zalloc() other than it must be a positive signed
integer. Therefore very large item numbers may cause the driver to
hang forever waiting for virtual memory resources that can never be
satisfied.

NOTES

If necessary, a hierarchy of state structures can be constructed by
embedding state pointers in higher order state structures.

DIAGNOSTICS

All of the messages described below usually indicate bugs in the
driver and should not appear in normal operation of the system.

WARNING: ddi_soft_state_zalloc: bad handle
WARNING: ddi_soft_state_free: bad handle
WARNING: ddi_soft_state_fini: bad handle

The implementation-dependent information kept in the state variable
is corrupt.

WARNING: ddi_soft_state_free: null handle
WARNING: ddi_soft_state_fini: null handle

The routine has been passed a null or corrupt state pointer. Check
that ddi_soft_state_init() has been called.

WARNING: ddi_soft_state_free: item %d not in range [0..%d]

The routine has been asked to free an item which was never allocated.
The message prints out the invalid item number and the acceptable
range.

January 16, 2006 DDI_SOFT_STATE(9F)