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


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


#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);


illumos DDI specific (illumos DDI).


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

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

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

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

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


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

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



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

The pointer to the state structure.


The allocation was successful.

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


The allocation was successful.

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.


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.


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 error;

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

int error;

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

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

switch (cmd) {
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);
return (DDI_FAILURE);

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

switch (cmd) {

instance = ddi_get_instance(dip);
ddi_soft_state_free(statep, instance);
return (DDI_SUCCESS);

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);


_fini(9E), _init(9E), attach(9E), detach(9E), ddi_get_instance(9F),
getminor(9F), kmem_zalloc(9F)

Writing Device Drivers


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.


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


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

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.

illumos January 16, 2006 DDI_SOFT_STATE(9F)