kstat - kernel statistics structure
#include <sys/types.h>
#include <sys/kstat.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>
illumos DDI specific (illumos DDI)
Each kernel statistic (kstat) exported by device drivers
consists of a header section and a data section. The kstat structure
is the header portion of the statistic.
A driver receives a pointer to a kstat structure from a
successful call to kstat_create(9F). Drivers should never allocate a
kstat structure in any other manner.
After allocation, the driver should perform any further
initialization needed before calling kstat_install(9F) to actually
export the kstat.
void *ks_data; /* kstat type-specif. data */
ulong_t ks_ndata; /* # of type-specif. data
records */
ulong_t ks_data_size; /* total size of kstat data
section */
int (*ks_update)(struct kstat *, int);
void *ks_private; /* arbitrary provider-private
data */
void *ks_lock; /* protects kstat's data */
The members of the kstat structure available to examine or
set by a driver are as follows:
ks_data
Points to the data portion of the
kstat. Either
allocated by
kstat_create(9F) for the drivers use, or by the driver if
it is using virtual
kstats.
ks_ndata
The number of data records in this
kstat. Set by
the
ks_update(9E) routine.
ks_data_size
The amount of data pointed to by
ks_data. Set by
the
ks_update(9E) routine.
ks_update
Pointer to a routine that dynamically updates
kstat. This is useful for drivers where the underlying device keeps
cheap hardware statistics, but where extraction is expensive. Instead of
constantly keeping the
kstat data section up to date, the driver can
supply a
ks_update(9E) function that updates the
kstat data
section on demand. To take advantage of this feature, set the
ks_update
field before calling
kstat_install(9F).
ks_private
Is a private field for the driver's use. Often used in
ks_update(9E).
ks_lock
Is a pointer to a mutex that protects this kstat.
kstat data sections are optionally protected by the per-kstat
ks_lock. If ks_lock is non-NULL, kstat clients
(such as /dev/kstat) will acquire this lock for all of their operations
on that kstat. It is up to the kstat provider to decide whether
guaranteeing consistent data to kstat clients is sufficiently important
to justify the locking cost. Note, however, that most statistic updates
already occur under one of the provider's mutexes. If the provider sets
ks_lock to point to that mutex, then kstat data locking is free.
ks_lock is really of type (kmutex_t*) and is declared as
(void*) in the kstat header. That way, users do not have to be
exposed to all of the kernel's lock-related data structures.