kstat(9s) [sunos man page]

kstat(9S)						    Data Structures for Drivers 						 kstat(9S)

NAME

       kstat - kernel statistics structure

SYNOPSIS

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

INTERFACE LEVEL

       Solaris DDI specific (Solaris DDI)

DESCRIPTION

       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  struc-
       ture in any other manner.

       After  allocation,  the	driver	should	perform  any further initialization needed before calling kstat_install(9F) to actually export the
       kstat.

STRUCTURE MEMBERS

       void	 *ks_data;	       /* kstat type-specific data */
       ulong_t	 ks_ndata;	       /* # of type-specific 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 this 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.

SEE ALSO

       kstat_create(9F)

       Writing Device Drivers

SunOS 5.10							    4 Apr 1994								 kstat(9S)

Check Out this Related Man Page

ks_update(9E)							Driver Entry Points						     ks_update(9E)

NAME

       ks_update - dynamically update kstats

SYNOPSIS

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

       int prefix_ks_update(kstat_t *ksp, int rw);

INTERFACE LEVEL

       Solaris DDI specific (Solaris DDI)

PARAMETERS

       ksp     Pointer to a kstat(9S) structure.

       rw      Read/Write flag. Possible values are

	       KSTAT_READ      Update kstat structure statistics from the driver.

	       KSTAT_WRITE     Update driver statistics from the kstat structure.

DESCRIPTION

       The  kstat  mechanism  allows  for  an optional ks_update() function to update kstat data.  This is useful for drivers where the underlying
       device keeps cheap hardware statistics, but extraction is expensive.  Instead of constantly keeping the kstat data section up to date,  the
       driver  can  supply  a  ks_update()  function  which updates the kstat's data section on demand. To take advantage of this feature, set the
       ks_update field before calling kstat_install(9F).

       The ks_update() function must have the following structure:

	 static int
	 xx_kstat_update(kstat_t *ksp, int rw)
	 {
	      if (rw == KSTAT_WRITE) {
		   /* update the native stats from ksp->ks_data */
		   /* return EACCES if you don't support this */
	      } else {
		   /* update ksp->ks_data from the native stats */
	      }
	      return(0);
	 }

       In general, the ks_update() routine may need to refer to provider-private data; for example, it may need a pointer to  the  provider's  raw
       statistics.  The ks_private field is available for this purpose.   Its use is entirely at the provider's discretion.

       No kstat locking should be done inside the ks_update() routine.	The caller will already be holding the kstat's	ks_lock (to ensure consis-
       tent data) and will prevent the kstat from being removed.

RETURN VALUES

       ks_update() should return

       0	  For success.

       EACCES	  If KSTAT_WRITE is not allowed.

       EIO	  For any other error.

SEE ALSO

       kstat_create(9F), kstat_install(9F), kstat(9S)

       Writing Device Drivers

SunOS 5.11							    27 May 1994 						     ks_update(9E)

Linux and UNIX Man Pages

kstat(9s) [sunos man page]

Check Out this Related Man Page