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KSTAT(4) Device Drivers Manual KSTAT(4)

kstat — kernel statistics

pseudo-device kstat

The /dev/kstat device exposes kernel statistics (kstats) to userland.

The kstat ioctl(2) calls are provided in <sys/kstat.h>.

With the exception of KSTATIOC_VERSION, the kstat ioctl(2) calls use the kstat_req structure to request or enumerate kernel statistic data from the kernel:

struct kstat_req {
	unsigned int		 ks_rflags;
#define KSTATIOC_F_IGNVER		(1 << 0)
	/* the current version of the kstat subsystem */
	unsigned int		 ks_version;

	uint64_t		 ks_id;

	char			 ks_provider[KSTAT_STRLEN];
	unsigned int		 ks_instance;
	char			 ks_name[KSTAT_STRLEN];
	unsigned int		 ks_unit;

	struct timespec		 ks_created;
	struct timespec		 ks_updated;
	struct timespec		 ks_interval;
	unsigned int		 ks_type;
	unsigned int		 ks_state;

	void			*ks_data;
	size_t			 ks_datalen;
	unsigned int		 ks_dataver;
};

The kstat subsystem increments a version number when a kstat is added to or removed from the subsystem so changes to the set of kstats can be detected. The current version can be requested with a KSTATIOC_VERSION ioctl(2) call. Programs requesting a kstat with the other ioctl(2) calls pass the current version in ks_version, and if the version differs an error will be returned with errno(2) set to EINVAL to indicate that the program should resynchronise with the kernel subsystem. This check can be disabled by setting the KSTATIOC_F_IGNVER flag in ks_rflags.

A kstat is identified by a 64bit number, or the combination of a provider name, instance number, name, and unit number.

Unless ks_data is NULL, the kstat subsystem will request an update of the statistics data and copy up to ks_datalen bytes of it to the specified memory.

The kstat ioctl(2) calls are as follows:

unsigned int
Get the current version of the set of kernel statistics.
struct kstat_req
Request the kstat identified by ks_id.
struct kstat_req
Request a kstat with an identifier greater than or equal to ks_id.
struct kstat_req
Request the kstat identified by ks_provider, ks_instance, ks_name, and ks_unit.
struct kstat_req
Request the kstat or next kstat from the set of kstats ordered by ks_provider, ks_instance, ks_name, and ks_unit.
struct kstat_req
Request the kstat identified by ks_name, ks_unit, ks_provider, and ks_instance.
struct kstat_req
Request the kstat or next kstat from the set of kstats ordered by ks_name, ks_unit, ks_provider, and ks_instance.

Upon the successful request of a kstat, the kstat driver will update the kstat_req structure with current information about that kstat. Updated fields include:

ks_version
The current version of the kstat subsystem.
ks_id
The 64bit unique identifier for the requested kstat. A kstat can be requested using this identifier and the KSTATIOC_FIND_ID ioctl(2) call.
ks_provider, ks_instance, ks_name, ks_unit
The fully specified identifier of the kstat. A kstat can be requested using these identifiers with the KSTATIOC_FIND_NAME and KSTATIOC_FIND_PROVIDER ioctl(2) calls. Groups of kstats with the same identifier or name can be enumerated or requested with the KSTATIOC_NFIND_NAME and KSTATIOC_NFIND_PROVIDER ioctl(2) calls without having to fetch the entire set of kstats and filtering them.
ks_created
The system uptime when the kstat was created and added to the kstat subsystem.
ks_updated
The system uptime at which the kstat data payload was last updated. A kstat provider may update data when requested, or report when data was last updated by some other process. ks_updated can by used by a program to identify if data has been updated, or for calculating rates of changes of values between updates.
ks_type
The type or structure of the data payload. Currently supported types are documented in kstat_create(9).
ks_datalen
The amount of data the kstat provides in bytes. When requesting kstat data, the program specifies the amount of space available at ks_data by setting this variable.

/dev/kstat
 

kstat_create(9), kstat_kv_init(9)

The kstat device appeared in OpenBSD 6.8.

January 14, 2022 OpenBSD-current