update the kstat header chain

Kernel Statistics Library (libkstat, -lkstat)

#include <kstat.h>

kstat_chain_update(kstat_ctl_t *kc);

The kstat_chain_update() function brings the user's kstat header chain in sync with that of the kernel. The kstat chain is a linked list of kstat headers (kstat_t's) pointed to by ‘kc->kc_chain’, which is initialized by kstat_open(3KSTAT). This chain constitutes a list of all kstats currently in the system.

During normal operation, the kernel creates new kstats and deletes old ones as various device instances are added and removed, thereby causing the user's copy of the kstat chain to become out of date. The kstat_chain_update() function detects this condition by comparing the kernel's current kstat chain ID (KCID), which is incremented every time the kstat chain changes, to the user's KCID, ‘kc->kc_chain_id’. If the KCIDs match, kstat_chain_update() does nothing. Otherwise, it deletes any invalid kstat headers from the user's kstat chain, adds any new ones, and sets ‘kc->kc_chain_id’ to the new KCID. All other kstat headers in the user's kstat chain are unmodified.

Because of the deletion process, any kstat_t structures retrieved by the kstat_lookup(3KSTAT) function or data pointers obtained through the kstat_data_lookup(3KSTAT) function are invalidated by a call to kstat_chain_update(). New lookup calls must be made to obtain fresh structures after each chain update.

Upon successful completion, kstat_chain_update() returns the new KCID if the kstat chain has changed and 0 if it has not changed. Otherwise, it returns -1 and sets errno to indicate the error.

kernel statistics driver character device

The kstat_chain_update() function will fail if:
The kstat was temporarily unavailable for reading or writing.
Insufficient storage space is available.
The given kstat could not be located for reading.
The data for the given kstat was too large to be stored in the structure.



kstat(3KSTAT), kstat_lookup(3KSTAT), kstat_open(3KSTAT), kstat_read(3KSTAT), attributes(7)
November 29, 2021 OmniOS