To get around the hurdle of all kstats being effectively private,
which in turn makes it difficult to effectively build any sort of
tools that use them, I'm proposing adding stability attributes to
kstats, similar to how dtrace providers have stability attributes. (I
believe this was originally suggested by Dan Price, though I'd have to
look -- the point is I don't want to falsely take credit for the
idea). The immediate need is as a prerequisite for the SNMP
performance MIB, so that it can be done right.
I'd like to throw out a proposed design for discussion (see below).
If a consensus can be reached, then I'd like to create an ARC case for
submission. I'm not sure it's big enough to warrant it's own project
(though if others disagree, I'm fine with that as well).
Stability attributes:
The thinking is unless there's a good reason to diverge, for
consistency (and sanity of someone trying to figure out what to use),
I think keeping it analogous to the dtrace attributes makes the most
sense:
typedef uint8_t kstat_stability_t;
KSTAT_STABILITY_INTERNAL internal to kstat system
KSTAT_STABILITY_PRIVATE private to ON, the default for all kstats
KSTAT_STABILITY_OBSOLETE scheduled for removal
KSTAT_STABILITY_EXTERNAL maintained by a 3rd party
KSTAT_STABILITY_UNSTABLE new or rapidly changing
KSTAT_STABILITY_EVOLVING less rapidly changing
KSTAT_STABILITY_STABLE mature interface
KSTAT_STABILITY_STANDARD industry standard
KSTAT_STABILITY_MAX maximum valid stability
Kernel Interfaces:
int kstat_set_stability(const char *ks_module, const char *ks_name,
kstat_stability_t stability);
Desc: set the kstat to a given stability level
Returns: 0 - success
EINVAL - stability level isn't valid
ENOENT - kstat doesn't exist
??: should this be mutable, or should it be allowed to only be set
once, and return an error from there on out?
int kstat_get_stability(const char *ks_module, const char *ks_name,
kstat_stability_t *stability);
Returns: 0 - stability value in stability. If the stability value was
not explicitly set, *stability contains KSTAT_STABILITY_PRIVATE.
ENOENT - kstat does not exist.
User interfaces:
int kstat_get_stability(kstat_ctl_t *kc, const char *ks_module, const
char *ks_name, kstat_stability_t *stability)
Similar to kernel interface
Returns 0 on success, -1 on failure. On failure, errno is set to:
ENOENT - kstat does not exist.
??: How should the perl module be updated.
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