[LTP] [RFC PATCH v2 5/7] docs: Update CGroups API

[Cyril Hrubis]

Hi!
> +static void setup(void)
> +{
> +	tst_cgroup_require(TST_CGROUP_MEMORY, NULL);
> +	cg = tst_cgroup_get_default();
> +	SAFE_CGROUP_PRINTF(&cg->cgroup.procs, "%d", getpid());
> +	SAFE_CGROUP_PRINTF(&cg->memory.max, "%lu", MEMSIZE);

I've been looking at the API for a while and I do not understand why we
need to create the tst_cgroup_files for each supported controller and
each node in the hierarchy. Why can't we make this more driver-like? All
we need to know is the controller type, cgroup version and file we want
to read/write.

If I were designing the API I would have made these so that they take a
pointer to a cgroup node, controller type and filename, then the
printf-like formatting.

So the end result would look like:

	SAFE_CGROUP_PRINTF(cg, TST_CGROUP_MEMORY, "memory.max", "%lu", MEMSIZE);

Which would be build on the top of:

int tst_cgroup_open(struct tst_cgroup *cg, enum tst_cgroup_ctrl ctrl, const char *fname);

And instead of storing the file structures into the tst_cgroup structure
we would translate the v2 to v1 on the fly. We would have to open and
close the files on each printf/scanf but I do not think that it's
unreasonable given the simplification of the interface.

We would end up with a simple translation tables for different
controllers instead of the structures that are allocated for each node
then, such as:

static const struct cgroup_map cgroup_memory_map[] = {
	{"memory.usage_in_bytes", "memory.current"},
	{"memory.limit_in_bytes", "memory.max"},
	{"memory.memsw.usage_in_bytes", "memory.swap.current"},
	{"memory.memsw.limitin_bytes", "memory.swap.max"},
	{}
};

Or is there a reason why this cannot be done so?

-- 
Cyril Hrubis
chrubis@suse.cz