Re: [PATCH bpf-next v1 3/5] bpf: Introduce cgroup iter

[Tejun Heo]

On Fri, May 20, 2022 at 01:21:31AM +0000, Yosry Ahmed wrote:
> From: Hao Luo <haoluo@xxxxxxxxxx>
> 
> Introduce a new type of iter prog: cgroup. Unlike other bpf_iter, this
> iter doesn't iterate a set of kernel objects. Instead, it is supposed to
> be parameterized by a cgroup id and prints only that cgroup. So one
> needs to specify a target cgroup id when attaching this iter. The target
> cgroup's state can be read out via a link of this iter.
> 
> Signed-off-by: Hao Luo <haoluo@xxxxxxxxxx>
> Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>

This could be me not understanding why it's structured this way but it keeps
bothering me that this is adding a cgroup iterator which doesn't iterate
cgroups. If all that's needed is extracting information from a specific
cgroup, why does this need to be an iterator? e.g. why can't I use
BPF_PROG_TEST_RUN which looks up the cgroup with the provided ID, flushes
rstat, retrieves whatever information necessary and returns that as the
result?

Thanks.

-- 
tejun