Re: Question about BPF_MAP_TYPE_CGROUP_STORAGE

[Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>]

On Fri, Apr 24, 2020 at 12:43:38PM -0400, Kenny Ho wrote:
> Hi Roman,
> 
> I am thinking of using the cgroup local storage as a way to implement
> per cgroup configurations that other kernel subsystem (gpu driver, for
> example) can have access to.  Is that ok or is that crazy?

If BPF is not involved at all, I'd say don't use it. Because beside providing
a generic BPF map interface (accessible from userspace and BPF), it's
just a page of memory "connected" to a cgroup.

If BPF is involved, let's discuss it in more details.

Thanks!

> 
> Regards,
> Kenny
> 
> On Fri, Apr 24, 2020 at 12:26 PM Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org> wrote:
> >
> > On Fri, Apr 24, 2020 at 12:17:55PM -0400, Kenny Ho wrote:
> > > Hi,
> > >
> > > From the documentation, eBPF maps allow sharing of data between eBPF
> > > kernel programs, kernel and user space applications.  Does that
> > > applies to BPF_MAP_TYPE_CGROUP_STORAGE?  If so, what is the correct
> > > way to access the cgroup storage from the linux kernel? I have been
> > > reading the __cgroup_bpf_attach function and how the storage are
> > > allocated and linked but I am not sure if I am on the right path.
> >
> > Hello, Kenny!
> >
> > Can you, please, elaborate a bit more on the problem, you're trying to solve?
> > What's the goal of accessing the cgroup storage from the kernel?
> >
> > Certainly you can get a pointer to an attached buffer if you have
> > a cgroup pointer. But what's next?
> >
> > Thanks!