Re: Accessing userspace created persistent eBPF maps from kernel bpf restricted C

[Jesper Dangaard Brouer <brouer@redhat.com>]

On Thu, 7 Sep 2017 14:37:42 -0700 Kiran T <kiran.lkml@gmail.com> wrote:

> The samples and test cases have examples showing how user space
> programs can pin maps and get pinned maps as FDs.  However, how would
> one access a user-space created pinned map from kernel space, without
> having to statically have a 'maps' section defined (and depend on the
> elf loader)?

Reading further in the thread, I do realize that you have special or
strange use case that is hard/impossible with bpf, as the map type is
needed at bpf load/verifier time.

(IMHO) A more common issue is: asking how can I change/update an
BPF-elf-object-file to use another bpf-map at load-time?

The use-case behind this question is:  I have pinned bpf-map accessible
via the filesystem (bpffs), and I want several BPF programs to
share-and-use this map (on the kernel side).

This is what I'm doing in my xdp_ddos01 example[1].  You can load
xdp_ddos01 on several NICs and they will all share and use the same
blacklist-maps. I've highlighted the code here[1]:

[1] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/samples/bpf/xdp_ddos01_blacklist_user.c#L186-L218

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer