Re: [net-next PATCH 2/4] samples/bpf: make bpf_load.c code compatible with ELF maps section changes

On Tue, 2 May 2017 17:54:51 -0700
Alexei Starovoitov [off-list ref] wrote:

On Tue, May 02, 2017 at 02:31:56PM +0200, Jesper Dangaard Brouer wrote:

quoted

This patch does proper parsing of the ELF "maps" section, in-order to
be both backwards and forwards compatible with changes to the map
definition struct bpf_map_def, which gets compiled into the ELF file.

The assumption is that new features with value zero, means that they
are not in-use.  For backward compatibility where loading an ELF file
with a smaller struct bpf_map_def, only copy objects ELF size, leaving
rest of loaders struct zero.  For forward compatibility where ELF file
have a larger struct bpf_map_def, only copy loaders own struct size
and verify that rest of the larger struct is zero, assuming this means
the newer feature was not activated, thus it should be safe for this
older loader to load this newer ELF file.

Fixes: fb30d4b71214 ("bpf: Add tests for map-in-map")
Fixes: 409526bea3c3 ("samples/bpf: bpf_load.c detect and abort if ELF maps section size is wrong")
Signed-off-by: Jesper Dangaard Brouer <redacted>  

I would just merge patches 2 and 3 to reduce churn,
but it looks like great improvement already.

I could have combined them, but I prefer keeping them separate to keep
the ELF changes separated from changing a sample program e.g.
map_perf_test_user.c.  IHMO is is cleaner this way.

Acked-by: Alexei Starovoitov <ast@kernel.org>

 
Thanks

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