Re: [PATCH bpf 2/2] bpf: selftests: Add non function pointer test to struct_ops

On Wed, Feb 10, 2021 at 02:54:40PM -0800, Andrii Nakryiko wrote:

On Wed, Feb 10, 2021 at 1:17 PM Martin KaFai Lau [off-list ref] wrote:

quoted

On Wed, Feb 10, 2021 at 12:27:38PM -0800, Andrii Nakryiko wrote:

quoted

On Tue, Feb 9, 2021 at 12:11 PM Martin KaFai Lau [off-list ref] wrote:

quoted

This patch adds a "void *owner" member.  The existing
bpf_tcp_ca test will ensure the bpf_cubic.o and bpf_dctcp.o
can be loaded.

Signed-off-by: Martin KaFai Lau <redacted>
---

Acked-by: Andrii Nakryiko <andrii@kernel.org>

What will happen if BPF code initializes such non-func ptr member?
Will libbpf complain or just ignore those values? Ignoring initialized
members isn't great.

The latter. libbpf will ignore non-func ptr member.  The non-func ptr
member stays zero when it is passed to the kernel.

libbpf can be changed to copy this non-func ptr value.
The kernel will decide what to do with it.  It will
then be consistent with int/array member like ".name"
and ".flags" where the kernel will verify the value.
I can spin v2 to do that.

I was thinking about erroring out on non-zero fields, but if you think
it's useful to pass through values, it could be done, but will require
more and careful code, probably. So, basically, don't feel obligated
to do this in this patch set.

You meant it needs different handling in copying ptr value
than copying int/char[]?