On Fri, Apr 12, 2024 at 2:08 PM Kui-Feng Lee <thinker.li@xxxxxxxxx> wrote:
>
> The arrays of kptr, bpf_rb_root, and bpf_list_head didn't work as
> global variables. This was due to these types being initialized and
> verified in a special manner in the kernel. This patchset allows BPF
> programs to declare arrays of kptr, bpf_rb_root, and bpf_list_head in
> the global namespace.
>
> The main change is to add "nelems" to btf_fields. The value of
> "nelems" represents the number of elements in the array if a btf_field
> represents an array. Otherwise, "nelem" will be 1. The verifier
> verifies these types based on the information provided by the
> btf_field.
>
> The value of "size" will be the size of the entire array if a
> btf_field represents an array. Dividing "size" by "nelems" gives the
> size of an element. The value of "offset" will be the offset of the
> beginning for an array. By putting this together, we can determine the
> offset of each element in an array. For example,
>
> struct bpf_cpumask __kptr * global_mask_array[2];
Looks like this patch set enables arrays only.
Meaning the following is supported already:
+private(C) struct bpf_spin_lock glock_c;
+private(C) struct bpf_list_head ghead_array1 __contains(foo, node2);
+private(C) struct bpf_list_head ghead_array2 __contains(foo, node2);
while this support is added:
+private(C) struct bpf_spin_lock glock_c;
+private(C) struct bpf_list_head ghead_array1[3] __contains(foo, node2);
+private(C) struct bpf_list_head ghead_array2[2] __contains(foo, node2);
Am I right?
What about the case when bpf_list_head is wrapped in a struct?
private(C) struct foo {
struct bpf_list_head ghead;
} ghead;
that's not enabled in this patch. I think.
And the following:
private(C) struct foo {
struct bpf_list_head ghead;
} ghead[2];
or
private(C) struct foo {
struct bpf_list_head ghead[2];
} ghead;
Won't work either.
I think eventually we want to support all such combinations and
the approach proposed in this patch with 'nelems'
won't work for wrapper structs.
I think it's better to unroll/flatten all structs and arrays
and represent them as individual elements in the flattened
structure. Then there will be no need to special case array with 'nelems'.
All special BTF types will be individual elements with unique offset.
Does this make sense?
pw-bot: cr
