On 10/31/23 17:02, Martin KaFai Lau wrote:
On 10/31/23 4:34 PM, Kui-Feng Lee wrote:
diff --git a/include/linux/btf.h b/include/linux/btf.h
index a8813605f2f6..954536431e0b 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -12,6 +12,8 @@
#include <uapi/linux/bpf.h>
#define BTF_TYPE_EMIT(type) ((void)(type *)0)
+#define BTF_STRUCT_OPS_TYPE_EMIT(type) {((void)(struct type *)0); \
((void)(struct type *)0); is new. Why is it needed?
This is a trick of BTF to force compiler generate type info for
the given type. Without trick, compiler may skip these types if these
type are not used at all in the module. For example, modules usually
don't use value types of struct_ops directly.
It is not the value type and value type emit is understood. It is the
struct_ops type itself and it is new addition in this patchset afaict.
The value type emit is in the next line which was cut out from the
context here.
I mean both of them are required.
In the case of a dummy implementation, struct_ops type itself properly
never being used, only being declared by the module. Without this line,
the module developer will fail to load a struct_ops map of the dummy
type. This line is added to avoid this awful situation.
