On Thu, Dec 19, 2019 at 11:22:17PM -0800, Martin Lau wrote:
> [ ... ]
>
> > > +/* __bpf_##_name (e.g. __bpf_tcp_congestion_ops) is the map's value
> > > + * exposed to the userspace and its btf-type-id is stored
> > > + * at the map->btf_vmlinux_value_type_id.
> > > + *
> > > + * The *_name##_dummy is to ensure the BTF type is emitted.
> > > + */
> > > +
> > > #define BPF_STRUCT_OPS_TYPE(_name) \
> > > -extern struct bpf_struct_ops bpf_##_name;
> > > +extern struct bpf_struct_ops bpf_##_name; \
> > > + \
> > > +static struct __bpf_##_name { \
> > > + BPF_STRUCT_OPS_COMMON_VALUE; \
> > > + struct _name data ____cacheline_aligned_in_smp; \
> > > +} *_name##_dummy;
> >
> > There are other ways to retain types in debug info without
> > creating new variables. For example, you can use it in a cast
> > like
> > (void *)(struct __bpf_##_name *)v
> hmm... What is v?
Got it. "v" could be any dummy pointer in a function.
I will use (void) instead of (void *) to avoid compiler warning.
>
> > Not sure whether we could easily find a place for such casting or not.
This can be done in bpf_struct_ops_init().
Thanks for the tips!
