On Wed, 27 May 2020 08:27:36 -0600
David Ahern <dsah...@gmail.com> wrote:
> On 5/27/20 4:26 AM, Jesper Dangaard Brouer wrote:
> > IMHO we really need to leverage BTF here, as I'm sure we need to do more
> > extensions, and this size matching will get more and more unmaintainable.
> >
> > With BTF in place, dumping the map via bpftool, will also make the
> > fields "self-documenting".
>
> furthermore, the kernel is changing the value - an fd is passed in and
> an id is returned. I do not see how any of this fits into BTF.
It can, as BTF actually support union's (I just tested that).
For the sake of end-users understanding this, I do wonder if it is
better to define the struct without the union, and have longer names
that will be part of BTF description, e.g (dumped via bpftool):
struct dev_map_ext_val {
u32 ifindex;
int bpf_prog_fd_write;
u32 bpf_prog_id_read;
};
But a union would also work (also tested via BPF loading and BTF dumpinmg):
struct dev_map_ext_val {
u32 ifindex;
union {
int bpf_prog_fd_write;
u32 bpf_prog_id_read;
};
};
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
