On Mon, Aug 21, 2017 at 05:47:13PM +0800, Jiri Benc wrote:
> On Mon, 21 Aug 2017 17:15:42 +0800, Yang, Yi wrote:
> > The issue is it is used union in
> >
> > struct nsh_hdr {
> > ovs_be16 ver_flags_ttl_len;
> > uint8_t md_type;
> > uint8_t next_proto;
> > ovs_16aligned_be32 path_hdr;
> > union {
> > struct nsh_md1_ctx md1;
> > struct nsh_md2_tlv md2;
> > };
> > };
>
> This should work (modulo the non-kernel type names, of course). Did you
> mean to put [] after md2?
Yes, the original version has [] after md2.
>
> > in Linux kernel build, it complained it, I changed it to
>
> What was the error message?
./include/net/nsh.h:213:25: error: flexible array member in union
struct nsh_md2_tlv md2[];
^
>
> > struct nsh_hdr {
> > ovs_be16 ver_flags_ttl_len;
> > uint8_t md_type;
> > uint8_t next_proto;
> > ovs_16aligned_be32 path_hdr;
> > union {
> > struct nsh_md1_ctx md1;
> > struct nsh_md2_tlv md2[0];
> > };
> > };
>
> I wouldn't use this. First, zero length array is a GCC extension. It
> would indeed be better not to use that in uAPI. Second, I wouldn't even
> use a flexible array member here, see my reply to Jan for the reasons.
>
> Note that I commented on struct nsh_md2_tlv having __u8[] as the last
> member which IMHO makes good sense. I'm not entirely sure what C99 says
> about flexible array member being part of a struct inside union inside
> a struct, though. GCC seems to cope with that just fine but AFAIK it
> has some extension over the C standard wrt. flexible array members.
Yes, if struct nsh_md2_tlv has __u8[] as last field,
struct nsh_md2_tlv {
__be16 md_class;
u8 type;
u8 length;
u8 md_value[];
};
struct nsh_hdr {
__be16 ver_flags_ttl_len;
u8 md_type;
u8 next_proto;
__be32 path_hdr;
union {
struct nsh_md1_ctx md1;
struct nsh_md2_tlv md2;
};
};
it is ok, so let us use this one.
>
> > I don't know how we can support this, is it a must-have thing?
>
> What would happen if you get a GSO packet? Ports of an ovs bridge claim
> GSO support, thus they may get a GSO packet. You have to handle it one
> way or the other: either software segment the packet before pushing the
> header, or implement proper GSO support for NSH.
This is an issue, I'll investigate it and find a way to handle this.
>
> > But struct nsh_hdr had different struct from struct ovs_key_nsh, we
> > have no way to make them completely same, do you mean we should use the
> > same name if they are same fields and represent the same thing?
>
> Yes.
>
> Thanks,
>
> Jiri
