On 5/27/20 4:26 AM, Jesper Dangaard Brouer wrote: >> @@ -108,9 +118,13 @@ static int dev_map_init_map(struct bpf_dtab *dtab, >> union bpf_attr *attr) >> u64 cost = 0; >> int err; >> >> - /* check sanity of attributes */ >> + /* check sanity of attributes. 2 value sizes supported: >> + * 4 bytes: ifindex >> + * 8 bytes: ifindex + prog fd >> + */ >> if (attr->max_entries == 0 || attr->key_size != 4 || >> - attr->value_size != 4 || attr->map_flags & ~DEV_CREATE_FLAG_MASK) >> + (attr->value_size != 4 && attr->value_size != 8) || > > 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". > > I will try to implement something that uses BTF for this case (and cpumap). >
as mentioned in a past response, BTF does not make any fields special and this code should not assume it either. You need to know precisely which 4 bytes is the program fd that needs to be looked up, and that AFAIK is beyond the scope of BTF.
