Tom Herbert wrote on Fri, Aug 03, 2018:
> struct my_proto {
> struct _hdr {
> uint32_t len;
> } hdr;
> char data[32];
> } __attribute__((packed));
>
> // use htons to use LE header size, since load_half does a first convertion
> // from network byte order
> const char *bpf_prog_string = " \
> ssize_t bpf_prog1(struct __sk_buff *skb) \
> { \
> return bpf_htons(load_half(skb, 0)) + 4; \
> }";
>
> The length in hdr is uint32_t above, but this looks like it's being
> read as a short.
Err, I agree this is obviously wrong here (I can blame my lack of
attention to this and the example I used), but this isn't the problem as
the actual size is between 0 and 32 -- I could use any size I want here
and the result would the same.
A "real" problem with the conversion program would mean that my example
would not work if I slow it down, but I can send as many packet as I
want if I uncomment the usleep() on the client side or if I just
throttle the network stack with a loud tcpdump writing to stdout -- that
means the algorithm is working even if it's making some badly-sized
conversions.
(Just to make sure I did fix it to htonl(load_word()) and I can confirm
there is no difference)
Thanks,
--
Dominique Martinet
