17 Oct
2015
17 Oct
'15
10:53 a.m.
Hi Neels and Pablo,
first of all, it is great to see this code appear, I never liked libgtp
much either...
On Thu, Oct 15, 2015 at 03:32:02PM +0200, Neels Hofmeyr wrote:
Life would be too simple for that. It there is both byte-endinanness
and bit-endianness. And if you define bit-fields using the c syntax,
then (at least on all platforms I know), you have to split your
definition like above. Look at the definitions of IP header and TCP
header in your /usr/include/netinet/ip.h or /usr/include/netinet/tcp.h
The struct itself (for 16bit/32bit members of the struct) dosen't care.
And the function you refer to takes host-byte-order input and then
pushes the values as network byte ordre to the msgb, which I think is
fine.
yes, that is the preferred method.
Well, that's how we generaly deal with TLVs in libosmocore based
programs :)
On a BE system the htonl() will evaporate and you end up with doning
only a shift-right by 8, which is probably not what you wanted, indeed.
+struct
gtp0_header {
+#if BYTE_ORDER == BIG_ENDIAN
+ uint8_t version:3,
+ pt:1,
+ spare:3,
+ snn:1;
+#elif BYTE_ORDER == LITTLE_ENDIAN
+ uint8_t snn:1,
+ spare:3,
+ pt:1,
+ version:3;
Hmm, endianness is about *byte* order, not *bit* order, right? to use one of the existing decoding functions for
endianness instead:
- ntohs()/ntohl()
that doesn't help you with what pablo defined, as it is about an uint8_t ;)
+ gtp0h->seq = htons(seq);
+ gtp0h->tid = htobe64(tid);
Ah, here it is: htons() stored in the header struct.
I'd prefer a host-byte-order struct. +void
gtp0_header_end(struct gtp0_header *gtp0h, struct msgb *msg)
+{
+ gtp0h->length = htons(msg->len - sizeof(*gtp0h));
With msgb_alloc_headroom(), it is possible to first write the IEs to the
msgb, and then prepend the header with the correct size later on. See for
example in openbsc, gprs_gsup_msgb_alloc() and ipa_msg_push_header(). +static const
struct tlv_definition gtp_pdp_create_req_attr_tlvdef = {
+ .def = {
+ [GTPV0_IE_QOS_PROFILE] = { TLV_TYPE_FIXED, 3 },
+};
I can't begin to express how much better this looks than the old gtpie.h! +void
*msgb_tv_put_be24(struct msgb *msg, int type, uint32_t value)
+{
+ value = htonl(value & 0x00ffffff) >> 8;
heh, interesting :)
This won't work on a BE system. You can't portably do a
host CPU shift-right on a network byte order value. Imagining a class: Big Endian 101, Professor asks:
"Can anyone explain
the results of this code on a big endian and a little endian system?"
Half an hour of vigorous discussion follows.
Beware, Pablo is a CS Professor at Sevilla University ;)
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
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