No support for segmented odp packet in tcp_output & ofp_sosend_dgram

[HsuJv]

Hi there

I know that we have set the Interface MTU to 1500 at

ofp/include/api/ofp_config.h

Line 61 in f6580bb

#define OFP_MTU_SIZE 1500

which is smaller than the packet size(1856) set at

ofp/include/api/ofp_config.h

Line 56 in f6580bb

#define SHM_PKT_POOL_BUFFER_SIZE 1856

But in my use case, I'd like to make the MTU configurable to meet the requirements of jumbo frames (both TCP & UDP).

If I increase my MTU to some value that is greater than the packet size, it will result in a segmented odp_packet_t.
But the memcpy here in ofp_tcp_output.c

ofp/src/ofp_tcp_output.c

Lines 870 to 871 in f6580bb

	ofp_sockbuf_copy_out(&so->so_snd, off, len,
	(char *)odp_packet_data(m) + hdrlen);

and the memcpy here in ofp_uipc_socket.c

ofp/src/ofp_uipc_socket.c

Line 1009 in f6580bb

memcpy(p, data, resid);

do not check the segmented packets at all, which will cause a buffer overflow.

A simple approach to duplicate this issue is to reduce the SHM_PKT_POOL_BUFFER_SIZE to 1024 or smaller. Or calling ofp_sendto on the UDP sockets with len set to 2000 or greater.

Are there any plans to support this feature?

BRs.

[bogdanPricope]

Hi @HsuJv,

To support jumbo frames you will need to:

1. re-write ofp_mtu_set() to actually set the the MTU on the interface (odp_pktio_maxlen_set() ??) considering max capabilities (capa.maxlen.max_output, capa.maxlen.max_input) etc. Can be tricky .. if I remember correctly, ODP is considering ETH header in this frame size.
2. Set a pkt_pool.buffer_size large enough for your use-case
3. Fix the two memory copies... Good find!!

My code is different .. cannot say right now if this is enough.
I don't have plans to contribute to the project (I have my own version) but maybe the other members will. Else, it does not seems too complicated.

BRs

[bogdanPricope]

Btw, pkt segments are not well supported in the entire stack... you should try to keep it simple with large enough packets and first segment size = pkt size...

[HsuJv]

Hi @bogdanPricope

Thanks for the quick reply.

For your answer:

1. Yes, I've already hooked the ofp_mtu_set with a function pointer to export it to my application so that I can change it dynamic ly.
2. Actually it is not a feasible approach to increase buffer_size as it will consume a lot more memory for connections that run small packets and will decrease the capability of traffic offload of my application sharply.
3. Yes the memory copies are the root cause. I've not walked through the whole packet paths but I found that the ofp_cksum in ofp_in_cksum.c did do the segment check. So I assume that at least some of the developer has taken the segmented packets into consideration.

So in a short, fixing the issues with segmented packets seems necessary for memory saving and may not be very complicated work. It seems that this project has been active again recently so I submitted issues here to let the contributors know.

BRs.