Re: [dpdk-dev] [dpdk-stable] [PATCH v6] ip_frag: remove padding length of fragment

[Thomas Monjalon <thomas@monjalon.net>]

> > In some situations, we would get several ip fragments, which total
> > data length is less than min_ip_len(64) and padding with zeros.
> > We simulated intermediate fragments by modifying the MTU.
> > To illustrate the problem, we simplify the packet format and
> > ignore the impact of the packet header.In namespace2,
> > a packet whose data length is 1520 is sent.
> > When the packet passes tap2, the packet is divided into two
> > fragments: fragment A and B, similar to (1520 = 1510 + 10).
> > When the packet passes tap3, the larger fragment packet A is
> > divided into two fragments A1 and A2, similar to (1510 = 1500 + 10).
> > Finally, the bond interface receives three fragments:
> > A1, A2, and B (1520 = 1500 + 10 + 10).
> > One fragmented packet A2 is smaller than the minimum Ethernet
> > frame length, so it needs to be padded.
> > 
> > |---------------------------------------------------|
> > |                      HOST                         |
> > | |--------------|   |----------------------------| |
> > | |      ns2     |   |      |--------------|      | |
> > | |  |--------|  |   |  |--------|    |--------|  | |
> > | |  |  tap1  |  |   |  |  tap2  | ns1|  tap3  |  | |
> > | |  |mtu=1510|  |   |  |mtu=1510|    |mtu=1500|  | |
> > | |--|1.1.1.1 |--|   |--|1.1.1.2 |----|2.1.1.1 |--| |
> > |    |--------|         |--------|    |--------|    |
> > |         |                 |              |        |
> > |         |-----------------|              |        |
> > |                                          |        |
> > |                                      |--------|   |
> > |                                      |  bond  |   |
> > |--------------------------------------|mtu=1500|---|
> >                                        |--------|
> > 
> > When processing the preceding packets above,
> > DPDK would aggregate fragmented packets A2 and B.
> > And error packets are generated, which padding(zero)
> > is displayed in the middle of the packet.
> > 
> > A2 + B:
> > 0000   fa 16 3e 9f fb 82 fa 47 b2 57 dc 20 08 00 45 00
> > 0010   00 33 b4 66 00 ba 3f 01 c1 a5 01 01 01 01 02 01
> > 0020   01 02 c0 c1 c2 c3 c4 c5 c6 c7 00 00 00 00 00 00
> > 0030   00 00 00 00 00 00 00 00 00 00 00 00 c8 c9 ca cb
> > 0040   cc cd ce cf d0 d1 d2 d3 d4 d5 d6 d7 d8 d9 da db
> > 0050   dc dd de df e0 e1 e2 e3 e4 e5 e6
> > 
> > So, we would calculate the length of padding, and remove
> > the padding in pkt_len and data_len before aggregation.
> > And also we have the fix for both ipv4 and ipv6.
> > 
> > Fixes: 7f0983ee331c ("ip_frag: check fragment length of incoming packet")
> > Cc: stable@dpdk.org
> > 
> > Signed-off-by: Yicai Lu <luyicai@huawei.com>
> 
> Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>

Applied, thanks