> -----Original Message-----
> From: Ananyev, Konstantin [mailto:konstantin.anan...@intel.com]
> Sent: Monday, December 14, 2020 10:45 PM
> To: luyicai <luyi...@huawei.com>; dev@dpdk.org
> Cc: Zhoujingbin (Robin, Russell Lab) <zhoujing...@huawei.com>; chenchanghu
> <chenchan...@huawei.com>; Lilijun (Jerry) <jerry.lili...@huawei.com>;
> Linhaifeng <haifeng....@huawei.com>; Guohongzhi (Russell Lab)
> <guohongz...@huawei.com>; wangyunjian <wangyunj...@huawei.com>;
> sta...@dpdk.org
> Subject: RE: [dpdk-dev] [PATCH v5] ip_frag: remove padding length of fragment
> Hi Yicai,
> 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.
>
> Fixes: 7f0983ee331c ("ip_frag: check fragment length of incoming
> packet")
> Cc: sta...@dpdk.org
>
> Signed-off-by: Yicai Lu <luyi...@huawei.com>
> ---
> v4 -> v5: Update the comments and description.
> ---
> lib/librte_ip_frag/rte_ipv4_reassembly.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/lib/librte_ip_frag/rte_ipv4_reassembly.c
> b/lib/librte_ip_frag/rte_ipv4_reassembly.c
> index 1dda8ac..fdf66a4 100644
> --- a/lib/librte_ip_frag/rte_ipv4_reassembly.c
> +++ b/lib/librte_ip_frag/rte_ipv4_reassembly.c
> @@ -104,6 +104,7 @@ struct rte_mbuf *
> const unaligned_uint64_t *psd;
> uint16_t flag_offset, ip_ofs, ip_flag;
> int32_t ip_len;
> + int32_t trim;
>
> flag_offset = rte_be_to_cpu_16(ip_hdr->fragment_offset);
> ip_ofs = (uint16_t)(flag_offset & RTE_IPV4_HDR_OFFSET_MASK); @@
> -117,14 +118,15 @@ struct rte_mbuf *
>
> ip_ofs *= RTE_IPV4_HDR_OFFSET_UNITS;
> ip_len = rte_be_to_cpu_16(ip_hdr->total_length) - mb->l3_len;
> + trim = mb->pkt_len - (ip_len + mb->l3_len + mb->l2_len);
>
> IP_FRAG_LOG(DEBUG, "%s:%d:\n"
> - "mbuf: %p, tms: %" PRIu64
> - ", key: <%" PRIx64 ", %#x>, ofs: %u, len: %d, flags: %#x\n"
> + "mbuf: %p, tms: %" PRIu64 ", key: <%" PRIx64 ", %#x>"
> + "ofs: %u, len: %d, padding: %d, flags: %#x\n"
> "tbl: %p, max_cycles: %" PRIu64 ", entry_mask: %#x, "
> "max_entries: %u, use_entries: %u\n\n",
> __func__, __LINE__,
> - mb, tms, key.src_dst[0], key.id, ip_ofs, ip_len, ip_flag,
> + mb, tms, key.src_dst[0], key.id, ip_ofs, ip_len, trim, ip_flag,
> tbl, tbl->max_cycles, tbl->entry_mask, tbl->max_entries,
> tbl->use_entries);
>
> @@ -134,6 +136,10 @@ struct rte_mbuf *
> return NULL;
> }
>
> + if (unlikely(trim > 0)) {
> + rte_pktmbuf_trim(mb, trim);
> + }
> As a nit {} braces are not required for single expression.
> LGTM in general, just one thing: shouldn't we have the same fix for ipv6 then?
> Konstantin
Hi Konstantin,
Thanks!
During the problem analysis, we have discussed on ipv6
and concluded that it does not exist in ipv6.
For ipv6, it consists of the following parts:
basic header = 40(bytes)
DMAC = 6(bytes)
SMAC = 6(bytes)
Type = 2(bytes)
CRC = 4(bytes)
fragment header = 8(bytes)
...
40 + 6 + 6 + 2 + 4 + 8 = 66 (bytes)
Total is already greater than min_ip_len(64). So it doesn't
need to be padded with zeros.
> +
> /* try to find/add entry into the fragment's table. */
> if ((fp = ip_frag_find(tbl, dr, &key, tms)) == NULL) {
> IP_FRAG_MBUF2DR(dr, mb);
> --
> 1.9.5.msysgit.1
