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对IP分片源码增加了注释，并对文档进行了修改
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luozh committed Oct 30, 2017
1 parent 7114119 commit a647c97
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Showing 2 changed files with 36 additions and 135 deletions.
128 changes: 10 additions & 118 deletions IP分片和重组.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -16,123 +16,15 @@
3）分片攻击。黑客可能截获最后一个分片，导致接收端永远接收不到，将导致接收端等待，知道接收端发送ICMP重组超时差错报文。如果这种情况多，
将导致内存资源耗尽，无法进行正常业务处理。
4）
2.rte_ipv4_fragment_packet函数用于IP分片。
int32_t rte_ipv4_fragment_packet(struct rte_mbuf *pkt_in,//用于分片的mbuf数据
struct rte_mbuf **pkts_out,//用于存储分片后mbuf的缓冲区
uint16_t nb_pkts_out,//缓冲区的大小
uint16_t mtu_size,//MTU的长度
struct rte_mempool *pool_direct,
struct rte_mempool *pool_indirect)
{
struct rte_mbuf *in_seg = NULL;
struct ipv4_hdr *in_hdr;
uint32_t out_pkt_pos, in_seg_data_pos;
uint32_t more_in_segs;
uint16_t fragment_offset, flag_offset, frag_size;

frag_size = (uint16_t)(mtu_size - sizeof(struct ipv4_hdr));

/* Fragment size should be a multiply of 8. */
IP_FRAG_ASSERT((frag_size & IPV4_HDR_FO_MASK) == 0);

//获取ipv4头部
in_hdr = rte_pktmbuf_mtod(pkt_in, struct ipv4_hdr *);
flag_offset = rte_cpu_to_be_16(in_hdr->fragment_offset);

//判断分段标识是否被设置
if (unlikely ((flag_offset & IPV4_HDR_DF_MASK) != 0))
return -ENOTSUP;

//判断剩余缓冲区是否能够存储所有的分段数据。其中frag_size表示每个报文能够存储数据的空间大小，nb_pkts_out表示缓冲区个数
//(pkt_in->pkt_len - sizeof (struct ipv4_hdr))表示报文出去IPv4头部后剩余的报文长度
if (unlikely(frag_size * nb_pkts_out <
(uint16_t)(pkt_in->pkt_len - sizeof (struct ipv4_hdr))))
return -EINVAL;

in_seg = pkt_in;
in_seg_data_pos = sizeof(struct ipv4_hdr);
out_pkt_pos = 0;
fragment_offset = 0;

more_in_segs = 1;
while (likely(more_in_segs)) {
struct rte_mbuf *out_pkt = NULL, *out_seg_prev = NULL;
uint32_t more_out_segs;
struct ipv4_hdr *out_hdr;

/* Allocate direct buffer */
out_pkt = rte_pktmbuf_alloc(pool_direct);
if (unlikely(out_pkt == NULL)) {
__free_fragments(pkts_out, out_pkt_pos);
return -ENOMEM;
}

/* Reserve space for the IP header that will be built later */
out_pkt->data_len = sizeof(struct ipv4_hdr);
out_pkt->pkt_len = sizeof(struct ipv4_hdr);

out_seg_prev = out_pkt;
more_out_segs = 1;
while (likely(more_out_segs && more_in_segs)) {
struct rte_mbuf *out_seg = NULL;
uint32_t len;

/* Allocate indirect buffer */
out_seg = rte_pktmbuf_alloc(pool_indirect);
if (unlikely(out_seg == NULL)) {
rte_pktmbuf_free(out_pkt);
__free_fragments(pkts_out, out_pkt_pos);
return -ENOMEM;
}
out_seg_prev->next = out_seg;
out_seg_prev = out_seg;

/* Prepare indirect buffer */
rte_pktmbuf_attach(out_seg, in_seg);
len = mtu_size - out_pkt->pkt_len;
if (len > (in_seg->data_len - in_seg_data_pos)) {
len = in_seg->data_len - in_seg_data_pos;
}
out_seg->data_off = in_seg->data_off + in_seg_data_pos;
out_seg->data_len = (uint16_t)len;
out_pkt->pkt_len = (uint16_t)(len +
out_pkt->pkt_len);
out_pkt->nb_segs += 1;
in_seg_data_pos += len;

/* Current output packet (i.e. fragment) done ? */
if (unlikely(out_pkt->pkt_len >= mtu_size))
more_out_segs = 0;

/* Current input segment done ? */
if (unlikely(in_seg_data_pos == in_seg->data_len)) {
in_seg = in_seg->next;
in_seg_data_pos = 0;

if (unlikely(in_seg == NULL))
more_in_segs = 0;
}
}

/* Build the IP header */
out_hdr = rte_pktmbuf_mtod(out_pkt, struct ipv4_hdr *);

__fill_ipv4hdr_frag(out_hdr, in_hdr,
(uint16_t)out_pkt->pkt_len,
flag_offset, fragment_offset, more_in_segs);

fragment_offset = (uint16_t)(fragment_offset +
out_pkt->pkt_len - sizeof(struct ipv4_hdr));

out_pkt->ol_flags |= PKT_TX_IP_CKSUM;
out_pkt->l3_len = sizeof(struct ipv4_hdr);

/* Write the fragment to the output list */
pkts_out[out_pkt_pos] = out_pkt;
out_pkt_pos ++;
}

return out_pkt_pos;
}
2.rte_ipv4_fragment_packet函数用于IP分片，其声明如下
int32_t rte_ipv4_fragment_packet(struct rte_mbuf *pkt_in,//用于分片的mbuf数据
struct rte_mbuf **pkts_out,//用于存储分片后mbuf的缓冲区
uint16_t nb_pkts_out,//缓冲区的大小
uint16_t mtu_size,//MTU的长度
struct rte_mempool *pool_direct, //用于分配直接mbuf的内存池
struct rte_mempool *pool_indirect)//用于分配间接mbuf的内存池
此函数会为每一个分片分配一个直接mbuf和不定个数的间接mbuf组成一个mbuf链，每一个mbuf链用于保存一个mbuf分片数据。每一个直接mbuf的数据区只保存IPv4头部，间接m
buf保存分片数据。
调用此此函数时，需要将传入mbuf的ipv4头部的DF字段设置为0，表示允许分片。

二、重组
43 changes: 26 additions & 17 deletions dpdk-16.04/dpdk-16.04/lib/librte_ip_frag/rte_ipv4_fragmentation.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -91,11 +91,11 @@ static inline void __free_fragments(struct rte_mbuf *mb[], uint32_t num)
* Otherwise - (-1) * <errno>.
*/
int32_t
rte_ipv4_fragment_packet(struct rte_mbuf *pkt_in,
struct rte_mbuf **pkts_out,
uint16_t nb_pkts_out,
uint16_t mtu_size,
struct rte_mempool *pool_direct,
rte_ipv4_fragment_packet(struct rte_mbuf *pkt_in, //分片的结构
struct rte_mbuf **pkts_out, //保存分片后mbuf的缓冲区
uint16_t nb_pkts_out, //缓冲区剩余空间个数
uint16_t mtu_size, //mtu的大小
struct rte_mempool *pool_direct,
struct rte_mempool *pool_indirect)
{
struct rte_mbuf *in_seg = NULL;
Expand All @@ -104,19 +104,21 @@ rte_ipv4_fragment_packet(struct rte_mbuf *pkt_in,
uint32_t more_in_segs;
uint16_t fragment_offset, flag_offset, frag_size;

//达到mtu除去IPv4头还能保存的数据长度大小
frag_size = (uint16_t)(mtu_size - sizeof(struct ipv4_hdr));

/* Fragment size should be a multiply of 8. */
//分片的大小必须为8的整数倍
IP_FRAG_ASSERT((frag_size & IPV4_HDR_FO_MASK) == 0);

//获取IP头部的16位的标识字段
in_hdr = rte_pktmbuf_mtod(pkt_in, struct ipv4_hdr *);
flag_offset = rte_cpu_to_be_16(in_hdr->fragment_offset);

/* If Don't Fragment flag is set */
//标识字段的DF位是否0，如果为1,标识不能进行分片
if (unlikely ((flag_offset & IPV4_HDR_DF_MASK) != 0))
return -ENOTSUP;

/* Check that pkts_out is big enough to hold all fragments */
//检查缓冲区的空间是否能够保存所有的分片后的数据。
if (unlikely(frag_size * nb_pkts_out <
(uint16_t)(pkt_in->pkt_len - sizeof (struct ipv4_hdr))))
return -EINVAL;
Expand All @@ -133,13 +135,15 @@ rte_ipv4_fragment_packet(struct rte_mbuf *pkt_in,
struct ipv4_hdr *out_hdr;

/* Allocate direct buffer */
//分配一个直接的mbuf，也就是mbuf链的第一个.除了最后一个mbuf链外，其他的mbuf链为一个完整的分片数据（即为8的整数倍）
out_pkt = rte_pktmbuf_alloc(pool_direct);
if (unlikely(out_pkt == NULL)) {
__free_fragments(pkts_out, out_pkt_pos);
return -ENOMEM;
}

/* Reserve space for the IP header that will be built later */
//直接mbuf只用于保存IPv4头部
out_pkt->data_len = sizeof(struct ipv4_hdr);
out_pkt->pkt_len = sizeof(struct ipv4_hdr);

Expand All @@ -150,38 +154,41 @@ rte_ipv4_fragment_packet(struct rte_mbuf *pkt_in,
uint32_t len;

/* Allocate indirect buffer */
//分配一个间接mbuf结构，用于保存除了IPV4头部的剩余分片数据
out_seg = rte_pktmbuf_alloc(pool_indirect);
if (unlikely(out_seg == NULL)) {
rte_pktmbuf_free(out_pkt);
__free_fragments(pkts_out, out_pkt_pos);
return -ENOMEM;
}
//将次间接mbuf分片加入链表中
out_seg_prev->next = out_seg;
out_seg_prev = out_seg;

/* Prepare indirect buffer */
//将用于分片的mbuf attach到间接分片mbuf上
rte_pktmbuf_attach(out_seg, in_seg);
len = mtu_size - out_pkt->pkt_len;
len = mtu_size - out_pkt->pkt_len;//剩余能够保存的数据长度
if (len > (in_seg->data_len - in_seg_data_pos)) {
len = in_seg->data_len - in_seg_data_pos;
}
out_seg->data_off = in_seg->data_off + in_seg_data_pos;
out_seg->data_len = (uint16_t)len;
out_seg->data_off = in_seg->data_off + in_seg_data_pos;//此分片数据的起始偏移
out_seg->data_len = (uint16_t)len;//此分片mbuf保存的数据数据长度
out_pkt->pkt_len = (uint16_t)(len +
out_pkt->pkt_len);
out_pkt->nb_segs += 1;
in_seg_data_pos += len;
out_pkt->pkt_len);//整个数据链的数据长度和
out_pkt->nb_segs += 1;//分片个数+1
in_seg_data_pos += len;//下一个数据偏移

/* Current output packet (i.e. fragment) done ? */
if (unlikely(out_pkt->pkt_len >= mtu_size))
if (unlikely(out_pkt->pkt_len >= mtu_size))//如果此直接mbuf的数据总长度够了一个MTU长度，那么会申请一个新的直接mbuf保存剩余的数据。
more_out_segs = 0;

/* Current input segment done ? */
if (unlikely(in_seg_data_pos == in_seg->data_len)) {
if (unlikely(in_seg_data_pos == in_seg->data_len)) {//如果用于分片的mbuf链的当前mbuf封装玩，那么进行此链的下一个mbuf。
in_seg = in_seg->next;
in_seg_data_pos = 0;

if (unlikely(in_seg == NULL))
if (unlikely(in_seg == NULL))//如果mbuf链的所有mbuf都完成分片，那么将more_in_segs设置为0，也就是结束分片标记设置为0
more_in_segs = 0;
}
}
Expand All @@ -190,10 +197,12 @@ rte_ipv4_fragment_packet(struct rte_mbuf *pkt_in,

out_hdr = rte_pktmbuf_mtod(out_pkt, struct ipv4_hdr *);

//分装修改IPv4头部数据，包括片偏移，总长度，检验和封装为0
__fill_ipv4hdr_frag(out_hdr, in_hdr,
(uint16_t)out_pkt->pkt_len,
flag_offset, fragment_offset, more_in_segs);

//求此片的偏移字段的值，第一个分片此值为0
fragment_offset = (uint16_t)(fragment_offset +
out_pkt->pkt_len - sizeof(struct ipv4_hdr));

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