vpp之节点报⽂处理流程分析
这⾥以vpp提供的节点sample例⼦为例来分析vpp的节点对报⽂处理的流程
vpp/src/examples/sample-plugin/sample
$ll
total 56
-rw-rw-r-- 1 ych ych  886 Apr  1 17:
-rw-rw-r-- 1 ych ych 17933 Apr  1 17:34 node.c
-rw-rw-r-- 1 ych ych  712 Apr  1 17:34 sample_all_api_h.h
-rw-rw-r-- 1 ych ych  1068 Apr  1 17:34 sample.api
-rw-rw-r-- 1 ych ych  6569 Apr  1 17:34 sample.c
-rw-rw-r-- 1 ych ych  1135 Apr  1 17:34 sample.h
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rw-rw-r-- 1 ych ych  960 Apr  1 17:34 sample_msg_enum.h
-rw-rw-r-- 1 ych ych  5512 Apr  1 17:34 sample_test.c
vpp的每⼀个插件internal节点报⽂处理函数⼤致如下函数，我对函数每⼀步都做了具体解释，具体我们看下⾯的函数就好。
VLIB_NODE_FN (sample_node)(vlib_main_t * vm, vlib_node_runtime_t * node,
vlib_frame_t * frame)
{
u32 n_left_from,*from,*to_next;
sample_next_t next_index;
u32 pkts_swapped =0;
/* 本节点收到的vector包的起始地址 */
from = vlib_frame_vector_args (frame);
/* 本节点收到的vector包数 */
n_left_from = frame->n_vectors;
/* cached_next_index记录着上⼀次经过该节点时的next_index
next_index对应着VLIB_REGISTER_NODE (sample_node).next_nodes中下⼀节点的索引 */
next_index = node->cached_next_index;
while(n_left_from >0)
{
u32 n_left_to_next;
/* to_next: next_index所指下⼀个节点的收包缓存的空闲位置⾸地址 */
/* n_left_to_next：下⼀个节点收包缓存的空闲位置总数 */
vlib_get_next_frame (vm, node, next_index, to_next, n_left_to_next);
/
* ⼀次性处理两个包 */
while(n_left_from >=4&& n_left_to_next >=2)
{
/* next0和next1指明包的下⼀个节点索引值 */
u32 next0 = SAMPLE_NEXT_INTERFACE_OUTPUT;
u32 next1 = SAMPLE_NEXT_INTERFACE_OUTPUT;
u32 sw_if_index0, sw_if_index1;
u8 tmp0[6], tmp1[6];
ethernet_header_t *en0,*en1;
u32 bi0, bi1;
vlib_buffer_t *b0,*b1;
/
* Prefetch next iteration. */
/* from[2]和from[3]是第2和第3个buf的索引，如果这⾥有第2和第3报⽂进来
的话，就是放在from[2]和from[3]索引位置，所以这⾥对其做指令预取*/
{
vlib_buffer_t *p2,*p3;
p2 = vlib_get_buffer (vm, from[2]);
p3 = vlib_get_buffer (vm, from[3]);
vlib_prefetch_buffer_header (p2, LOAD);
vlib_prefetch_buffer_header (p3, LOAD);
CLIB_PREFETCH (p2->data, CLIB_CACHE_LINE_BYTES, STORE);    CLIB_PREFETCH (p3->data, CLIB_CACHE_LINE_BYTES, STORE); }
/* speculatively enqueue b0 and b1 to the current next frame */
/* from[0]和from[1]中保存的是本节点收到包的包索引值，
这⾥直接把from[0]和from[1]放到to_next[0]和to_next[1]⾥⾯了,
这⾥的意思是假设直接把报⽂放到next_index对应下⼀个节点的收包缓存⾥⾯了，后⾯vlib_validate_buffer_enqueue_x2宏会对其做调整      */
to_next[0]= bi0 = from[0];
to_next[1]= bi1 = from[1];
/* 偏移from和to_next指针的位置，并减少n_left_from和n_left_to_next 这⾥n_left_from表⽰当前节点收到的报⽂总数
⽽n_left_to_next表⽰下⼀个节点收包缓存队列的最⼤数量
*/
from +=2;
to_next +=2;
n_left_from -=2;
n_left_to_next -=2;
/* 根据buf index从当前node⾥⾯拿到对应的vlib_buffer_t */
b0 = vlib_get_buffer (vm, bi0);
b1 = vlib_get_buffer (vm, bi1);
ASSERT (b0->current_data ==0);
ASSERT (b1->current_data ==0);
/* 从vlib_buffer_t获取报⽂地址 */
en0 = vlib_buffer_get_current (b0);
en1 = vlib_buffer_get_current (b1);
/* 下⾯这⼀段只是交换以太⽹报⽂的mac地址 */
/
* This is not the fastest way to swap src + dst mac addresses */
#define _(a) tmp0[a] = en0->src_address[a];
foreach_mac_address_offset;
#undef _
#define _(a) en0->src_address[a] = en0->dst_address[a];
foreach_mac_address_offset;
#undef _
#define _(a) en0->dst_address[a] = tmp0[a];
foreach_mac_address_offset;
#undef _
#define _(a) tmp1[a] = en1->src_address[a];
foreach_mac_address_offset;
#undef _
#define _(a) en1->src_address[a] = en1->dst_address[a];
foreach_mac_address_offset;
#undef _
#define _(a) en1->dst_address[a] = tmp1[a];
foreach_mac_address_offset;
#undef _
/* 获取rx的if index后设置到tx if index⾥⾯ */
sw_if_index0 = vnet_buffer (b0)->sw_if_index[VLIB_RX];
sw_if_index1 = vnet_buffer (b1)->sw_if_index[VLIB_RX];
/
* Send pkt back out the RX interface */
vnet_buffer (b0)->sw_if_index[VLIB_TX]= sw_if_index0;
vnet_buffer (b1)->sw_if_index[VLIB_TX]= sw_if_index1;
pkts_swapped +=2;
if(PREDICT_FALSE ((node->flags & VLIB_NODE_FLAG_TRACE)))
if(PREDICT_FALSE ((node->flags & VLIB_NODE_FLAG_TRACE)))
{
if(b0->flags & VLIB_BUFFER_IS_TRACED)
{
sample_trace_t *t =
vlib_add_trace (vm, node, b0,sizeof(*t));
t->sw_if_index = sw_if_index0;
t->next_index = next0;
clib_memcpy_fast (t->new_src_mac, en0->src_address,
sizeof(t->new_src_mac));
clib_memcpy_fast (t->new_dst_mac, en0->dst_address,
sizeof(t->new_dst_mac));
}
if(b1->flags & VLIB_BUFFER_IS_TRACED)
{
sample_trace_t *t =
vlib_add_trace (vm, node, b1,sizeof(*t));
t->sw_if_index = sw_if_index1;
t->next_index = next1;
clib_memcpy_fast (t->new_src_mac, en1->src_address,
sizeof(t->new_src_mac));
clib_memcpy_fast (t->new_dst_mac, en1->dst_address,
sizeof(t->new_dst_mac));
}
}
/* verify speculative enqueues, maybe switch current next frame */
/*
next_index：默认的下⼀结点的index
next0：实际的下⼀个结点的index
next0 == next_index则不需要做特别的处理，报⽂会⾃动进⼊下⼀个节点        next0 != next_index则需要对该数据包做调整，从之前next_index对应
的frame中删除，添加到next0对应的frame中
next1的判断和next0⼀样
*/
vlib_validate_buffer_enqueue_x2 (vm, node, next_index,
to_next, n_left_to_next,
bi0, bi1, next0, next1);
}
/* ⼀次性处理⼀个包, 处理逻辑和上⾯⼀直 */
while(n_left_from >0&& n_left_to_next >0)
{
u32 bi0;
vlib_buffer_t *b0;
u32 next0 = SAMPLE_NEXT_INTERFACE_OUTPUT;
u32 sw_if_index0;
u8 tmp0[6];
ethernet_header_t *en0;
/* speculatively enqueue b0 to the current next frame */
bi0 = from[0];
to_next[0]= bi0;
from +=1;
to_next +=1;
n_left_from -=1;
n_left_to_next -=1;
b0 = vlib_get_buffer (vm, bi0);
/*
* Direct from the driver, we should be at offset 0
* aka at &b0->data[0]
*/
ASSERT (b0->current_data ==0);
en0 = vlib_buffer_get_current (b0);
/* This is not the fastest way to swap src + dst mac addresses */
#define _(a) tmp0[a] = en0->src_address[a];offset指令是什么意思
foreach_mac_address_offset;
#undef _
#define _(a) en0->src_address[a] = en0->dst_address[a];
foreach_mac_address_offset;
#undef _
#define _(a) en0->dst_address[a] = tmp0[a];
foreach_mac_address_offset;
#undef _
sw_if_index0 = vnet_buffer (b0)->sw_if_index[VLIB_RX];
/* Send pkt back out the RX interface */
vnet_buffer (b0)->sw_if_index[VLIB_TX]= sw_if_index0;
if(PREDICT_FALSE ((node->flags & VLIB_NODE_FLAG_TRACE)
&&(b0->flags & VLIB_BUFFER_IS_TRACED)))
{
sample_trace_t *t = vlib_add_trace (vm, node, b0,sizeof(*t));
t->sw_if_index = sw_if_index0;
t->next_index = next0;
clib_memcpy_fast (t->new_src_mac, en0->src_address,
sizeof(t->new_src_mac));
clib_memcpy_fast (t->new_dst_mac, en0->dst_address,
sizeof(t->new_dst_mac));
}
pkts_swapped +=1;
/* verify speculative enqueue, maybe switch current next frame */
vlib_validate_buffer_enqueue_x1 (vm, node, next_index,
to_next, n_left_to_next,
bi0, next0);
}
/* 所有流程都正确处理完毕后，下⼀结点的frame上已经有本结点处理过后的数据索引执⾏该函数，将相关信息登记到vlib_pending_frame_t中，准备开始调度处理
*/
vlib_put_next_frame (vm, node, next_index, n_left_to_next);
}
vlib_node_increment_counter (vm, sample_node.index,
SAMPLE_ERROR_SWAPPED, pkts_swapped);
return frame->n_vectors;
}

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