p4factory下 targets/basic_rout

p4factory/targets/basic_routing/p4src代码解读

headers.p4

header_type ethernet_t {
    fields {
        dstAddr : 48;
        srcAddr : 48;
        etherType : 16;
    }
}

header_type ipv4_t {
    fields {
        version : 4;
        ihl : 4;
        diffserv : 8;
        totalLen : 16;
        identification : 16;
        flags : 3;
        fragOffset : 13;
        ttl : 8;
        protocol : 8;
        hdrChecksum : 16;
        srcAddr : 32;
        dstAddr: 32;
    }
}

定义了一个以太网包头，以及一个IPV4包头

parser.p4

parser start {
    return parse_ethernet;
}

#define ETHERTYPE_IPV4 0x0800

header ethernet_t ethernet;

parser parse_ethernet {
    extract(ethernet);
    return select(latest.etherType) {
        ETHERTYPE_IPV4 : parse_ipv4;
        default: ingress;
    }
}

header ipv4_t ipv4;

field_list ipv4_checksum_list {         //提取包的field_list
        ipv4.version;
        ipv4.ihl;
        ipv4.diffserv;
        ipv4.totalLen;
        ipv4.identification;
        ipv4.flags;
        ipv4.fragOffset;
        ipv4.ttl;
        ipv4.protocol;
        ipv4.srcAddr;
        ipv4.dstAddr;
}

field_list_calculation ipv4_checksum {
    input {
        ipv4_checksum_list;
    }
    algorithm : csum16;
    output_width : 16;
}             //通过实例计算出校验和

calculated_field ipv4.hdrChecksum  {
    verify ipv4_checksum;
    update ipv4_checksum;
}           //与该包的校验和想比较，看是否正确

parser parse_ipv4 {
    extract(ipv4);
    return ingress;
}

解释可以看这张图

报文进来后，直接到了parse_ethernet解析器，然后提取ethernet实例的etherType判断是否位0x800如果是在进入到parse_ipv4解析器否则，到达状态_condition_()

中间有个field_list_calculation ipv4_checksum 可以理解成是通过实例化的其他的field字段计算出checksum

calculated_field ipv4.hdrChecksum 计算出来的ipv4_checksum在于刚刚包的hdrChecksum作对比，判断是否一样，然后在更新他

basic_routing.p4

#include "headers.p4"
#include "parser.p4"

#define PORT_VLAN_TABLE_SIZE                   32768
#define BD_TABLE_SIZE                          65536
#define IPV4_LPM_TABLE_SIZE                    16384
#define IPV4_HOST_TABLE_SIZE                   131072
#define NEXTHOP_TABLE_SIZE                     32768
#define REWRITE_MAC_TABLE_SIZE                 32768

#define VRF_BIT_WIDTH                          12
#define BD_BIT_WIDTH                           16
#define IFINDEX_BIT_WIDTH                      10

/* METADATA */
header_type ingress_metadata_t {                //用户自定义元数据
    fields {
        vrf : VRF_BIT_WIDTH;                   /* VRF */
        bd : BD_BIT_WIDTH;                     /* ingress BD */
        nexthop_index : 16;                    /* final next hop index */
    }
}

metadata ingress_metadata_t ingress_metadata;

action on_miss() {
}

action set_bd(bd) {
    modify_field(ingress_metadata.bd, bd);    //设置元数据的bd值
}

table port_mapping {
    reads {
        standard_metadata.ingress_port : exact;
    }
    actions {
        set_bd;
    }
    size : PORT_VLAN_TABLE_SIZE;
}

action set_vrf(vrf) {
    modify_field(ingress_metadata.vrf, vrf);
}

table bd {
    reads {
        ingress_metadata.bd : exact;
    }
    actions {
        set_vrf;
    }
    size : BD_TABLE_SIZE;
}

action fib_hit_nexthop(nexthop_index) {
    modify_field(ingress_metadata.nexthop_index, nexthop_index);
    subtract_from_field(ipv4.ttl, 1);              //让ipv4包ttl-1
}

table ipv4_fib {
    reads {
        ingress_metadata.vrf : exact;
        ipv4.dstAddr : exact;
    }
    actions {
        on_miss;
        fib_hit_nexthop;
    }
    size : IPV4_HOST_TABLE_SIZE;
}

table ipv4_fib_lpm {
    reads {
        ingress_metadata.vrf : exact;
        ipv4.dstAddr : lpm;
    }
    actions {
        on_miss;
        fib_hit_nexthop;
    }
    size : IPV4_LPM_TABLE_SIZE;
}

action set_egress_details(egress_spec) {
    modify_field(standard_metadata.egress_spec, egress_spec);
}

table nexthop {
    reads {
        ingress_metadata.nexthop_index : exact;
    }
    actions {
        on_miss;
        set_egress_details;
    }
    size : NEXTHOP_TABLE_SIZE;
}

control ingress {                   //ingress流控制程序，规定了匹配过程
    if (valid(ipv4)) {
        /* derive ingress_metadata.bd */
        apply(port_mapping);

        /* derive ingress_metadata.vrf */
        apply(bd);

        /* fib lookup, set ingress_metadata.nexthop_index */
        apply(ipv4_fib) {
            on_miss {
                apply(ipv4_fib_lpm);
            }
        }

        /* derive standard_metadata.egress_spec from ingress_metadata.nexthop_index */
        apply(nexthop);
    }
}

action rewrite_src_dst_mac(smac, dmac) {
    modify_field(ethernet.srcAddr, smac);
    modify_field(ethernet.dstAddr, dmac);
}

table rewrite_mac {
    reads {
        ingress_metadata.nexthop_index : exact;
    }
    actions {
        on_miss;
        rewrite_src_dst_mac;
    }
    size : REWRITE_MAC_TABLE_SIZE;
}

control egress {                     //egress的流控制程序
    /* set smac and dmac from ingress_metadata.nexthop_index */
    apply(rewrite_mac);
}

这个也可以从图可得他想要实现的结果

上图两个团员可以看作是查表，线上文字代表执行相应的动作。下面解释一下这张图

首先一个有效ipv4实例进来后先进行端口的匹配，设置bd，然后接着匹配bd表，设置vrf，然后在匹配ipv4_fib这张表匹配到就到下一跳去处理，接下应该都比较好理解。

处理完ingress后在进入buffer区，然后在进行egress的处理，这里egress只有匹配一张表rewite_mac。

输出结果展示

Packet in on port 2 length 100; first bytes:
00010203 04050006 0708090a 08004500
new packet, len : 100, ingress : 2
rmt proc returns 0
ingress_pipeline: packet dequeued          
parsing start
parsing parse_ethernet
parsing parse_ipv4
payload length: 66
all checksums are correct            //检验和正确，开始进入相应匹配
Applying table port_mapping
Lookup key for port_mapping:           //端口匹配
	standard_metadata_ingress_port: 0x00000002, 
table hit

**********
entry at index 1:
	key:
		standard_metadata_ingress_port: 0x00000002 (0 0 0 2),//key值
	action:
		set_bd     //动作
	action data:
		bd: 0x0000000a (0 0 0 10),	 //等下要赋值的数据
**********

action set_bd
action data:
	bd: 0x0000000a (0 0 0 10),	        //执行完成
executing next table for action
Applying table bd
Lookup key for bd:
	ingress_metadata_bd: 0x0000000a,             //bd匹配
table hit

**********
entry at index 0:
	key:
		ingress_metadata_bd: 0x0000000a (0 0 0 10),	  //找到了表项
	action:
		set_vrf
	action data:
		vrf: 0x0000001e (0 0 0 30),	
**********

action set_vrf
action data:
	vrf: 0x0000001e (0 0 0 30),	
executing next table for action
Applying table ipv4_fib                 //匹配路由表
Lookup key for ipv4_fib:
	ingress_metadata_vrf: 0x0000001e, ipv4_dstAddr: 0x0a000002, 
table miss, applying default action
action on_miss                     //没有匹配到，执行on_miss操作
executing next table for action           
Applying table ipv4_fib_lpm         //执行ipv4路由表的另一种lpm匹配、
									//与上面ipv4_fib区别的的是 ipv4_fib是
									//精确匹配，而ipv4_fib_lpm执行的是三									 //重匹配 
								//“动作-匹配表的每个表项都有一个掩码，将									//掩码和字段值进行逻辑与运算，再执行匹									//配。”
Lookup key for ipv4_fib_lpm:
	ingress_metadata_vrf: 0x0000001e, ipv4_dstAddr: 0x0a000002, 
table hit

**********
entry at index 1:
	key:
		ingress_metadata_vrf: 0x0000001e (0 0 0 30),	ipv4_dstAddr: 0x0a000000 (10 0 0 0),	
	prefix_length:
		40
	action:
		fib_hit_nexthop
	action data:
		nexthop_index: 0x00000003 (0 0 0 3),	
**********

action fib_hit_nexthop         
action data:
	nexthop_index: 0x00000003 (0 0 0 3),	 //设置下一跳索引
executing next table for action
Applying table nexthop
Lookup key for nexthop:
	ingress_metadata_nexthop_index: 0x00000003, 
table hit

**********
entry at index 2:
	key:
		ingress_metadata_nexthop_index: 0x00000003 (0 0 0 3),	
	action:
		set_egress_details
	action data:
		egress_spec: 0x00000003 (0 0 0 3),	
**********

action set_egress_details
action data:
	egress_spec: 0x00000003 (0 0 0 3),	
executing next table for action     //设置下一跳egress出端口
total length for outgoing pkt: 100
deparsing ethernet         //逆解析ethernet解析器刚刚解析的过程
deparsing ipv4				//逆解析刚刚ipv4解析器逆解析的港城
total length for outgoing meta: 26  //总的要进入egress元数据长度为26
copying metadata               //赋值元数据
deparsing standard_metadata    //逆解析固有元数据
deparsing ingress_metadata		//你解析用户自定义元数据
queuing system: packet dequeued
egress port set to 3
instance type set to 0
egress_pipeline: packet dequeued
parsing start
parsing parse_ethernet
parsing parse_ipv4            //然后在向刚刚那样解析一次
payload length: 66
extracting metadata           //提取元数据
extracting all metadata for 0x7f9ef0000930
Applying table rewrite_mac
Lookup key for rewrite_mac:
	ingress_metadata_nexthop_index: 0x00000003, 
table hit

**********
entry at index 2:
	key:
		ingress_metadata_nexthop_index: 0x00000003 (0 0 0 3),	
	action:
		rewrite_src_dst_mac
	action data:
		smac: 0x010303030303,	dmac: 0x000303030303,	
**********

action rewrite_src_dst_mac
action data:
	smac: 0x010303030303,	dmac: 0x000303030303,   //重写源目mac	
executing next table for action
total lenth for outgoing pkt: 100
deparsing ethernet
deparsing ipv4              //在逆解析一次
outgoing thread: packet dequeued
outgoing thread: sending pkt: Size[100]: Port[3]  //包从端口3送出去