自定义Action
一、定义新Action
在这个例子中，我们实现了一个OpenFlow动作修改TCP数据包的接收窗口值。使用与下面的示例类似的实验者消息来创建新动作或新消息。
1.定义新Action的字段类型
首先，OFPAT_SET_RWND字段应该添加到openflow.h文件的ofp_action_type枚举当中。
/* file:include/openflow/openflow.h
* Add OFPAT_POP_PBB
* after the last defined type
*/
enum ofp_action_type {
OFPAT_OUTPUT = 0, /* Output to switch port. */
...
OFPAT_PUSH_PBB = 26, /* Push a new PBB service tag (I-TAG) */
OFPAT_POP_PBB = 27, /* Pop the outer PBB service tag (I-TAG) */
OFPAT_SET_RWND = 28, /* Set TCP RWND value. */
OFPAT_EXPERIMENTER = 0xffff
}
2.定义新Action的Openflow消息格式
/* file:include/openflow/openflow.h
* Struct representing the set rwnd action.
* All OpenFlow messages are 8 bytes
* aligned, thus padding is added
*/
/* Action structure for OFPAT_SET_RWND. */
struct ofp_action_set_rwnd
{
uint16_t type; /* OFPAT_SET_RWND. */
uint16_t len; /* Length is 8. */
uint16_t rwnd; /* rwnd value. */
uint8_t pad[2];
};
3.定义新Action的交换机内部数据呈现格式
/* file:oflib/ofl-actions.h
* Internal representation of
* OFPAT_SET_RWND.
*/
struct ofl_action_set_rwnd {
struct ofl_action_header header; /* OFPAT_SET_RWND. */
uint16_t rwnd;
};
4.定义新Action的Openflow格式与交换机内部格式转换规则（pack与unpack）
//pack
size_t
ofl_actions_pack(struct ofl_action_header *src, struct ofp_action_header *dst, uint8_t* data, struct ofl_exp *exp) {
dst->type = htons(src->type);
memset(dst->pad, 0x00, 4);
switch (src->type) {
case OFPAT_OUTPUT: {
struct ofl_action_output *sa = (struct ofl_action_output *)src;
struct ofp_action_output *da = (struct ofp_action_output *)dst;
da->len = htons(sizeof(struct ofp_action_output));
da->port = htonl(sa->port);
da->max_len = htons(sa->max_len);
memset(da->pad, 0x00, 6);
return sizeof(struct ofp_action_output);
}
/* Most actions are omited for space */
case OFPAT_SET_RWND:{
struct ofl_action_set_rwnd *sa = (struct ofl_action_set_rwnd *) src;
struct ofp_action_set_rwnd *da = (struct ofp_action_set_rwnd *) dst;
da->len = htons(sizeof(struct ofp_action_set_rwnd));
da->rwnd = htons(sa->rwnd);
memset(da->pad, 0x00, 2);
return sizeof(struct ofp_action_set_rwnd);
}
};
}
ofl_err
ofl_actions_unpack(struct ofp_action_header *src, size_t *len, struct ofl_action_header **dst, struct ofl_exp *exp) {
if (*len < sizeof(struct ofp_action_header)) {
VLOG_WARN(LOG_MODULE, "Received action is too short (%zu).", *len);
return ofl_error(OFPET_BAD_ACTION, OFPBAC_BAD_LEN);
}
if (*len < ntohs(src->len)) {
VLOG_WARN(LOG_MODULE, "Received action has invalid length (set to %u, but only %zu received).", ntohs(src->len), *len);
return ofl_error(OFPET_BAD_ACTION, OFPBAC_BAD_LEN);
}
if ((ntohs(src->len) % 8) != 0) {
VLOG_WARN(LOG_MODULE, "Received action length is not a multiple of 64 bits (%u).", ntohs(src->len));
return ofl_error(OFPET_BAD_ACTION, OFPBAC_BAD_LEN);
}
switch (ntohs(src->type)) {
case OFPAT_OUTPUT: {
//...
}
/* Most actions omited for space */
case OFPAT_SET_RWND: {
struct ofp_action_set_rwnd *sa;
struct ofl_action_set_rwnd *da;
if (*len < sizeof(struct ofp_action_set_rwnd)) {
VLOG_WARN(LOG_MODULE, "Received SET_RWND action has invalid length (%zu).", *len);
return ofl_error(OFPET_BAD_ACTION, OFPBAC_BAD_LEN);
}
sa = (struct ofp_action_set_rwnd *)src;
da = (struct ofl_action_set_rwnd *)malloc(sizeof(struct ofl_action_set_rwnd));
da->rwnd = sa->rwnd;
*len -= sizeof(struct ofp_action_set_rwnd);
*dst = (struct ofl_action_header *)da;
break;
}
};
}
二、在交换机端处理新Action
1.处理新Action的函数
static void
set_rwnd(struct packet *pkt, struct ofl_action_set_nw_ttl *act) {
packet_handle_std_validate(pkt->handle_std);
if (pkt->handle_std->proto->tcp != NULL) {
struct tcp_header *tcp = pkt->handle_std->proto->tcp;
uint16_t old_rwnd = tcp->winsz;
uint16_t new_rwnd = htons(act->rwnd);
tcp->tcp_csum = recalc_csum16(tcp->tcp_csum, old_rwnd, new_rwnd);
tcp->winsz = new_rwnd;
packet_modified (pkt);
}
else {
VLOG_WARN(LOG_MODULE, "Trying to execute SET_NW_TTL action on packet with no ipv4 or ipv6.");
}
}
2.使用上述函数
dp_execute_action(struct packet *pkt,
struct ofl_action_header *action) {
if (VLOG_IS_DBG_ENABLED(LOG_MODULE)) {
char *a = ofl_action_to_string(action, pkt->dp->exp);
VLOG_DBG(LOG_MODULE, "executing action %s.", a);
free(a);
}
switch (action->type) {
case (OFPAT_SET_FIELD): {
set_field(pkt,(struct ofl_action_set_field*) action);
break;
}
/* Most actions omited for space */
case (OFPAT_SET_RWND):{
set_rwnd(pkt, (struct ofl_action_set_rwnd*)action);
break;
}
};
}
