suricata 3.1 源码分析33 （FlowWorker处理流程2 - FlowHandlePacket）

void FlowHandlePacket(ThreadVars *tv, DecodeThreadVars *dtv, Packet *p)
{
    /* Get this packet's flow from the hash. FlowHandlePacket() will setup
     * a new flow if nescesary. If we get NULL, we're out of flow memory.
     * The returned flow is locked. */

//获取包对应的流，找不到就新建流，返回流指针，返回空说明内存不足
    Flow *f = FlowGetFlowFromHash(tv, dtv, p, &p->flow);
    if (f == NULL)
        return;

    /* set the flow in the packet */
//设置包的标记为属于某条流
    p->flags |= PKT_HAS_FLOW;
    return;
}

Flow *FlowGetFlowFromHash(ThreadVars *tv, DecodeThreadVars *dtv, const Packet *p, Flow **dest)
{
    Flow *f = NULL;

    /* get our hash bucket and lock it */
    const uint32_t hash = p->flow_hash;
//获取对应的bucket
    FlowBucket *fb = &flow_hash[hash % flow_config.hash_size];
    FBLOCK_LOCK(fb);

    SCLogDebug("fb %p fb->head %p", fb, fb->head);

    /* see if the bucket already has a flow */
/*如果p->flow_hash找不到对应的FlowBucket，则新建flow挂到对
应的bucket上，并通过参数dest返回*/
    if (fb->head == NULL) {
        f = FlowGetNew(tv, dtv, p);
        if (f == NULL) {
            FBLOCK_UNLOCK(fb);
            return NULL;
        }

        /* flow is locked */
        fb->head = f;
        fb->tail = f;

        /* got one, now lock, initialize and return */
        FlowInit(f, p);
        f->flow_hash = hash;
        f->fb = fb;

        /* update the last seen timestamp of this flow */
        COPY_TIMESTAMP(&p->ts,&f->lastts);
        FlowReference(dest, f);

        FBLOCK_UNLOCK(fb);
        return f;
    }

    /* ok, we have a flow in the bucket. Let's find out if it is our flow */
    f = fb->head;

    /* see if this is the flow we are looking for */
//如果packet和bucket的第一个flow不匹配（五元组+vlan不完全相同）
    if (FlowCompare(f, p) == 0) {
        Flow *pf = NULL; /* previous flow */

        while (f) {
            pf = f;
            f = f->hnext;
/*若遍历整个bucket链表找不到对应的flow，则新建flow挂到对应
的bucket上，并通过参数dest返回*/
            if (f == NULL) {
                f = pf->hnext = FlowGetNew(tv, dtv, p);
                if (f == NULL) {
                    FBLOCK_UNLOCK(fb);
                    return NULL;
                }
                fb->tail = f;

                /* flow is locked */

                f->hprev = pf;

                /* initialize and return */
                FlowInit(f, p);
                f->flow_hash = hash;
                f->fb = fb;

                /* update the last seen timestamp of this flow */
                COPY_TIMESTAMP(&p->ts,&f->lastts);
                FlowReference(dest, f);

                FBLOCK_UNLOCK(fb);
                return f;
            }

/*若遍历bucket链表找到对应的flow，将当前flow放到bucket的flow->head，
判断流重用，并通过参数dest返回*/
            if (FlowCompare(f, p) != 0) {
                /* we found our flow, lets put it on top of the
                 * hash list -- this rewards active flows */
                if (f->hnext) {
                    f->hnext->hprev = f->hprev;
                }
                if (f->hprev) {
                    f->hprev->hnext = f->hnext;
                }
                if (f == fb->tail) {
                    fb->tail = f->hprev;
                }

                f->hnext = fb->head;
                f->hprev = NULL;
                fb->head->hprev = f;
                fb->head = f;

                /* found our flow, lock & return */
                FLOWLOCK_WRLOCK(f);
                if (unlikely(TcpSessionPacketSsnReuse(p, f, f->protoctx) == 1)) {
                    f = TcpReuseReplace(tv, dtv, fb, f, hash, p);
                    if (f == NULL) {
                        FBLOCK_UNLOCK(fb);
                        return NULL;
                    }
                }

                /* update the last seen timestamp of this flow */
                COPY_TIMESTAMP(&p->ts,&f->lastts);
                FlowReference(dest, f);

                FBLOCK_UNLOCK(fb);
                return f;
            }
        }
    }

    /* lock & return */
/*如果packet和bucket的第一个flow匹配（五元组+vlan相同），
判断流重用，并通过参数dest返回*/
    FLOWLOCK_WRLOCK(f);
    if (unlikely(TcpSessionPacketSsnReuse(p, f, f->protoctx) == 1)) {
        f = TcpReuseReplace(tv, dtv, fb, f, hash, p);
        if (f == NULL) {
            FBLOCK_UNLOCK(fb);
            return NULL;
        }
    }

    /* update the last seen timestamp of this flow */
    COPY_TIMESTAMP(&p->ts,&f->lastts);
    FlowReference(dest, f);

    FBLOCK_UNLOCK(fb);
    return f;
}