netmap用户层接口使用

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netmap初始化

打开网卡，

struct nmreq base_nmd;
bzero(&base_nmd, sizeof(base_nmd));
g.nmd = nm_open(g.ifname, &base_nmd, 0, NULL);
if (g.nmd == NULL) {
	D("Unable to open %s: %s", g.ifname, strerror(errno));
	goto out;
}

由于网卡内部可能会存在多个ring，netmap可以只操作指定ring，

//follow upper code
struct nm_desc saved_desc = *g.nmd;
saved_desc.self = &saved_desc;
saved_desc.mem = NULL;
nm_close(g.nmd);
saved_desc.req.nr_flags &= ~NR_REG_MASK;
saved_desc.req.nr_flags |= NR_REG_ONE_NIC;
saved_desc.req.nr_ringid = 0;
g.nmd = nm_open(g.ifname, &base_nmd, NM_OPEN_IFNAME, &saved_desc);
if (g.nmd == NULL) {
	D("Unable to open %s: %s", g.ifname, strerror(errno));
	goto out;
}

netmap发送

有两种模式，一直是同步死等，

if (ioctl(pfd.fd, NIOCTXSYNC, NULL) < 0) {
	D("ioctl error on queue %d: %s", targ->me,
			strerror(errno));
	goto quit;
}

第二种用poll异步超时等待，poll可能是超时，也可能是内部错误，

if (poll(&pfd, 1, 2000) <= 0) {
	if (targ->cancel)
		break;
	D("poll error/timeout on queue %d: %s", targ->me,
		strerror(errno));
	// goto quit;
}
if (pfd.revents & POLLERR) {
	D("poll error on %d ring %d-%d", pfd.fd,
		targ->nmd->first_tx_ring, targ->nmd->last_tx_ring);
	goto quit;
}

等待通过之后，表明网卡有硬件资源可以发包，循环检测当前文件句柄的netmap ring的剩余空间，如果为空则查找下一个ring。发包过程，主要调用两个接口，nm_ring_space和NETMAP_BUF宏。

for (i = targ->nmd->first_tx_ring; i <= targ->nmd->last_tx_ring; i++) {
	txring = NETMAP_TXRING(nifp, i);
	if (nm_ring_empty(txring))
		continue;
	n = nm_ring_space(ring);
	if (n < count)
		count = n;
	for (fcnt = nfrags, sent = 0; sent < count; sent++) {
		struct netmap_slot *slot = &ring->slot[cur];
		char *p = NETMAP_BUF(ring, slot->buf_idx);
		int buf_changed = slot->flags & NS_BUF_CHANGED;
		...
		} else if ((options & OPT_COPY) || buf_changed) {
			nm_pkt_copy(frame, p, size);
			if (fcnt == nfrags)
				update_addresses(pkt, g);
		} else if (options & OPT_MEMCPY) {
		...
		cur = nm_ring_next(ring, cur);
	}
	ring->head = ring->cur = cur;
}

netmap退出时检测所有包都已发送，

/* flush any remaining packets */
ioctl(pfd.fd, NIOCTXSYNC, NULL);
/* final part: wait all the TX queues to be empty. */
for (i = targ->nmd->first_tx_ring; i <= targ->nmd->last_tx_ring; i++) {
	txring = NETMAP_TXRING(nifp, i);
	while (!targ->cancel && nm_tx_pending(txring)) {
		RD(5, "pending tx tail %d head %d on ring %d",
			txring->tail, txring->head, i);
		ioctl(pfd.fd, NIOCTXSYNC, NULL);
		usleep(1); /* wait 1 tick */
	}
}

netmap接收

和发送一样有两个方式，同步，

if (ioctl(pfd.fd, NIOCRXSYNC, NULL) < 0) {
	D("ioctl error on queue %d: %s", targ->me,
			strerror(errno));
	goto quit;
}

异步，

if (poll(&pfd, 1, 1 * 1000) <= 0 && !targ->g->forever) {
	clock_gettime(CLOCK_REALTIME_PRECISE, &targ->toc);
	targ->toc.tv_sec -= 1; /* Subtract timeout time. */
	goto out;
}

if (pfd.revents & POLLERR) {
	D("poll err");
	goto quit;
}

接收过程，

for (i = targ->nmd->first_rx_ring; i <= targ->nmd->last_rx_ring; i++) {
	rxring = NETMAP_RXRING(nifp, i);
	if (nm_ring_empty(rxring))
		continue;
	cur = ring->cur;
	n = nm_ring_space(ring);
	for (rx = 0; rx < limit; rx++) {
		struct netmap_slot *slot = &ring->slot[cur];
		char *p = NETMAP_BUF(ring, slot->buf_idx);
		*bytes += slot->len;
		//your recv code here
		cur = nm_ring_next(ring, cur);
	}
	ring->head = ring->cur = cur;
}