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Commit 0690899b authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by David S. Miller
Browse files

tun: experimental zero copy tx support 



Let vhost-net utilize zero copy tx when used with tun.

Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent dcc0fb78

drivers/net/tun.c

+134 −12
Original line number Diff line number Diff line
@@ -100,6 +100,8 @@ do { \ 
} while (0)

#endif



#define GOODCOPY_LEN 128



#define FLT_EXACT_COUNT 8

struct tap_filter {

	unsigned int    count;    /* Number of addrs. Zero means disabled */
@@ -604,19 +606,100 @@ static struct sk_buff *tun_alloc_skb(struct tun_struct *tun, 
	return skb;

}



/* set skb frags from iovec, this can move to core network code for reuse */

static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,

				  int offset, size_t count)

{

	int len = iov_length(from, count) - offset;

	int copy = skb_headlen(skb);

	int size, offset1 = 0;

	int i = 0;



	/* Skip over from offset */

	while (count && (offset >= from->iov_len)) {

		offset -= from->iov_len;

		++from;

		--count;

	}



	/* copy up to skb headlen */

	while (count && (copy > 0)) {

		size = min_t(unsigned int, copy, from->iov_len - offset);

		if (copy_from_user(skb->data + offset1, from->iov_base + offset,

				   size))

			return -EFAULT;

		if (copy > size) {

			++from;

			--count;

			offset = 0;

		} else

			offset += size;

		copy -= size;

		offset1 += size;

	}



	if (len == offset1)

		return 0;



	while (count--) {

		struct page *page[MAX_SKB_FRAGS];

		int num_pages;

		unsigned long base;

		unsigned long truesize;



		len = from->iov_len - offset;

		if (!len) {

			offset = 0;

			++from;

			continue;

		}

		base = (unsigned long)from->iov_base + offset;

		size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;

		if (i + size > MAX_SKB_FRAGS)

			return -EMSGSIZE;

		num_pages = get_user_pages_fast(base, size, 0, &page[i]);

		if (num_pages != size) {

			for (i = 0; i < num_pages; i++)

				put_page(page[i]);

			return -EFAULT;

		}

		truesize = size * PAGE_SIZE;

		skb->data_len += len;

		skb->len += len;

		skb->truesize += truesize;

		atomic_add(truesize, &skb->sk->sk_wmem_alloc);

		while (len) {

			int off = base & ~PAGE_MASK;

			int size = min_t(int, len, PAGE_SIZE - off);

			__skb_fill_page_desc(skb, i, page[i], off, size);

			skb_shinfo(skb)->nr_frags++;

			/* increase sk_wmem_alloc */

			base += size;

			len -= size;

			i++;

		}

		offset = 0;

		++from;

	}

	return 0;

}



/* Get packet from user space buffer */

static ssize_t tun_get_user(struct tun_struct *tun,

			    const struct iovec *iv, size_t count,

			    int noblock)

static ssize_t tun_get_user(struct tun_struct *tun, void *msg_control,

			    const struct iovec *iv, size_t total_len,

			    size_t count, int noblock)

{

	struct tun_pi pi = { 0, cpu_to_be16(ETH_P_IP) };

	struct sk_buff *skb;

	size_t len = count, align = NET_SKB_PAD;

	size_t len = total_len, align = NET_SKB_PAD;

	struct virtio_net_hdr gso = { 0 };

	int offset = 0;

	int copylen;

	bool zerocopy = false;

	int err;



	if (!(tun->flags & TUN_NO_PI)) {

		if ((len -= sizeof(pi)) > count)

		if ((len -= sizeof(pi)) > total_len)

			return -EINVAL;



		if (memcpy_fromiovecend((void *)&pi, iv, 0, sizeof(pi)))
@@ -625,7 +708,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, 
	}



	if (tun->flags & TUN_VNET_HDR) {

		if ((len -= tun->vnet_hdr_sz) > count)

		if ((len -= tun->vnet_hdr_sz) > total_len)

			return -EINVAL;



		if (memcpy_fromiovecend((void *)&gso, iv, offset, sizeof(gso)))
@@ -647,14 +730,46 @@ static ssize_t tun_get_user(struct tun_struct *tun, 
			return -EINVAL;

	}



	skb = tun_alloc_skb(tun, align, len, gso.hdr_len, noblock);

	if (msg_control)

		zerocopy = true;



	if (zerocopy) {

		/* Userspace may produce vectors with count greater than

		 * MAX_SKB_FRAGS, so we need to linearize parts of the skb

		 * to let the rest of data to be fit in the frags.

		 */

		if (count > MAX_SKB_FRAGS) {

			copylen = iov_length(iv, count - MAX_SKB_FRAGS);

			if (copylen < offset)

				copylen = 0;

			else

				copylen -= offset;

		} else

				copylen = 0;

		/* There are 256 bytes to be copied in skb, so there is enough

		 * room for skb expand head in case it is used.

		 * The rest of the buffer is mapped from userspace.

		 */

		if (copylen < gso.hdr_len)

			copylen = gso.hdr_len;

		if (!copylen)

			copylen = GOODCOPY_LEN;

	} else

		copylen = len;



	skb = tun_alloc_skb(tun, align, copylen, gso.hdr_len, noblock);

	if (IS_ERR(skb)) {

		if (PTR_ERR(skb) != -EAGAIN)

			tun->dev->stats.rx_dropped++;

		return PTR_ERR(skb);

	}



	if (skb_copy_datagram_from_iovec(skb, 0, iv, offset, len)) {

	if (zerocopy)

		err = zerocopy_sg_from_iovec(skb, iv, offset, count);

	else

		err = skb_copy_datagram_from_iovec(skb, 0, iv, offset, len);



	if (err) {

		tun->dev->stats.rx_dropped++;

		kfree_skb(skb);

		return -EFAULT;
@@ -728,12 +843,18 @@ static ssize_t tun_get_user(struct tun_struct *tun, 
		skb_shinfo(skb)->gso_segs = 0;

	}



	/* copy skb_ubuf_info for callback when skb has no error */

	if (zerocopy) {

		skb_shinfo(skb)->destructor_arg = msg_control;

		skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;

	}



	netif_rx_ni(skb);



	tun->dev->stats.rx_packets++;

	tun->dev->stats.rx_bytes += len;



	return count;

	return total_len;

}



static ssize_t tun_chr_aio_write(struct kiocb *iocb, const struct iovec *iv,
@@ -748,7 +869,7 @@ static ssize_t tun_chr_aio_write(struct kiocb *iocb, const struct iovec *iv, 


	tun_debug(KERN_INFO, tun, "tun_chr_write %ld\n", count);



	result = tun_get_user(tun, iv, iov_length(iv, count),

	result = tun_get_user(tun, NULL, iv, iov_length(iv, count), count,

			      file->f_flags & O_NONBLOCK);



	tun_put(tun);
@@ -962,8 +1083,8 @@ static int tun_sendmsg(struct kiocb *iocb, struct socket *sock, 
		       struct msghdr *m, size_t total_len)

{

	struct tun_struct *tun = container_of(sock, struct tun_struct, socket);

	return tun_get_user(tun, m->msg_iov, total_len,

			    m->msg_flags & MSG_DONTWAIT);

	return tun_get_user(tun, m->msg_control, m->msg_iov, total_len,

			    m->msg_iovlen, m->msg_flags & MSG_DONTWAIT);

}



static int tun_recvmsg(struct kiocb *iocb, struct socket *sock,
@@ -1133,6 +1254,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr) 
		sock_init_data(&tun->socket, sk);

		sk->sk_write_space = tun_sock_write_space;

		sk->sk_sndbuf = INT_MAX;

		sock_set_flag(sk, SOCK_ZEROCOPY);



		tun_sk(sk)->tun = tun;