Re: [PATCH v2 1/3] tun: Unify vnet implementation

Both tun and tap exposes the same set of virtio-net-related features.
Unify their implementations to ease future changes.

Signed-off-by: Akihiko Odaki <redacted>
---
 MAINTAINERS            |   1 +
 drivers/net/Kconfig    |   5 ++
 drivers/net/Makefile   |   1 +
 drivers/net/tap.c      | 172 ++++++----------------------------------
 drivers/net/tun.c      | 208 ++++++++-----------------------------------------
 drivers/net/tun_vnet.c | 186 +++++++++++++++++++++++++++++++++++++++++++
 drivers/net/tun_vnet.h |  24 ++++++
 7 files changed, 273 insertions(+), 324 deletions(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index 910305c11e8a..1be8a452d11f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -23903,6 +23903,7 @@ F:	Documentation/networking/tuntap.rst
 F:	arch/um/os-Linux/drivers/
 F:	drivers/net/tap.c
 F:	drivers/net/tun.c
+F:	drivers/net/tun_vnet.h
 
 TURBOCHANNEL SUBSYSTEM
 M:	"Maciej W. Rozycki" <macro@orcam.me.uk>

diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 1fd5acdc73c6..255c8f9f1d7c 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig

@@ -395,6 +395,7 @@ config TUN
 	tristate "Universal TUN/TAP device driver support"
 	depends on INET
 	select CRC32
+	select TUN_VNET

 static struct proto tap_proto = {
 	.name = "tap",

@@ -641,10 +576,10 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
 	struct sk_buff *skb;
 	struct tap_dev *tap;
 	unsigned long total_len = iov_iter_count(from);
-	unsigned long len = total_len;
+	unsigned long len;
 	int err;
 	struct virtio_net_hdr vnet_hdr = { 0 };
-	int vnet_hdr_len = 0;
+	int hdr_len;
 	int copylen = 0;
 	int depth;
 	bool zerocopy = false;

@@ -652,38 +587,20 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
 	enum skb_drop_reason drop_reason;
 
 	if (q->flags & IFF_VNET_HDR) {
-		vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
-
-		err = -EINVAL;
-		if (len < vnet_hdr_len)
-			goto err;
-		len -= vnet_hdr_len;
-
-		err = -EFAULT;
-		if (!copy_from_iter_full(&vnet_hdr, sizeof(vnet_hdr), from))
-			goto err;
-		iov_iter_advance(from, vnet_hdr_len - sizeof(vnet_hdr));
-		if ((vnet_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
-		     tap16_to_cpu(q, vnet_hdr.csum_start) +
-		     tap16_to_cpu(q, vnet_hdr.csum_offset) + 2 >
-			     tap16_to_cpu(q, vnet_hdr.hdr_len))
-			vnet_hdr.hdr_len = cpu_to_tap16(q,
-				 tap16_to_cpu(q, vnet_hdr.csum_start) +
-				 tap16_to_cpu(q, vnet_hdr.csum_offset) + 2);
-		err = -EINVAL;
-		if (tap16_to_cpu(q, vnet_hdr.hdr_len) > len)
+		hdr_len = tun_vnet_hdr_get(READ_ONCE(q->vnet_hdr_sz), q->flags, from, &vnet_hdr);
+		if (hdr_len < 0) {
+			err = hdr_len;
 			goto err;
+		}
+	} else {
+		hdr_len = 0;
 	}
 
-	err = -EINVAL;
-	if (unlikely(len < ETH_HLEN))
-		goto err;
-

+	len = iov_iter_count(from);
 	if (msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY)) {
 		struct iov_iter i;
 
-		copylen = vnet_hdr.hdr_len ?
-			tap16_to_cpu(q, vnet_hdr.hdr_len) : GOODCOPY_LEN;
+		copylen = hdr_len ? hdr_len : GOODCOPY_LEN;
 		if (copylen > good_linear)
 			copylen = good_linear;
 		else if (copylen < ETH_HLEN)

@@ -697,7 +614,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
 
 	if (!zerocopy) {
 		copylen = len;
-		linear = tap16_to_cpu(q, vnet_hdr.hdr_len);
+		linear = hdr_len;
 		if (linear > good_linear)
 			linear = good_linear;
 		else if (linear < ETH_HLEN)

@@ -732,9 +649,8 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
 	}
 	skb->dev = tap->dev;
 
-	if (vnet_hdr_len) {
-		err = virtio_net_hdr_to_skb(skb, &vnet_hdr,
-					    tap_is_little_endian(q));
+	if (q->flags & IFF_VNET_HDR) {
+		err = tun_vnet_hdr_to_skb(q->flags, skb, &vnet_hdr);
 		if (err) {
 			rcu_read_unlock();
 			drop_reason = SKB_DROP_REASON_DEV_HDR;

@@ -797,23 +713,17 @@ static ssize_t tap_put_user(struct tap_queue *q,
 	int total;
 
 	if (q->flags & IFF_VNET_HDR) {
-		int vlan_hlen = skb_vlan_tag_present(skb) ? VLAN_HLEN : 0;
 		struct virtio_net_hdr vnet_hdr;
 
 		vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
-		if (iov_iter_count(iter) < vnet_hdr_len)
-			return -EINVAL;
-
-		if (virtio_net_hdr_from_skb(skb, &vnet_hdr,
-					    tap_is_little_endian(q), true,
-					    vlan_hlen))
-			BUG();
 
-		if (copy_to_iter(&vnet_hdr, sizeof(vnet_hdr), iter) !=
-		    sizeof(vnet_hdr))
-			return -EFAULT;
+		ret = tun_vnet_hdr_from_skb(q->flags, NULL, skb, &vnet_hdr);
+		if (ret < 0)
+			goto done;
 
-		iov_iter_advance(iter, vnet_hdr_len - sizeof(vnet_hdr));
+		ret = tun_vnet_hdr_put(vnet_hdr_len, iter, &vnet_hdr);
+		if (ret < 0)
+			goto done;