On Thu, Jan 09, 2025 at 06:38:10PM +0900, Akihiko Odaki wrote:

On 2025/01/09 16:40, Michael S. Tsirkin wrote:

quoted

On Thu, Jan 09, 2025 at 02:32:25AM -0500, Michael S. Tsirkin wrote:

quoted

On Thu, Jan 09, 2025 at 03:58:45PM +0900, Akihiko Odaki wrote:

quoted

The specification says the device MUST set num_buffers to 1 if
VIRTIO_NET_F_MRG_RXBUF has not been negotiated.

Signed-off-by: Akihiko Odaki <redacted>

How do we know this is v1 and not v0? Confused.

Ah I got it, you assume userspace will over-write it
if VIRTIO_NET_F_MRG_RXBUF is set.
If we are leaving this up to userspace, why not let it do
it always?

tun may be used with vhost_net, which does not set the field.

I'd fix that in vhost net.

quoted

quoted

quoted

---
  drivers/net/tap.c      |  2 +-
  drivers/net/tun.c      |  6 ++++--
  drivers/net/tun_vnet.c | 14 +++++++++-----
  drivers/net/tun_vnet.h |  4 ++--
  4 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 60804855510b..fe9554ee5b8b 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c

@@ -713,7 +713,7 @@ static ssize_t tap_put_user(struct tap_queue *q,
  	int total;
  	if (q->flags & IFF_VNET_HDR) {
-		struct virtio_net_hdr vnet_hdr;
+		struct virtio_net_hdr_v1 vnet_hdr;
  		vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index dbf0dee92e93..f211d0580887 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c

@@ -1991,7 +1991,9 @@ static ssize_t tun_put_user_xdp(struct tun_struct *tun,
  	size_t total;
  	if (tun->flags & IFF_VNET_HDR) {
-		struct virtio_net_hdr gso = { 0 };
+		struct virtio_net_hdr_v1 gso = {
+			.num_buffers = __virtio16_to_cpu(true, 1)
+		};
  		vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
  		ret = tun_vnet_hdr_put(vnet_hdr_sz, iter, &gso);

@@ -2044,7 +2046,7 @@ static ssize_t tun_put_user(struct tun_struct *tun,
  	}
  	if (vnet_hdr_sz) {
-		struct virtio_net_hdr gso;
+		struct virtio_net_hdr_v1 gso;
  		ret = tun_vnet_hdr_from_skb(tun->flags, tun->dev, skb, &gso);
  		if (ret < 0)

diff --git a/drivers/net/tun_vnet.c b/drivers/net/tun_vnet.c
index ffb2186facd3..a7a7989fae56 100644
--- a/drivers/net/tun_vnet.c
+++ b/drivers/net/tun_vnet.c

@@ -130,15 +130,17 @@ int tun_vnet_hdr_get(int sz, unsigned int flags, struct iov_iter *from,
  EXPORT_SYMBOL_GPL(tun_vnet_hdr_get);
  int tun_vnet_hdr_put(int sz, struct iov_iter *iter,
-		     const struct virtio_net_hdr *hdr)
+		     const struct virtio_net_hdr_v1 *hdr)
  {
+	int content_sz = MIN(sizeof(*hdr), sz);
+
  	if (iov_iter_count(iter) < sz)
  		return -EINVAL;
-	if (copy_to_iter(hdr, sizeof(*hdr), iter) != sizeof(*hdr))
+	if (copy_to_iter(hdr, content_sz, iter) != content_sz)
  		return -EFAULT;
-	if (iov_iter_zero(sz - sizeof(*hdr), iter) != sz - sizeof(*hdr))
+	if (iov_iter_zero(sz - content_sz, iter) != sz - content_sz)
  		return -EFAULT;
  	return 0;

@@ -154,11 +156,11 @@ EXPORT_SYMBOL_GPL(tun_vnet_hdr_to_skb);
  int tun_vnet_hdr_from_skb(unsigned int flags, const struct net_device *dev,
  			  const struct sk_buff *skb,
-			  struct virtio_net_hdr *hdr)
+			  struct virtio_net_hdr_v1 *hdr)
  {
  	int vlan_hlen = skb_vlan_tag_present(skb) ? VLAN_HLEN : 0;
-	if (virtio_net_hdr_from_skb(skb, hdr,
+	if (virtio_net_hdr_from_skb(skb, (struct virtio_net_hdr *)hdr,
  				    tun_vnet_is_little_endian(flags), true,
  				    vlan_hlen)) {
  		struct skb_shared_info *sinfo = skb_shinfo(skb);

@@ -176,6 +178,8 @@ int tun_vnet_hdr_from_skb(unsigned int flags, const struct net_device *dev,
  		return -EINVAL;
  	}
+	hdr->num_buffers = 1;
+
  	return 0;
  }
  EXPORT_SYMBOL_GPL(tun_vnet_hdr_from_skb);

diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h
index 2dfdbe92bb24..d8fd94094227 100644
--- a/drivers/net/tun_vnet.h
+++ b/drivers/net/tun_vnet.h

@@ -12,13 +12,13 @@ int tun_vnet_hdr_get(int sz, unsigned int flags, struct iov_iter *from,
  		     struct virtio_net_hdr *hdr);
  int tun_vnet_hdr_put(int sz, struct iov_iter *iter,
-		     const struct virtio_net_hdr *hdr);
+		     const struct virtio_net_hdr_v1 *hdr);
  int tun_vnet_hdr_to_skb(unsigned int flags, struct sk_buff *skb,
  			const struct virtio_net_hdr *hdr);
  int tun_vnet_hdr_from_skb(unsigned int flags, const struct net_device *dev,
  			  const struct sk_buff *skb,
-			  struct virtio_net_hdr *hdr);
+			  struct virtio_net_hdr_v1 *hdr);
  #endif /* TUN_VNET_H */

-- 
2.47.1