linux-kernel - Re: [PATCH v2 3/3] tun: Set num

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Message-ID: <20250109023144-mutt-send-email-mst@kernel.org>
Date: Thu, 9 Jan 2025 02:32:18 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Akihiko Odaki <akihiko.odaki@...nix.com>
Cc: Jonathan Corbet <corbet@....net>,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	Jason Wang <jasowang@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	linux-kselftest@...r.kernel.org,
	Yuri Benditovich <yuri.benditovich@...nix.com>,
	Andrew Melnychenko <andrew@...nix.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	gur.stavi@...wei.com, devel@...nix.com
Subject: Re: [PATCH v2 3/3] tun: Set num_buffers for virtio 1.0

On Thu, Jan 09, 2025 at 03:58:45PM +0900, Akihiko Odaki wrote:
> 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 <akihiko.odaki@...nix.com>


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

> ---
>  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