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Message-ID: <293ce6ac-4bf8-4b26-9291-023b7e101572@daynix.com>
Date: Thu, 9 Jan 2025 20:10:41 +0900
From: Akihiko Odaki <akihiko.odaki@...nix.com>
To: "Michael S. Tsirkin" <mst@...hat.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 2025/01/09 19:54, Michael S. Tsirkin wrote:
> On Thu, Jan 09, 2025 at 06:38:10PM +0900, Akihiko Odaki wrote:
>> On 2025/01/09 16:40, Michael S. Tsirkin wrote:
>>> On Thu, Jan 09, 2025 at 02:32:25AM -0500, Michael S. Tsirkin wrote:
>>>> 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.
>>>
>>> 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.

Let's see what filesystem and networking people will say for the earlier 
patch. We can fix num_buffers for free if the earlier patch is getting 
merged. We will need to come up with another solution otherwise.

> 
> 
>>>
>>>>> ---
>>>>>    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
>>>
> 


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