Re: [PATCH v2 3/3] tun: Set num_buffers for virtio 1.0

Akihiko Odaki
2025-01-09T11:10:47Z

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@daynix.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
>>>
>