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Message-ID: <20250109055425-mutt-send-email-mst@kernel.org>
Date: Thu, 9 Jan 2025 05:54:41 -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 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.
> >
> > > > ---
> > > > 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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