Subject: Re: [PATCH 2/2] net/packet: send and receive pkt with given vnet_hdr_sz

From: "Michael S. Tsirkin" <[email-masked]>
Date: Fri, 10 Feb 2023 03:10:04 -0500

On Fri, Feb 10, 2023 at 12:01:03PM +0800, 沈安琪(凛玥) wrote:
> 
> 在 2023/2/9 下午9:07, Michael S. Tsirkin 写道:
> > On Thu, Feb 09, 2023 at 08:43:15PM +0800, 沈安琪(凛玥) wrote:
> > > From: "Jianfeng Tan" <[email-masked]>
> > > 
> > > When raw socket is used as the backend for kernel vhost, currently it
> > > will regard the virtio net header as 10-byte, which is not always the
> > > case since some virtio features need virtio net header other than
> > > 10-byte, such as mrg_rxbuf and VERSION_1 that both need 12-byte virtio
> > > net header.
> > > 
> > > Instead of hardcoding virtio net header length to 10 bytes, tpacket_snd,
> > > tpacket_rcv, packet_snd and packet_recvmsg now get the virtio net header
> > > size that is recorded in packet_sock to indicate the exact virtio net
> > > header size that virtio user actually prepares in the packets. By doing
> > > so, it can fix the issue of incorrect mac header parsing when these
> > > virtio features that need virtio net header other than 10-byte are
> > > enable.
> > > 
> > > Signed-off-by: Jianfeng Tan <[email-masked]>
> > > Co-developed-by: Anqi Shen <[email-masked]>
> > > Signed-off-by: Anqi Shen <[email-masked]>
> > Does it handle VERSION_1 though? That one is also LE.
> > Would it be better to pass a features bitmap instead?
> 
> 
> Thanks for quick reply!
> 
> I am a little confused abot what "LE" presents here?

LE == little_endian.
Little endian format.

> For passing a features bitmap to af_packet here, our consideration is
> whether it will be too complicated for af_packet to understand the virtio
> features bitmap in order to get the vnet header size. For now, all the
> virtio features stuff is handled by vhost worker and af_packet actually does
> not need to know much about virtio features. Would it be better if we keep
> the virtio feature stuff in user-level and let user-level tell af_packet how
> much space it should reserve?

Presumably, we'd add an API in include/linux/virtio_net.h ?

> > 
> > 
> > > ---
> > >   net/packet/af_packet.c | 48 +++++++++++++++++++++++++++++++++---------------
> > >   1 file changed, 33 insertions(+), 15 deletions(-)
> > > 
> > > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> > > index ab37baf..4f49939 100644
> > > --- a/net/packet/af_packet.c
> > > +++ b/net/packet/af_packet.c
> > > @@ -2092,18 +2092,25 @@ static unsigned int run_filter(struct sk_buff *skb,
> > >   }
> > >   static int packet_rcv_vnet(struct msghdr *msg, const struct sk_buff *skb,
> > > -			   size_t *len)
> > > +			   size_t *len, int vnet_hdr_sz)
> > >   {
> > >   	struct virtio_net_hdr vnet_hdr;
> > > +	int ret;
> > > -	if (*len < sizeof(vnet_hdr))
> > > +	if (*len < vnet_hdr_sz)
> > >   		return -EINVAL;
> > > -	*len -= sizeof(vnet_hdr);
> > > +	*len -= vnet_hdr_sz;
> > >   	if (virtio_net_hdr_from_skb(skb, &vnet_hdr, vio_le(), true, 0))
> > >   		return -EINVAL;
> > > -	return memcpy_to_msg(msg, (void *)&vnet_hdr, sizeof(vnet_hdr));
> > > +	ret = memcpy_to_msg(msg, (void *)&vnet_hdr, sizeof(vnet_hdr));
> > > +
> > > +	/* reserve space for extra info in vnet_hdr if needed */
> > > +	if (ret == 0)
> > > +		iov_iter_advance(&msg->msg_iter, vnet_hdr_sz - sizeof(vnet_hdr));
> > > +
> > > +	return ret;
> > >   }
> > >   /*
> > > @@ -2311,7 +2318,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
> > >   				       (maclen < 16 ? 16 : maclen)) +
> > >   				       po->tp_reserve;
> > >   		if (po->has_vnet_hdr) {
> > > -			netoff += sizeof(struct virtio_net_hdr);
> > > +			netoff += po->vnet_hdr_sz;
> > >   			do_vnet = true;
> > >   		}
> > >   		macoff = netoff - maclen;
> > > @@ -2552,16 +2559,23 @@ static int __packet_snd_vnet_parse(struct virtio_net_hdr *vnet_hdr, size_t len)
> > >   }
> > >   static int packet_snd_vnet_parse(struct msghdr *msg, size_t *len,
> > > -				 struct virtio_net_hdr *vnet_hdr)
> > > +				 struct virtio_net_hdr *vnet_hdr, int vnet_hdr_sz)
> > >   {
> > > -	if (*len < sizeof(*vnet_hdr))
> > > +	int ret;
> > > +
> > > +	if (*len < vnet_hdr_sz)
> > >   		return -EINVAL;
> > > -	*len -= sizeof(*vnet_hdr);
> > > +	*len -= vnet_hdr_sz;
> > >   	if (!copy_from_iter_full(vnet_hdr, sizeof(*vnet_hdr), &msg->msg_iter))
> > >   		return -EFAULT;
> > > -	return __packet_snd_vnet_parse(vnet_hdr, *len);
> > > +	ret = __packet_snd_vnet_parse(vnet_hdr, *len);
> > > +
> > > +	/* move iter to point to the start of mac header */
> > > +	if (ret == 0)
> > > +		iov_iter_advance(&msg->msg_iter, vnet_hdr_sz - sizeof(struct virtio_net_hdr));
> > > +	return ret;
> > >   }
> > >   static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
> > > @@ -2730,6 +2744,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
> > >   	int status = TP_STATUS_AVAILABLE;
> > >   	int hlen, tlen, copylen = 0;
> > >   	long timeo = 0;
> > > +	int vnet_hdr_sz;
> > >   	mutex_lock(&po->pg_vec_lock);
> > > @@ -2811,8 +2826,9 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
> > >   		tlen = dev->needed_tailroom;
> > >   		if (po->has_vnet_hdr) {
> > >   			vnet_hdr = data;
> > > -			data += sizeof(*vnet_hdr);
> > > -			tp_len -= sizeof(*vnet_hdr);
> > > +			vnet_hdr_sz = po->vnet_hdr_sz;
> > > +			data += vnet_hdr_sz;
> > > +			tp_len -= vnet_hdr_sz;
> > >   			if (tp_len < 0 ||
> > >   			    __packet_snd_vnet_parse(vnet_hdr, tp_len)) {
> > >   				tp_len = -EINVAL;
> > > @@ -2947,6 +2963,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
> > >   	int offset = 0;
> > >   	struct packet_sock *po = pkt_sk(sk);
> > >   	bool has_vnet_hdr = false;
> > > +	int vnet_hdr_sz;
> > >   	int hlen, tlen, linear;
> > >   	int extra_len = 0;
> > > @@ -2991,7 +3008,8 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
> > >   	if (sock->type == SOCK_RAW)
> > >   		reserve = dev->hard_header_len;
> > >   	if (po->has_vnet_hdr) {
> > > -		err = packet_snd_vnet_parse(msg, &len, &vnet_hdr);
> > > +		vnet_hdr_sz = po->vnet_hdr_sz;
> > > +		err = packet_snd_vnet_parse(msg, &len, &vnet_hdr, vnet_hdr_sz);
> > >   		if (err)
> > >   			goto out_unlock;
> > >   		has_vnet_hdr = true;
> > > @@ -3068,7 +3086,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
> > >   		err = virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le());
> > >   		if (err)
> > >   			goto out_free;
> > > -		len += sizeof(vnet_hdr);
> > > +		len += vnet_hdr_sz;
> > >   		virtio_net_hdr_set_proto(skb, &vnet_hdr);
> > >   	}
> > > @@ -3452,10 +3470,10 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
> > >   	packet_rcv_try_clear_pressure(pkt_sk(sk));
> > >   	if (pkt_sk(sk)->has_vnet_hdr) {
> > > -		err = packet_rcv_vnet(msg, skb, &len);
> > > +		vnet_hdr_len = pkt_sk(sk)->vnet_hdr_sz;
> > > +		err = packet_rcv_vnet(msg, skb, &len, vnet_hdr_len);
> > >   		if (err)
> > >   			goto out_free;
> > > -		vnet_hdr_len = sizeof(struct virtio_net_hdr);
> > >   	}
> > >   	/* You lose any data beyond the buffer you gave. If it worries
> > > -- 
> > > 1.8.3.1