On Fri, Dec 9, 2022 at 3:11 AM Jesper Dangaard Brouer
<jbrouer@xxxxxxxxxx> wrote:
>
>
> On 06/12/2022 03.45, Stanislav Fomichev wrote:
> > There is an ndo handler per kfunc, the verifier replaces a call to the
> > generic kfunc with a call to the per-device one.
> >
> > For XDP, we define a new kfunc set (xdp_metadata_kfunc_ids) which
> > implements all possible metatada kfuncs. Not all devices have to
> > implement them. If kfunc is not supported by the target device,
> > the default implementation is called instead.
> >
> > Upon loading, if BPF_F_XDP_HAS_METADATA is passed via prog_flags,
> > we treat prog_index as target device for kfunc resolution.
> >
>
> [...cut...]
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index 5aa35c58c342..2eabb9157767 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -74,6 +74,7 @@ struct udp_tunnel_nic_info;
> > struct udp_tunnel_nic;
> > struct bpf_prog;
> > struct xdp_buff;
> > +struct xdp_md;
> >
> > void synchronize_net(void);
> > void netdev_set_default_ethtool_ops(struct net_device *dev,
> > @@ -1611,6 +1612,10 @@ struct net_device_ops {
> > ktime_t (*ndo_get_tstamp)(struct net_device *dev,
> > const struct skb_shared_hwtstamps *hwtstamps,
> > bool cycles);
> > + bool (*ndo_xdp_rx_timestamp_supported)(const struct xdp_md *ctx);
> > + u64 (*ndo_xdp_rx_timestamp)(const struct xdp_md *ctx);
> > + bool (*ndo_xdp_rx_hash_supported)(const struct xdp_md *ctx);
> > + u32 (*ndo_xdp_rx_hash)(const struct xdp_md *ctx);
> > };
> >
>
> Would it make sense to add a 'flags' parameter to ndo_xdp_rx_timestamp
> and ndo_xdp_rx_hash ?
>
> E.g. we could have a "STORE" flag that asks the kernel to store this
> information for later. This will be helpful for both the SKB and
> redirect use-cases.
> For redirect e.g into a veth, then BPF-prog can use the same function
> bpf_xdp_metadata_rx_hash() to receive the RX-hash, as it can obtain the
> "stored" value (from the BPF-prog that did the redirect).
>
> (p.s. Hopefully a const 'flags' variable can be optimized when unrolling
> to eliminate store instructions when flags==0)
Are we concerned that doing this without a flag and with another
function call will be expensive?
For xdp->skb path, I was hoping we would be to do something like:
timestamp = bpf_xdp_metadata_rx_hash(ctx);
bpf_xdp_metadata_export_rx_hash_to_skb(ctx, timestamp);
This should also let the users adjust the metadata before storing it.
Am I missing something here? Why would the flag be preferable?
> > /**
> > diff --git a/include/net/xdp.h b/include/net/xdp.h
> > index 55dbc68bfffc..c24aba5c363b 100644
> > --- a/include/net/xdp.h
> > +++ b/include/net/xdp.h
> > @@ -409,4 +409,33 @@ void xdp_attachment_setup(struct xdp_attachment_info *info,
> >
> > #define DEV_MAP_BULK_SIZE XDP_BULK_QUEUE_SIZE
> >
> > +#define XDP_METADATA_KFUNC_xxx \
> > + XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_TIMESTAMP_SUPPORTED, \
> > + bpf_xdp_metadata_rx_timestamp_supported) \
> > + XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_TIMESTAMP, \
> > + bpf_xdp_metadata_rx_timestamp) \
> > + XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_HASH_SUPPORTED, \
> > + bpf_xdp_metadata_rx_hash_supported) \
> > + XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_HASH, \
> > + bpf_xdp_metadata_rx_hash) \
> > +
> > +enum {
> > +#define XDP_METADATA_KFUNC(name, str) name,
> > +XDP_METADATA_KFUNC_xxx
> > +#undef XDP_METADATA_KFUNC
> > +MAX_XDP_METADATA_KFUNC,
> > +};
> > +
> > +#ifdef CONFIG_NET
> > +u32 xdp_metadata_kfunc_id(int id);
> > +#else
> > +static inline u32 xdp_metadata_kfunc_id(int id) { return 0; }
> > +#endif
> > +
> > +struct xdp_md;
> > +bool bpf_xdp_metadata_rx_timestamp_supported(const struct xdp_md *ctx);
> > +u64 bpf_xdp_metadata_rx_timestamp(const struct xdp_md *ctx);
> > +bool bpf_xdp_metadata_rx_hash_supported(const struct xdp_md *ctx);
> > +u32 bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx);
> > +
>
