On Thu, May 18, 2023 at 12:22 PM Stanislav Fomichev <sdf@xxxxxxxxxx> wrote:
>
> On 05/18, Maciej Fijalkowski wrote:
> > From: Tirthendu Sarkar <tirthendu.sarkar@xxxxxxxxx>
> >
> > Use the 'options' field in xdp_desc as a packet continuity marker. Since
> > 'options' field was unused till now and was expected to be set to 0, the
> > 'eop' descriptor will have it set to 0, while the non-eop descriptors
> > will have to set it to 1. This ensures legacy applications continue to
> > work without needing any change for single-buffer packets.
> >
> > Add helper functions and extend xskq_prod_reserve_desc() to use the
> > 'options' field.
> >
> > Signed-off-by: Tirthendu Sarkar <tirthendu.sarkar@xxxxxxxxx>
> > ---
> > include/uapi/linux/if_xdp.h | 16 ++++++++++++++++
> > net/xdp/xsk.c | 8 ++++----
> > net/xdp/xsk_queue.h | 12 +++++++++---
> > 3 files changed, 29 insertions(+), 7 deletions(-)
> >
> > diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h
> > index a78a8096f4ce..4acc3a9430f3 100644
> > --- a/include/uapi/linux/if_xdp.h
> > +++ b/include/uapi/linux/if_xdp.h
> > @@ -108,4 +108,20 @@ struct xdp_desc {
> >
> > /* UMEM descriptor is __u64 */
> >
> > +/* Flag indicating that the packet continues with the buffer pointed out by the
> > + * next frame in the ring. The end of the packet is signalled by setting this
> > + * bit to zero. For single buffer packets, every descriptor has 'options' set
> > + * to 0 and this maintains backward compatibility.
> > + */
> > +#define XDP_PKT_CONTD (1 << 0)
> > +
> > +/* Maximum number of descriptors supported as frags for a packet. So the total
> > + * number of descriptors supported for a packet is XSK_DESC_MAX_FRAGS + 1. The
> > + * max frags supported by skb is 16 for page sizes greater than 4K and 17 or
>
> This is now a config option CONFIG_MAX_SKB_FRAGS. Can we use it
> directly?
Also it doesn't look right to expose kernel internal config in uapi
especially since XSK_DESC_MAX_FRAGS is not guaranteed to be 16.
