Re: xdp generic default option

On 8/20/20 2:25 AM, Jesper Dangaard Brouer wrote:

quoted

quoted

diff --git a/net/core/dev.c b/net/core/dev.c
index a00aa737ce29..1f85880ee412 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -8747,9 +8747,9 @@ static enum bpf_xdp_mode dev_xdp_mode(u32 flags)
 {
        if (flags & XDP_FLAGS_HW_MODE)
                return XDP_MODE_HW;
-       if (flags & XDP_FLAGS_DRV_MODE)
-               return XDP_MODE_DRV;
-       return XDP_MODE_SKB;
+       if (flags & XDP_FLAGS_SKB_MODE)
+               return XDP_MODE_SKB;
+       return XDP_MODE_DRV;
 }
 

I think the better way would be to choose XDP_MODE_DRV if ndo_bpf !=
NULL and XDP_MODE_SKB otherwise. That seems to be matching original
behavior, no?

Yes, but this silent fallback to XDP_MODE_SKB (generic-XDP) have
cause a lot of support issues in the past.  I wish we could change it.
We already changed all the samples/bpf/ to ask for XDP_FLAGS_DRV_MODE,
so they behave this way.

I would prefer the flags check in Lorenzo's proposed patch which is an
explicit opt in to the SKB mode.