Re: [PATCH bpf-next v5 2/2] bpf, xdp: restructure redirect actions

[Daniel Borkmann]

On 2/27/21 1:21 PM, Björn Töpel wrote:
[...]

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 008691fd3b58..a7752badc2ec 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -646,11 +646,20 @@ struct bpf_redirect_info {
        u32 flags;
        u32 tgt_index;
        void *tgt_value;
-       struct bpf_map *map;
+       u32 map_id;
+       u32 tgt_type;
        u32 kern_flags;
        struct bpf_nh_params nh;
  };

+enum xdp_redirect_type {

+       XDP_REDIR_UNSET,
+       XDP_REDIR_DEV_IFINDEX,

[...]

+       XDP_REDIR_DEV_MAP,
+       XDP_REDIR_CPU_MAP,
+       XDP_REDIR_XSK_MAP,

Did you eval whether for these maps we can avoid the redundant def above by just
passing in map->map_type as ri->tgt_type and inferring the XDP_REDIR_UNSET from
invalid map_id of 0 (given the idr will never allocate such)?

[...]

@@ -4068,10 +4039,9 @@ BPF_CALL_2(bpf_xdp_redirect, u32, ifindex, u64, flags)
        if (unlikely(flags))
                return XDP_ABORTED;

- ri->flags = flags;

-       ri->tgt_index = ifindex;
-       ri->tgt_value = NULL;
-       WRITE_ONCE(ri->map, NULL);
+       ri->tgt_type = XDP_REDIR_DEV_IFINDEX;
+       ri->tgt_index = 0;
+       ri->tgt_value = (void *)(long)ifindex;

nit: Bit ugly to pass this in /read out this way, maybe union if we cannot use
tgt_index?

        return XDP_REDIRECT;
  }
diff --git a/net/xdp/xskmap.c b/net/xdp/xskmap.c
index 711acb3636b3..2c58d88aa69d 100644
--- a/net/xdp/xskmap.c
+++ b/net/xdp/xskmap.c
@@ -87,7 +87,6 @@ static void xsk_map_free(struct bpf_map *map)
  {
        struct xsk_map *m = container_of(map, struct xsk_map, map);

- bpf_clear_redirect_map(map);

        synchronize_net();
        bpf_map_area_free(m);
  }
@@ -229,7 +228,8 @@ static int xsk_map_delete_elem(struct bpf_map *map, void 
*key)

static int xsk_map_redirect(struct bpf_map *map, u32 ifindex, u64 flags)

  {
-       return __bpf_xdp_redirect_map(map, ifindex, flags, 
__xsk_map_lookup_elem);
+       return __bpf_xdp_redirect_map(map, ifindex, flags, 
__xsk_map_lookup_elem,
+                                     XDP_REDIR_XSK_MAP);
  }

void xsk_map_try_sock_delete(struct xsk_map *map, struct xdp_sock *xs,