[PATCH bpf-next v2 2/2] bpf: implement map_gen_lookup() callback for XSKMAP

["Björn Töpel" <bjorn.topel@gmail.com>]

From: Maciej Fijalkowski <maciej.fijalkowski@intel.com>

I gave a shot for implementing map_gen_lookup() for xskmap just to wipe
away the tears from the bulk redirect struggle... not sure whether it's
still needed anyway since Bjorn posted a patch where he removes the
bpf_map_lookup_elem call from XDP program that libbpf is attaching for
AF_XDP socks.

Let me know what you think, tested it out and seems to do the job,
didn't check the perf difference. If that's useful, then devmap would
have mostly the same implementation.

Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
---
 kernel/bpf/xskmap.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/kernel/bpf/xskmap.c b/kernel/bpf/xskmap.c
index a83e92fe2971..62ce88e57d98 100644
--- a/kernel/bpf/xskmap.c
+++ b/kernel/bpf/xskmap.c
@@ -163,6 +163,22 @@ struct xdp_sock *__xsk_map_lookup_elem(struct bpf_map *map, u32 key)
 	return xs;
 }
 
+static u32 xsk_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf)
+{
+	const int ret = BPF_REG_0, mp = BPF_REG_1, index = BPF_REG_2;
+	struct bpf_insn *insn = insn_buf;
+
+	*insn++ = BPF_LDX_MEM(BPF_W, ret, index, 0);
+	*insn++ = BPF_JMP_IMM(BPF_JGE, ret, map->max_entries, 5);
+	*insn++ = BPF_ALU64_IMM(BPF_LSH, ret, ilog2(sizeof(struct xsk_sock *)));
+	*insn++ = BPF_ALU64_IMM(BPF_ADD, mp, offsetof(struct xsk_map, xsk_map));
+	*insn++ = BPF_ALU64_REG(BPF_ADD, ret, mp);
+	*insn++ = BPF_LDX_MEM(BPF_DW, ret, ret, 0);
+	*insn++ = BPF_JMP_IMM(BPF_JA, 0, 0, 1);
+	*insn++ = BPF_MOV64_IMM(ret, 0);
+	return insn - insn_buf;
+}
+
 int __xsk_map_redirect(struct bpf_map *map, struct xdp_buff *xdp,
 		       struct xdp_sock *xs)
 {
@@ -303,6 +319,7 @@ const struct bpf_map_ops xsk_map_ops = {
 	.map_free = xsk_map_free,
 	.map_get_next_key = xsk_map_get_next_key,
 	.map_lookup_elem = xsk_map_lookup_elem,
+	.map_gen_lookup = xsk_map_gen_lookup,
 	.map_lookup_elem_sys_only = xsk_map_lookup_elem_sys_only,
 	.map_update_elem = xsk_map_update_elem,
 	.map_delete_elem = xsk_map_delete_elem,
-- 
2.20.1