bpf: add a longest prefix match trie map implementation

This trie implements a longest prefix match algorithm that can be used
to match IP addresses to a stored set of ranges.

Internally, data is stored in an unbalanced trie of nodes that has a
maximum height of n, where n is the prefixlen the trie was created
with.

Tries may be created with prefix lengths that are multiples of 8, in
the range from 8 to 2048. The key used for lookup and update operations
is a struct bpf_lpm_trie_key, and the value is a uint64_t.

The code carries more information about the internal implementation.

Signed-off-by: Daniel Mack <[email protected]>
Reviewed-by: David Herrmann <[email protected]>
Acked-by: Alexei Starovoitov <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

include/uapi/linux/bpf.h

@@ -63,6 +63,12 @@ struct bpf_insn {
  __s32 imm; /* signed immediate constant */
 };
 
+/* Key of an a BPF_MAP_TYPE_LPM_TRIE entry */
+struct bpf_lpm_trie_key {
+ __u32 prefixlen; /* up to 32 for AF_INET, 128 for AF_INET6 */
+ __u8 data[0]; /* Arbitrary size */
+};
+
 /* BPF syscall commands, see bpf(2) man-page for details. */
 enum bpf_cmd {
  BPF_MAP_CREATE,
@@ -89,6 +95,7 @@ enum bpf_map_type {
  BPF_MAP_TYPE_CGROUP_ARRAY,
  BPF_MAP_TYPE_LRU_HASH,
  BPF_MAP_TYPE_LRU_PERCPU_HASH,
+ BPF_MAP_TYPE_LPM_TRIE,
 };
 
 enum bpf_prog_type {

kernel/bpf/Makefile

@@ -1,7 +1,7 @@
 obj-y := core.o
 
 obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o
-obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o
+obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o
 ifeq ($(CONFIG_PERF_EVENTS),y)
 obj-$(CONFIG_BPF_SYSCALL) += stackmap.o
 endif