bpf: generalize and export map_get_next_key for arrays

The kernel/bpf/array.c file defines the array_map_get_next_key()
function which finds the next key for array maps. It actually doesn't
use any map fields besides the generic max_entries field. Generalize
it, and export as bpf_array_get_next_key() such that it can be
re-used by other array-like maps.

Signed-off-by: Anton Protopopov <[email protected]>
Acked-by: Eduard Zingerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: aspsk

include/linux/bpf.h

@@ -2107,6 +2107,12 @@ struct bpf_array {
 	};
 };
 
+/*
+ * The bpf_array_get_next_key() function may be used for all array-like
+ * maps, i.e., maps with u32 keys with range [0 ,..., max_entries)
+ */
+int bpf_array_get_next_key(struct bpf_map *map, void *key, void *next_key);
+
 #define BPF_COMPLEXITY_LIMIT_INSNS      1000000 /* yes. 1M insns */
 #define MAX_TAIL_CALL_CNT 33
 

kernel/bpf/arraymap.c

@@ -335,18 +335,17 @@ int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value)
 }
 
 /* Called from syscall */
-static int array_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
+int bpf_array_get_next_key(struct bpf_map *map, void *key, void *next_key)
 {
-	struct bpf_array *array = container_of(map, struct bpf_array, map);
 	u32 index = key ? *(u32 *)key : U32_MAX;
 	u32 *next = (u32 *)next_key;
 
-	if (index >= array->map.max_entries) {
+	if (index >= map->max_entries) {
 		*next = 0;
 		return 0;
 	}
 
-	if (index == array->map.max_entries - 1)
+	if (index == map->max_entries - 1)
 		return -ENOENT;
 
 	*next = index + 1;
@@ -789,7 +788,7 @@ const struct bpf_map_ops array_map_ops = {
 	.map_alloc_check = array_map_alloc_check,
 	.map_alloc = array_map_alloc,
 	.map_free = array_map_free,
-	.map_get_next_key = array_map_get_next_key,
+	.map_get_next_key = bpf_array_get_next_key,
 	.map_release_uref = array_map_free_internal_structs,
 	.map_lookup_elem = array_map_lookup_elem,
 	.map_update_elem = array_map_update_elem,
@@ -815,7 +814,7 @@ const struct bpf_map_ops percpu_array_map_ops = {
 	.map_alloc_check = array_map_alloc_check,
 	.map_alloc = array_map_alloc,
 	.map_free = array_map_free,
-	.map_get_next_key = array_map_get_next_key,
+	.map_get_next_key = bpf_array_get_next_key,
 	.map_lookup_elem = percpu_array_map_lookup_elem,
 	.map_gen_lookup = percpu_array_map_gen_lookup,
 	.map_update_elem = array_map_update_elem,
@@ -1204,7 +1203,7 @@ const struct bpf_map_ops prog_array_map_ops = {
 	.map_poke_track = prog_array_map_poke_track,
 	.map_poke_untrack = prog_array_map_poke_untrack,
 	.map_poke_run = prog_array_map_poke_run,
-	.map_get_next_key = array_map_get_next_key,
+	.map_get_next_key = bpf_array_get_next_key,
 	.map_lookup_elem = fd_array_map_lookup_elem,
 	.map_delete_elem = fd_array_map_delete_elem,
 	.map_fd_get_ptr = prog_fd_array_get_ptr,
@@ -1308,7 +1307,7 @@ const struct bpf_map_ops perf_event_array_map_ops = {
 	.map_alloc_check = fd_array_map_alloc_check,
 	.map_alloc = array_map_alloc,
 	.map_free = perf_event_fd_array_map_free,
-	.map_get_next_key = array_map_get_next_key,
+	.map_get_next_key = bpf_array_get_next_key,
 	.map_lookup_elem = fd_array_map_lookup_elem,
 	.map_delete_elem = fd_array_map_delete_elem,
 	.map_fd_get_ptr = perf_event_fd_array_get_ptr,
@@ -1344,7 +1343,7 @@ const struct bpf_map_ops cgroup_array_map_ops = {
 	.map_alloc_check = fd_array_map_alloc_check,
 	.map_alloc = array_map_alloc,
 	.map_free = cgroup_fd_array_free,
-	.map_get_next_key = array_map_get_next_key,
+	.map_get_next_key = bpf_array_get_next_key,
 	.map_lookup_elem = fd_array_map_lookup_elem,
 	.map_delete_elem = fd_array_map_delete_elem,
 	.map_fd_get_ptr = cgroup_fd_array_get_ptr,
@@ -1429,7 +1428,7 @@ const struct bpf_map_ops array_of_maps_map_ops = {
 	.map_alloc_check = fd_array_map_alloc_check,
 	.map_alloc = array_of_map_alloc,
 	.map_free = array_of_map_free,
-	.map_get_next_key = array_map_get_next_key,
+	.map_get_next_key = bpf_array_get_next_key,
 	.map_lookup_elem = array_of_map_lookup_elem,
 	.map_delete_elem = fd_array_map_delete_elem,
 	.map_fd_get_ptr = bpf_map_fd_get_ptr,