On 8/13/25 12:39 AM, Maciej Żenczykowski wrote:
BPF_MAP_LOOKUP_AND_DELETE_BATCH keys & values == NULL
seems like a nice way to simply quickly clear a map.
This will change existing API as users will expect
some error (e.g., -EFAULT) return when keys or values is NULL.
We have a 'flags' field in uapi header in
struct { /* struct used by BPF_MAP_*_BATCH commands */
__aligned_u64 in_batch; /* start batch,
* NULL to start from beginning
*/
__aligned_u64 out_batch; /* output: next start batch */
__aligned_u64 keys;
__aligned_u64 values;
__u32 count; /* input/output:
* input: # of key/value
* elements
* output: # of filled elements
*/
__u32 map_fd;
__u64 elem_flags;
__u64 flags;
} batch;
we can add a flag in 'flags' like BPF_F_CLEAR_MAP_IF_KV_NULL with a comment
that if keys or values is NULL, the batched elements will be cleared.
BPF_MAP_LOOKUP keys/values == NULL might be useful if we just want
the values/keys and don't want to bother copying the keys/values...
BPF_MAP_LOOKUP keys & values == NULL might be useful to count
the number of populated entries.
bpf_map_lookup_elem() does not have flags field, so we probably should not
change existins semantics.
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: Stanislav Fomichev <sdf@xxxxxxxxxxx>
Signed-off-by: Maciej Żenczykowski <maze@xxxxxxxxxx>
---
kernel/bpf/hashtab.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 5001131598e5..8fbdd000d9e0 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -1873,9 +1873,9 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
rcu_read_unlock();
bpf_enable_instrumentation();
- if (bucket_cnt && (copy_to_user(ukeys + total * key_size, keys,
+ if (bucket_cnt && (ukeys && copy_to_user(ukeys + total * key_size, keys,
key_size * bucket_cnt) ||
- copy_to_user(uvalues + total * value_size, values,
+ uvalues && copy_to_user(uvalues + total * value_size, values,
value_size * bucket_cnt))) {
ret = -EFAULT;
goto after_loop;
