On 1/6/25 3:53 PM, Charalampos Stylianopoulos wrote:
This patch series provides an easy way for userspace applications to query the number of entries currently present in a map. Currently, the number of entries in a map is accessible only from kernel space and eBPF programs. A userspace program that wants to track map utilization has to create and attach an eBPF program solely for that purpose. This series makes the number of entries in a map easily accessible, by extending the main bpf syscall with a new command. The command supports only maps that already track utilization, namely hash maps, LPM maps and queue/stack maps.
An earlier attempt to directly expose it to user space can be found here [0], which eventually led to [1] to only expose it via kfunc for BPF programs in order to avoid extending UAPI. Perhaps instead add a small libbpf helper (e.g. bpf_map__current_entries to complement bpf_map__max_entries) which does all the work to extract that info via [1] underneath? Thanks, Daniel [0] https://lore.kernel.org/bpf/20230531110511.64612-1-aspsk@xxxxxxxxxxxxx/ [1] https://lore.kernel.org/bpf/20230705160139.19967-1-aspsk@xxxxxxxxxxxxx/ https://lore.kernel.org/bpf/20230719092952.41202-1-aspsk@xxxxxxxxxxxxx/
Charalampos Stylianopoulos (4): bpf: Add map_num_entries map op bpf: Add bpf command to get number of map entries libbpf: Add support for MAP_GET_NUM_ENTRIES command selftests/bpf: Add tests for bpf_map_get_num_entries include/linux/bpf.h | 3 ++ include/linux/bpf_local_storage.h | 1 + include/uapi/linux/bpf.h | 17 +++++++++ kernel/bpf/devmap.c | 14 ++++++++ kernel/bpf/hashtab.c | 10 ++++++ kernel/bpf/lpm_trie.c | 8 +++++ kernel/bpf/queue_stack_maps.c | 11 +++++- kernel/bpf/syscall.c | 32 +++++++++++++++++ tools/include/uapi/linux/bpf.h | 17 +++++++++ tools/lib/bpf/bpf.c | 16 +++++++++ tools/lib/bpf/bpf.h | 2 ++ tools/lib/bpf/libbpf.map | 1 + .../bpf/map_tests/lpm_trie_map_basic_ops.c | 5 +++ tools/testing/selftests/bpf/test_maps.c | 35 +++++++++++++++++++ 14 files changed, 171 insertions(+), 1 deletion(-)
