sdf@xxxxxxxxxx writes:
>> +``BPF_MAP_TYPE_HASH`` and ``BPF_MAP_TYPE_PERCPU_HASH`` provide general
>> +purpose hash map storage. Both the key and the value can be structs,
>> +allowing for composite keys and values. The maximum number of entries is
>> +defined in max_entries and is limited to 2^32. The kernel is responsible
>
> Do we really need to mention 2^32 limit here? It really depends on
> the key/value sizes, right?
>
> Instead, might be worth talking about how/when this memory is allocated and
> mention BPF_F_NO_PREALLOC?
Good suggestion. I'll incorporate this into v2.
>> +.. c:function::
>> + long bpf_map_update_elem(struct bpf_map *map, const void *key, const void *value, u60
>> flags)
>
> s/u60/u64/
Good catch, thanks.
>> +Kernel
>> +------
>> +
>> +.. code-block:: c
>> +
>> + #include <linux/bpf.h>
>> + #include <bpf/bpf_helpers.h>
>> +
>> + struct key {
>> + __u32 srcip;
>> + };
>> +
>> + struct value {
>> + __u64 packets;
>> + __u64 bytes;
>> + };
>> +
>> + struct {
>> + __uint(type, BPF_MAP_TYPE_LRU_HASH);
>> + __uint(max_entries, 32);
>> + __type(key, struct key);
>> + __type(value, struct value);
>> + } packet_stats SEC(".maps");
>> +
>> + static inline void count_by_srcip(__u32 srcip, int bytes)
>> + {
>> + struct key key = {
>> + .srcip = srcip
>> + };
>> + struct value *value = bpf_map_lookup_elem(&packet_stats, &key);
>> + if (value) {
>> + __sync_fetch_and_add(&value->packets, 1);
>> + __sync_fetch_and_add(&value->bytes, bytes);
>> + } else {
>> + struct value newval = { 1, bytes };
>> + bpf_map_update_elem(&packet_stats, &key, &newval, BPF_NOEXIST);
>> + }
>> + }
>> +
>> +Userspace
>> +---------
>> +
>> +.. code-block:: c
>> +
>> + #include <bpf/libbpf.h>
>> + #include <bpf/bpf.h>
>> +
>> + static void print_values(int map_fd)
>> + {
>> + struct key *cur_key = NULL;
>> + struct key next_key;
>> + int next;
>> + do {
>> + next = bpf_map_get_next_key(stats_fd, cur_key, &next_key);
>> + if (next == -ENOENT)
>> + break;
>> + if (next < 0) {
>> + fprintf(stderr, "bpf_map_get_next_key %d returned %s\n",
>> stats_fd, strerror(-next));
>> + break;
>> + }
>> +
>> + struct in_addr src_addr = {
>> + .s_addr = next_key.srcip
>> + };
>> + char *src_ip = inet_ntoa(src_addr);
>> +
>> + struct value value;
>> + int ret = bpf_map_lookup_elem(stats_fd, &next_key, &value);
>> + if (ret < 0) {
>> + fprintf(stderr, "Failed to lookup elem with key %s: %s\n",
>> src_ip, strerror(-ret));
>> + break;
>> + }
>> + printf("%s: %lld packets, %lld bytes\n", src_ip, value.packets,
>> value.bytes);
>> + cur_key = &next_key;
>> + } while (next == 0);
>> + }
>
> Instead of adding c code, maybe add pointers to specific file within
> tools/testing/selftests/bpf/progs ? That's what we've done for
> prog_cgroup_sockopt; the actual tests are a bit more maintained than
> the doc :-)
I tried to cut the examples to the minimum that was still complete
enough to show use in context. Happy to try cutting the examples down to
a sequence of shorter snippets and and links to samples/bpf and
tools/testing/selftests/bpf/progs. I'll need to reference samples/bpf
because there are no bpf_map_get_next_key examples in
tools/testing/selftests/bpf/progs.
Donald.
