Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes:
> On Sat, Mar 28, 2020 at 11:29 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote:
>>
>> For internal maps (most notably the maps backing global variables), libbpf
>> uses an internal mmaped area to store the data after opening the object.
>> This data is subsequently copied into the kernel map when the object is
>> loaded.
>>
>> This adds a function to set a new value for that data, which can be used to
>> before it is loaded into the kernel. This is especially relevant for RODATA
>> maps, since those are frozen on load.
>>
>> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
>> ---
>> v3:
>> - Add a setter for the initial value instead of a getter for the pointer to it
>> - Add selftest
>> v2:
>> - Add per-map getter for data area instead of a global rodata getter for bpf_obj
>>
>> tools/lib/bpf/libbpf.c | 11 +++++++++++
>> tools/lib/bpf/libbpf.h | 2 ++
>> tools/lib/bpf/libbpf.map | 1 +
>> 3 files changed, 14 insertions(+)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 085e41f9b68e..f9953a8ffcfa 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -6756,6 +6756,17 @@ void *bpf_map__priv(const struct bpf_map *map)
>> return map ? map->priv : ERR_PTR(-EINVAL);
>> }
>>
>> +int bpf_map__set_initial_value(struct bpf_map *map,
>> + void *data, size_t size)
>
> nit: const void *
ACK.
>> +{
>> + if (!map->mmaped || map->libbpf_type == LIBBPF_MAP_KCONFIG ||
>> + size != map->def.value_size)
>> + return -EINVAL;
>> +
>
> How about also checking that bpf_map wasn't yet created? Checking
> map->fd >= 0 should be enough.
Yup, makes sense.
>> + memcpy(map->mmaped, data, size);
>> + return 0;
>> +}
>> +
>> bool bpf_map__is_offload_neutral(const struct bpf_map *map)
>> {
>> return map->def.type == BPF_MAP_TYPE_PERF_EVENT_ARRAY;
>> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
>> index d38d7a629417..ee30ed487221 100644
>> --- a/tools/lib/bpf/libbpf.h
>> +++ b/tools/lib/bpf/libbpf.h
>> @@ -407,6 +407,8 @@ typedef void (*bpf_map_clear_priv_t)(struct bpf_map *, void *);
>> LIBBPF_API int bpf_map__set_priv(struct bpf_map *map, void *priv,
>> bpf_map_clear_priv_t clear_priv);
>> LIBBPF_API void *bpf_map__priv(const struct bpf_map *map);
>> +LIBBPF_API int bpf_map__set_initial_value(struct bpf_map *map,
>> + void *data, size_t size);
>> LIBBPF_API int bpf_map__reuse_fd(struct bpf_map *map, int fd);
>> LIBBPF_API int bpf_map__resize(struct bpf_map *map, __u32 max_entries);
>> LIBBPF_API bool bpf_map__is_offload_neutral(const struct bpf_map *map);
>> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
>> index 5129283c0284..f46873b9fe5e 100644
>> --- a/tools/lib/bpf/libbpf.map
>> +++ b/tools/lib/bpf/libbpf.map
>> @@ -243,5 +243,6 @@ LIBBPF_0.0.8 {
>> bpf_link__pin;
>> bpf_link__pin_path;
>> bpf_link__unpin;
>> + bpf_map__set_initial_value;
>> bpf_program__set_attach_target;
>> } LIBBPF_0.0.7;
>> --
>> 2.26.0
>>
