Allow the use of custom keys in BPF_HASH_OF_MAPS

[masibw]

close #3496
Hi team. I wrote a macro that can use custom key for BPF_HASH_OF_MAPS.

But in c++, get_map_in_map_table is shared to BPF_ARRAY_OF_MAPS.
So, when using BPF_ARRAY_OF_MAPS, we have to declare like this.

auto t = bpf.get_map_in_map_table<int>("maps_array");

Is it okay?

-- solved --
Maybe I could wrote about BPF_HASH_OF_MAPS macro. But .cc files have errors. I've never write c++ programs, Can anyone help me?

In file included from /home/*/bcc/tests/cc/test_map_in_map.cc:21:
In file included from /home/*/bcc/src/cc/api/BPF.h:25:
/home/*/bcc/src/cc/api/BPFTable.h:487:15: error: function 'ebpf::BPFMapInMapTable<custom_key>::update_value' is used but not defined in this translation unit, and cannot be defined in any other translation unit because its type does not have linkage
  StatusTuple update_value(const KeyType& key, const int& inner_map_fd);
              ^
/home/*/bcc/tests/cc/test_map_in_map.cc:182:13: note: used here
    res = t.update_value(hash_key, ex1_fd);

This is probably due to the fact that the definition and implementation are in separate files, but if I write it in the header file, the following error occurs. I don't know which one is closer to the solution, so I pushed the one where the definition and implementation are in separate files.

In file included from /home/*/bcc/tests/cc/test_map_in_map.cc:21:
In file included from /home/*/bcc/src/cc/api/BPF.h:25:
/home/*/bcc/src/cc/api/BPFTable.h:499:23: error: const_cast from 'char *(*)(const char *, int) throw()' to 'custom_key *' is not allowed
    if (!this->remove(const_cast<KeyType*>(&index)))

[chenhengqi]

The implementation of a template class should be in header file.

[masibw]

Thanks for replying @chenhengqi, like this code?

but I have this error.

In file included from /home/*/bcc/tests/cc/test_map_in_map.cc:21:
In file included from /home/*/bcc/src/cc/api/BPF.h:25:
/home/*/bcc/src/cc/api/BPFTable.h:499:23: error: const_cast from 'char *(*)(const char *, int) throw()' to 'custom_key *' is not allowed
    if (!this->remove(const_cast<KeyType*>(&index)))

[chenhengqi]

remove(&key) not remove(&index)

[chenhengqi]

style: 2 space for indention, 1 space after comma.

[masibw]

Thanks, fixed

[masibw]

remove(&key) not remove(&index)

Oh, I'm sorry. I made a terrible mistake. 😢
Thanks to you, it's working now.

[yonghong-song]

[buildbot, test this please]

[masibw]

Sorry, I made a mistake with the test_map_in_map.py file name.

[yonghong-song]

[buildbot, test this please]

[yonghong-song]

test_map_in_map.py failed, probably due to python3 compatibility.

42: Traceback (most recent call last):
42:   File "/home/fedora/jenkins/workspace/bcc-pr/label/fc28/tests/python/test_map_in_map.py", line 160, in test_hash_table_custom_key
42:     assert(ex1_map[ct.c_int(0)] >= 1)
42: TypeError: '>=' not supported between instances of 'c_int' and 'int'

[yonghong-song]

[buildbot, ok to test]

[masibw]

test_map_in_map.py failed, probably due to python3 compatibility.

OK, probably fixed.

[yonghong-song]

LGTM. Thanks!