Fix issues with pinned sk_storage map

[yonghong-song]

The BPF_SK_STORAGE map is defined as below:

  #define BPF_SK_STORAGE(_name, _leaf_type) \
  struct _name##_table_t { \
    int key; \
    _leaf_type leaf; \
    void * (*sk_storage_get) (void *, void *, int); \
    int (*sk_storage_delete) (void *); \
    u32 flags; \
  };

The structure has two func pointer members, sk_storage_get and
sk_storage_delete, which will be translated to corresponding
bpf helpers by rewriter.

If a BPF_SK_STORAGE map is pinned to bpffs, the map can be
used in another bcc based process with BPF_TABLE_PINNED macro.

  #define BPF_TABLE_PINNED(_table_type, _key_type, _leaf_type, _name, _max_entries, _pinned) \
  BPF_TABLE(_table_type ":" _pinned, _key_type, _leaf_type, _name, _max_entries)

Miao Xu reported an issue such that the structure supporting BPF_TABLE
does not have func pointer member sk_storage_get and sk_storage_delete and
this may cause BPF program compilation failure. For example,
without helpers.h change in this patch, the test case in this patch will have the
following error:

  /virtual/main.c:14:22: error: no member named 'sk_storage_get' in 'struct sk_stg_table_t'
          val = sk_stg.sk_storage_get(sk, NULL, BPF_SK_STORAGE_GET_F_CREATE);

To fix the above issue, we need to add sk_storage_get and
sk_storage_delete to BPF_F_TABLE macro. I also added
{task, inode}storage{get, delete} func pointer members
to BPF_F_TABLE macro. Some other map macros like BPF_SOCKMAP,
BPF_SOCKHASH, etc. also have special func pointer members.
But I leave them for future patches if we have use cases for it.

Signed-off-by: Yonghong Song yhs@fb.com

[davemarchevsky]

Thanks for the detailed explanation! LGTM

To confirm my understanding, is this the rewriter magic you're referring to?

[yonghong-song]

To confirm my understanding, is this the rewriter magic you're referring to?

Yes, it is.