Remove ENGINE variables from private structures

[jogme]

Most of our structures should be private, but would need investigating one by one. A list to start with:

apps/engine.c:261: in struct util_store_cap_data
  vars: engine
  decl: ENGINE *engine

crypto/dsa/dsa_local.h:21: in struct dsa_st
  vars: engine
  decl: ENGINE *engine

crypto/evp/evp_local.h:11: in struct evp_md_ctx_st
  vars: engine
  decl: ENGINE *engine

crypto/evp/evp_local.h:26: in struct evp_cipher_ctx_st
  vars: engine
  decl: ENGINE *engine

crypto/engine/eng_table.c:14: in struct st_engine_pile
  vars: funct
  decl: ENGINE *funct

crypto/engine/tb_asnmth.c:134: in struct ENGINE_FIND_STR
  vars: e
  decl: ENGINE *e

crypto/store/store_local.h:63: in struct ossl_store_loader_st
  vars: engine
  decl: ENGINE *engine

crypto/dh/dh_local.h:22: in struct dh_st
  vars: engine
  decl: ENGINE *engine

crypto/rsa/rsa_local.h:47: in struct rsa_st
  vars: engine
  decl: ENGINE *engine

crypto/ec/ec_local.h:208: in struct ec_key_st
  vars: engine
  decl: ENGINE *engine

include/crypto/evp.h:88: in struct evp_pkey_ctx_st
  vars: engine
  decl: ENGINE *engine

include/crypto/evp.h:542: in struct evp_pkey_st
  vars: engine
  decl: ENGINE *engine

include/crypto/evp.h:543: in struct evp_pkey_st
  vars: pmeth_engine
  decl: ENGINE *pmeth_engine

[mbroz]

For the record, these cannot be modified/removed:

• DSA_get0_engine(), DH_get0_engine(), RSA_get0_engine(), EC_KEY_get0_engine() - public API, now return NULL
• crypto/engine - completely remove later, it make no sense to broke the engine handling code
• store/store_local.h - public API, cannot remove
• struct evp_pkey_ctx_st (EVP_PKEY_CTX), evp_pkey_st (EVP_PKEY) - public API, cannot remove

[t8m]

• DSA_get0_engine(), DH_get0_engine(), RSA_get0_engine(), EC_KEY_get0_engine() - public API, now return NULL

Why? These are already deprecated, in a world without ENGINEs they do not have any use. Please just remove them.

• crypto/engine - completely remove later, it make no sense to broke the engine handling code

??

• store/store_local.h - public API, cannot remove

?? store_local.h is not public API. The only public API is in include/openssl headers.

• struct evp_pkey_ctx_st (EVP_PKEY_CTX), evp_pkey_st (EVP_PKEY) - public API, cannot remove

Same as above, definitions of these structs (not the opaque typedefs!) are not a public API.

[mbroz]

• DSA_get0_engine(), DH_get0_engine(), RSA_get0_engine(), EC_KEY_get0_engine() - public API, now return NULL

Why? These are already deprecated, in a world without ENGINEs they do not have any use. Please just remove them.

yes, but then this is another sub issue (if we want to split it to so many pieces...)

The same applies for the rest - if it is ok to remove it now, I will do it.

...

• struct evp_pkey_ctx_st (EVP_PKEY_CTX), evp_pkey_st (EVP_PKEY) - public API, cannot remove

Same as above, definitions of these structs (not the opaque typedefs!) are not a public API.

Yes, struct is not public, but I was not sure touching internal struct used for public context is ok (with typedef perhaps it is :)

[t8m]

Yes, struct is not public, but I was not sure touching internal struct used for public context is ok (with typedef perhaps it is :)

It will just be an opaque typedef starting from 4.0.

[t8m]

yes, but then this is another sub issue (if we want to split it to so many pieces...)

I would not split this particular thing out because it is a direct implication of removal of the pointer from the structure.

[mbroz]

Updated mbroz/openssl@331bbf8

The API removal *get_engines() is yet for discussion - can do it later (I have patch locally on top of this one).

I do not touch apps/engine.c and crypto/engine - I think we will simple remove whole code en-bloc in another sub issue.