layer: refactor and better describe the API

- The API and ABI for modules changes slightly (details below).
  KR_MODULE_API is bumped to avoid loading incompatible code.
  We have bumped libkres ABIVER since the last release 1.1.1,
  so leaving that one intact.

- Make KR_STATE_YIELD not reuse 0 value anymore.
  It's easy to e.g. return kr_ok() by mistake.
- struct kr_layer_t:
  * ::mm was unused, uninitialized, etc.
  * Make ::state an int, as it was everywhere else.
  * void *data was ugly and always containing struct kr_request *
- struct kr_layer_api:
  * Drop the void* parameter from ::begin, as it was only used
    for the request which is available as ctx->req anyway
    (formerly ctx->data).
  * Drop ::fail.  It wasn't even called.  Modules can watch for
    KR_STATE_FAIL in ::finish.
- Document the apparent meaning of the layer interface, deduced mainly
  from the way it's used in the code.  Caveats:
  * enum knot_layer_state handling seems to assume that it holds exactly
    one of the possibilities at a time.  The cookie module does NOT
    follow that (intentionally), apparently depending on the exact
    implementation of the handling at that moment.  It feels fragile.
  * I was unable to deduce a plausible description of when ::reset is
    called.  It's practically unused in modules, too.

1 files changed, 6 insertions, 6 deletions

diff --git a/daemon/ffimodule.c b/daemon/ffimodule.c
index 65410a36..af7e46da 100644
--- a/daemon/ffimodule.c
+++ b/daemon/ffimodule.c
@@ -146,23 +146,23 @@ static int l_ffi_deinit(struct kr_module *module)
 	lua_rawgeti(L, LUA_REGISTRYINDEX, cb_slot[SLOT_ ## slot]); \
 	lua_pushnumber(L, ctx->state)
 
-static int l_ffi_layer_begin(kr_layer_t *ctx, void *module_param)
+static int l_ffi_layer_begin(kr_layer_t *ctx)
 {
 	LAYER_FFI_CALL(ctx, begin);
-	lua_pushlightuserdata(L, ctx->data);
+	lua_pushlightuserdata(L, ctx->req);
 	return l_ffi_call(L, 2);
 }
 
 static int l_ffi_layer_reset(kr_layer_t *ctx)
 {
 	LAYER_FFI_CALL(ctx, reset);
-	lua_pushlightuserdata(L, ctx->data);
+	lua_pushlightuserdata(L, ctx->req);
 	return l_ffi_call(L, 2);
 }
 
 static int l_ffi_layer_finish(kr_layer_t *ctx)
 {
-	struct kr_request *req = ctx->data;
+	struct kr_request *req = ctx->req;
 	LAYER_FFI_CALL(ctx, finish);
 	lua_pushlightuserdata(L, req);
 	lua_pushlightuserdata(L, req->answer);
@@ -175,7 +175,7 @@ static int l_ffi_layer_consume(kr_layer_t *ctx, knot_pkt_t *pkt)
 		return ctx->state; /* Already failed, skip */
 	}
 	LAYER_FFI_CALL(ctx, consume);
-	lua_pushlightuserdata(L, ctx->data);
+	lua_pushlightuserdata(L, ctx->req);
 	lua_pushlightuserdata(L, pkt);
 	return l_ffi_call(L, 3);
 }
@@ -186,7 +186,7 @@ static int l_ffi_layer_produce(kr_layer_t *ctx, knot_pkt_t *pkt)
 		return ctx->state; /* Already failed or done, skip */
 	}
 	LAYER_FFI_CALL(ctx, produce);
-	lua_pushlightuserdata(L, ctx->data);
+	lua_pushlightuserdata(L, ctx->req);
 	lua_pushlightuserdata(L, pkt);
 	return l_ffi_call(L, 3);
 }