[dnssec] keystore: internal context initialization via pointer

Some providers may not need the context.

dnssec/lib/keystore/internal.h

@@ -8,7 +8,7 @@
 
 typedef struct keystore_functions {
 	// construction of internal context
-	void *(*ctx_new)(void *custom_data);
+	int (*ctx_new)(void **ctx_ptr, void *custom_data);
 	void (*ctx_free)(void *ctx);
 	// keystore open/close
 	int (*open)(void *ctx, const char *config);

dnssec/lib/keystore/keystore.c

@@ -23,13 +23,13 @@ int keystore_create(dnssec_keystore_t **store_ptr,
 
 	store->functions = functions;
 
-	store->ctx = functions->ctx_new(ctx_custom_data);
-	if (!store->ctx) {
+	int result = functions->ctx_new(&store->ctx, ctx_custom_data);
+	if (result != DNSSEC_EOK) {
 		free(store);
 		return DNSSEC_ENOMEM;
 	}
 
-	int result = functions->open(store->ctx, open_config);
+	result = functions->open(store->ctx, open_config);
 	if (result != DNSSEC_EOK) {
 		dnssec_keystore_close(store);
 		return result;

dnssec/lib/keystore/pkcs11.c

@@ -14,9 +14,15 @@ typedef struct pkcs11_ctx {
 
 /* -- internal API --------------------------------------------------------- */
 
-static void *pkcs11_ctx_new(_unused_ void *data)
+static int pkcs11_ctx_new(void **ctx_ptr, _unused_ void *data)
 {
-	return calloc(1, sizeof(pkcs11_ctx_t));
+	pkcs11_ctx_t *ctx = calloc(1, sizeof(*ctx));
+	if (!ctx) {
+		return DNSSEC_ENOMEM;
+	}
+
+	*ctx_ptr = ctx;
+	return DNSSEC_EOK;
 }
 
 static void pkcs11_ctx_free(void *ctx)

dnssec/lib/keystore/pkcs8.c

@@ -20,19 +20,21 @@ typedef struct pkcs8_ctx {
 
 /* -- internal API --------------------------------------------------------- */
 
-static void *pkcs8_ctx_new(void *data)
+static int pkcs8_ctx_new(void **ctx_ptr, void *data)
 {
+	assert(ctx_ptr);
 	assert(data);
 
 	pkcs8_ctx_t *ctx = calloc(1, sizeof(*ctx));
 	if (!ctx) {
-		return NULL;
+		return DNSSEC_ENOMEM;
 	}
 
 	dnssec_keystore_pkcs8_functions_t *functions = data;
 	ctx->functions = functions;
 
-	return ctx;
+	*ctx_ptr = ctx;
+	return DNSSEC_EOK;
 }
 
 static void pkcs8_ctx_free(void *ctx)