crypto: hmac: introduce qcrypto_hmac_ctx_new for nettle-backend

Extracts qcrypto_hmac_ctx_new() from qcrypto_hmac_new() for
nettle-backend impls.

Reviewed-by: Gonglei <arei.gonglei@huawei.com>
Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

crypto/hmac-nettle.c

@@ -97,11 +97,11 @@ bool qcrypto_hmac_supports(QCryptoHashAlgorithm alg)
     return false;
 }
 
-QCryptoHmac *qcrypto_hmac_new(QCryptoHashAlgorithm alg,
-                              const uint8_t *key, size_t nkey,
-                              Error **errp)
+static QCryptoHmacNettle *
+qcrypto_hmac_ctx_new(QCryptoHashAlgorithm alg,
+                     const uint8_t *key, size_t nkey,
+                     Error **errp)
 {
-    QCryptoHmac *hmac;
     QCryptoHmacNettle *ctx;
 
     if (!qcrypto_hmac_supports(alg)) {
@@ -110,16 +110,11 @@ QCryptoHmac *qcrypto_hmac_new(QCryptoHashAlgorithm alg,
         return NULL;
     }
 
-    hmac = g_new0(QCryptoHmac, 1);
-    hmac->alg = alg;
-
     ctx = g_new0(QCryptoHmacNettle, 1);
 
     qcrypto_hmac_alg_map[alg].setkey(&ctx->u, nkey, key);
 
-    hmac->opaque = ctx;
-
-    return hmac;
+    return ctx;
 }
 
 void qcrypto_hmac_free(QCryptoHmac *hmac)
@@ -173,3 +168,22 @@ int qcrypto_hmac_bytesv(QCryptoHmac *hmac,
 
     return 0;
 }
+
+QCryptoHmac *qcrypto_hmac_new(QCryptoHashAlgorithm alg,
+                              const uint8_t *key, size_t nkey,
+                              Error **errp)
+{
+    QCryptoHmac *hmac;
+    QCryptoHmacNettle *ctx;
+
+    ctx = qcrypto_hmac_ctx_new(alg, key, nkey, errp);
+    if (!ctx) {
+        return NULL;
+    }
+
+    hmac = g_new0(QCryptoHmac, 1);
+    hmac->alg = alg;
+    hmac->opaque = ctx;
+
+    return hmac;
+}