util: Perform proper virRandomBytes return value checking

Document the return value of virRandomBytes as 0 or some errno value and
then make sure all callers make the proper checks.

src/util/vircrypto.c

@@ -315,7 +315,7 @@ virCryptoGenerateRandom(size_t nbytes)
     /* If we don't have gnutls_rnd(), we will generate a less cryptographically
      * strong master buf from /dev/urandom.
      */
-    if ((ret = virRandomBytes(buf, nbytes)) < 0) {
+    if ((ret = virRandomBytes(buf, nbytes))) {
         virReportSystemError(ret, "%s", _("failed to generate byte stream"));
         VIR_FREE(buf);
         return NULL;

src/util/virrandom.c

@@ -167,6 +167,8 @@ uint32_t virRandomInt(uint32_t max)
  *
  * Generate a stream of random bytes from /dev/urandom
  * into @buf of size @buflen
+ *
+ * Returns 0 on success or an errno on failure
  */
 int
 virRandomBytes(unsigned char *buf,

tests/vircryptotest.c

@@ -87,9 +87,11 @@ testCryptoEncrypt(const void *opaque)
         VIR_ALLOC_N(iv, ivlen) < 0)
         goto cleanup;
 
-    if (virRandomBytes(enckey, enckeylen) < 0 ||
-        virRandomBytes(iv, ivlen) < 0)
+    if (virRandomBytes(enckey, enckeylen) ||
+        virRandomBytes(iv, ivlen)) {
+        fprintf(stderr, "Failed to generate random bytes\n");
         goto cleanup;
+    }
 
     if (virCryptoEncryptData(data->algorithm, enckey, enckeylen, iv, ivlen,
                              data->input, data->inputlen,

tests/virrandomtest.c

@@ -40,7 +40,7 @@ testRandomBytes(const void *unused ATTRIBUTE_UNUSED)
     if (VIR_ALLOC_N(data, datalen) < 0)
         return -1;
 
-    if (virRandomBytes(data, datalen) < 0) {
+    if (virRandomBytes(data, datalen)) {
         fprintf(stderr, "Failed to generate random bytes");
         goto cleanup;
     }