storage: Need to refresh secret for luks volume after volume refresh

A LUKS volume uses the volume secret type just like the QCOW2 secret, so
adjust the loading of the default secrets to handle any volume that the
virStorageFileGetMetadataFromBuf code has deemed to be an encrypted volume
to search for the volume's secret. This lookup is done by volume usage
where the usage is expected to be the path to volume.

src/storage/storage_backend_fs.c

@@ -1270,8 +1270,8 @@ virStorageBackendFileSystemVolDelete(virConnectPtr conn ATTRIBUTE_UNUSED,
  * @conn: Connection pointer to fetch secret
  * @vol: volume being refreshed
  *
- * If the volume had a QCOW secret generated, we need to regenerate the
- * secret
+ * If the volume had a secret generated, we need to regenerate the
+ * encryption secret information
  *
  * Returns 0 if no secret or secret setup was successful,
  * -1 on failures w/ error message set
@@ -1283,12 +1283,16 @@ virStorageBackendFileSystemLoadDefaultSecrets(virConnectPtr conn,
     virSecretPtr sec;
     virStorageEncryptionSecretPtr encsec = NULL;
 
-    /* Only necessary for qcow format */
-    if (!vol->target.encryption ||
-        vol->target.encryption->format != VIR_STORAGE_ENCRYPTION_FORMAT_QCOW ||
-        vol->target.encryption->nsecrets != 0)
+    if (!vol->target.encryption || vol->target.encryption->nsecrets != 0)
         return 0;
 
+    /* The encryption secret for qcow2 and luks volumes use the path
+     * to the volume, so look for a secret with the path. If not found,
+     * then we cannot generate the secret after a refresh (or restart).
+     * This may be the case if someone didn't follow instructions and created
+     * a usage string that although matched with the secret usage string,
+     * didn't contain the path to the volume. We won't error in that case,
+     * but we also cannot find the secret. */
     if (!(sec = virSecretLookupByUsage(conn, VIR_SECRET_USAGE_TYPE_VOLUME,
                                        vol->target.path)))
         return 0;