storage: netfs: Split up and tidy up NFS storage pool source function

Extract the NFS related stuff into a separate function and tidy up the
rest of the code so we can reuse it to add gluster backend detection.

Additionally avoid reporting of errors from "showmount" and return an
empty source list instead. This will help when adding other detection
backends.

src/storage/storage_backend_fs.c

@@ -242,10 +242,8 @@ virStorageBackendFileSystemNetFindPoolSourcesFunc(char **const groups,
 }
 
 
-static char *
-virStorageBackendFileSystemNetFindPoolSources(virConnectPtr conn ATTRIBUTE_UNUSED,
-                                              const char *srcSpec,
-                                              unsigned int flags)
+static void
+virStorageBackendFileSystemNetFindNFSPoolSources(virNetfsDiscoverState *state)
 {
     /*
      *  # showmount --no-headers -e HOSTNAME
@@ -261,6 +259,29 @@ virStorageBackendFileSystemNetFindPoolSources(virConnectPtr conn ATTRIBUTE_UNUSE
     int vars[] = {
         1
     };
+
+    virCommandPtr cmd = NULL;
+
+    cmd = virCommandNewArgList(SHOWMOUNT,
+                               "--no-headers",
+                               "--exports",
+                               state->host,
+                               NULL);
+
+    if (virCommandRunRegex(cmd, 1, regexes, vars,
+                           virStorageBackendFileSystemNetFindPoolSourcesFunc,
+                           &state, NULL) < 0)
+        virResetLastError();
+
+    virCommandFree(cmd);
+}
+
+
+static char *
+virStorageBackendFileSystemNetFindPoolSources(virConnectPtr conn ATTRIBUTE_UNUSED,
+                                              const char *srcSpec,
+                                              unsigned int flags)
+{
     virNetfsDiscoverState state = {
         .host = NULL,
         .list = {
@@ -270,15 +291,14 @@ virStorageBackendFileSystemNetFindPoolSources(virConnectPtr conn ATTRIBUTE_UNUSE
         }
     };
     virStoragePoolSourcePtr source = NULL;
-    char *retval = NULL;
+    char *ret = NULL;
     size_t i;
-    virCommandPtr cmd = NULL;
 
     virCheckFlags(0, NULL);
 
     if (!srcSpec) {
-        virReportError(VIR_ERR_INVALID_ARG,
-                       "%s", _("hostname must be specified for netfs sources"));
+        virReportError(VIR_ERR_INVALID_ARG, "%s",
+                       _("hostname must be specified for netfs sources"));
         return NULL;
     }
 
@@ -294,19 +314,9 @@ virStorageBackendFileSystemNetFindPoolSources(virConnectPtr conn ATTRIBUTE_UNUSE
 
     state.host = source->hosts[0].name;
 
-    cmd = virCommandNewArgList(SHOWMOUNT,
-                               "--no-headers",
-                               "--exports",
-                               source->hosts[0].name,
-                               NULL);
+    virStorageBackendFileSystemNetFindNFSPoolSources(&state);
 
-    if (virCommandRunRegex(cmd, 1, regexes, vars,
-                           virStorageBackendFileSystemNetFindPoolSourcesFunc,
-                           &state, NULL) < 0)
-        goto cleanup;
-
-    retval = virStoragePoolSourceListFormat(&state.list);
-    if (retval == NULL)
+    if (!(ret = virStoragePoolSourceListFormat(&state.list)))
         goto cleanup;
 
  cleanup:
@@ -315,8 +325,7 @@ virStorageBackendFileSystemNetFindPoolSources(virConnectPtr conn ATTRIBUTE_UNUSE
     VIR_FREE(state.list.sources);
 
     virStoragePoolSourceFree(source);
-    virCommandFree(cmd);
-    return retval;
+    return ret;
 }