[PATCH] qcow2: Use a GString in report_unsupported_feature()

[Alberto Garcia <berto@igalia.com>]

This is a bit more efficient than having to allocate and free memory
for each item.

The default size (60) is enough for all the existing incompatible
features.

Suggested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Alberto Garcia <berto@igalia.com>
---
 block/qcow2.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index cef9d72b3a..ecf6827420 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -453,16 +453,15 @@ static void cleanup_unknown_header_ext(BlockDriverState *bs)
 static void report_unsupported_feature(Error **errp, Qcow2Feature *table,
                                        uint64_t mask)
 {
-    char *features = g_strdup("");
-    char *old;
+    GString *features = g_string_sized_new(60);
 
     while (table && table->name[0] != '\0') {
         if (table->type == QCOW2_FEAT_TYPE_INCOMPATIBLE) {
             if (mask & (1ULL << table->bit)) {
-                old = features;
-                features = g_strdup_printf("%s%s%.46s", old, *old ? ", " : "",
-                                           table->name);
-                g_free(old);
+                if (features->len > 0) {
+                    g_string_append(features, ", ");
+                }
+                g_string_append_printf(features, "%.46s", table->name);
                 mask &= ~(1ULL << table->bit);
             }
         }
@@ -470,14 +469,15 @@ static void report_unsupported_feature(Error **errp, Qcow2Feature *table,
     }
 
     if (mask) {
-        old = features;
-        features = g_strdup_printf("%s%sUnknown incompatible feature: %" PRIx64,
-                                   old, *old ? ", " : "", mask);
-        g_free(old);
+        if (features->len > 0) {
+            g_string_append(features, ", ");
+        }
+        g_string_append_printf(features,
+                               "Unknown incompatible feature: %" PRIx64, mask);
     }
 
-    error_setg(errp, "Unsupported qcow2 feature(s): %s", features);
-    g_free(features);
+    error_setg(errp, "Unsupported qcow2 feature(s): %s", features->str);
+    g_string_free(features, TRUE);
 }
 
 /*
-- 
2.20.1