block: sort formats alphabetically in bdrv_iterate_format()

Format names are best consumed in alphabetical order.  This makes
human-readable output easy to produce.

bdrv_iterate_format() already has an array of format strings.  Sort them
before invoking the iteration callback.
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NBenoît Canet <benoit.canet@nodalink.com>

block.c

@@ -3744,11 +3744,17 @@ const char *bdrv_get_format_name(BlockDriverState *bs)
     return bs->drv ? bs->drv->format_name : NULL;
 }
 
+static int qsort_strcmp(const void *a, const void *b)
+{
+    return strcmp(a, b);
+}
+
 void bdrv_iterate_format(void (*it)(void *opaque, const char *name),
                          void *opaque)
 {
     BlockDriver *drv;
     int count = 0;
+    int i;
     const char **formats = NULL;
 
     QLIST_FOREACH(drv, &bdrv_drivers, list) {
@@ -3762,10 +3768,16 @@ void bdrv_iterate_format(void (*it)(void *opaque, const char *name),
             if (!found) {
                 formats = g_renew(const char *, formats, count + 1);
                 formats[count++] = drv->format_name;
-                it(opaque, drv->format_name);
             }
         }
     }
+
+    qsort(formats, count, sizeof(formats[0]), qsort_strcmp);
+
+    for (i = 0; i < count; i++) {
+        it(opaque, formats[i]);
+    }
+
     g_free(formats);
 }