1 files changed, 30 insertions, 3 deletions

diff --git a/block/dmg.c b/block/dmg.c
index 422136276a..675e840ca5 100644
--- a/block/dmg.c
+++ b/block/dmg.c
@@ -254,6 +254,25 @@ static int dmg_read_mish_block(BDRVDMGState *s, DmgHeaderState *ds,
     for (i = s->n_chunks; i < s->n_chunks + chunk_count; i++) {
         s->types[i] = buff_read_uint32(buffer, offset);
         if (!dmg_is_known_block_type(s->types[i])) {
+            switch (s->types[i]) {
+            case UDBZ:
+                warn_report_once("dmg-bzip2 module is missing, accessing bzip2 "
+                                 "compressed blocks will result in I/O errors");
+                break;
+            case ULFO:
+                warn_report_once("dmg-lzfse module is missing, accessing lzfse "
+                                 "compressed blocks will result in I/O errors");
+                break;
+            case UDCM:
+            case UDLE:
+                /* Comments and last entry can be ignored without problems */
+                break;
+            default:
+                warn_report_once("Image contains chunks of unknown type %x, "
+                                 "accessing them will result in I/O errors",
+                                 s->types[i]);
+                break;
+            }
             chunk_count--;
             i--;
             offset += 40;
@@ -444,9 +463,17 @@ static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
     if (ret < 0) {
         return ret;
     }
-
-    block_module_load_one("dmg-bz2");
-    block_module_load_one("dmg-lzfse");
+    /*
+     * NB: if uncompress submodules are absent,
+     * ie block_module_load return value == 0, the function pointers
+     * dmg_uncompress_bz2 and dmg_uncompress_lzfse will be NULL.
+     */
+    if (block_module_load("dmg-bz2", errp) < 0) {
+        return -EINVAL;
+    }
+    if (block_module_load("dmg-lzfse", errp) < 0) {
+        return -EINVAL;
+    }
 
     s->n_chunks = 0;
     s->offsets = s->lengths = s->sectors = s->sectorcounts = NULL;