From: Kevin Wolf <kwolf@redhat.com>

Signed-off-by: Claudio Fontana <cfontana@suse.de>
---
 block/dmg.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/block/dmg.c b/block/dmg.c
index 837f18aa20..96f8c2d14f 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;
-- 
2.26.2

The patch looks like a useful improvement on its own.  But I wonder
whether users would appreciate a configuration knob to fail open right
away instead of risking I/O errors later.