blk_unref() can't report any errors that happen while closing the image.
For example, if qcow2 hits an -ENOSPC error while writing out dirty
bitmaps when it's closed, it prints error messages to stderr, but
'qemu-img commit' won't see any error return value and will therefore
look successful with exit code 0.

In order to fix this, manually inactivate the image first before calling
blk_unref(). This already performs the operations that would be most
likely to fail while closing the image, but it can still return errors.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 qemu-img.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/qemu-img.c b/qemu-img.c
index 439d8de1e3..22d6ecefd5 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -449,6 +449,11 @@ static BlockBackend *img_open(bool image_opts,
         blk = img_open_file(filename, NULL, fmt, flags, writethrough, quiet,
                             force_share);
     }
+
+    if (blk) {
+        blk_set_force_allow_inactivate(blk);
+    }
+
     return blk;
 }
 
@@ -1119,6 +1124,14 @@ unref_backing:
 done:
     qemu_progress_end();
 
+    /*
+     * Manually inactivate the image first because this way we can know whether
+     * an error occurred. blk_unref() doesn't tell us about failures.
+     */
+    ret = bdrv_inactivate_all();
+    if (ret < 0 && !local_err) {
+        error_setg_errno(&local_err, -ret, "Error while closing the image");
+    }
     blk_unref(blk);
 
     if (local_err) {
-- 
2.38.1