1 files changed, 38 insertions, 3 deletions

diff --git a/block.c b/block.c
index 3feac08535..5ba3435f8f 100644
--- a/block.c
+++ b/block.c
@@ -1137,7 +1137,7 @@ static int bdrv_open_flags(BlockDriverState *bs, int flags)
 
 static void update_flags_from_options(int *flags, QemuOpts *opts)
 {
-    *flags &= ~BDRV_O_CACHE_MASK;
+    *flags &= ~(BDRV_O_CACHE_MASK | BDRV_O_RDWR | BDRV_O_AUTO_RDONLY);
 
     assert(qemu_opt_find(opts, BDRV_OPT_CACHE_NO_FLUSH));
     if (qemu_opt_get_bool_del(opts, BDRV_OPT_CACHE_NO_FLUSH, false)) {
@@ -1149,8 +1149,6 @@ static void update_flags_from_options(int *flags, QemuOpts *opts)
         *flags |= BDRV_O_NOCACHE;
     }
 
-    *flags &= ~BDRV_O_RDWR;
-
     assert(qemu_opt_find(opts, BDRV_OPT_READ_ONLY));
     if (!qemu_opt_get_bool_del(opts, BDRV_OPT_READ_ONLY, false)) {
         *flags |= BDRV_O_RDWR;
@@ -2262,6 +2260,18 @@ static void bdrv_parent_cb_change_media(BlockDriverState *bs, bool load)
     }
 }
 
+/* Return true if you can reach parent going through child->inherits_from
+ * recursively. If parent or child are NULL, return false */
+static bool bdrv_inherits_from_recursive(BlockDriverState *child,
+                                         BlockDriverState *parent)
+{
+    while (child && child != parent) {
+        child = child->inherits_from;
+    }
+
+    return child != NULL;
+}
+
 /*
  * Sets the backing file link of a BDS. A new reference is created; callers
  * which don't need their own reference any more must call bdrv_unref().
@@ -2269,6 +2279,9 @@ static void bdrv_parent_cb_change_media(BlockDriverState *bs, bool load)
 void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
                          Error **errp)
 {
+    bool update_inherits_from = bdrv_chain_contains(bs, backing_hd) &&
+        bdrv_inherits_from_recursive(backing_hd, bs);
+
     if (backing_hd) {
         bdrv_ref(backing_hd);
     }
@@ -2284,6 +2297,12 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
 
     bs->backing = bdrv_attach_child(bs, backing_hd, "backing", &child_backing,
                                     errp);
+    /* If backing_hd was already part of bs's backing chain, and
+     * inherits_from pointed recursively to bs then let's update it to
+     * point directly to bs (else it will become NULL). */
+    if (update_inherits_from) {
+        backing_hd->inherits_from = bs;
+    }
     if (!bs->backing) {
         bdrv_unref(backing_hd);
     }
@@ -3836,6 +3855,8 @@ BlockDriverState *bdrv_find_base(BlockDriverState *bs)
 int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
                            const char *backing_file_str)
 {
+    BlockDriverState *explicit_top = top;
+    bool update_inherits_from;
     BdrvChild *c, *next;
     Error *local_err = NULL;
     int ret = -EIO;
@@ -3851,6 +3872,16 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
         goto exit;
     }
 
+    /* If 'base' recursively inherits from 'top' then we should set
+     * base->inherits_from to top->inherits_from after 'top' and all
+     * other intermediate nodes have been dropped.
+     * If 'top' is an implicit node (e.g. "commit_top") we should skip
+     * it because no one inherits from it. We use explicit_top for that. */
+    while (explicit_top && explicit_top->implicit) {
+        explicit_top = backing_bs(explicit_top);
+    }
+    update_inherits_from = bdrv_inherits_from_recursive(base, explicit_top);
+
     /* success - we can delete the intermediate states, and link top->base */
     /* TODO Check graph modification op blockers (BLK_PERM_GRAPH_MOD) once
      * we've figured out how they should work. */
@@ -3886,6 +3917,10 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
         bdrv_unref(top);
     }
 
+    if (update_inherits_from) {
+        base->inherits_from = explicit_top->inherits_from;
+    }
+
     ret = 0;
 exit:
     bdrv_unref(top);