[Qemu-devel] [PATCH 01/18] block: Add BdrvDeletedStatus

[Max Reitz]

Sometimes an operation may delete a BDS.  It may then not be trivial to
determine this because the BDS object itself cannot be accessed
afterwards.  With this patch, one can attach a BdrvDeletedStatus object
to a BDS which can be used to safely query whether the BDS still exists
even after it has been deleted.

Signed-off-by: Max Reitz <address@hidden>
---
 include/block/block_int.h | 12 ++++++++++++
 block.c                   |  6 ++++++
 2 files changed, 18 insertions(+)

diff --git a/include/block/block_int.h b/include/block/block_int.h
index ba4c383393..eaeaad9428 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -498,6 +498,13 @@ typedef struct BdrvAioNotifier {
     QLIST_ENTRY(BdrvAioNotifier) list;
 } BdrvAioNotifier;
 
+typedef struct BdrvDeletedStatus {
+    /* Set to true by bdrv_delete() */
+    bool deleted;
+
+    QLIST_ENTRY(BdrvDeletedStatus) next;
+} BdrvDeletedStatus;
+
 struct BdrvChildRole {
     /* If true, bdrv_replace_node() doesn't change the node this BdrvChild
      * points to. */
@@ -706,6 +713,11 @@ struct BlockDriverState {
 
     /* Only read/written by whoever has set active_flush_req to true.  */
     unsigned int flushed_gen;             /* Flushed write generation */
+
+    /* When bdrv_delete() is invoked, it will walk through this list
+     * and set every entry's @deleted field to true.  The entries will
+     * not be freed automatically. */
+    QLIST_HEAD(, BdrvDeletedStatus) deleted_status;
 };
 
 struct BlockBackendRootState {
diff --git a/block.c b/block.c
index 6dd47e414e..0b55c5a41c 100644
--- a/block.c
+++ b/block.c
@@ -3246,10 +3246,16 @@ out:
 
 static void bdrv_delete(BlockDriverState *bs)
 {
+    BdrvDeletedStatus *del_stat;
+
     assert(!bs->job);
     assert(bdrv_op_blocker_is_empty(bs));
     assert(!bs->refcnt);
 
+    QLIST_FOREACH(del_stat, &bs->deleted_status, next) {
+        del_stat->deleted = true;
+    }
+
     bdrv_close(bs);
 
     /* remove from list, if necessary */
-- 
2.13.5