[Qemu-devel] [PATCH v4 02/13] block: Add op blocker notifier list

[Fam Zheng <famz@redhat.com>]

BDS users can register a notifier and get notified about op blocker
changes.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
 block.c                   | 35 +++++++++++++++++++++++++++++++++++
 include/block/block.h     |  8 ++++++++
 include/block/block_int.h |  3 +++
 3 files changed, 46 insertions(+)

diff --git a/block.c b/block.c
index 7904098..9714603 100644
--- a/block.c
+++ b/block.c
@@ -3375,6 +3375,19 @@ struct BdrvOpBlocker {
     QLIST_ENTRY(BdrvOpBlocker) list;
 };
 
+/* Add a notifier which will be notified when the first blocker of some type is
+ * added to bs, or when the last blocker is removed. The notifier handler
+ * should receive a BlockOpEvent data.
+ *
+ * Caller must hold bs->aio_context; the notifier handler is also called with
+ * it held.
+ */
+void bdrv_op_blocker_add_notifier(BlockDriverState *bs,
+                                  Notifier *notifier)
+{
+    notifier_list_add(&bs->op_blocker_notifiers, notifier);
+}
+
 bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp)
 {
     BdrvOpBlocker *blocker;
@@ -3391,26 +3404,48 @@ bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp)
     return false;
 }
 
+static void bdrv_op_blocker_notify(BlockDriverState *bs, BlockOpType op,
+                                   Error *reason, bool blocking)
+{
+    BlockOpEvent event = (BlockOpEvent) {
+        op = op,
+        reason = reason,
+        blocking = blocking,
+    };
+
+    notifier_list_notify(&bs->op_blocker_notifiers, &event);
+}
+
 void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason)
 {
+    bool blocked;
     BdrvOpBlocker *blocker;
     assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
 
     blocker = g_new0(BdrvOpBlocker, 1);
     blocker->reason = reason;
+    blocked = !QLIST_EMPTY(&bs->op_blockers[op]);
     QLIST_INSERT_HEAD(&bs->op_blockers[op], blocker, list);
+    if (!blocked) {
+        bdrv_op_blocker_notify(bs, op, reason, true);
+    }
 }
 
 void bdrv_op_unblock(BlockDriverState *bs, BlockOpType op, Error *reason)
 {
+    bool blocked;
     BdrvOpBlocker *blocker, *next;
     assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
+    blocked = !QLIST_EMPTY(&bs->op_blockers[op]);
     QLIST_FOREACH_SAFE(blocker, &bs->op_blockers[op], list, next) {
         if (blocker->reason == reason) {
             QLIST_REMOVE(blocker, list);
             g_free(blocker);
         }
     }
+    if (blocked && QLIST_EMPTY(&bs->op_blockers[op])) {
+        bdrv_op_blocker_notify(bs, op, reason, false);
+    }
 }
 
 void bdrv_op_block_all(BlockDriverState *bs, Error *reason)
diff --git a/include/block/block.h b/include/block/block.h
index 906fb31..3420b2c 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -163,6 +163,12 @@ typedef enum BlockOpType {
     BLOCK_OP_TYPE_MAX,
 } BlockOpType;
 
+typedef struct {
+    BlockOpType type;
+    Error *reason;
+    bool blocking;
+} BlockOpEvent;
+
 void bdrv_iostatus_enable(BlockDriverState *bs);
 void bdrv_iostatus_reset(BlockDriverState *bs);
 void bdrv_iostatus_disable(BlockDriverState *bs);
@@ -491,6 +497,8 @@ void bdrv_disable_copy_on_read(BlockDriverState *bs);
 void bdrv_ref(BlockDriverState *bs);
 void bdrv_unref(BlockDriverState *bs);
 
+void bdrv_op_blocker_add_notifier(BlockDriverState *bs,
+                                  Notifier *notifier);
 bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp);
 void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason);
 void bdrv_op_unblock(BlockDriverState *bs, BlockOpType op, Error *reason);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index db29b74..29d1c84 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -418,6 +418,9 @@ struct BlockDriverState {
     /* operation blockers */
     QLIST_HEAD(, BdrvOpBlocker) op_blockers[BLOCK_OP_TYPE_MAX];
 
+    /* Callback when one list in op_blockers has "empty" status change. */
+    NotifierList op_blocker_notifiers;
+
     /* long-running background operation */
     BlockJob *job;
 
-- 
2.4.1