[Qemu-devel] [PATCH 04/10] block: Propagate AioContext change to parents

[Kevin Wolf <kwolf@redhat.com>]

All block nodes and users in any connected component of the block graph
must be in the same AioContext, so changing the AioContext of one node
must not only change all of its children, but all of its parents (and
in turn their children etc.) as well.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 include/block/block.h     |  2 ++
 include/block/block_int.h |  1 +
 block.c                   | 48 ++++++++++++++++++++++++++++++++++-----
 3 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/include/block/block.h b/include/block/block.h
index 649aa5b86d..b72110f315 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -590,6 +590,8 @@ void bdrv_coroutine_enter(BlockDriverState *bs, Coroutine *co);
  * This function must be called with iothread lock held.
  */
 void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context);
+void bdrv_set_aio_context_ignore(BlockDriverState *bs,
+                                 AioContext *new_context, GSList **ignore);
 int bdrv_try_set_aio_context(BlockDriverState *bs, AioContext *ctx,
                              Error **errp);
 int bdrv_child_try_set_aio_context(BlockDriverState *bs, AioContext *ctx,
diff --git a/include/block/block_int.h b/include/block/block_int.h
index aa2c638b02..1eebc7c8f3 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -694,6 +694,7 @@ struct BdrvChildRole {
 
     bool (*can_set_aio_ctx)(BdrvChild *child, AioContext *ctx,
                             GSList **ignore, Error **errp);
+    void (*set_aio_ctx)(BdrvChild *child, AioContext *ctx, GSList **ignore);
 };
 
 extern const BdrvChildRole child_file;
diff --git a/block.c b/block.c
index e36c72e297..b8bd20a234 100644
--- a/block.c
+++ b/block.c
@@ -943,6 +943,13 @@ static bool bdrv_child_cb_can_set_aio_ctx(BdrvChild *child, AioContext *ctx,
     return bdrv_can_set_aio_context(bs, ctx, ignore, errp);
 }
 
+static void bdrv_child_cb_set_aio_ctx(BdrvChild *child, AioContext *ctx,
+                                      GSList **ignore)
+{
+    BlockDriverState *bs = child->opaque;
+    return bdrv_set_aio_context_ignore(bs, ctx, ignore);
+}
+
 /*
  * Returns the options and flags that a temporary snapshot should get, based on
  * the originally requested flags (the originally requested image will have
@@ -1011,6 +1018,7 @@ const BdrvChildRole child_file = {
     .detach          = bdrv_child_cb_detach,
     .inactivate      = bdrv_child_cb_inactivate,
     .can_set_aio_ctx = bdrv_child_cb_can_set_aio_ctx,
+    .set_aio_ctx     = bdrv_child_cb_set_aio_ctx,
 };
 
 /*
@@ -1038,6 +1046,7 @@ const BdrvChildRole child_format = {
     .detach          = bdrv_child_cb_detach,
     .inactivate      = bdrv_child_cb_inactivate,
     .can_set_aio_ctx = bdrv_child_cb_can_set_aio_ctx,
+    .set_aio_ctx     = bdrv_child_cb_set_aio_ctx,
 };
 
 static void bdrv_backing_attach(BdrvChild *c)
@@ -1162,6 +1171,7 @@ const BdrvChildRole child_backing = {
     .inactivate      = bdrv_child_cb_inactivate,
     .update_filename = bdrv_backing_update_filename,
     .can_set_aio_ctx = bdrv_child_cb_can_set_aio_ctx,
+    .set_aio_ctx     = bdrv_child_cb_set_aio_ctx,
 };
 
 static int bdrv_open_flags(BlockDriverState *bs, int flags)
@@ -5732,10 +5742,10 @@ static void bdrv_attach_aio_context(BlockDriverState *bs,
     bs->walking_aio_notifiers = false;
 }
 
-/* The caller must own the AioContext lock for the old AioContext of bs, but it
- * must not own the AioContext lock for new_context (unless new_context is
- * the same as the current context of bs). */
-void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context)
+/* @ignore will accumulate all visited BdrvChild object. The caller is
+ * responsible for freeing the list afterwards. */
+void bdrv_set_aio_context_ignore(BlockDriverState *bs,
+                                 AioContext *new_context, GSList **ignore)
 {
     BdrvChild *child;
 
@@ -5746,7 +5756,20 @@ void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context)
     bdrv_drained_begin(bs);
 
     QLIST_FOREACH(child, &bs->children, next) {
-        bdrv_set_aio_context(child->bs, new_context);
+        if (g_slist_find(*ignore, child)) {
+            continue;
+        }
+        *ignore = g_slist_prepend(*ignore, child);
+        bdrv_set_aio_context_ignore(child->bs, new_context, ignore);
+    }
+    QLIST_FOREACH(child, &bs->parents, next_parent) {
+        if (g_slist_find(*ignore, child)) {
+            continue;
+        }
+        if (child->role->set_aio_ctx) {
+            *ignore = g_slist_prepend(*ignore, child);
+            child->role->set_aio_ctx(child, new_context, ignore);
+        }
     }
 
     bdrv_detach_aio_context(bs);
@@ -5760,6 +5783,16 @@ void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context)
     aio_context_release(new_context);
 }
 
+/* The caller must own the AioContext lock for the old AioContext of bs, but it
+ * must not own the AioContext lock for new_context (unless new_context is
+ * the same as the current context of bs). */
+void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context)
+{
+    GSList *ignore_list = NULL;
+    bdrv_set_aio_context_ignore(bs, new_context, &ignore_list);
+    g_slist_free(ignore_list);
+}
+
 static bool bdrv_parent_can_set_aio_context(BdrvChild *c, AioContext *ctx,
                                             GSList **ignore, Error **errp)
 {
@@ -5832,7 +5865,10 @@ int bdrv_child_try_set_aio_context(BlockDriverState *bs, AioContext *ctx,
         return -EPERM;
     }
 
-    bdrv_set_aio_context(bs, ctx);
+    ignore = ignore_child ? g_slist_prepend(NULL, ignore_child) : NULL;
+    bdrv_set_aio_context_ignore(bs, ctx, &ignore);
+    g_slist_free(ignore);
+
     return 0;
 }
 
-- 
2.20.1