We are going to increase usage of collecting nodes in a list to then
update, and calling bdrv_topological_dfs() each time is not convenient,
and not correct as we are going to interleave graph modifying with
filling the node list.

So, let's switch to a function that takes any list of nodes, adds all
their subtrees and do topological sort. And finally, refresh
permissions.

While being here, make the function public, as we'll want to use it
from blockdev.c in near future.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@openvz.org>
---
 block.c | 51 ++++++++++++++++++++++++++++++++-------------------
 1 file changed, 32 insertions(+), 19 deletions(-)

diff --git a/block.c b/block.c
index f3ed351360..9009f73534 100644
--- a/block.c
+++ b/block.c
@@ -2487,8 +2487,12 @@ static int bdrv_node_refresh_perm(BlockDriverState *bs, BlockReopenQueue *q,
     return 0;
 }
 
-static int bdrv_list_refresh_perms(GSList *list, BlockReopenQueue *q,
-                                   Transaction *tran, Error **errp)
+/*
+ * @list is a product of bdrv_topological_dfs() (may be called several times) -
+ * a topologically sorted subgraph.
+ */
+static int bdrv_do_refresh_perms(GSList *list, BlockReopenQueue *q,
+                                 Transaction *tran, Error **errp)
 {
     int ret;
     BlockDriverState *bs;
@@ -2510,6 +2514,24 @@ static int bdrv_list_refresh_perms(GSList *list, BlockReopenQueue *q,
     return 0;
 }
 
+/*
+ * @list is any list of nodes. List is completed by all subtreees and
+ * topologically sorted. It's not a problem if some node occurs in the @list
+ * several times.
+ */
+static int bdrv_list_refresh_perms(GSList *list, BlockReopenQueue *q,
+                                   Transaction *tran, Error **errp)
+{
+    g_autoptr(GHashTable) found = g_hash_table_new(NULL, NULL);
+    g_autoptr(GSList) refresh_list = NULL;
+
+    for ( ; list; list = list->next) {
+        refresh_list = bdrv_topological_dfs(refresh_list, found, list->data);
+    }
+
+    return bdrv_do_refresh_perms(refresh_list, q, tran, errp);
+}
+
 void bdrv_get_cumulative_perm(BlockDriverState *bs, uint64_t *perm,
                               uint64_t *shared_perm)
 {
@@ -2570,7 +2592,7 @@ static int bdrv_refresh_perms(BlockDriverState *bs, Transaction *tran,
         tran = local_tran = tran_new();
     }
 
-    ret = bdrv_list_refresh_perms(list, NULL, tran, errp);
+    ret = bdrv_do_refresh_perms(list, NULL, tran, errp);
 
     if (local_tran) {
         tran_finalize(local_tran, ret);
@@ -4339,7 +4361,6 @@ int bdrv_reopen_multiple(BlockReopenQueue *bs_queue, Error **errp)
     BlockReopenQueueEntry *bs_entry, *next;
     AioContext *ctx;
     Transaction *tran = tran_new();
-    g_autoptr(GHashTable) found = NULL;
     g_autoptr(GSList) refresh_list = NULL;
 
     assert(qemu_get_current_aio_context() == qemu_get_aio_context());
@@ -4369,18 +4390,15 @@ int bdrv_reopen_multiple(BlockReopenQueue *bs_queue, Error **errp)
         bs_entry->prepared = true;
     }
 
-    found = g_hash_table_new(NULL, NULL);
     QTAILQ_FOREACH(bs_entry, bs_queue, entry) {
         BDRVReopenState *state = &bs_entry->state;
 
-        refresh_list = bdrv_topological_dfs(refresh_list, found, state->bs);
+        refresh_list = g_slist_prepend(refresh_list, state->bs);
         if (state->old_backing_bs) {
-            refresh_list = bdrv_topological_dfs(refresh_list, found,
-                                                state->old_backing_bs);
+            refresh_list = g_slist_prepend(refresh_list, state->old_backing_bs);
         }
         if (state->old_file_bs) {
-            refresh_list = bdrv_topological_dfs(refresh_list, found,
-                                                state->old_file_bs);
+            refresh_list = g_slist_prepend(refresh_list, state->old_file_bs);
         }
     }
 
@@ -5100,7 +5118,6 @@ static int bdrv_replace_node_common(BlockDriverState *from,
                                     Error **errp)
 {
     Transaction *tran = tran_new();
-    g_autoptr(GHashTable) found = NULL;
     g_autoptr(GSList) refresh_list = NULL;
     BlockDriverState *to_cow_parent = NULL;
     int ret;
@@ -5141,10 +5158,8 @@ static int bdrv_replace_node_common(BlockDriverState *from,
         bdrv_remove_child(bdrv_filter_or_cow_child(to_cow_parent), tran);
     }
 
-    found = g_hash_table_new(NULL, NULL);
-
-    refresh_list = bdrv_topological_dfs(refresh_list, found, to);
-    refresh_list = bdrv_topological_dfs(refresh_list, found, from);
+    refresh_list = g_slist_prepend(refresh_list, to);
+    refresh_list = g_slist_prepend(refresh_list, from);
 
     ret = bdrv_list_refresh_perms(refresh_list, NULL, tran, errp);
     if (ret < 0) {
@@ -5227,7 +5242,6 @@ int bdrv_replace_child_bs(BdrvChild *child, BlockDriverState *new_bs,
 {
     int ret;
     Transaction *tran = tran_new();
-    g_autoptr(GHashTable) found = NULL;
     g_autoptr(GSList) refresh_list = NULL;
     BlockDriverState *old_bs = child->bs;
 
@@ -5239,9 +5253,8 @@ int bdrv_replace_child_bs(BdrvChild *child, BlockDriverState *new_bs,
 
     bdrv_replace_child_tran(child, new_bs, tran);
 
-    found = g_hash_table_new(NULL, NULL);
-    refresh_list = bdrv_topological_dfs(refresh_list, found, old_bs);
-    refresh_list = bdrv_topological_dfs(refresh_list, found, new_bs);
+    refresh_list = g_slist_prepend(refresh_list, old_bs);
+    refresh_list = g_slist_prepend(refresh_list, new_bs);
 
     ret = bdrv_list_refresh_perms(refresh_list, NULL, tran, errp);
 
-- 
2.35.1

On 30.03.22 23:28, Vladimir Sementsov-Ogievskiy wrote:
> We are going to increase usage of collecting nodes in a list to then
> update, and calling bdrv_topological_dfs() each time is not convenient,
> and not correct as we are going to interleave graph modifying with
> filling the node list.
>
> So, let's switch to a function that takes any list of nodes, adds all
> their subtrees and do topological sort. And finally, refresh
> permissions.
>
> While being here, make the function public, as we'll want to use it
> from blockdev.c in near future.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@openvz.org>
> ---
>   block.c | 51 ++++++++++++++++++++++++++++++++-------------------
>   1 file changed, 32 insertions(+), 19 deletions(-)
>
> diff --git a/block.c b/block.c
> index f3ed351360..9009f73534 100644
> --- a/block.c
> +++ b/block.c

[...]

> @@ -2510,6 +2514,24 @@ static int bdrv_list_refresh_perms(GSList *list, BlockReopenQueue *q,
>       return 0;
>   }
>   
> +/*
> + * @list is any list of nodes. List is completed by all subtreees and

*subtrees

With that fixed:

Reviewed-by: Hanna Reitz <hreitz@redhat.com>

> + * topologically sorted. It's not a problem if some node occurs in the @list
> + * several times.
> + */
> +static int bdrv_list_refresh_perms(GSList *list, BlockReopenQueue *q,
> +                                   Transaction *tran, Error **errp)
> +{
> +    g_autoptr(GHashTable) found = g_hash_table_new(NULL, NULL);
> +    g_autoptr(GSList) refresh_list = NULL;
> +
> +    for ( ; list; list = list->next) {
> +        refresh_list = bdrv_topological_dfs(refresh_list, found, list->data);
> +    }
> +
> +    return bdrv_do_refresh_perms(refresh_list, q, tran, errp);
> +}
> +