Let check_to_replace_node() use the more specialized
bdrv_recurse_can_replace() instead of
bdrv_recurse_is_first_non_filter(), which is too restrictive.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index de53addeb0..7608f21570 100644
--- a/block.c
+++ b/block.c
@@ -6243,6 +6243,17 @@ bool bdrv_recurse_can_replace(BlockDriverState *bs,
     return false;
 }
 
+/*
+ * Check whether the given @node_name can be replaced by a node that
+ * has the same data as @parent_bs.  If so, return @node_name's BDS;
+ * NULL otherwise.
+ *
+ * @node_name must be a (recursive) *child of @parent_bs (or this
+ * function will return NULL).
+ *
+ * The result (whether the node can be replaced or not) is only valid
+ * for as long as no graph changes occur.
+ */
 BlockDriverState *check_to_replace_node(BlockDriverState *parent_bs,
                                         const char *node_name, Error **errp)
 {
@@ -6267,8 +6278,11 @@ BlockDriverState *check_to_replace_node(BlockDriverState *parent_bs,
      * Another benefit is that this tests exclude backing files which are
      * blocked by the backing blockers.
      */
-    if (!bdrv_recurse_is_first_non_filter(parent_bs, to_replace_bs)) {
-        error_setg(errp, "Only top most non filter can be replaced");
+    if (!bdrv_recurse_can_replace(parent_bs, to_replace_bs)) {
+        error_setg(errp, "Cannot replace '%s' by a node mirrored from '%s', "
+                   "because it cannot be guaranteed that doing so would not "
+                   "lead to an abrupt change of visible data",
+                   node_name, parent_bs->node_name);
         to_replace_bs = NULL;
         goto out;
     }
-- 
2.23.0

11.11.2019 19:02, Max Reitz wrote:
> Let check_to_replace_node() use the more specialized
> bdrv_recurse_can_replace() instead of
> bdrv_recurse_is_first_non_filter(), which is too restrictive.

or not enough restrictive in case of quorum

> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>   block.c | 18 ++++++++++++++++--
>   1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/block.c b/block.c
> index de53addeb0..7608f21570 100644
> --- a/block.c
> +++ b/block.c
> @@ -6243,6 +6243,17 @@ bool bdrv_recurse_can_replace(BlockDriverState *bs,
>       return false;
>   }
>   
> +/*
> + * Check whether the given @node_name can be replaced by a node that
> + * has the same data as @parent_bs.  If so, return @node_name's BDS;
> + * NULL otherwise.
> + *
> + * @node_name must be a (recursive) *child of @parent_bs (or this
> + * function will return NULL).
> + *
> + * The result (whether the node can be replaced or not) is only valid
> + * for as long as no graph changes occur.

actually, no graph changes neither any permission changes or updates.

> + */
>   BlockDriverState *check_to_replace_node(BlockDriverState *parent_bs,
>                                           const char *node_name, Error **errp)
>   {
> @@ -6267,8 +6278,11 @@ BlockDriverState *check_to_replace_node(BlockDriverState *parent_bs,
>        * Another benefit is that this tests exclude backing files which are
>        * blocked by the backing blockers.
>        */
> -    if (!bdrv_recurse_is_first_non_filter(parent_bs, to_replace_bs)) {
> -        error_setg(errp, "Only top most non filter can be replaced");
> +    if (!bdrv_recurse_can_replace(parent_bs, to_replace_bs)) {
> +        error_setg(errp, "Cannot replace '%s' by a node mirrored from '%s', "
> +                   "because it cannot be guaranteed that doing so would not "
> +                   "lead to an abrupt change of visible data",
> +                   node_name, parent_bs->node_name);
>           to_replace_bs = NULL;
>           goto out;
>       }
> 

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

-- 
Best regards,
Vladimir

Am 11.11.2019 um 17:02 hat Max Reitz geschrieben:
> Let check_to_replace_node() use the more specialized
> bdrv_recurse_can_replace() instead of
> bdrv_recurse_is_first_non_filter(), which is too restrictive.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/block.c b/block.c
> index de53addeb0..7608f21570 100644
> --- a/block.c
> +++ b/block.c
> @@ -6243,6 +6243,17 @@ bool bdrv_recurse_can_replace(BlockDriverState *bs,
>      return false;
>  }
>  
> +/*
> + * Check whether the given @node_name can be replaced by a node that
> + * has the same data as @parent_bs.  If so, return @node_name's BDS;
> + * NULL otherwise.
> + *
> + * @node_name must be a (recursive) *child of @parent_bs (or this
> + * function will return NULL).
> + *
> + * The result (whether the node can be replaced or not) is only valid
> + * for as long as no graph changes occur.
> + */
>  BlockDriverState *check_to_replace_node(BlockDriverState *parent_bs,
>                                          const char *node_name, Error **errp)
>  {
> @@ -6267,8 +6278,11 @@ BlockDriverState *check_to_replace_node(BlockDriverState *parent_bs,
>       * Another benefit is that this tests exclude backing files which are
>       * blocked by the backing blockers.
>       */
> -    if (!bdrv_recurse_is_first_non_filter(parent_bs, to_replace_bs)) {
> -        error_setg(errp, "Only top most non filter can be replaced");
> +    if (!bdrv_recurse_can_replace(parent_bs, to_replace_bs)) {
> +        error_setg(errp, "Cannot replace '%s' by a node mirrored from '%s', "
> +                   "because it cannot be guaranteed that doing so would not "
> +                   "lead to an abrupt change of visible data",
> +                   node_name, parent_bs->node_name);

If this function is only supposed to be used in the context of the
mirror job, moving it into block/mirror.c could be considered as a
cleanup on top.

Kevin