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Re: [PATCH v12 02/14] block: add insert/remove node functions


From: Vladimir Sementsov-Ogievskiy
Subject: Re: [PATCH v12 02/14] block: add insert/remove node functions
Date: Fri, 23 Oct 2020 17:24:08 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0

22.10.2020 21:13, Andrey Shinkevich wrote:
Provide API for a node insertion to and removal from a backing chain.

Suggested-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
---
  block.c               | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
  include/block/block.h |  3 +++
  2 files changed, 52 insertions(+)

diff --git a/block.c b/block.c
index 430edf7..502b483 100644
--- a/block.c
+++ b/block.c
@@ -4670,6 +4670,55 @@ static void bdrv_delete(BlockDriverState *bs)
      g_free(bs);
  }
+BlockDriverState *bdrv_insert_node(BlockDriverState *bs, QDict *node_options,
+                                   int flags, Error **errp)
+{
+    BlockDriverState *new_node_bs;
+    Error *local_err = NULL;
+
+    new_node_bs =  bdrv_open(NULL, NULL, node_options, flags, errp);
+    if (new_node_bs == NULL) {
+        error_prepend(errp, "Could not create node: ");
+        return NULL;
+    }
+
+    bdrv_drained_begin(bs);
+    bdrv_replace_node(bs, new_node_bs, &local_err);
+    bdrv_drained_end(bs);
+
+    if (local_err) {
+        bdrv_unref(new_node_bs);
+        error_propagate(errp, local_err);
+        return NULL;
+    }
+
+    return new_node_bs;
+}
+
+void bdrv_remove_node(BlockDriverState *bs)
+{
+    BdrvChild *child;
+    BlockDriverState *inferior_bs;
+
+    child = bdrv_filter_or_cow_child(bs);
+    if (!child) {
+        return;
+    }
+    inferior_bs = child->bs;
+
+    /* Retain the BDS until we complete the graph change. */
+    bdrv_ref(inferior_bs);
+    /* Hold a guest back from writing while permissions are being reset. */
+    bdrv_drained_begin(inferior_bs);
+    /* Refresh permissions before the graph change. */
+    bdrv_child_refresh_perms(bs, child, &error_abort);
+    bdrv_replace_node(bs, inferior_bs, &error_abort);
+
+    bdrv_drained_end(inferior_bs);
+    bdrv_unref(inferior_bs);
+    bdrv_unref(bs);
+}

The function is unused, and as I understand can't work as intended without 
s->active handling. I think it should be dropped

+
  /*
   * Run consistency checks on an image
   *
diff --git a/include/block/block.h b/include/block/block.h
index d16c401..ae7612f 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -350,6 +350,9 @@ void bdrv_append(BlockDriverState *bs_new, BlockDriverState 
*bs_top,
                   Error **errp);
  void bdrv_replace_node(BlockDriverState *from, BlockDriverState *to,
                         Error **errp);
+BlockDriverState *bdrv_insert_node(BlockDriverState *bs, QDict *node_options,
+                                   int flags, Error **errp);
+void bdrv_remove_node(BlockDriverState *bs);
int bdrv_parse_aio(const char *mode, int *flags);
  int bdrv_parse_cache_mode(const char *mode, int *flags, bool *writethrough);



--
Best regards,
Vladimir



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