[Qemu-devel] [PATCH v2 01/12] block: Add BDS.never_freeze

[Max Reitz]

The commit and the mirror block job must be able to drop their filter
node at any point.  However, this will not be possible if any of the
BdrvChild links to them is frozen.  Therefore, we need to prevent them
from ever becoming frozen.

Signed-off-by: Max Reitz <address@hidden>
Reviewed-by: Andrey Shinkevich <address@hidden>
Reviewed-by: Alberto Garcia <address@hidden>
---
 include/block/block_int.h | 3 +++
 block.c                   | 8 ++++++++
 block/commit.c            | 4 ++++
 block/mirror.c            | 4 ++++
 4 files changed, 19 insertions(+)

diff --git a/include/block/block_int.h b/include/block/block_int.h
index fce9a9e7ee..bc378a49dc 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -908,6 +908,9 @@ struct BlockDriverState {
 
     /* Only read/written by whoever has set active_flush_req to true.  */
     unsigned int flushed_gen;             /* Flushed write generation */
+
+    /* BdrvChild links to this node may never be frozen */
+    bool never_freeze;
 };
 
 struct BlockBackendRootState {
diff --git a/block.c b/block.c
index 1652f3d29b..a06f07347f 100644
--- a/block.c
+++ b/block.c
@@ -4420,6 +4420,14 @@ int bdrv_freeze_backing_chain(BlockDriverState *bs, 
BlockDriverState *base,
         return -EPERM;
     }
 
+    for (i = bs; i != base; i = backing_bs(i)) {
+        if (i->backing && backing_bs(i)->never_freeze) {
+            error_setg(errp, "Cannot freeze '%s' link to '%s'",
+                       i->backing->name, backing_bs(i)->node_name);
+            return -EPERM;
+        }
+    }
+
     for (i = bs; i != base; i = backing_bs(i)) {
         if (i->backing) {
             i->backing->frozen = true;
diff --git a/block/commit.c b/block/commit.c
index ca7e408b26..2c5a6d4ebc 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -298,6 +298,10 @@ void commit_start(const char *job_id, BlockDriverState *bs,
     if (!filter_node_name) {
         commit_top_bs->implicit = true;
     }
+
+    /* So that we can always drop this node */
+    commit_top_bs->never_freeze = true;
+
     commit_top_bs->total_sectors = top->total_sectors;
 
     bdrv_append(commit_top_bs, top, &local_err);
diff --git a/block/mirror.c b/block/mirror.c
index 2fcec70e35..8cb75fb409 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1551,6 +1551,10 @@ static BlockJob *mirror_start_job(
     if (!filter_node_name) {
         mirror_top_bs->implicit = true;
     }
+
+    /* So that we can always drop this node */
+    mirror_top_bs->never_freeze = true;
+
     mirror_top_bs->total_sectors = bs->total_sectors;
     mirror_top_bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED;
     mirror_top_bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
-- 
2.21.0