commit e5182c1c57ac9aa0e9c399b9c60af3c41cff35b4
author Max Reitz <mreitz@redhat.com> Wed Jul 03 19:28:02 2019 +0200
committer Max Reitz <mreitz@redhat.com> Mon Jul 15 15:48:40 2019 +0200
tree 04e54401d154ee49cc0c0855dccef3a9413b04c8
parent 95667c3be0c9f5fc62f58fe845879250f63f7d32

block: Add BDS.never_freeze

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 <mreitz@redhat.com>
Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20190703172813.6868-2-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

block.c

diff --git a/block.c b/block.c
index c139540..6565192 100644
--- a/block.c
+++ b/block.c
@@ -4417,6 +4417,14 @@
     }
 
     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;
         }

block/commit.c

diff --git a/block/commit.c b/block/commit.c
index ca7e408..2c5a6d4 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -298,6 +298,10 @@
     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);

block/mirror.c

diff --git a/block/mirror.c b/block/mirror.c
index 2fcec70..8cb75fb 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1551,6 +1551,10 @@
     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 |

include/block/block_int.h

diff --git a/include/block/block_int.h b/include/block/block_int.h
index d6415b5..5090253 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -885,6 +885,9 @@
 
     /* 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 {