[PATCH v4 3/4] replication: Properly attach children

[Lukas Straub]

The replication driver needs access to the children block-nodes of
it's child so it can issue bdrv_make_empty() and bdrv_co_pwritev()
to manage the replication. However, it does this by directly copying
the BdrvChilds, which is wrong.

Fix this by properly attaching the block-nodes with
bdrv_attach_child() and requesting the required permissions.

This ultimatively fixes a potential crash in replication_co_writev(),
because it may write to s->secondary_disk if it is in state
BLOCK_REPLICATION_FAILOVER_FAILED, without requesting write
permissions first. And now the workaround in
secondary_do_checkpoint() can be removed.

Signed-off-by: Lukas Straub <lukasstraub2@web.de>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/replication.c | 30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/block/replication.c b/block/replication.c
index 25bbdf5d4b..b74192f795 100644
--- a/block/replication.c
+++ b/block/replication.c
@@ -165,7 +165,12 @@ static void replication_child_perm(BlockDriverState *bs, 
BdrvChild *c,
                                    uint64_t perm, uint64_t shared,
                                    uint64_t *nperm, uint64_t *nshared)
 {
-    *nperm = BLK_PERM_CONSISTENT_READ;
+    if (role & BDRV_CHILD_PRIMARY) {
+        *nperm = BLK_PERM_CONSISTENT_READ;
+    } else {
+        *nperm = 0;
+    }
+
     if ((bs->open_flags & (BDRV_O_INACTIVE | BDRV_O_RDWR)) == BDRV_O_RDWR) {
         *nperm |= BLK_PERM_WRITE;
     }
@@ -557,8 +562,25 @@ static void replication_start(ReplicationState *rs, 
ReplicationMode mode,
             return;
         }

-        s->hidden_disk = hidden_disk;
-        s->secondary_disk = secondary_disk;
+        bdrv_ref(hidden_disk->bs);
+        s->hidden_disk = bdrv_attach_child(bs, hidden_disk->bs, "hidden disk",
+                                           &child_of_bds, BDRV_CHILD_DATA,
+                                           &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            aio_context_release(aio_context);
+            return;
+        }
+
+        bdrv_ref(secondary_disk->bs);
+        s->secondary_disk = bdrv_attach_child(bs, secondary_disk->bs,
+                                              "secondary disk", &child_of_bds,
+                                              BDRV_CHILD_DATA, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            aio_context_release(aio_context);
+            return;
+        }

         /* start backup job now */
         error_setg(&s->blocker,
@@ -664,7 +686,9 @@ static void replication_done(void *opaque, int ret)
     if (ret == 0) {
         s->stage = BLOCK_REPLICATION_DONE;

+        bdrv_unref_child(bs, s->secondary_disk);
         s->secondary_disk = NULL;
+        bdrv_unref_child(bs, s->hidden_disk);
         s->hidden_disk = NULL;
         s->error = 0;
     } else {
--
2.20.1

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