From 1ffa7d12a15fdc4f1bbed59bf5d3292ac2b574b3 Mon Sep 17 00:00:00 2001
From: Jeffrey Cody <jcody@redhat.com>
Date: Mon, 12 Jun 2017 14:46:56 +0200
Subject: [PATCH 11/13] block: fix external snapshot abort permission error

RH-Author: Jeffrey Cody <jcody@redhat.com>
Message-id: <14e6e82657b93fb6bec16eddce051ced36db5ff9.1497278737.git.jcody@redhat.com>
Patchwork-id: 75593
O-Subject: [RHEV-7.4 qemu-kvm-rhev PATCH 1/1] block: fix external snapshot abort permission error
Bugzilla: 1447184
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
RH-Acked-by: Max Reitz <mreitz@redhat.com>
RH-Acked-by: John Snow <jsnow@redhat.com>

In external_snapshot_abort(), we try to undo what was done in
external_snapshot_prepare() calling bdrv_replace_node() to swap the
nodes back.  However, we receive a permissions error as writers are
blocked on the old node, which is now the new node backing file.

An easy fix (initially suggested by Kevin Wolf) is to call
bdrv_set_backing_hd() on the new node, to set the backing node to NULL.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 719fc28c80a22ab9f1533d775bae09c14442bbbe)
Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 blockdev.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/blockdev.c b/blockdev.c
index 4432143..a3a0731 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1847,7 +1847,11 @@ static void external_snapshot_abort(BlkActionState *common)
                              DO_UPCAST(ExternalSnapshotState, common, common);
     if (state->new_bs) {
         if (state->overlay_appended) {
+            bdrv_ref(state->old_bs);   /* we can't let bdrv_set_backind_hd()
+                                          close state->old_bs; we need it */
+            bdrv_set_backing_hd(state->new_bs, NULL, &error_abort);
             bdrv_replace_node(state->new_bs, state->old_bs, &error_abort);
+            bdrv_unref(state->old_bs); /* bdrv_replace_node() ref'ed old_bs */
         }
     }
 }
-- 
1.8.3.1