At 2015/6/18 20:47, Stefan Hajnoczi Wrote:
On Thu, Jun 18, 2015 at 04:49:11PM +0800, Wen Congyang wrote:
Signed-off-by: Wen Congyang <we...@cn.fujitsu.com>
Signed-off-by: zhanghailiang <zhang.zhanghaili...@huawei.com>
Signed-off-by: Gonglei <arei.gong...@huawei.com>
---
block.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/block.c b/block.c
index d1ed227..0b41af4 100644
--- a/block.c
+++ b/block.c
@@ -1294,6 +1294,14 @@ static int
bdrv_open_backing_reference_file(BlockDriverState *bs,
}
backing_hd = blk_bs(backing_blk);
+ /* Don't allow a disk use backing reference target */
+ ret = blk_attach_dev(backing_hd->blk, bs);
+ if (ret < 0) {
+ error_setg(errp, "backing_hd %s is used by the other device model",
+ backing_name);
+ goto free_exit;
+ }
Can you explain the purpose of this patch?
I'm not sure blk_attach_dev() is the appropriate API. It is only used
by emulated devices but not by the run-time NBD server, for example.
This means you are not preventing all other users from accessing this
BDS.
The op blockers mechanism is normally used to prevent operations on a
BDS. See bdrv_op_is_blocked() and bdrv_op_block().
NBD server will write to this BDS(backing reference target). So I cannot use
bdrv_op_block(). If some emulated devices also write to it, the data will
be broken. The purpose is that: this BDS cannot be attached, and any
emulated
devices will meet some erros if it tries to attach to this BDS.
Thanks
Wen Congyang
Stefan
