On 04.12.20 23:07, Vladimir Sementsov-Ogievskiy wrote:
From: Andrey Shinkevich <andrey.shinkev...@virtuozzo.com>

This patch completes the series with the COR-filter applied to
block-stream operations.

Adding the filter makes it possible in future implement discarding
copied regions in backing files during the block-stream job, to reduce
the disk overuse (we need control on permissions).

Also, the filter now is smart enough to do copy-on-read with specified
base, so we have benefit on guest reads even when doing block-stream of
the part of the backing chain.

Several iotests are slightly modified due to filter insertion.

Signed-off-by: Andrey Shinkevich <andrey.shinkev...@virtuozzo.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
---
  block/stream.c             | 78 ++++++++++++++++++++++++++------------
  tests/qemu-iotests/030     |  8 ++--
  tests/qemu-iotests/141.out |  2 +-
  tests/qemu-iotests/245     | 20 ++++++----
  4 files changed, 72 insertions(+), 36 deletions(-)

diff --git a/block/stream.c b/block/stream.c
index a7fd8945ad..b92f7de55b 100644
--- a/block/stream.c
+++ b/block/stream.c

[...]

@@ -295,17 +287,49 @@ void stream_start(const char *job_id, BlockDriverState 
*bs,

[...]

+    opts = qdict_new();
+
+    qdict_put_str(opts, "driver", "copy-on-read");
+    qdict_put_str(opts, "file", bdrv_get_node_name(bs));
+    /* Pass the base_overlay node name as 'bottom' to COR driver */
+    qdict_put_str(opts, "bottom", base_overlay->node_name);

Hm.  Should we set this option even if no base was specified?

On one hand, omitting this option would cor_co_preadv_part() a bit quicker.

On the other, what happens when you add a backing file below the bottom node during streaming (yes, a largely theoretical case)... Now, all data from it is ignored. That seemed a bit strange to me at first, but on second thought, it makes more sense. Doing anything else would produce a garbage result basically, because stream_run() doesn’t take such a change into account.

So...  After all I think I agree with setting @bottom unconditionally.

And that’s the only comment I had. :)

Reviewed-by: Max Reitz <mre...@redhat.com>


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