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Re: [PATCH v7 29/47] blockdev: Use CAF in external_snapshot_prepare()

From: Andrey Shinkevich
Subject: Re: [PATCH v7 29/47] blockdev: Use CAF in external_snapshot_prepare()
Date: Mon, 20 Jul 2020 19:08:44 +0300
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.9.0

On 25.06.2020 18:21, Max Reitz wrote:
This allows us to differentiate between filters and nodes with COW
backing files: Filters cannot be used as overlays at all (for this

Signed-off-by: Max Reitz <mreitz@redhat.com>
  blockdev.c | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index 1eb0fcdea2..aabe51036d 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1549,7 +1549,12 @@ static void external_snapshot_prepare(BlkActionState 
          goto out;
- if (state->new_bs->backing != NULL) {
+    if (state->new_bs->drv->is_filter) {

Is there a chance to get a filter here? If so, is that when a user specifies the file name of such a kind “filter[filter-name]:foo.qcow2” or somehow else?


+        error_setg(errp, "Filters cannot be used as overlays");
+        goto out;
+    }
+    if (bdrv_cow_child(state->new_bs)) {
          error_setg(errp, "The overlay already has a backing image");
          goto out;

Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>

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