[Libguestfs] [nbdkit PATCH 2/3] vddk: Do not report hole extents to be zero with single-link=true

[Martin Kletzander]

the data in holes is actually not zeros as there might be a parent image having
other data.  Properly reporting (non-)zero hole extents allows clients to have
information about whether the data in the image is unallocated, but the read
will return zero blocks (HOLE+ZERO) or whether the data is just not in this
later of the image (only HOLE).

Signed-off-by: Martin Kletzander <mkletzan at redhat.com>
---
 plugins/vddk/vddk.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/plugins/vddk/vddk.c b/plugins/vddk/vddk.c
index 8cf54f6e2b96..cda670325b85 100644
--- a/plugins/vddk/vddk.c
+++ b/plugins/vddk/vddk.c
@@ -773,9 +773,17 @@ static int
 add_extent (struct nbdkit_extents *extents,
             uint64_t *position, uint64_t next_position, bool is_hole)
 {
-  const uint32_t type = is_hole ? NBDKIT_EXTENT_HOLE|NBDKIT_EXTENT_ZERO : 0;
+  uint32_t type = 0;
   const uint64_t length = next_position - *position;
 
+  if (is_hole) {
+    type = NBDKIT_EXTENT_HOLE;
+    /* Images opened as single link might be backed by another file in the
+       chain, so the holes are not guaranteed to be zeros. */
+    if (!single_link)
+      type |= NBDKIT_EXTENT_ZERO;
+  }
+
   assert (*position <= next_position);
   if (*position == next_position)
     return 0;
-- 
2.21.0