qapi/block-core: Improve MapEntry documentation

MapEntry and BlockDeviceMapEntry are kind of the same thing, and the
latter is not used, so we want to remove it.  However, the documentation
it provides for some fields is better than that of MapEntry, so steal
some of it for the latter.

(And adjust them a bit in the process, because I feel like we can make
them even clearer.)

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20201104165513.72720-2-mreitz@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 13 insertions, 5 deletions

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 1b8b4156b4..3f86675357 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -244,17 +244,25 @@
 #
 # Mapping information from a virtual block range to a host file range
 #
-# @start: the start byte of the mapped virtual range
+# @start: virtual (guest) offset of the first byte described by this
+#         entry
 #
 # @length: the number of bytes of the mapped virtual range
 #
-# @data: whether the mapped range has data
+# @data: reading the image will actually read data from a file (in
+#        particular, if @offset is present this means that the sectors
+#        are not simply preallocated, but contain actual data in raw
+#        format)
 #
-# @zero: whether the virtual blocks are zeroed
+# @zero: whether the virtual blocks read as zeroes
 #
-# @depth: the depth of the mapping
+# @depth: number of layers (0 = top image, 1 = top image's backing
+#         file, ..., n - 1 = bottom image (where n is the number of
+#         images in the chain)) before reaching one for which the
+#         range is allocated
 #
-# @offset: the offset in file that the virtual sectors are mapped to
+# @offset: if present, the image file stores the data for this range
+#          in raw format at the given (host) offset
 #
 # @filename: filename that is referred to by @offset
 #