[PULL 01/15] qcow2: Add incompatibility note between backing files and raw external data files

[Kevin Wolf <kwolf@redhat.com>]

From: Alberto Garcia <berto@igalia.com>

Backing files and raw external data files are mutually exclusive.
The documentation of the raw external data bit (in autoclear_features)
already indicates that, but we should also mention it on the other
side.

Suggested-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-Id: <20200410121816.8334-1-berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 docs/interop/qcow2.txt | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
index 640e0eca40..298a031310 100644
--- a/docs/interop/qcow2.txt
+++ b/docs/interop/qcow2.txt
@@ -25,6 +25,9 @@ The first cluster of a qcow2 image contains the file header:
                     is stored (NB: The string is not null terminated). 0 if the
                     image doesn't have a backing file.
 
+                    Note: backing files are incompatible with raw external data
+                    files (auto-clear feature bit 1).
+
          16 - 19:   backing_file_size
                     Length of the backing file name in bytes. Must not be
                     longer than 1023 bytes. Undefined if the image doesn't have
-- 
2.25.3