[PATCH] Document qemu-img options data_file and data_file_raw

[Connor Kuehl <ckuehl@redhat.com>]

The contents of this patch were initially developed and posted by Han
Han[1], however, it appears the original patch was not applied. Since
then, the relevant documentation has been moved and adapted to a new
format.

I've taken most of the original wording and tweaked it according to
some of the feedback from the original patch submission. I've also
adapted it to restructured text, which is the format the documentation
currently uses.

[1] https://lists.nongnu.org/archive/html/qemu-block/2019-10/msg01253.html

Reported-by: Han Han <hhan@redhat.com>
Co-developed-by: Han Han <hhan@redhat.com>
Fixes: https://bugzilla.redhat.com/1763105
Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
---
 docs/tools/qemu-img.rst | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/docs/tools/qemu-img.rst b/docs/tools/qemu-img.rst
index b615aa8419..5cc585dc27 100644
--- a/docs/tools/qemu-img.rst
+++ b/docs/tools/qemu-img.rst
@@ -866,6 +866,18 @@ Supported image file formats:
     issue ``lsattr filename`` to check if the NOCOW flag is set or not
     (Capital 'C' is NOCOW flag).
 
+  ``data_file``
+    Pathname that refers to a file that will store all guest data. If
+    this option is used, the qcow2 file will only contain the image's
+    metadata.
+
+  ``data_file_raw``
+    If this option is set to ``on``, QEMU will always keep the external
+    data file consistent as a standalone read-only raw image. The default
+    value is ``off``.
+
+    This option can only be enabled if ``data_file`` is set.
+
 ``Other``
 
   QEMU also supports various other image file formats for
-- 
2.29.2