guix system: Add 'vm-image' action and '--image-size' option.

* guix/scripts/system.scm (%options): Add --image-size.
  (%default-options): Add 'image-size'.
  (guix-system)[parse-options]: Handle the 'vm-image' action.
  Honor them.
  (show-help): Update accordingly.
* doc/guix.texi (Invoking guix system): Add 'vm-image'.

1 files changed, 7 insertions, 1 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 863fce8307..ebd1ff5416 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -2982,7 +2982,8 @@ guix system @var{options}@dots{} @var{action} @var{file}
 
 @var{file} must be the name of a file containing an
 @code{operating-system} declaration.  @var{action} specifies how the
-operating system is instantiate.  Currently only one value is supported:
+operating system is instantiate.  Currently the following values are
+supported:
 
 @table @code
 @item vm
@@ -2991,6 +2992,11 @@ Build a virtual machine that contain the operating system declared in
 @var{file}, and return a script to run that virtual machine (VM).
 
 The VM shares its store with the host system.
+
+@item vm-image
+Return a virtual machine image of the operating system declared in
+@var{file} that stands alone.  Use the @option{--image-size} option to
+specify the size of the image.
 @end table
 
 @var{options} can contain any of the common build options provided by