ref-manual/variables.rst: document SSTATE_SKIP_CREATION

(From yocto-docs rev: 40045299491087d3f7d269b696ae48d513dae435)

Signed-off-by: Etienne Cordonnier <ecordonnier@snap.com>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
(cherry picked from commit 3982720668aafa18c9ed27304d09f896740b1653)
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

documentation/ref-manual/variables.rst

@@ -8726,6 +8726,26 @@ system and gives an overview of their function and contents.
 
       For details on the process, see the :ref:`ref-classes-staging` class.
 
+   :term:`SSTATE_SKIP_CREATION`
+      The :term:`SSTATE_SKIP_CREATION` variable can be used to skip the
+      creation of :ref:`shared state <overview-manual/concepts:shared state cache>`
+      tarball files. It makes sense e.g. for image creation tasks as tarring images
+      and keeping them in sstate would consume a lot of disk space.
+
+      In general it is not recommended to use this variable as missing sstate
+      artefacts adversely impact the build, particularly for entries in the
+      middle of dependency chains. The case it can make sense is where the
+      size and time costs of the artefact are similar to just running the
+      tasks. This generally only applies to end artefact output like images.
+
+      The syntax to disable it for one task is::
+
+         SSTATE_SKIP_CREATION:task-image-complete = "1"
+
+      The syntax to disable it for the whole recipe is::
+
+         SSTATE_SKIP_CREATION = "1"
+
    :term:`STAGING_BASE_LIBDIR_NATIVE`
       Specifies the path to the ``/lib`` subdirectory of the sysroot
       directory for the build host.