ref-manual: tasks: do_cleansstate: recommend using '-f' instead for a shared sstate

do_cleansstat can produce build errors when using a shared sstate cache.

Add a note to clearly discourage, provide a safe alternative (bitbake -f),
and the rationale.

Suggested-by: Quentin Schulz  <quentin.schulz@theobroma-systems.com>
Link: https://lore.kernel.org/yocto-docs/20240219155513.76738-1-luca.ceresoli@bootlin.com/T/#m5529687ecb0f9ec2dacddcb6ff58e2df73af9cde
(From yocto-docs rev: 6fb06bb4a917c1515e54fa3e699119f6bbb85767)

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/documentation/ref-manual/tasks.rst b/documentation/ref-manual/tasks.rst
index 16b48ca0bc..c28cd7a94a 100644
--- a/documentation/ref-manual/tasks.rst
+++ b/documentation/ref-manual/tasks.rst
@@ -516,6 +516,18 @@ scratch is guaranteed.
 
 .. note::
 
+   Using :ref:`ref-tasks-cleansstate` with a shared :term:`SSTATE_DIR` is
+   not recommended because it could trigger an error during the build of a
+   separate BitBake instance. This is because the builds check sstate "up
+   front" but download the files later, so it if is deleted in the
+   meantime, it will cause an error but not a total failure as it will
+   rebuild it.
+
+   The reliable and preferred way to force a new build is to use ``bitbake
+   -f`` instead.
+
+.. note::
+
    The :ref:`ref-tasks-cleansstate` task cannot remove sstate from a remote sstate
    mirror. If you need to build a target from scratch using remote mirrors, use
    the "-f" option as follows::