[PATCH v6 2/6] run imager in buildchroot-host on cross

[Felix Moessbauer <felix.moessbauer@siemens.com>]

When globally enabling ISAR_CROSS_COMPILE, the imager and compression
tasks run in the host buildchroot as well (instead of the target
buildchroot).

Similar to the cross support for DPKG recipes, this can be toggled
on a per-image basis by setting ISAR_CROSS_COMPILE in the image recipe.

Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
---
 doc/user_manual.md                         | 11 +++++++++++
 meta/classes/image-tools-extension.bbclass |  3 ---
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/doc/user_manual.md b/doc/user_manual.md
index 5b2387d8..f38a133e 100644
--- a/doc/user_manual.md
+++ b/doc/user_manual.md
@@ -986,6 +986,17 @@ built for the compat arch need to be tagged individually by setting
 `PACKAGE_ARCH = "${COMPAT_DISTRO_ARCH}"` in the package recipe. Non-tagged
 packages will continue to be built for the primary target architecture.
 
+### Cross Support for Imagers
+
+If `ISAR_CROSS_COMPILE = "1"`, the imager and optional compression tasks
+run in the host buildchroot instead of the target buildchroot.
+This gives a significant speedup when compressing the generated image,
+as the compression is not emulated.
+
+In case your setup does not support cross-imaging, you can disable this
+just for the particular image by adding `ISAR_CROSS_COMPILE = "0"` to your
+image recipe.
+
 
 ## Examining and debugging package generation inside their buildchroot
 
diff --git a/meta/classes/image-tools-extension.bbclass b/meta/classes/image-tools-extension.bbclass
index b9968139..e13d4a3f 100644
--- a/meta/classes/image-tools-extension.bbclass
+++ b/meta/classes/image-tools-extension.bbclass
@@ -5,9 +5,6 @@
 #
 # This file extends the image.bbclass to supply tools for futher imager functions
 
-# Imager are expected to run natively, thus will use the target buildchroot.
-ISAR_CROSS_COMPILE = "0"
-
 inherit buildchroot
 
 IMAGER_INSTALL ??= ""
-- 
2.30.2