[PATCH 4/4] isar-image: add support for OE's ROOTFS_*_COMMAND

[Cedric Hombourger <Cedric_Hombourger@mentor.com>]

OpenEmbedded allows custom functions to be called at various stages of
the root file-system generation process. Add similar capabilities to
Isar.

Signed-off-by: Cedric Hombourger <Cedric_Hombourger@mentor.com>
---
 doc/user_manual.md                   | 10 ++++++++++
 meta-isar/classes/isar-image.bbclass | 17 +++++++++++++++++
 meta/lib/oe/utils.py                 | 11 +++++++++++
 3 files changed, 38 insertions(+)
 create mode 100644 meta/lib/oe/utils.py

diff --git a/doc/user_manual.md b/doc/user_manual.md
index b702c28..0c4ed4a 100644
--- a/doc/user_manual.md
+++ b/doc/user_manual.md
@@ -527,6 +527,16 @@ was assembled. Isar provides scripts for Debian and Raspbian. In the event where
 used, your custom image recipe may need to set `DISTRO_CONFIG_SCRIPT` and use `SRC_URI` and `FILESPATH` for the script to
 be copied into the work directory (`WORKDIR`).
 
+Custom (python) functions may also be called at various steps during the root file-system generation process. They should
+be listed in either `ROOTFS_PREPROCESS_COMMAND` for any functions to be called before the root file-system gets populated,
+`ROOTFS_POSTINSTALL_COMMAND` for functions to be called right after selected packages were installed and finally
+`ROOTFS_POSTPROCESS_COMMAND` after the final configuration script and clean-up tasks were called. Functions listed in these
+variables should be separated by a semi-colon sign (;).
+
+It should also be noted that Isar may no longer execute commands from the created root file-system after it was cleaned-up
+(binaries required to support emulation of foreign architectures would have been removed). Please consider this when
+designing functions to be called from `ROOTFS_POSTPROCESS_COMMAND`.
+
 ---
 
 ## Add a Custom Application
diff --git a/meta-isar/classes/isar-image.bbclass b/meta-isar/classes/isar-image.bbclass
index e0508be..d5358e0 100644
--- a/meta-isar/classes/isar-image.bbclass
+++ b/meta-isar/classes/isar-image.bbclass
@@ -64,9 +64,26 @@ isar_image_cleanup() {
     sudo rm -f "${IMAGE_ROOTFS}/etc/apt/apt.conf.d/55isar-fallback.conf"
 }
 
+ROOTFS_PREPROCESS_COMMAND ?= ""
+ROOTFS_POSTINSTALL_COMMAND ?= ""
+ROOTFS_POSTPROCESS_COMMAND ?= ""
+
 python do_rootfs() {
+    from oe.utils import execute_pre_post_process
+
     bb.build.exec_func("isar_image_gen_fstab", d)
+
+    pre_process_cmds = d.getVar("ROOTFS_PREPROCESS_COMMAND")
+    execute_pre_post_process(d, pre_process_cmds)
+
     bb.build.exec_func("isar_image_gen_rootfs", d)
+
+    post_install_cmds = d.getVar("ROOTFS_POSTINSTALL_COMMAND")
+    execute_pre_post_process(d, post_install_cmds)
+
     bb.build.exec_func("isar_image_conf_rootfs", d)
     bb.build.exec_func("isar_image_cleanup", d)
+
+    post_process_cmds = d.getVar("ROOTFS_POSTPROCESS_COMMAND")
+    execute_pre_post_process(d, post_process_cmds)
 }
diff --git a/meta/lib/oe/utils.py b/meta/lib/oe/utils.py
new file mode 100644
index 0000000..dc3a872
--- /dev/null
+++ b/meta/lib/oe/utils.py
@@ -0,0 +1,11 @@
+# heavily stripped-down copy of OE's meta/lib/oe/utils.py
+
+def execute_pre_post_process(d, cmds):
+    if cmds is None:
+        return
+
+    for cmd in cmds.strip().split(';'):
+        cmd = cmd.strip()
+        if cmd != '':
+            bb.note("Executing %s ..." % cmd)
+            bb.build.exec_func(cmd, d)
-- 
2.11.0