[Buildroot] [PATCH 22/24 v2] fs: add pre- and post-command hooks

[Yann E. MORIN]

In some cases, the directory structure we want in the filesystem is not
exactly what we have in target/

For example, when systemd is used on a read-only rootfs, /var must be a
tmpfs. However, we may have packages that install stuff in there, and
set important rights (via the permission-table). So, at build time, we
need /var to be a symlink to the remanent location (/usr/share/factory)
while at runtime we need /var to be a directory.

One option would have seen to be do have /var as a real directory even
during build time, and in a target-finalize hook, move everything out of
there and into the "factory" location. However, that's not possible
because it's too early: some packages may want to set ownership and/or
acces rights on directories or files in /var, and this is only done in
the fakeroot script, which is called only later during the assembling of
the filesystem images.

Also, there would have been no way to undo the tweak (i.e. we need to
restore the /var symlink so that subsequent builds continue to work) if
it were done as a target-finalize hook.

The only solution is to allow packages to register pre- and post-hooks
that are called right before and right after the rootfs commands are
executed.

Those hooks are not documented on-purpose; they are probably going to be
used only by systemd.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998 at free.fr>
---
 fs/common.mk           | 4 ++++
 package/pkg-generic.mk | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/fs/common.mk b/fs/common.mk
index b7202c3..8feb172 100644
--- a/fs/common.mk
+++ b/fs/common.mk
@@ -92,7 +92,11 @@ endif
 	$$(call PRINTF,$$(PACKAGES_PERMISSIONS_TABLE)) >> $$(FULL_DEVICE_TABLE)
 	echo "$$(HOST_DIR)/usr/bin/makedevs -d $$(FULL_DEVICE_TABLE) $$(TARGET_DIR)" >> $$(FAKEROOT_SCRIPT)
 endif
+	$$(foreach hook,$$(FS_INIT_PRE_CMD_HOOKS),\
+		$$(call PRINTF,$$($$(hook))) >>$$(FAKEROOT_SCRIPT))
 	$$(call PRINTF,$$(ROOTFS_$(2)_CMD)) >> $$(FAKEROOT_SCRIPT)
+	$$(foreach hook,$$(FS_INIT_POST_CMD_HOOKS),\
+		$$(call PRINTF,$$($$(hook))) >>$$(FAKEROOT_SCRIPT))
 	chmod a+x $$(FAKEROOT_SCRIPT)
 	PATH=$$(BR_PATH) $$(HOST_DIR)/usr/bin/fakeroot -- $$(FAKEROOT_SCRIPT)
 	$$(INSTALL) -m 0644 support/misc/target-dir-warning.txt $$(TARGET_DIR_WARNING_FILE)
diff --git a/package/pkg-generic.mk b/package/pkg-generic.mk
index 4415342..2f80392 100644
--- a/package/pkg-generic.mk
+++ b/package/pkg-generic.mk
@@ -559,6 +559,8 @@ $(2)_POST_INSTALL_IMAGES_HOOKS  ?=
 $(2)_PRE_LEGAL_INFO_HOOKS       ?=
 $(2)_POST_LEGAL_INFO_HOOKS      ?=
 $(2)_TARGET_FINALIZE_HOOKS      ?=
+$(2)_FS_PRE_CMD_HOOKS           ?=
+$(2)_FS_POST_CMD_HOOKS          ?=
 
 # human-friendly targets and target sequencing
 $(1):			$(1)-install
@@ -860,6 +862,8 @@ ifneq ($$($(2)_USERS),)
 PACKAGES_USERS += $$($(2)_USERS)$$(sep)
 endif
 TARGET_FINALIZE_HOOKS += $$($(2)_TARGET_FINALIZE_HOOKS)
+FS_INIT_PRE_CMD_HOOKS += $$($(2)_FS_PRE_CMD_HOOKS)
+FS_INIT_POST_CMD_HOOKS += $$($(2)_FS_POST_CMD_HOOKS)
 
 ifeq ($$($(2)_SITE_METHOD),svn)
 DL_TOOLS_DEPENDENCIES += svn
-- 
2.7.4