[Buildroot] [PATCH 3/4] Makefile: check rootfs overlays with BR2_ROOTFS_MERGED_USR enabled

Carlos Santos casantos at datacom.ind.br
Sun May 6 21:31:15 UTC 2018

Since commit 0db34529f48 we use rsync with the --keep-dirlinks option to
prevent overlays from accidentally overwriding /{usr,bin,sbin,lib} links
when BR2_ROOTFS_MERGED_USR option is enabled. Unfortunately this also
prevents replacing a symlink by a directory on purpose (e.g. /var/log,
to persist system logs).

Steps to reproduce:

- mkdir some_path/rootfs-overlay/var/log
- enable BR2_ROOTFS_OVERLAY="some_path/rootfs-overlay"
- run 'make'
- 'target/var/log' is still a symlink to '../tmp', not a directory

Fix the problem by adding a step in target-finalize that checks each
overlay, using the same criteria used in skeleton-custom.mk.

Add a paragraph to the documentation clarifying that rootfs overlays
should not contain /bin, /lib or /sbin.

Signed-off-by: Carlos Santos <casantos at datacom.ind.br>
 Makefile                         | 20 +++++++++++++++++---
 docs/manual/customize-rootfs.txt |  5 +++++
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index c024c65f78..dc51269143 100644
--- a/Makefile
+++ b/Makefile
@@ -746,11 +746,25 @@ endif
 	@$(call MESSAGE,"Sanitizing RPATH in target tree")
 	$(TOPDIR)/support/scripts/fix-rpath target
+# For a merged /usr, ensure that /lib, /bin and /sbin and their /usr
+# counterparts are appropriately setup as symlinks ones to the others.
+ifeq ($(BR2_ROOTFS_MERGED_USR),y)
+	@$(foreach d, $(call qstrip,$(BR2_ROOTFS_OVERLAY)), \
+		$(call MESSAGE,"Sanity check in overlay $(d)"); \
+		not_merged_dirs="$$(support/scripts/check-merged-usr.sh $(d))"; \
+		test -n "$$not_merged_dirs" && { \
+			echo "ERROR: The overlay in $(d) is not" \
+				"using a merged /usr for the following directories:" \
+				$$not_merged_dirs; \
+			exit 1; \
+		} || true$(sep))
+endif # merged /usr
 	@$(foreach d, $(call qstrip,$(BR2_ROOTFS_OVERLAY)), \
 		$(call MESSAGE,"Copying overlay $(d)"); \
-		rsync -a --ignore-times --keep-dirlinks $(RSYNC_VCS_EXCLUSIONS) \
-			--chmod=u=rwX,go=rX --exclude .empty --exclude '*~' \
-			$(d)/ $(TARGET_DIR)$(sep))
+		$(call SYSTEM_RSYNC,$(d),$(TARGET_DIR))$(sep))
 	@$(foreach s, $(call qstrip,$(BR2_ROOTFS_POST_BUILD_SCRIPT)), \
 		$(call MESSAGE,"Executing post-build script $(s)"); \
diff --git a/docs/manual/customize-rootfs.txt b/docs/manual/customize-rootfs.txt
index 8982e03498..5dbbe86044 100644
--- a/docs/manual/customize-rootfs.txt
+++ b/docs/manual/customize-rootfs.txt
@@ -22,6 +22,11 @@ A filesystem overlay is a tree of files that is copied directly
   etc., files called +.empty+ and files ending in +~+ are excluded from
   the copy.
+Overlays should not contain the '/bin', '/lib' or '/sbin' paths, since
+  they are created during the build, either as directories or as
+  symbolic links to their counterparts under 'usr', depending on the
+  system configuration.
 As shown in xref:customize-dir-structure[], the recommended path for
   this overlay is +board/<company>/<boardname>/rootfs-overlay+.

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