system: add support for merged /usr/sbin (aka merged-bin)

Starting with version 256 [0], systemd warns when /usr/bin and
/usr/sbin are different directories; in the future, it may even
refuse to boot in such a situation.

Add support for merged-bin, not unlike the support we have for
merged-usr; we also make merged-bin a sub-case of merged-usr
(i.e. it is not possible to do merged-bin without merged-usr).

[0] https://github.com/systemd/systemd/blob/v256/NEWS#L265

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Acked-by: Arnout Vandecappelle <arnout@mind.be>
Acked-by: TIAN Yuanhao <tianyuanhao3@163.com>
Cc: Edgar Bonet <bonet@grenoble.cnrs.fr>
Signed-off-by: Romain Naour <romain.naour@smile.fr>

Makefile

@@ -785,6 +785,7 @@ endif
 	support/scripts/check-merged \
 		--type overlay \
 		$(if $(BR2_ROOTFS_MERGED_USR),--merged-usr) \
+		$(if $(BR2_ROOTFS_MERGED_BIN),--merged-bin) \
 		$(call qstrip,$(BR2_ROOTFS_OVERLAY))
 
 	$(foreach d, $(call qstrip,$(BR2_ROOTFS_OVERLAY)), \

package/skeleton-custom/skeleton-custom.mk

@@ -27,6 +27,7 @@ define SKELETON_CUSTOM_CONFIGURE_CMDS
 	support/scripts/check-merged \
 		--type skeleton \
 		$(if $(BR2_ROOTFS_MERGED_USR),--merged-usr) \
+		$(if $(BR2_ROOTFS_MERGED_BIN),--merged-bin) \
 		$(SKELETON_CUSTOM_PATH)
 endef
 

support/scripts/check-merged

@@ -1,7 +1,9 @@
 #!/usr/bin/env bash
 #
-# Check if a given custom skeleton or overlay complies to the merged /usr
+# Check if a given custom skeleton or overlay complies to the merged
 # requirements:
+#
+# - for merged-usr:
 #   /bin            missing, or a relative symlink to usr/bin
 #   /lib            missing, or a relative symlink to usr/lib
 #   /sbin           missing, or a relative symlink to usr/sbin
@@ -11,9 +13,14 @@
 #
 # *: must be present for skeletons, can be missing for overlays
 #
+# - for merged-bin: all of the above, except:
+#   /usr/sbin       missing, or a relative symlink to bin (thus points
+#                   to /usr/bin)
+#
 # Input:
 #   --type TYPE     the type of root to check: 'skeleton' or 'overlay'
 #   --merged-usr    check for merged /usr
+#   --merged-bin    check for merged /usr/bin
 #   $*:             the root directories (skeleton, overlays) to check
 # Output:
 #   stdout:         the list of non-compliant paths (empty if compliant).
@@ -22,12 +29,13 @@
 #   !0:             if any directory to check is improperly merged
 #
 
-opts="type:,merged-usr"
+opts="type:,merged-usr,merged-bin"
 ARGS="$(getopt -n check-merged -o "" -l "${opts}" -- "${@}")" || exit 1
 eval set -- "${ARGS}"
 
 type=
 merged_usr=false
+merged_bin=false
 while :; do
 	case "${1}" in
 	(--type)
@@ -38,6 +46,10 @@ while :; do
 		merged_usr=true
 		shift
 		;;
+	(--merged-bin)
+		merged_bin=true
+		shift
+		;;
 	(--)
 		shift
 		break
@@ -110,10 +122,14 @@ for root; do
 	if ${merged_usr}; then
 		test_dir "${type}" "${root}" "/" "usr/bin"
 		test_dir "${type}" "${root}" "/" "usr/lib"
-		test_dir "${type}" "${root}" "/" "usr/sbin"
 		test_merged "${type}" "${root}" "/" "bin" "usr/bin"
 		test_merged "${type}" "${root}" "/" "lib" "usr/lib"
 		test_merged "${type}" "${root}" "/" "sbin" "usr/sbin"
+		if ${merged_bin}; then
+			test_merged "${type}" "${root}" "/usr/" "sbin" "bin"
+		else
+			test_dir "${type}" "${root}" "/" "usr/sbin"
+		fi
 	fi
 done
 

system/Config.in

@@ -343,6 +343,16 @@ config BR2_ROOTFS_MERGED_USR
 	  symlinks to their counterparts in /usr. In this case, /usr can
 	  not be a separate filesystem.
 
+config BR2_ROOTFS_MERGED_BIN
+	bool "Merged /usr/bin"
+	depends on BR2_ROOTFS_MERGED_USR
+	help
+	  If you say 'n' here, then /usr/bin and /usr/sbin will be
+	  separate directories; this is the historical UNIX way.
+
+	  If you say 'y' here, then /usr/sbin will be a relative
+	  symlink to /usr/bin.
+
 if BR2_ROOTFS_SKELETON_DEFAULT
 
 config BR2_TARGET_ENABLE_ROOT_LOGIN
@@ -529,6 +539,7 @@ endif # BR2_ROOTFS_SKELETON_DEFAULT
 
 config BR2_SYSTEM_DEFAULT_PATH
 	string "Set the system's default PATH"
+	default "/usr/bin" if BR2_ROOTFS_MERGED_BIN
 	default "/usr/bin:/usr/sbin" if BR2_ROOTFS_MERGED_USR
 	default "/bin:/sbin:/usr/bin:/usr/sbin"
 	help

system/system.mk

@@ -32,18 +32,30 @@
 #   set inittab to remount root read-write or read-only
 #
 
-# This function handles the merged or non-merged /usr cases
+# This function handles the merged or non-merged /usr, and merged or
+# non-merged /usr/bin cases
 ifeq ($(BR2_ROOTFS_MERGED_USR),y)
+ifeq ($(BR2_ROOTFS_MERGED_BIN),y)
+define SYSTEM_SBIN_SYMLINKS_OR_DIRS
+	ln -snf bin $(1)/usr/sbin
+endef
+else
+define SYSTEM_SBIN_SYMLINKS_OR_DIRS
+	$(INSTALL) -d -m 0755 $(1)/usr/sbin
+endef
+endif
 define SYSTEM_USR_SYMLINKS_OR_DIRS
 	ln -snf usr/bin $(1)/bin
 	ln -snf usr/sbin $(1)/sbin
 	ln -snf usr/lib $(1)/lib
+	$(SYSTEM_SBIN_SYMLINKS_OR_DIRS)
 endef
 else
 define SYSTEM_USR_SYMLINKS_OR_DIRS
 	$(INSTALL) -d -m 0755 $(1)/bin
 	$(INSTALL) -d -m 0755 $(1)/sbin
 	$(INSTALL) -d -m 0755 $(1)/lib
+	$(INSTALL) -d -m 0755 $(1)/usr/sbin
 endef
 endif