skeleton: Have a portable remount RW/RO

With systemd, inittab is useless, but it's also where we stored a 'mount -o remount ...' to toggle the rootfs ro/rw at the demand of the user.

Instead, doing a simple 'mount -a -o remount' should change the flag of every mountpoint by reading /etc/fstab.

Therefore, we now modify /etc/fstab, which happens to be read by systemd also and so, everyone benefits.

---
v1 -> v2:
- Rebase on current master ('null' was removed from inittab)
- 'Rework' sed expression (add quote, remove curly braces, remove useless escape of comma)

---
 package/busybox/inittab      | 3 +--
 package/skeleton/skeleton.mk | 8 ++++----
 package/sysvinit/inittab     | 3 +--
 3 files changed, 6 insertions(+), 8 deletions(-)

index 24d9199..7202474 100644
@@ -15,10 +15,9 @@
 
 # Startup the system
 ::sysinit:/bin/mount -t proc proc /proc
-::sysinit:/bin/mount -o remount,rw /
 ::sysinit:/bin/mkdir -p /dev/pts
 ::sysinit:/bin/mkdir -p /dev/shm
-::sysinit:/bin/mount -a
+::sysinit:/bin/mount -a -o remount
 ::sysinit:/bin/hostname -F /etc/hostname
 # now run any rc scripts
 ::sysinit:/etc/init.d/rcS

index 48e7085..ae8f429 100644
@@ -142,14 +142,14 @@ endif
 
 ifeq ($(BR2_INIT_BUSYBOX)$(BR2_INIT_SYSV),y)
 ifeq ($(BR2_TARGET_GENERIC_REMOUNT_ROOTFS_RW),y)
-# Find commented line, if any, and remove leading '#'s
+# Find 'ro,' (avoid 'root') in the first line and change it to 'rw,'
 define SKELETON_SYSTEM_REMOUNT_RW
-	$(SED) '/^#.*-o remount,rw \/$$/s~^#\+~~' $(TARGET_DIR)/etc/inittab
+	$(SED) '0,/ro,/s/ro,/rw,/' $(TARGET_DIR)/etc/fstab
 endef
 else
-# Find uncommented line, if any, and add a leading '#'
+# Find rw on the first line and change it to ro
 define SKELETON_SYSTEM_REMOUNT_RW
-	$(SED) '/^[^#].*-o remount,rw \/$$/s~^~#~' $(TARGET_DIR)/etc/inittab
+	$(SED) '0,/rw/s/rw/ro/' $(TARGET_DIR)/etc/fstab
 endef
 endif
 TARGET_FINALIZE_HOOKS += SKELETON_SYSTEM_REMOUNT_RW

index fc0c9b5..4b8cfd7 100644
@@ -5,10 +5,9 @@
 id:3:initdefault:
 
 si0::sysinit:/bin/mount -t proc proc /proc
-si1::sysinit:/bin/mount -o remount,rw /
 si2::sysinit:/bin/mkdir -p /dev/pts
 si3::sysinit:/bin/mkdir -p /dev/shm
-si4::sysinit:/bin/mount -a
+si4::sysinit:/bin/mount -a -o remount
 si5::sysinit:/bin/hostname -F /etc/hostname
 si6::sysinit:/etc/init.d/rcS
 

2.5.3

Dear Maxime,

sorry for having kind of endorsed this patch in its v1, but now I tested it and it seems flawed in its very core (unless I'm still drunk).

Maybe it should, but it doesn't:

# cat /etc/fstab
# <file system>	<mount pt>	<type>	<options>	<dump>	<pass>
/dev/root	/		ext2	rw,noauto	0	1
proc		/proc		proc	defaults	0	0
devpts		/dev/pts	devpts	defaults,gid=5,mode=620	0	0
tmpfs		/dev/shm	tmpfs	mode=0777	0	0
tmpfs		/tmp		tmpfs	mode=1777	0	0
tmpfs		/run		tmpfs	mode=0755,nosuid,nodev	0	0
sysfs		/sys		sysfs	defaults	0	0
# mount
/dev/root on / type ext2 (ro,relatime,errors=remount-ro)
devtmpfs on /dev type devtmpfs 
(rw,relatime,size=62812k,nr_inodes=15703,mode=755)
proc on /proc type proc (rw,relatime)
# /bin/mount -a -o remount
# mount
/dev/root on / type ext2 (ro,relatime,errors=remount-ro)
devtmpfs on /dev type devtmpfs 
(rw,relatime,size=62812k,nr_inodes=15703,mode=755)
proc on /proc type proc (rw,relatime)
#

It's still mounted ro. Removing the noauto for /dev/root/ does not change the result.

This is using the default mount from busybox on qemu_arm_versatile_defconfig with an external toolchain. Wild guess: are you using the full-featured mount command from util-linux? Or maybe systemd ships it own mount command with this feature?

Luca

Hi Luca,

I'll test this on my side, I remember it worked (I created this patch during the Buildroot Summer Camp and had not sent it yet, but I clearly remember having testing it), as you said, maybe I was util the full blown mount, I'll test and respin. I'll mark this as "Changes Requested" for the moment.

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