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This change makes more of the root filesyste metadata static across builds, but
more can be done there. It also changes the root filesystem to use ext2 as
we don't need journaling in normal mode. Optionally we could use ext3 for
non-verified if desired (it's an easy change).
In particular, this change cleans up the following:
- clears the rootfs uuid
- labels it C-ROOT (instead of C-KEYFOB)
- removes reserved inodes and blocks
The major feature of this change, however, is that it adds two simple
helpers to common.sh: disable_rw_mount and enable_rw_mount. They will
set high order byte (le) in the ro compat field to be 0xff. This will
tell the kernel that the filesystem uses features R24-R31 which are safe
for use on the running kernel iff the filesystem is mounted read-only.
These functions are called in cros_make_image_bootable and
mount_gpt_image, respectively. mount_gpt_image will always
enable_rw_mount and cros_make_image_bootable will disable_rw_mount if
--enable_rootfs_verification is true.
The approach is ugly but reasonably well contained. If ext2 ever gets a
new revision and new features in the same range are introduced, then we
would be getting inconsistent behavior. That said, it is unlikely that
that churmn will happen and if the impact is negative, it will ideally
show up during testing.
N.B., this will likely result in changes needing to be made to the
signing scripts in vboot_reference to ensure that rw mounting is
enabled/disabled in the same way (E.g., during stamping).
BUG=chromium-os:7468
TEST=- built x86-generic, imaged to usb stick, attempted to mount rw /dev/sdc3 on the host and was properly bounced.
- booted to the image just fine on a dogfood device.
- mod'd for recovery, then installed and booted.
- mod_image_for_test runs with no errors; booted the resulting image as well
- booted a factory_install with the pending dm changes
- BVT passed with build_image x86-generic (vboot enabled)
- [in progress] autotest that checks if the rootdev = /dev/dm-0 and
then does a dumpe2fs | grep -q FEATURE_R31
Review URL: http://codereview.chromium.org/3916002
Change-Id: If4dcba7568a110f4e32627c916d9e5741e5e5414