initramfs-framework: support rootflags and rootfstype boot parameter
These two parameters are supported by the kernel
(https://www.kernel.org/doc/Documentation/kernel-parameters.txt). When
an initramfs is used, the kernel does not mount the rootfs and the
initramfs needs to react to them.
The boot parameters can be set both by the image creator and
by users.
Supporting these two parameters is useful:
- rootflags is needed to ensure that the rootfs is already mounted as
intended in the time between starting init and init remounting
it (as systemd does); this is critical for IMA where iversion must be
active already when system starts writing files.
- setting it correctly up-front avoids messages from the kernel ("cannot
mount ... as ext2 because ...") when trying to guess the desired type.
For example, assuming that only one of ext4/ext3/ext2 is set,
rootfstype could be set in an image recipe with:
APPEND_append = "${@''.join([' rootfstype=' + i for i in ['ext4', 'ext3', 'ext2'] if i in d.getVar('IMAGE_FSTYPES', True).split()])}"
Signed-off-by: Patrick Ohly <patrick.ohly@intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
