I am trying to update a custom initramfs init script to mount a squashfs image as the root file system. I have been testing the mounting of a squash image to a loop device in read only, mounting another empty file to another loop device in read-write, and using device mapper to create a rw snapshot of the ro loop device.
I've made it this far with my test script (running as root):
mkdir /tmp/squash_rw dev=$(losetup -f) losetup -r $dev /mcp_fs.sqsh ovl=/overlay newdevname=overlay size=$(blockdev --getsz "$dev") loop=$(losetup -f --show -- "$ovl") printf '%s\n' "0 $size snapshot $dev $loop P 8" | dmsetup create "$newdevname"
I then use touch to test whether the new device mounts as rw but errors with a notice that it is a Read-Only device.
# touch /tmp/squash_rw/test touch: cannot touch '/tmp/squash_rw/test': Read-only file system
I am using a gentoo distribution and Linux kernel 3.10.6 with device mapper and squashfs modules included. Many references suggest to use a dracut initramfs but I am trying to get the init script I was provided by a vendor to work.
I have been stuck on this for a few days and would greatly appreciate any help anyone can provide.
After continuing to research and experiment, it appears as though the devmapper device I am making assumes the filesystem of the first device which is getting merged together. If I use the squashfs device, the devmapper device is readonly, if I use the rw image, then the devmapper device is rw but when mounted doesn't contain the content from the squash file.