Where does the root file system (ie, / not /system) come from on Android? I can see that /system is mounted
cat /proc/mounts rootfs / rootfs ro,relatime 0 0 ... /dev/block/mtdblock8 /system ext4 ro,noatime,nodiratime,barrier=1,data=ordered,noauto_da_alloc 0 0 /dev/block/mtdblock6 /data ext4 rw,nosuid,nodev,noatime,nodiratime,barrier=1,data=ordered,noauto_da_alloc 0 0
I can see that /system and /data are mounted from mtdblockX devices. And that / is mounted on the 'virtual' type 'rootfs'.
There are a bunch of files and directories in / (I'm interested in /sbin) that don't seem to be mounted on a mount point over /. Where do those files come from? (I want to get RW access to /sbin) Is this done with some 'chroot' magic? -- it it from some 'boot' image? (In this specific example I'm using a Minix Neo X5 with Android)