Right now, attempt to update mounted TMPFS(5) fs from read-only to read-write or vica-versa is unsupported. Mmoreover, it might also cause very mysterious error message, if you have size parameter set in the /etc/fstab (as you probably should). This patch adds this missing functionality.
+ echo '/dev/null /mnt tmpfs ro,size=100k 0 0'
+ sudo mount -F my.fstab /mnt
+ sudo mount -F my.fstab -u -o rw /mnt
mount: tmpfs: mount option <size> is unknown: Operation not supported