[Buildroot] Is there a way to automatically detect the minimum required BR2_TARGET_ROOTFS_EXT2_SIZE?

[Ciro Santilli]

https://stackoverflow.com/questions/49211241/is-there-a-way-to-automatically-detect-the-minimum-required-br2-target-rootfs-ex

I'm when making a big non-embedded image, I keep hitting the error:

    *** Maybe you need to increase the filesystem size
(BR2_TARGET_ROOTFS_EXT2_SIZE)

and then I have to do a `du` on `output/target` to find out how big I
have to make `BR2_TARGET_ROOTFS_EXT2_SIZE`.

Is there a way to automate this, or a decent workaround?

Some workarounds I'm considering:

* put the big stuff under 9p:
https://superuser.com/questions/628169/how-to-share-a-directory-with-the-host-without-networking-in-qemu
* use CPIO and `-initrd`