Re: [OE-core] [PATCH] overlayfs.bbclass: generate overlayfs mount units

["Vyacheslav Yurkov" <uvv.mail@gmail.com>]

Hi Andrei,
Like you mentioned, it's application specific. The advantage of 
overlayfs here is that you preserve the data that was changed by user 
(in case of persistent storage), which of course would hide the data 
from rootfs, or your just see the defaults from rootfs if the data was 
not changed. With bind mounts you would need to copy default data first 
into your tmpfs/ext4 bind mount if you wanna have defaults.

Vyacheslav
> I was looking into something like this lately. There are actually two kinds of write access - volatile (tmpfs) and persistent (to disk). So my approach would have been to use bind mounts from a tmpfs/ext4 based on configuration per recipe. Is there any advantage to working with overlayfs in this case? The main idea is to have state that doesn't come from the ro part of the OS because otherwise, updates will be shadowed by the overlayfs. So I fail to see the advantage of using a set of overlayfs mounts instead of bind mounts. At least with bind mounts, it will always shadow the rootfs bits so you can catch early this case.
>
> Depending on your use case, most of the times, you'd want this "state" setup happening pre init (in initramfs, for example), especially if you want to handle persistent systemd logging or machine id, etc.
>