How to specify the mount points for multiple lower layers?

How to specify the mount points for multiple lower layers?

[Alkis Georgopoulos]

 From https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt:
mount -t overlay overlay -olowerdir=/lower1:/lower2:/lower3 /merged

How can I specify that I want e.g. lower2 to be mounted at merged/home?

If all lower* layers can only be mounted at /merged, then I don't see 
any way at all that overlayfs would allow me to combine e.g.
Partition  MountDir  MergedDir
------------------------------
/dev/sda1  /root-fs  /merged
/dev/sda2  /home-fs  /merged/home

I even tried to create a fake directory structure like this:
/dev/sda2 /fakedir/home /merged
...so that I would mount /dev/sda2 to /fakedir/home, and then try to use 
lower2=/fakedir, but then I got a different issue, that overlayfs 
doesn't include submounts, so sda2 wasn't visible at all then.

So I was unable to combine the root and home partitions to the correct 
paths using overlayfs (I'm planning to use a tmpfs as the upper dir 
later on).

Any help? Thank you!

Re: How to specify the mount points for multiple lower layers?

[Miklos Szeredi]

On Thu, Aug 6, 2015 at 10:25 AM, Alkis Georgopoulos <alkisg@gmail.com> wrote:
> From https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt:
> mount -t overlay overlay -olowerdir=/lower1:/lower2:/lower3 /merged
>
> How can I specify that I want e.g. lower2 to be mounted at merged/home?
>
> If all lower* layers can only be mounted at /merged, then I don't see any
> way at all that overlayfs would allow me to combine e.g.
> Partition  MountDir  MergedDir
> ------------------------------
> /dev/sda1  /root-fs  /merged
> /dev/sda2  /home-fs  /merged/home
>
> I even tried to create a fake directory structure like this:
> /dev/sda2 /fakedir/home /merged
> ...so that I would mount /dev/sda2 to /fakedir/home, and then try to use
> lower2=/fakedir, but then I got a different issue, that overlayfs doesn't
> include submounts, so sda2 wasn't visible at all then.
>
> So I was unable to combine the root and home partitions to the correct paths
> using overlayfs (I'm planning to use a tmpfs as the upper dir later on).
>
> Any help? Thank you!

Create two overlays: one for root and one for home (which includes the
additional home-fs).

Does that work for you?

Thanks,
Miklos

Re: How to specify the mount points for multiple lower layers?

[Alkis Georgopoulos]

On 12/08/2015 12:39 μμ, Miklos Szeredi wrote:
>
> Create two overlays: one for root and one for home (which includes the
> additional home-fs).
>
> Does that work for you?


Yes, thank you, I wasn't able to do it with the multiple lower layers 
syntax,
but I was able to do it with multiple overlayfs mounts.

Thanks!