On 26/12/2011 18:03, Joakim Tjernlund wrote:
> I am contemplating a greater problem too. Our system require we can install
> multiple versions of our SW and switch between them. This is easy to do when it
> comes to our own app but not when one want to upgrade core parts of the system, like
> libc etc.
>
> So I am thinking one could use --bind mounts and switch_root to solve that. Basically
> one has a skeleton root FS with /bin, /lib, /usr /opt etc.
> Each upgrade goes into dirs like:
>    bin_1.x.y/ usr_1.x.y/ lib_1.x.y/ opt_1.x.y/ sbin_1.x.y/
> Then, from an initramfs, one selects which of xxx_1.x.y dir one wants to use
> and --bind mounts them under the corresponding skeleton dir.
>

I'm doing something like this using aufs.  The performance seems "not 
bad", but you get a couple MB or so memory hit.  (I'm using squashfs as 
well, so unsure which causes the main memory increase).

I think if the device is reasonably beefy then you should have no 
problem with aufs or some similar overlay filesystem (I think some new 
one got added to kernel recently?).  Failing that, what about good old 
"cp -a" to merge all the input dirs?  Takes some time and disk space, 
but nice and simple?

Good luck

Ed W