On 5/30/2012 3:08 AM, Sameer Naik wrote:
Thanks for the quick response. I will check out the links Bartos provided.
Certainly, my query is not related to busybox, but where else can i
find a better community for my query :)
Regards
~Sameer
Indeed, you're posting your question to a lot of people who have done
this exact thing :-)
I found aufs to be more experimental with lots of fancy features... but
wasn't stable enough for me. (this changes over time and by kernel
version, of course, but when I tested it 3 years ago I got some strange
results) Unionfs has worked flawlessly for me on multiple kernels.
Unionfs has one problem though: the only way to get correct behavior is
to merge path A and B onto mountpoint C. (C can't be the same as A or B).
What I came up with was to use the rootfs that Linux creates for the
initramfs, and have the following symlink pattern:
/etc -> /union/etc
/bin -> /union/bin
...
/union/etc -> /initrd/etc
/union/bin -> /initrd/bin
...
All of that lives in the initramfs and is loaded immediately.
Then, I mount the system image at /sysimage, and then
mount -t unionfs -o dirs=/initrd=rw:/sysimage/fhs=ro none /union || die
"Failed to set up unionfs";
This hides the second level of symlinks and uses the unionfs
*atomically*, and since I'm using the rootfs, I don't have to mount my
own tmpfs or switchroot or anything like that. Also, my system uses the
one busybox binary that it loaded out of initramfs for the entire life
of the system, so no need to worry about freeing up the resources used
by the initramfs.
Also, the entire system becomes writable, and if I want to know what I
changed I can just rsync /initrd to my development machine and see what
new files exist, and integrate them into my next system image. I can
also selective revert things to default while the system is running by
deleting files out of /initrd.
-Mike
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