On Tue, Mar 3, 2015 at 6:12 PM, Atom2 <ariel.atom2@xxxxxxxxxx> wrote: > Mikolos, > thanks for joining the party. > > Am 03.03.15 um 16:14 schrieb Miklos Szeredi: > >> Atom2, >> >>> The use case behind that is to be able to backup only files from the >>> upperdir for several systems sharing a common lowerdir filesystem. I have >>> used that (scripted approach via rsync) now for quiet some time and a few >>> kernels back and it seemed to have worked very well. >> >> >> Why don't you just back up the upper directory itself instead of >> messing around with device numbers? > > > I am not aware of any such option, but if you could explain that a little > bit more in detail, I am happy to explore other options. > > Just for everybody to be on the same page: In my use case the r/o lowerdir's > root directory is also the root of my file system (which is shared across > many systems) from which (all) the systems boot. Using an initramfs during > the boot process, the upperdir file system (which is different per system) > is then r/w overlay-mounted over the common r/o lowerdir's root directory in > order to catch any r/w access to the file system. > > So in essence and according to my understanding there's no direct access to > (only) the r/w upperdir (or only the lowerdir) from within any of the > running systems other than using the device field to see where a file system > entry actually exists - at least that's my current understanding. Having access to the upperdir is just your own choice. Without knowing the details of how you set up the mounts I can't give you a concrete example, but see for example the pivot_root(8) man page on how to get access to your old mountpoint. You can also use bind mounts to clone the upperdir into the overlay namespace. Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
