On Thu, Sep 13, 2018 at 10:03 PM Jonathan Busby <jdb2@xxxxxxxxx> wrote: > > > > -------- Forwarded Message -------- > Subject: Re: How to access "upper" directory of overlayfs programatically > Date: Thu, 13 Sep 2018 13:01:16 -0500 > From: Jonathan Busby <jdb2@xxxxxxxxx> > To: Amir Goldstein <amir73il@xxxxxxxxx> > > > > On 09/13/2018 12:33 PM, Jonathan Busby wrote: > > > > > > On 09/12/2018 02:48 PM, Amir Goldstein wrote: > >> [changing over to overlayfs list] > > > > Thanks for this! :D I had been searching for an overlayfs mailing list > > but it seems I overlooked unionfs. > > > >> > >> On Wed, Sep 12, 2018 at 8:52 PM Jonathan Busby <jdb2@xxxxxxxxx> wrote: > >>> > >>> Hello. I'm new to this list and I don't know if this is the right forum > >>> for my question, but, I've asked this same question on many forums and > >>> never received an answer -- please don't flame me. > >>> > >>> I have a Debian based Linux live system which is running out of RAM and > >>> was booted without the "persistent" boot option, so the capser-rw > >>> filesystem was never created. > >>> > >>> I wish to gain access to the "upper" directory of the overlayfs > >>> filesystem in the casper init scripts initramfs "/cow/upper" filesystem > >>> so that I may programatically save the filesystem, hopefully without > >>> having to re-implement cp. > >>> > >>> I know how to commit the changes of a Debian based live CD session to a > >>> storage device, but only if the live session in question was booted with > >>> the "persistent" option. > >>> > >>> I've looked at the overlayfs source code but I still can't figure out > >>> how to accomplish what I want. > >>> > >>> I'm sorry if this is stupid question -- hopefully it's not. > >>> > >> > >> I don't think the programmable API you think of exists, but maybe > >> you can get access to upper dir as admin user. > >> > >> Please share the init scripts responsible for the mounts at live CD boot > >> and the content of /proc/self/mountinfo > > > > The contents of /proc/self/mountinfo are can be found here : > > > > https://pastebin.com/raw/9uQdJ66w > > > > The init scripts responsible for the live CD mounts can be found here : > > > > https://www.dropbox.com/s/j4zqsn8avxrv6zf/initrd-scripts.tar.gz?dl=0 > > > > Thanks, > > > > Jonathan > > > >> > >> Thanks, > >> Amir. > >> > > I forgot to mention that the init scripts that handle mounting the > overlayfs chroot are located in the /scripts/casper directory, and the > main script is just called "casper". > Jonathan, Not sure this is what you were looking for, but one thing you could try is to iterate the directories of root fs (similar to find / -xdev) executing stat() on files inside directories. Depending on your kernel version, the findings might vary, but I would expect all values of st_dev to be identical (this is what makes find -xdev stop on fs boundary). For non directories, the value of st_dev is an indication to the layer (at least in your specific non-same-fs combination of upper/lower). If you create a new file, it will be in upper, so you can use its st_dev as the identifier of the upper layer. All files with the same st_dev are either newly created files or modified files, so you can copy them to backup. Directories will not carry a similar indication if they are modified or new. This method will not give you the list of deleted files (whiteout in upper). Thanks, Amir.
