Alan DuBoff wrote: > On Tuesday 30 January 2007 12:59 am, Moinak Ghosh wrote: > >> You are talking about UnionFS here. It should be a good project to >> port the FreeBSD >> version of UnionFS along with a set of external patches that fix >> existing shortcomings. >> > > I'm not sure, I don't know anything about UnionFS. I'll need to look into > that. It seems more related to layering different devices, in the sense of > memory, optical, disk, etc...I was thinking of just layering the changes to > the root filesystem. So, let's say a person replaces sendmail, the system > would store information so that at boot time, it will place a symlink that > pointed to the new binary, which would get queried at boot time. At least > this is how I was thinking about it. >
UnionFS does exactly what you mentioned. It is a fan-out fs similar in some respects to cachefs and can merge multiple filesystem branches and make them look like one filesystem tree. Of course there are rules to handle duplicates etc. One thing it can do is merge a read-only tree with a read-write area. So any writes to files in the read-only tree causes that file to be copied to the read-write area and updated. All Linux LiveCDs uses UnionFS layered over the read-only CDROM and merged with a small ramdisk for the write capability. This way all read-write rootfs contents including /etc, /var etc reside on the CDROM resulting in a very small ramdisk. Regards, Moinak. > Before that point, to be able to store system configuration that would > normally be stored in /etc/*.conf files (or similar) and store that into SMF, > using the XML. > > So, I guess 2 different pieces, one that would layer the configuration > changes > to the root filesystem and store them into SMF. > > Then be able to layer any filesystem changes on top of that. > > In the middle is a read-only root filesystem, or at the bottom, depending on > how you like to look at it.;-) Somehow I was thinking to use the ZFS ACL for > this piece. > >
