On Thu, Oct 25, 2012 at 4:23 PM, Thomas Bächler <thomas@xxxxxxxxxxxxx> wrote: > Am 25.10.2012 15:50, schrieb Leonidas Spyropoulos: >> Hello all, >> >> Firstly can a TU or developer few it to the dev mailing list, as I don't >> have access. >> >> Archlinux is supporting btrfs for root filesystem some time now. Have any >> work or thoughts been done for supporting snapshots before update packages? >> This way you can keep record of what's happening to your system and easily >> rollback if something breaks. >> I know Fedora and Suse (if not mistaken) supports that with their package >> managers. >> >> Of course I am talking about an optional feature enabled only from the >> user, not by default. >> >> Thoughts, ideas, discussion are welcome. > > This is surely a great idea when you have filesystem-level snapshots (as > you have in btrfs). > > This sounds like something that can be easily written as a > proof-of-concept implementation in a shell script. Once you work out the > exact mechanics, we can consider either adding this to pacman or as an > external wrapper to pacman, whatever makes sense. (This would be a > discussion for the pacman-dev mailing list.) > > What I'm saying is: If you have a more detailed description of how this > scheme should work, preferably together with a simple implementation, > then a much more fruitful discussion will emerge. Basically you tell the FS to subvol / to a location like /.pacmansnaps/$datetime. In the initramfs, you need an emergency facility to let the user list the available subvols (btrfs su list /) and choose one to mount (which would require adding subvol=/foo/bar or subvolid=12345 to the rootflags). Another thing to think about would be garbage collection of old snapshots. btrfs also has a way of specifying the default mounted subvolume of a filesystem. I suppose a shell script would use the btrfs command to manipulate the FS, while pacman would probably use IOCTLs?
