On Wed, Apr 19, 2017 at 4:15 PM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > On Wed, Apr 19, 2017 at 1:34 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > >> I am contemplating a scheme similar to your suggestion, but instead of >> a shadow directory tree, index forward redirects by stable inode number >> and store upper and lower redirects as xattr, e.g.: >> >> workdir/inodes/#100 > > Interesting idea. I wanted to run another idea by you. Instead of storing the overlay inode index under workdir/inodes, store it under upperdir/lost+found. Crazy? think about it.. - User applications won't touch that dir, because it is already reserved for use by mkfs/fsck tools. - It is actually going to be used by a future fsck.overlay tool, to reindex after layers migration. - Taking the analogy to traditional lost+found even further, the files found in traditional lost+found are also named #<ino> and when you open them you get an fd to the inode. In case of hardlinked #<ino> (non-dir) you will actually get the same behavior as the traditional lost+found, except that inodes could have nlink > 1. directory inode entries could appear as empty dir to user or they could be stored as whiteouts, so user doesn't see them. - This keeps workdir content volatile (and not only workdir/work) it may matter because container managers would pack upper dir when committing changes to an image, but they would not pack workdir (I think). > >> contains xattrs: >> overlay.fh - fh of lower inode (whose ino is 100) >> overlay.redirect - path of lower inode (so fh and stale ino can be >> fixed after copying layers) >> overlay.upper - fh of upper inode >> overlay.path - path (*) of upper (so upper fh can be fixed after copying layers) > > I get ".redirect" and ".upper" but not the others. In fact the lower > fh can actually be used to generate the name of the file, so we don't > have to encode lower ino separately into the overlay fh. > Forgot to CC the list when I wrote that you are right. We don't need overlay.fh on the inode entry and overlay.path may be needed for a later "commit before migrate" tool, but don't need to worry about that now. Amir. -- 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
