On Mon, 2017-02-06 at 08:38 +0200, Amir Goldstein wrote: > On Mon, Feb 6, 2017 at 5:25 AM, J. R. Okajima <hooanon05g@xxxxxxxxx> > wrote: > > James Bottomley: > > > This allows any subtree to be uid/gid shifted and bound > > > elsewhere. It > > ::: > > > > Interesting. > > But I am afraid that the inconsistency problem of the inode numbers > > will happen. > > > > Yet another example that overlayfs already is in the process of > solving (it is fixed for stat of merged directory inode). > In fact, fir the case of single layer overlay (as well as shiftfs) > the solution is trivial - preserve underlying inode st_ino/d_ino and > use the overlayed fs st_dev. not sure I follow what st_ino is, do you mean s_root->d_inode->i_ino? or did you mean s_dev (which is more traditional)? The problem with this is there's no way to ensure global uniqueness in a mapping that goes (ino, ino) -> (ino) (or (s_dev, ino) -> (ino)) and I believe global uniqueness is more important because the i_ino is used in the hashed lookups. Secondly you're not guaranteed that s_root ->d_inode->i_ino is unique ... historically a lot of filesystems use a well known inode number as the root, that's why filehandles traditionally used something representing the device and the inode number (we also have s_dev uniqueness problems for tmpfs which is used in some overlays). We can certainly construct a filehandle using an export operations override that is unique and can be used to lookup the underlying object (based on the underlying device and inode). James
