On Wed, Jun 7, 2017 at 9:51 AM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > When inodes index feature is enabled, lookup in indexdir for the index > entry of lower real inode or copy up origin inode. The index entry name > is the hex representation of the lower inode file handle. > > If the index dentry in negative, then either no lower aliases have been > copied up yet, or aliases have been copied up in older kernels and are > not indexed. > > If the index dentry for a copy up origin inode is positive, but points > to an inode different than the upper inode, then either the upper inode > has been copied up and not indexed or it was indexed, but since then > index dir was cleared. Either way, that index cannot be used to indentify > the overlay inode. > > If a negative index dentry is found or a positive dentry that matches the > upper inode, store it in the overlay dentry to be used later. A non-upper > overlay dentry may still have a positive index from copy up of another > lower hardlink. This situation can be tested with the path type macros > OVL_TYPE_INDEX(type) && !OVL_TYPE_UPPER(type). > > This is going to be used to prevent breaking hardlinks on copy up. Why is a negative index (or any index, for that matter) stored in the overlay dentry? This seems a big waste, since the index dentry will be allocated for all lower files, yet never used unless copied up. Index is used: - at lookup need to find any copied up alias - at copyup need to set up new index In both cases we can just do a fresh lookup in the index dir with locks held (which is a good idea anyway). Something related: should upperdentry of aliases be hardlinked to the index on lookup and copy-up? Or should the "hardlink-up" be deferred until rename? I think updating as soon as possible is the simpler of the two. Thanks, Miklos
