Keeping reiserfs in the tree has certain costs. For example, I would very much like to remove the 'flags' argument to ->write_begin. We have the infrastructure in place to handle AOP_FLAG_NOFS differently, but AOP_FLAG_CONT_EXPAND is still around, used only by reiserfs. Looking over the patches to reiserfs over the past couple of years, there are fixes for a few syzbot reports and treewide changes. There don't seem to be any fixes for user-spotted bugs since 2019. Does reiserfs still have a large install base that is just very happy with an old stable filesystem? Or have all its users migrated to new and exciting filesystems with active feature development? We've removed support for senescent filesystems before (ext, xiafs), so it's not unprecedented. But while I have a clear idea of the benefits to other developers of removing reiserfs, I don't have enough information to weigh the costs to users. Maybe they're happy with having 5.15 support for their reiserfs filesystems and can migrate to another filesystem before they upgrade their kernel after 5.15. Another possibility beyond outright removal would be to trim the kernel code down to read-only support for reiserfs. Most of the quirks of reiserfs have to do with write support, so this could be a useful way forward. Again, I don't have a clear picture of how people actually use reiserfs, so I don't know whether it is useful or not. NB: Please don't discuss the personalities involved. This is purely a "we have old code using old APIs" discussion.
