Gao Xiang <gaoxiang25@xxxxxxxxxx> writes: > On Mon, Dec 02, 2019 at 09:10:45PM -0800, Daniel Rosenberg wrote: >> Ext4 and F2fs are both using casefolding, and they, along with any other >> filesystem that adds the feature, will be using identical dentry_ops. >> Additionally, those dentry ops interfere with the dentry_ops required >> for fscrypt once we add support for casefolding and encryption. >> Moving this into the vfs removes code duplication as well as the >> complication with encryption. >> >> Currently this is pretty close to just moving the existing f2fs/ext4 >> code up a level into the vfs, although there is a lot of room for >> improvement now. >> >> Signed-off-by: Daniel Rosenberg <drosen@xxxxxxxxxx> > > I'm afraid that such vfs modification is unneeded. > > Just a quick glance it seems just can be replaced by introducing some > .d_cmp, .d_hash helpers (or with little modification) and most non-Android > emulated storage files are not casefolded (even in Android). > > "those dentry ops interfere with the dentry_ops required for fscrypt", > I don't think it's a real diffculty and it could be done with some > better approach instead. It would be good to avoid dentry_ops in general for these cases. It doesn't just interfere with fscrypt, but also overlayfs and others. The difficulty is that it is not trivial to change dentry_ops after dentries are already installed in the dcache. Which means that it is hard to use different dentry_ops for different parts of the filesystem, for instance when converting a directory to case-insensitive or back to case-sensitive. In fact, currently and for case-insensitive at least, we install generic hooks for the entire case-insensitive filesystem and use it even for !IS_CASEFOLDED() directories. This breaks overlayfs even if we don't have a single IS_CASEFOLDED() directory at all, just by having the superblock flag, we *must* set the dentry_ops, which already breaks overlayfs. I think Daniel's approach of moving this into VFS is the simplest way to actually solve the issue, instead of extending and duplicating a lot of functionality into filesystem hooks to support the possible mixes of case-insensitive, overlayfs and fscrypt. -- Gabriel Krisman Bertazi
