Amir Goldstein <amir73il@xxxxxxxxx> writes: > On Sun, Jun 2, 2019 at 9:01 PM Theodore Ts'o <tytso@xxxxxxx> wrote: >> >> On Sun, Jun 02, 2019 at 09:42:54AM +0300, Amir Goldstein wrote: >> > [+cc ext4] Heads up on bug reports "Overlayfs fails to mount with ext4" >> > >> > On Sat, Jun 1, 2019 at 11:02 PM Marco Nelissen <marco.nelissen@xxxxxxxxx> wrote: >> > > >> > > According to the documentation, "The lower filesystem can be any filesystem >> > > supported by Linux", however this appears to not actually be the case, since >> > > using a vfat filesystem results in the mount command printing "mount: >> > > wrong fs type, bad option, bad superblock on overlay, missing codepage or >> > > helper program, or other error", with dmesg saying "overlayfs: filesystem on >> > > '/boot' not supported". >> > > (that's from ovl_mount_dir_noesc(), when ovl_dentry_weird() returns nonzero) >> > >> > Specifically for vfat it is weird because of >> > dentry->d_flags & (DCACHE_OP_HASH | DCACHE_OP_COMPARE) >> > because it is case insensitive. >> > [...] >> > >> > I am guessing when people start using case insensitive enabled ext4, >> > this problem >> > is going to surface, because the same ext4 (e.g. root fs) could be >> > used for samba >> > export (case insensitive) and docker storage (overlayfs). >> > [...] >> >> We *might* be able to only set the dentry functions on directory >> entries belonging to directories which have the casefold flag set, >> instead of simply setting it on all ext4 dentry entries. But still >> won't change the fact that overlayfs is going to have case >> insensitivity support if we want the combination of overlayfs && >> casefold to be supported. >> > > My intention was not that overlayfs should support casefold, just that > an isolated casefold subdir in an ext4 fs shouldn't make the entire fs > not usable with overlayfs. That is a reasonable request. I discussed a bit with Ted about how to not set dentry functions filesystem wide, because that gets in the way of fscrypt. I don't have a definite answer on how to do it, but it is something that I will try to fix to enable fscrypt+casefold support. > Incidentally, we already ran into a similar issue with ext4 encryption. > Issue was reported by OpenWRT developers and fixed by: > d456a33f041a fscrypt: only set dentry_operations on ciphertext dentries > > I recon casefold is taking a similar direction to the fs/crypto library, so > solution should be similar as well. > > BTW, is casefold feature mutually exclusive with encryption feature? > Because if it isn't, d_set_d_op() in __fscrypt_prepare_lookup() is > going to WARN_ON dentry already has ext4_dentry_ops. Not yet, and that is part of the reason. Right now, these two features cannot be enable simultaneously, but it is on my todo list to support that case. > Thanks, > Amir. -- Gabriel Krisman Bertazi
