Hi all, We would like to support the usage of casefold filesystems with overlayfs to be used with container tools. This use case requires a simple setup, where every layer will have the same encoding setting (i.e. Unicode version and flags), using one upper and one lower layer. * Implementation When merge layers, ovl uses a red-black tree to check if a given dentry name from a lower layers already exists in the upper layer. For merging case-insensitive names, we need to store then in tree casefolded. However, when displaying to the user the dentry name, we need to respect the name chosen when the file was created (e.g. Picture.PNG, instead of picture.png). To achieve this, I create a new field for cache entries that stores the casefolded names and a function ovl_strcmp() that uses this name for searching the rb_tree. For composing the layer, ovl uses the original name, keeping it consistency with whatever name the user created. The rest of the patches are mostly for checking if casefold is being consistently used across the layers and dropping the mount restrictions that prevented case-insensitive filesystems to be mounted. Thanks for the feedback! --- Changes in v3: - Rebased on top of vfs-6.18.misc branch - Added more guards for casefolding things inside of IS_ENABLED(UNICODE) - Refactor the strncmp() patch to do a single kmalloc() per rb_tree operation - Instead of casefolding the cache entry name everytime per strncmp(), casefold it once and reuse it for every strncmp(). - Created ovl_dentry_ci_operations to not override dentry ops set by ovl_dentry_operations - Instead of setting encoding just when there's a upper layer, set it for any first layer (ofs->fs[0].sb), regardless of it being upper or not. - Rewrote the patch that set inode flags - Check if every dentry is consistent with the root dentry regarding casefold v2: https://lore.kernel.org/r/20250805-tonyk-overlayfs-v2-0-0e54281da318@xxxxxxxxxx Changes in v2: - Almost a full rewritten from the v1. v1: https://lore.kernel.org/lkml/20250409-tonyk-overlayfs-v1-0-3991616fe9a3@xxxxxxxxxx/ --- André Almeida (7): ovl: Store casefold name for case-insentive dentries ovl: Create ovl_casefold() to support casefolded strncmp() fs: Create sb_same_encoding() helper ovl: Ensure that all mount points have the same encoding ovl: Set case-insensitive dentry operations for ovl sb ovl: Add S_CASEFOLD as part of the inode flag to be copied ovl: Support case-insensitive lookup fs/overlayfs/namei.c | 17 +++--- fs/overlayfs/overlayfs.h | 2 +- fs/overlayfs/ovl_entry.h | 1 + fs/overlayfs/params.c | 7 +-- fs/overlayfs/readdir.c | 133 ++++++++++++++++++++++++++++++++++++++++++----- fs/overlayfs/super.c | 39 ++++++++++++++ fs/overlayfs/util.c | 8 +-- include/linux/fs.h | 19 +++++++ 8 files changed, 195 insertions(+), 31 deletions(-) --- base-commit: 0fdf709a849f773c9b23b0d9fff2a25de056ddd5 change-id: 20250409-tonyk-overlayfs-591f5e4d407a Best regards, -- André Almeida <andrealmeid@xxxxxxxxxx>
