On Thu, Aug 14, 2025 at 7:22 PM André Almeida <andrealmeid@xxxxxxxxxx> wrote:
>
> Prepare for mounting layers with case-insensitive dentries in order to
> supporting such layers in overlayfs, while enforcing uniform casefold
> layers.
>
> Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx>
Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> Changes from v4:
> - Move relaxation of dentry_weird to the last patch
> - s/filesystems/layerss
> - Commit now says "Prepare for" instead of "Support"
> ---
> fs/overlayfs/ovl_entry.h | 1 +
> fs/overlayfs/params.c | 15 ++++++++++++---
> fs/overlayfs/params.h | 1 +
> 3 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index 4c1bae935ced274f93a0d23fe10d34455e226ec4..1d4828dbcf7ac4ba9657221e601bbf79d970d225 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -91,6 +91,7 @@ struct ovl_fs {
> struct mutex whiteout_lock;
> /* r/o snapshot of upperdir sb's only taken on volatile mounts */
> errseq_t errseq;
> + bool casefold;
> };
>
> /* Number of lower layers, not including data-only layers */
> diff --git a/fs/overlayfs/params.c b/fs/overlayfs/params.c
> index f4e7fff909ac49e2f8c58a76273426c1158a7472..17d2354ba88d92e1d9653e8cb1382d860a7329c5 100644
> --- a/fs/overlayfs/params.c
> +++ b/fs/overlayfs/params.c
> @@ -277,16 +277,25 @@ static int ovl_mount_dir_check(struct fs_context *fc, const struct path *path,
> enum ovl_opt layer, const char *name, bool upper)
> {
> struct ovl_fs_context *ctx = fc->fs_private;
> + struct ovl_fs *ofs = fc->s_fs_info;
> + bool is_casefolded = ovl_dentry_casefolded(path->dentry);
>
> if (!d_is_dir(path->dentry))
> return invalfc(fc, "%s is not a directory", name);
>
> /*
> * Allow filesystems that are case-folding capable but deny composing
> - * ovl stack from case-folded directories.
> + * ovl stack from inconsistent case-folded directories.
> */
> - if (ovl_dentry_casefolded(path->dentry))
> - return invalfc(fc, "case-insensitive directory on %s not supported", name);
> + if (!ctx->casefold_set) {
> + ofs->casefold = is_casefolded;
> + ctx->casefold_set = true;
> + }
> +
> + if (ofs->casefold != is_casefolded) {
> + return invalfc(fc, "case-%ssensitive directory on %s is inconsistent",
> + is_casefolded ? "in" : "", name);
> + }
>
> if (ovl_dentry_weird(path->dentry))
> return invalfc(fc, "filesystem on %s not supported", name);
> diff --git a/fs/overlayfs/params.h b/fs/overlayfs/params.h
> index c96d939820211ddc63e265670a2aff60d95eec49..ffd53cdd84827cce827e8852f2de545f966ce60d 100644
> --- a/fs/overlayfs/params.h
> +++ b/fs/overlayfs/params.h
> @@ -33,6 +33,7 @@ struct ovl_fs_context {
> struct ovl_opt_set set;
> struct ovl_fs_context_layer *lower;
> char *lowerdir_all; /* user provided lowerdir string */
> + bool casefold_set;
> };
>
> int ovl_init_fs_context(struct fs_context *fc);
>
> --
> 2.50.1
>
