linux-kernel - Re: [PATCH v4 1/9] ovl: Support mounting case-insensitive enabled filesystems

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Message-ID: <CAOQ4uxiENaCd7RcAS8j+UUNmtmOzKZ3BwBWst=fKN6zWLZyvuQ@mail.gmail.com>
Date: Thu, 14 Aug 2025 10:35:50 +0200
From: Amir Goldstein <amir73il@...il.com>
To: André Almeida <andrealmeid@...lia.com>
Cc: Miklos Szeredi <miklos@...redi.hu>, Theodore Tso <tytso@....edu>, 
	Gabriel Krisman Bertazi <krisman@...nel.org>, linux-unionfs@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	kernel-dev@...lia.com
Subject: Re: [PATCH v4 1/9] ovl: Support mounting case-insensitive enabled filesystems

Hi Andre,

As a methodology in patch series, although they are often merged together
we want to abide by the concept of bisectability of the series, so it is not
good practice to "Support mounting case-insensitive enabled filesystems"
before this support is fully implemented.

Suggest to change the title of this patch to:
"ovl: Prepare for mounting case-insensitive enabled filesystems"
which implements the logic of enforcing "uniform casefolded layers"
but do not change ovl_dentry_weird() yet - do that in patch 9, so that
both lookup and mount of casefolded dirs are allowed together.

commit message need to be changed of course.

On Thu, Aug 14, 2025 at 12:37 AM André Almeida <andrealmeid@...lia.com> wrote:
>
> Enable mounting filesystems with case-insensitive dentries in order to
> support such filesystems in overlayfs.
>
> Signed-off-by: André Almeida <andrealmeid@...lia.com>
> ---
> Changes from v3:
> - Move this patch to be ealier in the series
> - Split this patch with the ovl_lookup_single() restriction patch
> ---
>  fs/overlayfs/ovl_entry.h |  1 +
>  fs/overlayfs/params.c    | 15 ++++++++++++---
>  fs/overlayfs/params.h    |  1 +
>  fs/overlayfs/util.c      |  8 ++++----
>  4 files changed, 18 insertions(+), 7 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);
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index a33115e7384c129c543746326642813add63f060..7a6ee058568283453350153c1720c35e11ad4d1b 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -210,11 +210,11 @@ bool ovl_dentry_weird(struct dentry *dentry)
>                 return true;
>
>         /*
> -        * Allow filesystems that are case-folding capable but deny composing
> -        * ovl stack from case-folded directories.
> +        * Exceptionally for casefold dentries, we accept that they have their
> +        * own hash and compare operations
>          */
> -       if (sb_has_encoding(dentry->d_sb))
> -               return IS_CASEFOLDED(d_inode(dentry));
> +       if (ovl_dentry_casefolded(dentry))
> +               return false;
>
>         return dentry->d_flags & (DCACHE_OP_HASH | DCACHE_OP_COMPARE);
>  }

Move relaxing of ovl_dentry_weird() to patch 9 please.

Thanks,
Amir.