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

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Message-Id: <20250813-tonyk-overlayfs-v4-1-357ccf2e12ad@igalia.com>
Date: Wed, 13 Aug 2025 19:36:37 -0300
From: André Almeida <andrealmeid@...lia.com>
To: Miklos Szeredi <miklos@...redi.hu>, Amir Goldstein <amir73il@...il.com>, 
 Theodore Tso <tytso@....edu>, Gabriel Krisman Bertazi <krisman@...nel.org>
Cc: 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, 
 André Almeida <andrealmeid@...lia.com>
Subject: [PATCH v4 1/9] ovl: Support mounting case-insensitive enabled
 filesystems

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);
 }

-- 
2.50.1