linux-kernel - [PATCH v2 1/6] fs: Add case sensitivity info to file

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Message-ID: <20251211152116.480799-2-cel@kernel.org>
Date: Thu, 11 Dec 2025 10:21:11 -0500
From: Chuck Lever <cel@...nel.org>
To: Al Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>
Cc: <linux-fsdevel@...r.kernel.org>,
	linux-ext4@...r.kernel.org,
	<linux-nfs@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	hirofumi@...l.parknet.co.jp,
	almaz.alexandrovich@...agon-software.com,
	tytso@....edu,
	adilger.kernel@...ger.ca,
	Volker.Lendecke@...net.de,
	Chuck Lever <chuck.lever@...cle.com>
Subject: [PATCH v2 1/6] fs: Add case sensitivity info to file_kattr

From: Chuck Lever <chuck.lever@...cle.com>

Enable upper layers such as NFSD to retrieve case sensitivity
information from file systems by adding a case_info field to struct
file_kattr.

Add vfs_get_case_info() as a convenience helper for kernel
consumers. If a filesystem does not provide a fileattr_get hook, it
returns the default POSIX behavior (case-sensitive,
case-preserving), which is correct for the majority of Linux
file systems implementations.

Signed-off-by: Chuck Lever <chuck.lever@...cle.com>
---
 fs/file_attr.c           | 31 +++++++++++++++++++++++++++++++
 include/linux/fileattr.h | 23 +++++++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/fs/file_attr.c b/fs/file_attr.c
index 1dcec88c0680..609e890b5101 100644
--- a/fs/file_attr.c
+++ b/fs/file_attr.c
@@ -94,6 +94,37 @@ int vfs_fileattr_get(struct dentry *dentry, struct file_kattr *fa)
 }
 EXPORT_SYMBOL(vfs_fileattr_get);
 
+/**
+ * vfs_get_case_info - retrieve case sensitivity info for a filesystem
+ * @dentry:	the object to retrieve from
+ * @case_info:	pointer to store result
+ *
+ * Call i_op->fileattr_get() to retrieve case sensitivity information.
+ * If the filesystem does not provide a fileattr_get hook, return
+ * the default POSIX behavior (case-sensitive, case-preserving).
+ *
+ * Return: 0 on success, or a negative error on failure.
+ */
+int vfs_get_case_info(struct dentry *dentry, u32 *case_info)
+{
+	struct file_kattr fa = {};
+	int error;
+
+	/* Default: POSIX semantics (case-sensitive, case-preserving) */
+	*case_info = FILEATTR_CASEFOLD_NONE | FILEATTR_CASE_PRESERVING;
+
+	error = vfs_fileattr_get(dentry, &fa);
+	if (error == -ENOIOCTLCMD)
+		return 0;
+	if (error)
+		return error;
+
+	if (fa.case_info)
+		*case_info = fa.case_info;
+	return 0;
+}
+EXPORT_SYMBOL(vfs_get_case_info);
+
 static void fileattr_to_file_attr(const struct file_kattr *fa,
 				  struct file_attr *fattr)
 {
diff --git a/include/linux/fileattr.h b/include/linux/fileattr.h
index f89dcfad3f8f..55674d14f697 100644
--- a/include/linux/fileattr.h
+++ b/include/linux/fileattr.h
@@ -48,11 +48,33 @@ struct file_kattr {
 	u32	fsx_nextents;	/* nextents field value (get)	*/
 	u32	fsx_projid;	/* project identifier (get/set) */
 	u32	fsx_cowextsize;	/* CoW extsize field value (get/set)*/
+	u32	case_info;	/* case sensitivity behavior */
 	/* selectors: */
 	bool	flags_valid:1;
 	bool	fsx_valid:1;
 };
 
+/*
+ * Values for file_kattr.case_info.
+ */
+
+/* File name case is preserved at rest. */
+#define FILEATTR_CASE_PRESERVING	0x80000000
+
+/* Values stored in the low-order byte */
+enum fileattr_case_folding {
+	/* Code points are compared directly with no case folding. */
+	FILEATTR_CASEFOLD_NONE = 0,
+
+	/* ASCII case-insensitive: A-Z are treated as a-z. */
+	FILEATTR_CASEFOLD_ASCII,
+
+	/* Unicode case-insensitive matching. */
+	FILEATTR_CASEFOLD_UNICODE,
+};
+
+#define FILEATTR_CASEFOLD_TYPE		0x000000ff
+
 int copy_fsxattr_to_user(const struct file_kattr *fa, struct fsxattr __user *ufa);
 
 void fileattr_fill_xflags(struct file_kattr *fa, u32 xflags);
@@ -75,6 +97,7 @@ static inline bool fileattr_has_fsx(const struct file_kattr *fa)
 int vfs_fileattr_get(struct dentry *dentry, struct file_kattr *fa);
 int vfs_fileattr_set(struct mnt_idmap *idmap, struct dentry *dentry,
 		     struct file_kattr *fa);
+int vfs_get_case_info(struct dentry *dentry, u32 *case_info);
 int ioctl_getflags(struct file *file, unsigned int __user *argp);
 int ioctl_setflags(struct file *file, unsigned int __user *argp);
 int ioctl_fsgetxattr(struct file *file, void __user *argp);
-- 
2.52.0