[PATCH v2 1/6] fs: Add case sensitivity info to file_kattr

Chuck Lever
2025-12-11T15:21:53Z

From: Chuck Lever <chuck.lever@oracle.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@oracle.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