[PATCH v2 2/6] fat: Implement fileattr_get for case sensitivity

Chuck Lever
2025-12-11T15:21:54Z

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

Report FAT's case sensitivity behavior via the new file_kattr
case_info field. FAT filesystems are case-insensitive and do not
preserve case at rest (stored names are uppercased).

The case folding type depends on the mount options: when utf8 is
enabled, Unicode case folding is used; otherwise ASCII case folding.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
fs/fat/fat.h | 3 +++
fs/fat/file.c | 18 ++++++++++++++++++
fs/fat/namei_msdos.c | 1 +
fs/fat/namei_vfat.c | 1 +
4 files changed, 23 insertions(+)

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index d3e426de5f01..38da08d8fec4 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -10,6 +10,8 @@
#include <linux/fs_context.h>
#include <linux/fs_parser.h>

+struct file_kattr;
+
/*
* vfat shortname flags
*/
@@ -407,6 +409,7 @@ extern void fat_truncate_blocks(struct inode *inode, loff_t offset);
extern int fat_getattr(struct mnt_idmap *idmap,
const struct path *path, struct kstat *stat,
u32 request_mask, unsigned int flags);
+extern int fat_fileattr_get(struct dentry *dentry, struct file_kattr *fa);
extern int fat_file_fsync(struct file *file, loff_t start, loff_t end,
int datasync);

diff --git a/fs/fat/file.c b/fs/fat/file.c
index 4fc49a614fb8..123f4c1efdf4 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -16,6 +16,7 @@
#include <linux/fsnotify.h>
#include <linux/security.h>
#include <linux/falloc.h>
+#include <linux/fileattr.h>
#include "fat.h"

static long fat_fallocate(struct file *file, int mode,
@@ -395,6 +396,22 @@ void fat_truncate_blocks(struct inode *inode, loff_t offset)
fat_flush_inodes(inode->i_sb, inode, NULL);
}

+int fat_fileattr_get(struct dentry *dentry, struct file_kattr *fa)
+{
+ struct inode *inode = d_inode(dentry);
+ struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
+
+ /*
+ * FAT filesystems do not preserve case: stored names are
+ * uppercased. They are case-insensitive, using either ASCII
+ * or Unicode comparison depending on mount options.
+ */
+ fa->case_info = sbi->options.utf8 ?
+ FILEATTR_CASEFOLD_UNICODE : FILEATTR_CASEFOLD_ASCII;
+ return 0;
+}
+EXPORT_SYMBOL_GPL(fat_fileattr_get);
+
int fat_getattr(struct mnt_idmap *idmap, const struct path *path,
struct kstat *stat, u32 request_mask, unsigned int flags)
{
@@ -574,5 +591,6 @@ EXPORT_SYMBOL_GPL(fat_setattr);
const struct inode_operations fat_file_inode_operations = {
.setattr = fat_setattr,
.getattr = fat_getattr,
+ .fileattr_get = fat_fileattr_get,
.update_time = fat_update_time,
};
diff --git a/fs/fat/namei_msdos.c b/fs/fat/namei_msdos.c
index 0b920ee40a7f..380add5c6c66 100644
--- a/fs/fat/namei_msdos.c
+++ b/fs/fat/namei_msdos.c
@@ -640,6 +640,7 @@ static const struct inode_operations msdos_dir_inode_operations = {
.rename = msdos_rename,
.setattr = fat_setattr,
.getattr = fat_getattr,
+ .fileattr_get = fat_fileattr_get,
.update_time = fat_update_time,
};

diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
index 5dbc4cbb8fce..6cf513f97afa 100644
--- a/fs/fat/namei_vfat.c
+++ b/fs/fat/namei_vfat.c
@@ -1180,6 +1180,7 @@ static const struct inode_operations vfat_dir_inode_operations = {
.rename = vfat_rename2,
.setattr = fat_setattr,
.getattr = fat_getattr,
+ .fileattr_get = fat_fileattr_get,
.update_time = fat_update_time,
};

--
2.52.0