fat: Implement fileattr_get for case sensitivity

Report FAT's case sensitivity behavior via the FS_XFLAG_CASEFOLD
and FS_XFLAG_CASENONPRESERVING flags. FAT filesystems are
case-insensitive by default.

MSDOS supports a 'nocase' mount option that enables case-sensitive
behavior; check this option when reporting case sensitivity.

VFAT long filename entries preserve case; without VFAT, only
uppercased 8.3 short names are stored. MSDOS with 'nocase' also
preserves case since the name-formatting code skips upcasing when
'nocase' is set. Check both options when reporting case preservation.

Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Roland Mainz <roland.mainz@nrubsig.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://patch.msgid.link/20260507-case-sensitivity-v14-3-e62cc8200435@oracle.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

4 files changed, 41 insertions, 0 deletions

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 5a58f0bf8ce8..99ed9228a677 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
  */
@@ -408,6 +410,7 @@ 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);
+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 becccdd2e501..37e7049b4c8c 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -17,6 +17,7 @@
 #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,
@@ -398,6 +399,40 @@ 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 msdos_sb_info *sbi = MSDOS_SB(dentry->d_sb);
+	bool case_sensitive;
+
+	/*
+	 * FAT filesystems are case-insensitive by default. VFAT
+	 * becomes case-sensitive when mounted with 'check=strict',
+	 * which installs vfat_dentry_ops. MSDOS has no such option;
+	 * its 'nocase' mount option selects case-sensitive matching.
+	 *
+	 * VFAT long filename entries preserve case. Without VFAT, only
+	 * uppercased 8.3 short names are stored. MSDOS with 'nocase'
+	 * also preserves case.
+	 */
+	if (sbi->options.isvfat)
+		case_sensitive = sbi->options.name_check == 's';
+	else
+		case_sensitive = sbi->options.nocase;
+
+	if (!case_sensitive) {
+		fa->fsx_xflags |= FS_XFLAG_CASEFOLD;
+		fa->flags |= FS_CASEFOLD_FL;
+		if (!sbi->options.isvfat)
+			fa->fsx_xflags |= FS_XFLAG_CASENONPRESERVING;
+	}
+	if (d_inode(dentry)->i_flags & S_IMMUTABLE) {
+		fa->fsx_xflags |= FS_XFLAG_IMMUTABLE;
+		fa->flags |= FS_IMMUTABLE_FL;
+	}
+	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)
 {
@@ -575,5 +610,6 @@ 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 4cc65f330fb7..0fd2971ad4b1 100644
--- a/fs/fat/namei_msdos.c
+++ b/fs/fat/namei_msdos.c
@@ -644,6 +644,7 @@ 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 918b3756674c..e909447873e3 100644
--- a/fs/fat/namei_vfat.c
+++ b/fs/fat/namei_vfat.c
@@ -1185,6 +1185,7 @@ 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,
 };