linux-kernel - [PATCH v2 2/6] fat: Implement fileattr

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Message-ID: <20251211152116.480799-3-cel@kernel.org>
Date: Thu, 11 Dec 2025 10:21:12 -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 2/6] fat: Implement fileattr_get for case sensitivity

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