[PATCH v8 14/17] isofs: Implement fileattr_get for case sensitivity

From: Chuck Lever <redacted>

Upper layers such as NFSD need a way to query whether a
filesystem handles filenames in a case-sensitive manner so
they can provide correct semantics to remote clients. Without
this information, NFS exports of ISO 9660 filesystems cannot
properly advertise their filename case behavior.

Implement isofs_fileattr_get() to report ISO 9660 case handling
behavior via the FS_XFLAG_CASEFOLD flag. The 'check=r' (relaxed)
mount option enables case-insensitive lookups, and this setting
determines the value reported. By default, Joliet extensions
operate in relaxed mode while plain ISO 9660 uses strict
(case-sensitive) mode. All ISO 9660 variants are case-preserving,
meaning filenames are stored exactly as they appear on the disc.

The callback is registered only on isofs_dir_inode_operations
because isofs has no custom inode_operations for regular
files, and symlinks use the generic page_symlink_inode_operations.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Chuck Lever <redacted>
---
 fs/isofs/dir.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/isofs/dir.c b/fs/isofs/dir.c
index 2ca16c3fe5ef..225124eefa46 100644
--- a/fs/isofs/dir.c
+++ b/fs/isofs/dir.c

@@ -14,6 +14,7 @@
 #include <linux/gfp.h>
 #include <linux/filelock.h>
 #include "isofs.h"
+#include <linux/fileattr.h>
 
 int isofs_name_translate(struct iso_directory_record *de, char *new, struct inode *inode)
 {

@@ -267,6 +268,19 @@ static int isofs_readdir(struct file *file, struct dir_context *ctx)
 	return result;
 }
 
+static int isofs_fileattr_get(struct dentry *dentry, struct file_kattr *fa)
+{
+	struct isofs_sb_info *sbi = ISOFS_SB(dentry->d_sb);
+
+	/*
+	 * FS_XFLAG_CASEFOLD indicates case-insensitive lookups.
+	 * When check=r (relaxed) is set, lookups ignore case.
+	 */
+	if (sbi->s_check == 'r')
+		fa->fsx_xflags |= FS_XFLAG_CASEFOLD;
+	return 0;
+}
+
 const struct file_operations isofs_dir_operations =
 {
 	.llseek = generic_file_llseek,

@@ -281,6 +295,7 @@ const struct file_operations isofs_dir_operations =
 const struct inode_operations isofs_dir_inode_operations =
 {
 	.lookup = isofs_lookup,
+	.fileattr_get = isofs_fileattr_get,
 };
 
 

-- 
2.53.0