[PATCH v5 09/16] cifs: Implement fileattr_get for case sensitivity

[Chuck Lever <cel@kernel.org>]

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

Upper layers such as NFSD need a way to query whether a filesystem
handles filenames in a case-sensitive manner. The file_kattr
structure now provides case_insensitive and case_preserving fields
for this purpose, but CIFS does not yet report its case sensitivity
behavior through this interface.

Implement cifs_fileattr_get() to report CIFS/SMB case handling
behavior. CIFS servers (typically Windows or Samba) are usually
case-insensitive but case-preserving, meaning they ignore case
during lookups but store filenames exactly as provided.

The implementation reports case sensitivity based on the nocase
mount option, which reflects whether the client expects the server
to perform case-insensitive comparisons. When nocase is set, the
mount is reported as case-insensitive. The case_preserving field
is always set to true since SMB servers preserve filename case at
rest.

The callback is registered in all three inode_operations
structures (directory, file, and symlink) to ensure consistent
reporting across all inode types.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/smb/client/cifsfs.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c
index d9664634144d..563eece79b13 100644
--- a/fs/smb/client/cifsfs.c
+++ b/fs/smb/client/cifsfs.c
@@ -30,6 +30,7 @@
 #include <linux/xattr.h>
 #include <linux/mm.h>
 #include <linux/key-type.h>
+#include <linux/fileattr.h>
 #include <uapi/linux/magic.h>
 #include <net/ipv6.h>
 #include "cifsfs.h"
@@ -1193,6 +1194,20 @@ struct file_system_type smb3_fs_type = {
 MODULE_ALIAS_FS("smb3");
 MODULE_ALIAS("smb3");
 
+static int cifs_fileattr_get(struct dentry *dentry, struct file_kattr *fa)
+{
+	struct cifs_sb_info *cifs_sb = CIFS_SB(dentry->d_sb);
+	struct cifs_tcon *tcon = cifs_sb_master_tcon(cifs_sb);
+
+	/*
+	 * CIFS/SMB servers are typically case-insensitive and
+	 * case-preserving (the default). The nocase mount option
+	 * reflects what the client expects from the server.
+	 */
+	fa->case_insensitive = tcon->nocase;
+	return 0;
+}
+
 const struct inode_operations cifs_dir_inode_ops = {
 	.create = cifs_create,
 	.atomic_open = cifs_atomic_open,
@@ -1210,6 +1225,7 @@ const struct inode_operations cifs_dir_inode_ops = {
 	.listxattr = cifs_listxattr,
 	.get_acl = cifs_get_acl,
 	.set_acl = cifs_set_acl,
+	.fileattr_get = cifs_fileattr_get,
 };
 
 const struct inode_operations cifs_file_inode_ops = {
@@ -1220,6 +1236,7 @@ const struct inode_operations cifs_file_inode_ops = {
 	.fiemap = cifs_fiemap,
 	.get_acl = cifs_get_acl,
 	.set_acl = cifs_set_acl,
+	.fileattr_get = cifs_fileattr_get,
 };
 
 const char *cifs_get_link(struct dentry *dentry, struct inode *inode,
@@ -1254,6 +1271,7 @@ const struct inode_operations cifs_symlink_inode_ops = {
 	.setattr = cifs_setattr,
 	.permission = cifs_permission,
 	.listxattr = cifs_listxattr,
+	.fileattr_get = cifs_fileattr_get,
 };
 
 /*
-- 
2.52.0