ntfs: add fileattr query support

Add fileattr_get operations for files and directories, as well as the
existing symlink and special inode operation tables. Report compression,
encryption, immutable and append-only from cached inode state, and
FS_CASEFOLD_FL from the mount-wide case sensitivity policy.

This introduces querying only. It neither reads a private flag EA nor
allows userspace to change the reported flags.

Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

Documentation/filesystems/ntfs.rst

@@ -9,6 +9,7 @@ The Linux NTFS filesystem driver
 
    - Overview
    - Utilities support
+   - Linux file attributes
    - Supported mount options
 
 
@@ -34,6 +35,13 @@ The project is available at:
   https://github.com/ntfsprogs-plus/ntfsprogs-plus
 
 
+Linux file attributes
+=====================
+
+The driver supports querying compression, encryption, immutable, append-only
+and mount-wide case folding through lsattr(1). Case folding is reported
+according to the mount options.
+
 Supported mount options
 =======================
 

fs/ntfs/file.c

@@ -15,6 +15,7 @@
 #include <linux/posix_acl_xattr.h>
 #include <linux/compat.h>
 #include <linux/falloc.h>
+#include <linux/fileattr.h>
 #include <linux/file.h>
 #include <linux/filelock.h>
 #include <linux/list.h>
@@ -144,6 +145,35 @@ int ntfs_file_release(struct inode *vi, struct file *filp)
 	return 0;
 }
 
+/*
+ * ntfs_fileattr_get - inode_operations::fileattr_get
+ * @dentry: dentry to report the flags of
+ * @fa: filled in with the flags of @dentry
+ */
+int ntfs_fileattr_get(struct dentry *dentry, struct file_kattr *fa)
+{
+	struct inode *vi = d_inode(dentry);
+	struct ntfs_inode *ni = NTFS_I(vi);
+	u32 flags = 0;
+
+	if (NVolShutdown(ni->vol))
+		return -EIO;
+
+	if (NInoCompressed(ni) || NInoWofCompressed(ni))
+		flags |= FS_COMPR_FL;
+	if (NInoEncrypted(ni))
+		flags |= FS_ENCRYPT_FL;
+	if (vi->i_flags & S_IMMUTABLE)
+		flags |= FS_IMMUTABLE_FL;
+	if (vi->i_flags & S_APPEND)
+		flags |= FS_APPEND_FL;
+	if (!NVolCaseSensitive(ni->vol))
+		flags |= FS_CASEFOLD_FL;
+
+	fileattr_fill_flags(fa, flags);
+	return 0;
+}
+
 struct ntfs_fsync_attr {
 	struct list_head list;
 	struct inode *inode;
@@ -1426,6 +1456,7 @@ const struct file_operations ntfs_file_ops = {
 };
 
 const struct inode_operations ntfs_file_inode_ops = {
+	.fileattr_get	= ntfs_fileattr_get,
 	.setattr	= ntfs_setattr,
 	.getattr	= ntfs_getattr,
 	.listxattr	= ntfs_listxattr,
@@ -1435,12 +1466,14 @@ const struct inode_operations ntfs_file_inode_ops = {
 };
 
 const struct inode_operations ntfs_symlink_inode_operations = {
+	.fileattr_get	= ntfs_fileattr_get,
 	.get_link	= ntfs_get_link,
 	.setattr	= ntfs_setattr,
 	.listxattr	= ntfs_listxattr,
 };
 
 const struct inode_operations ntfs_special_inode_operations = {
+	.fileattr_get	= ntfs_fileattr_get,
 	.setattr	= ntfs_setattr,
 	.getattr	= ntfs_getattr,
 	.listxattr	= ntfs_listxattr,

fs/ntfs/namei.c

@@ -1660,6 +1660,7 @@ static int ntfs_link(struct dentry *old_dentry, struct inode *dir,
  * Inode operations for directories.
  */
 const struct inode_operations ntfs_dir_inode_ops = {
+	.fileattr_get	= ntfs_fileattr_get,
 	.lookup		= ntfs_lookup,	/* VFS: Lookup directory. */
 	.create		= ntfs_create,
 	.unlink		= ntfs_unlink,

fs/ntfs/ntfs.h

@@ -185,6 +185,8 @@ extern const struct inode_operations ntfs_dir_inode_ops;
 extern const struct  file_operations ntfs_empty_file_ops;
 extern const struct inode_operations ntfs_empty_inode_ops;
 
+int ntfs_fileattr_get(struct dentry *dentry, struct file_kattr *fa);
+
 extern const struct export_operations ntfs_export_ops;
 
 /*