fs: send fsnotify_xattr()/IN_ATTRIB from vfs_fileattr_set()/chattr(1)

Currently it seems impossible to observe these changes to the file's
attributes. It's useful to be able to do this to see when the file
becomes immutable, for example, so emit IN_ATTRIB via fsnotify_xattr(),
like when changing other inode attributes.

Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Link: https://patch.msgid.link/iyvn6qjotpu6cei5jdtsoibfcp6l6rgvn47cwgaucgtucpfy2s@tarta.nabijaczleweli.xyz
Signed-off-by: Jan Kara <jack@suse.cz>

Author: nabijaczleweli

fs/file_attr.c

@@ -2,6 +2,7 @@
 #include <linux/fs.h>
 #include <linux/security.h>
 #include <linux/fscrypt.h>
+#include <linux/fsnotify.h>
 #include <linux/fileattr.h>
 #include <linux/export.h>
 #include <linux/syscalls.h>
@@ -298,6 +299,7 @@ int vfs_fileattr_set(struct mnt_idmap *idmap, struct dentry *dentry,
 		err = inode->i_op->fileattr_set(idmap, dentry, fa);
 		if (err)
 			goto out;
+		fsnotify_xattr(dentry);
 	}
 
 out: