1 files changed, 14 insertions, 0 deletions

diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
index cf2a0e2330df..5fb341a16b52 100644
--- a/fs/ntfs/file.c
+++ b/fs/ntfs/file.c
@@ -1857,10 +1857,24 @@ static ssize_t ntfs_file_buffered_write(struct kiocb *iocb,
         if (ni->type != AT_INDEX_ALLOCATION) {
                 /* If file is encrypted, deny access, just like NT4. */
                 if (NInoEncrypted(ni)) {
+                        /*
+                         * Reminder for later: Encrypted files are _always_
+                         * non-resident so that the content can always be
+                         * encrypted.
+                         */
                         ntfs_debug("Denying write access to encrypted file.");
                         return -EACCES;
                 }
                 if (NInoCompressed(ni)) {
+                        /* Only unnamed $DATA attribute can be compressed. */
+                        BUG_ON(ni->type != AT_DATA);
+                        BUG_ON(ni->name_len);
+                        /*
+                         * Reminder for later: If resident, the data is not
+                         * actually compressed.  Only on the switch to non-
+                         * resident does compression kick in.  This is in
+                         * contrast to encrypted files (see above).
+                         */
                         ntfs_error(vi->i_sb, "Writing to compressed files is "
                                         "not implemented yet.  Sorry.");
                         return -EOPNOTSUPP;