On Wed, Aug 21, 2024 at 08:43:14AM -0400, Brian Foster wrote:

quoted

-	if ((mode & ~FALLOC_FL_KEEP_SIZE) && IS_APPEND(inode))
+	if (mode != FALLOC_FL_ALLOCATE_RANGE && IS_APPEND(inode))
 		return -EPERM;

Unless I'm misreading, this changes semantics by enforcing that we
cannot use KEEP_SIZE on append only files. That means one can no longer
do a post-eof prealloc without actually changing the file size, which on
a quick test seems to work today.

No, I think it was me misreading the old code.  And I'm a little worried
that no test cought it.