Don't let copy_file_range() use clones

I'm seeing a silly regression in generic/430: now that clones are
implemented, copy_file_range() has started to use them under the hood,
but it only wants to clone a portion of the file, and that's not
something I'm interested in supporting.

To avoid this on newer kernels, set ->copy_file_range() to the generic
implementation. For older kernels, start throwing errors if anything
calls apfs_remap_file_range() for partial ranges. This is the right
thing to do in general, since we don't support that.

Signed-off-by: Ernesto A. Fernández <ernesto@corellium.com>

extents.c

@@ -1504,6 +1504,10 @@ loff_t apfs_remap_file_range(struct file *src_file, loff_t off, struct file *dst
 	if (src_inode == dst_inode)
 		return -EINVAL;
 
+	/* We only want to clone whole files, like in the official driver */
+	if (off != 0 || destoff != 0 || len != 0)
+		return -EINVAL;
+
 	/*
 	 * Clones here work in two steps: first the user creates an empty target
 	 * file, and then the user calls the ioctl, which replaces the file with

file.c

@@ -137,6 +137,7 @@ const struct file_operations apfs_file_operations = {
 	.open			= generic_file_open,
 	.fsync			= apfs_fsync,
 	.unlocked_ioctl		= apfs_file_ioctl,
+	.copy_file_range	= generic_copy_file_range,
 	.remap_file_range	= apfs_remap_file_range,
 };