cifs: Set zero_point in the copy_file_range() and remap_file_range()

Set zero_point in the copy_file_range() and remap_file_range()
implementations so that we don't skip reading data modified on a
server-side copy.

Signed-off-by: David Howells <[email protected]>
cc: Steve French <[email protected]>
cc: Shyam Prasad N <[email protected]>
cc: Rohith Surabattula <[email protected]>
cc: Jeff Layton <[email protected]>
cc: [email protected]
cc: [email protected]
cc: [email protected]
cc: [email protected]

Author: dhowells

fs/smb/client/cifsfs.c

@@ -1287,6 +1287,8 @@ static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,
 	rc = cifs_flush_folio(target_inode, destend, &fstart, &fend, false);
 	if (rc)
 		goto unlock;
+	if (fend > target_cifsi->netfs.zero_point)
+		target_cifsi->netfs.zero_point = fend + 1;
 
 	/* Discard all the folios that overlap the destination region. */
 	cifs_dbg(FYI, "about to discard pages %llx-%llx\n", fstart, fend);
@@ -1305,6 +1307,8 @@ static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,
 			fscache_resize_cookie(cifs_inode_cookie(target_inode),
 					      new_size);
 		}
+		if (rc == 0 && new_size > target_cifsi->netfs.zero_point)
+			target_cifsi->netfs.zero_point = new_size;
 	}
 
 	/* force revalidate of size and timestamps of target file now
@@ -1396,6 +1400,8 @@ ssize_t cifs_file_copychunk_range(unsigned int xid,
 	rc = cifs_flush_folio(target_inode, destend, &fstart, &fend, false);
 	if (rc)
 		goto unlock;
+	if (fend > target_cifsi->netfs.zero_point)
+		target_cifsi->netfs.zero_point = fend + 1;
 
 	/* Discard all the folios that overlap the destination region. */
 	truncate_inode_pages_range(&target_inode->i_data, fstart, fend);