[iscsi] Send any padding inline with the data segment

Some iSCSI targets respond to a PDU before receiving the padding
bytes.  If the target responds quickly enough, this can cause iPXE to
start processing a new TX PDU before the padding bytes have been sent,
which results in a protocol violation.

Fix by always transmitting the padding bytes along with the data
segment.

Originally-fixed-by: Shyam Iyer <shyam_iyer@dell.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/iscsi.h

 	ISCSI_TX_AHS,
 	/** Sending the data segment */
 	ISCSI_TX_DATA,
-	/** Sending the data segment padding */
-	ISCSI_TX_DATA_PADDING,
 };
 
 /** State of an iSCSI RX engine */

src/net/tcp/iscsi.c

 	struct io_buffer *iobuf;
 	unsigned long offset;
 	size_t len;
+	size_t pad_len;
 
 	offset = ntohl ( data_out->offset );
 	len = ISCSI_DATA_LEN ( data_out->lengths );
+	pad_len = ISCSI_DATA_PAD_LEN ( data_out->lengths );
 
 	assert ( iscsi->command != NULL );
 	assert ( iscsi->command->data_out );
 	assert ( ( offset + len ) <= iscsi->command->data_out_len );
 
-	iobuf = xfer_alloc_iob ( &iscsi->socket, len );
+	iobuf = xfer_alloc_iob ( &iscsi->socket, ( len + pad_len ) );
 	if ( ! iobuf )
 		return -ENOMEM;
 	
 	copy_from_user ( iob_put ( iobuf, len ),
 			 iscsi->command->data_out, offset, len );
+	memset ( iob_put ( iobuf, pad_len ), 0, pad_len );
 
 	return xfer_deliver_iob ( &iscsi->socket, iobuf );
 }
 	struct iscsi_bhs_login_request *request = &iscsi->tx_bhs.login_request;
 	struct io_buffer *iobuf;
 	size_t len;
+	size_t pad_len;
 
 	len = ISCSI_DATA_LEN ( request->lengths );
-	iobuf = xfer_alloc_iob ( &iscsi->socket, len );
+	pad_len = ISCSI_DATA_PAD_LEN ( request->lengths );
+	iobuf = xfer_alloc_iob ( &iscsi->socket, ( len + pad_len ) );
 	if ( ! iobuf )
 		return -ENOMEM;
 	iob_put ( iobuf, len );
 	iscsi_build_login_request_strings ( iscsi, iobuf->data, len );
+	memset ( iob_put ( iobuf, pad_len ), 0, pad_len );
+
 	return xfer_deliver_iob ( &iscsi->socket, iobuf );
 }
 
 	}
 }
 
-/**
- * Transmit data padding of an iSCSI PDU
- *
- * @v iscsi		iSCSI session
- * @ret rc		Return status code
- * 
- * Handle transmission of any data padding in a PDU data segment.
- * iscsi::tx_bhs will be valid when this is called.
- */
-static int iscsi_tx_data_padding ( struct iscsi_session *iscsi ) {
-	static const char pad[] = { '\0', '\0', '\0' };
-	struct iscsi_bhs_common *common = &iscsi->tx_bhs.common;
-	size_t pad_len;
-	
-	pad_len = ISCSI_DATA_PAD_LEN ( common->lengths );
-	if ( ! pad_len )
-		return 0;
-
-	return xfer_deliver_raw ( &iscsi->socket, pad, pad_len );
-}
-
 /**
  * Complete iSCSI PDU transmission
  *
 		case ISCSI_TX_DATA:
 			tx = iscsi_tx_data;
 			tx_len = ISCSI_DATA_LEN ( common->lengths );
-			next_state = ISCSI_TX_DATA_PADDING;
-			break;
-		case ISCSI_TX_DATA_PADDING:
-			tx = iscsi_tx_data_padding;
-			tx_len = ISCSI_DATA_PAD_LEN ( common->lengths );
 			next_state = ISCSI_TX_IDLE;
 			break;
 		case ISCSI_TX_IDLE: