USB: serial: re-implement multi-urb writes in generic driver

Use dynamic transfer buffer sizes since it is more efficient to let the
host controller do the partitioning to fit endpoint size. This way we
also do not use more than one urb per write request.

Replace max_in_flight_urbs with multi_urb_write flag in struct
usb_serial_driver to enable multi-urb writes.

Use MAX_TX_URBS=40 and a max buffer size of PAGE_SIZE to prevent DoS
attacks.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 6 insertions, 3 deletions

diff --git a/include/linux/usb/serial.h b/include/linux/usb/serial.h
index ff8872eba3ac..2a3283761600 100644
--- a/include/linux/usb/serial.h
+++ b/include/linux/usb/serial.h
@@ -60,6 +60,8 @@ enum port_dev_state {
  * @write_urb: pointer to the bulk out struct urb for this port.
  * @write_fifo: kfifo used to buffer outgoing data
  * @write_urb_busy: port`s writing status
+ * @tx_bytes: number of bytes currently in host stack queues
+ * @tx_urbs: number of urbs currently in host stack queues
  * @bulk_out_endpointAddress: endpoint address for the bulk out pipe for this
  *      port.
  * @write_wait: a wait_queue_head_t used by the port.
@@ -98,8 +100,8 @@ struct usb_serial_port {
         int                     write_urb_busy;
         __u8                    bulk_out_endpointAddress;
 
-        int                     tx_bytes_flight;
-        int                     urbs_in_flight;
+        int                     tx_bytes;
+        int                     tx_urbs;
 
         wait_queue_head_t       write_wait;
         struct work_struct      work;
@@ -223,7 +225,8 @@ struct usb_serial_driver {
         struct device_driver    driver;
         struct usb_driver       *usb_driver;
         struct usb_dynids       dynids;
-        int                     max_in_flight_urbs;
+
+        unsigned char           multi_urb_write:1;
 
         size_t                  bulk_in_size;
         size_t                  bulk_out_size;