tty: make receive_buf() return the amout of bytes received

it makes it simpler to keep track of the amount of
bytes received and simplifies how flush_to_ldisc counts
the remaining bytes. It also fixes a bug of lost bytes
on n_tty when flushing too many bytes via the USB
serial gadget driver.

Tested-by: Stefan Bigler <stefan.bigler@keymile.com>
Tested-by: Toby Gray <toby.gray@realvnc.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 5 insertions, 4 deletions

diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
index ff7dc08696a8..5b07792ccb46 100644
--- a/include/linux/tty_ldisc.h
+++ b/include/linux/tty_ldisc.h
@@ -76,7 +76,7 @@
  *      tty device.  It is solely the responsibility of the line
  *      discipline to handle poll requests.
  *
- * void (*receive_buf)(struct tty_struct *, const unsigned char *cp,
+ * unsigned int (*receive_buf)(struct tty_struct *, const unsigned char *cp,
  *                     char *fp, int count);
  *
  *      This function is called by the low-level tty driver to send
@@ -84,7 +84,8 @@
  *      processing.  <cp> is a pointer to the buffer of input
  *      character received by the device.  <fp> is a pointer to a
  *      pointer of flag bytes which indicate whether a character was
- *      received with a parity error, etc.
+ *      received with a parity error, etc. Returns the amount of bytes
+ *      received.
  * 
  * void (*write_wakeup)(struct tty_struct *);
  *
@@ -140,8 +141,8 @@ struct tty_ldisc_ops {
         /*
          * The following routines are called from below.
          */
-        void    (*receive_buf)(struct tty_struct *, const unsigned char *cp,
-                               char *fp, int count);
+        unsigned int (*receive_buf)(struct tty_struct *,
+                        const unsigned char *cp, char *fp, int count);
         void    (*write_wakeup)(struct tty_struct *);
         void    (*dcd_change)(struct tty_struct *, unsigned int,
                                 struct pps_event_time *);