[PATCH v6 5/7] usb: gadget: u_serial: diagnose missed console messages

[MichaÅ MirosÅaw]

Insert markers in console stream marking places where data
is missing. This makes the hole in the data stand out clearly
instead of glueing together unrelated messages.

Example output as seen from USB host side:

[    0.064078] pinctrl core: registered pin 16 (UART3_RTS_N PC0) on 70000868.pinmux
[    0.064130] pinctrl
[missed 114987 bytes]
[    4.302299] udevd[134]: starting version 3.2.5
[    4.306845] random: udevd: uninitialized urandom read (16 bytes read)

Signed-off-by: MichaÅ MirosÅaw <mirq-linux@xxxxxxxxxxxx>
Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
  v6: rebased on balbi/testing/next
  v5: no changes
  v4: no changes
  v3: added example output
    + lowercase "missed"
  v2: commit message massage

---
 drivers/usb/gadget/function/u_serial.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
index 0da00546006f..a248ed0fd5d2 100644
--- a/drivers/usb/gadget/function/u_serial.c
+++ b/drivers/usb/gadget/function/u_serial.c
@@ -88,6 +88,7 @@ struct gs_console {
 	spinlock_t		lock;
 	struct usb_request	*req;
 	struct kfifo		buf;
+	size_t			missed;
 };
 
 /*
@@ -931,6 +932,15 @@ static void __gs_console_push(struct gs_console *cons)
 	if (!size)
 		return;
 
+	if (cons->missed && ep->maxpacket >= 64) {
+		char buf[64];
+		size_t len;
+
+		len = sprintf(buf, "\n[missed %zu bytes]\n", cons->missed);
+		kfifo_in(&cons->buf, buf, len);
+		cons->missed = 0;
+	}
+
 	req->length = size;
 	if (usb_ep_queue(ep, req, GFP_ATOMIC))
 		req->length = 0;
@@ -952,10 +962,13 @@ static void gs_console_write(struct console *co,
 {
 	struct gs_console *cons = container_of(co, struct gs_console, console);
 	unsigned long flags;
+	size_t n;
 
 	spin_lock_irqsave(&cons->lock, flags);
 
-	kfifo_in(&cons->buf, buf, count);
+	n = kfifo_in(&cons->buf, buf, count);
+	if (n < count)
+		cons->missed += count - n;
 
 	if (cons->req && !cons->req->length)
 		schedule_work(&cons->work);
-- 
2.20.1