[PATCH v4 5/6] usb: gadget: u_serial: diagnose missed console messages

[Michał Mirosław]

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: Michał Mirosław <mirq-li...@rere.qmqm.pl>
Reviewed-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
  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 ccfa8c6a35ac..c88ad020f9e2 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