[Xen-devel] Re: [PATCH] fix serial token buket

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Stefano Stabellini wrote:

> Using timespec in the serial token bucket causes problems with integer
> overflows.
> This patch fixes the issue using timeval instead of timespec variables,
> everywhere but from reading the current time with clock_gettime.
>



Oops, I forgot one substitution.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

---

diff -r 0ea6bd53cfb6 hw/serial.c
--- a/hw/serial.c       Thu Oct 23 10:26:02 2008 +0100
+++ b/hw/serial.c       Fri Nov 14 16:04:50 2008 +0000
@@ -155,8 +155,8 @@
    doesn't kill dom0.  Simple token bucket.  If we get some actual
    data from the user, instantly refil the bucket. */
 
-/* How long it takes to generate a token, in nanoseconds. */
-#define TOKEN_PERIOD 1000000
+/* How long it takes to generate a token, in microseconds. */
+#define TOKEN_PERIOD 1000
 /* Maximum and initial size of token bucket */
 #define TOKENS_MAX 100000
 
@@ -279,16 +279,19 @@
 
 static void serial_get_token(void)
 {
-    static struct timespec last_refil_time;
+    static struct timeval last_refil_time;
     static int started;
 
     assert(tokens_avail >= 0);
     if (!tokens_avail) {
-       struct timespec delta, now;
+       struct timespec now;
+       struct timeval delta;
        long generated;
 
        if (!started) {
-           clock_gettime(CLOCK_MONOTONIC, &last_refil_time);
+           clock_gettime(CLOCK_MONOTONIC, &now);
+           last_refil_time.tv_sec = now.tv_sec;
+           last_refil_time.tv_usec = now.tv_nsec / 1000;
            tokens_avail = TOKENS_MAX;
            started = 1;
            return;
@@ -296,35 +299,35 @@
     retry:
        clock_gettime(CLOCK_MONOTONIC, &now);
        delta.tv_sec = now.tv_sec - last_refil_time.tv_sec;
-       delta.tv_nsec = now.tv_nsec - last_refil_time.tv_nsec;
-       if (delta.tv_nsec < 0) {
-           delta.tv_nsec += 1000000000;
+       delta.tv_usec = (now.tv_nsec / 1000) - last_refil_time.tv_usec;
+       if (delta.tv_usec < 0) {
+           delta.tv_usec += 1000000;
            delta.tv_sec--;
        }
-       assert(delta.tv_nsec >= 0 && delta.tv_sec >= 0);
-       if (delta.tv_nsec < TOKEN_PERIOD) {
+       assert(delta.tv_usec >= 0 && delta.tv_sec >= 0);
+       if (delta.tv_sec == 0 && delta.tv_usec < TOKEN_PERIOD) {
            struct timespec ts;
            /* Wait until at least one token is available. */
-           ts.tv_sec = TOKEN_PERIOD / 1000000000;
-           ts.tv_nsec = TOKEN_PERIOD % 1000000000;
+           ts.tv_sec = TOKEN_PERIOD / 1000000;
+           ts.tv_nsec = (TOKEN_PERIOD % 1000000) * 1000;
            while (nanosleep(&ts, &ts) < 0 && errno == EINTR)
                ;
            goto retry;
        }
-        if (delta.tv_sec >= 2) {
+        if (delta.tv_sec >= 2000) {
             /* avoid arithmetic overflow if it has been ages */
-            delta.tv_sec = 2;
-            delta.tv_nsec = 0;
+            delta.tv_sec = 2000;
+            delta.tv_usec = 0;
         }
-       generated = (delta.tv_sec * 1000000000) / TOKEN_PERIOD;
+       generated = (delta.tv_sec * 1000000) / TOKEN_PERIOD;
        generated +=
-           ((delta.tv_sec * 1000000000) % TOKEN_PERIOD + delta.tv_nsec) / 
TOKEN_PERIOD;
+           ((delta.tv_sec * 1000000) % TOKEN_PERIOD + delta.tv_usec) / 
TOKEN_PERIOD;
        assert(generated > 0);
 
-       last_refil_time.tv_nsec += (generated * TOKEN_PERIOD) % 1000000000;
-       last_refil_time.tv_sec  += last_refil_time.tv_nsec / 1000000000;
-       last_refil_time.tv_nsec %= 1000000000;
-        last_refil_time.tv_sec  += (generated * TOKEN_PERIOD) / 1000000000;
+       last_refil_time.tv_usec += (generated * TOKEN_PERIOD) % 1000000;
+       last_refil_time.tv_sec  += last_refil_time.tv_usec / 1000000;
+       last_refil_time.tv_usec %= 1000000;
+       last_refil_time.tv_sec  += (generated * TOKEN_PERIOD) / 1000000;
        if (generated > TOKENS_MAX)
            generated = TOKENS_MAX;
        tokens_avail = generated;

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