[PATCH v5 1/2] xen/console: re-calibrate rate-limiter based on user input

From: Denis Mukhin <[email protected]> 

Current __printk_ratelimit() relies on hardcoded values 5000 and 10
respectively to program leaky-bucket message limiting.

Use 'ratelimit_ms' and 'ratelimit_burst' variables to re-calibrate
limiter.

Ensure rate limiter is disabled if either 'ratelimit_ms' or
'ratelimit_burst' is 0.

Fixes: 26cf03554a75 ("[XEN] Implement rate-limited logging.")
Signed-off-by: Denis Mukhin <[email protected]>
---
Changes since v4:
- dropped 'initialized' flag
- updated commit message, including Fixes tag
---
 xen/drivers/char/console.c | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index ea4e3ff34178..56bf111ef181 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -33,6 +33,7 @@
 #include <asm/setup.h>
 #include <xen/sections.h>
 #include <xen/consoled.h>
+#include <xen/xvmalloc.h>
 
 #ifdef CONFIG_X86
 #include <asm/guest.h>
@@ -1286,21 +1287,34 @@ bool __printk_ratelimit(unsigned int ratelimit_ms,
                         unsigned int ratelimit_burst)
 {
     static DEFINE_SPINLOCK(ratelimit_lock);
-    static unsigned long toks = 10 * 5 * 1000;
+    static unsigned long toks = ~0;
     static unsigned long last_msg;
     static unsigned int missed;
+    unsigned long limit;
+    unsigned long elapsed;
     unsigned long flags;
-    unsigned long long now = NOW(); /* ns */
     unsigned long ms;
+    s_time_t now;
 
-    do_div(now, 1000000);
-    ms = (unsigned long)now;
+    if ( !ratelimit_ms || !ratelimit_burst )
+        return true;
+
+    limit = DIM_MUL2(ratelimit_burst, ratelimit_ms);
+
+    now = NOW(); /* ns */
+    do_div(now, MILLISECS(1));
+    ms = now;
 
     spin_lock_irqsave(&ratelimit_lock, flags);
-    toks += ms - last_msg;
+
+    elapsed = ms - last_msg;
+    if ( toks >= limit || elapsed >= limit - toks )
+        toks = limit;
+    else
+        toks += elapsed;
+
     last_msg = ms;
-    if ( toks > (ratelimit_burst * ratelimit_ms))
-        toks = ratelimit_burst * ratelimit_ms;
+
     if ( toks >= ratelimit_ms )
     {
         unsigned int lost = missed;
-- 
2.54.0