[Xen-changelog] [xen staging] debugtrace: add entry when entry count is wrapping

[patchbot@xxxxxxx]

commit c82425e456ff04f727e252458abcaef76ef20045
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Thu Sep 12 15:13:47 2019 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Sep 12 15:13:47 2019 +0200

    debugtrace: add entry when entry count is wrapping
    
    The debugtrace entry count is a 32 bit variable, so it can wrap when
    lots of trace entries are being produced. Making it wider would result
    in a waste of buffer space as the printed count value would consume
    more bytes when not wrapping.
    
    So instead of letting the count value grow to huge values let it wrap
    and add a wrap counter printed in this situation. This will keep the
    needed buffer space at today's value while avoiding to loose a way to
    sort all entries in case multiple trace buffers are involved.
    
    Note that the wrap message will be printed before the first trace
    entry in case output is switched to console early. This is on purpose
    in order to enable a future support of debugtrace to console without
    any allocated buffer.
    
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/common/debugtrace.c | 33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/xen/common/debugtrace.c b/xen/common/debugtrace.c
index 9b60c95959..5d22d431ad 100644
--- a/xen/common/debugtrace.c
+++ b/xen/common/debugtrace.c
@@ -15,11 +15,14 @@
 #include <xen/spinlock.h>
 #include <xen/watchdog.h>
 
+#define DEBUGTRACE_COUNT_WRAP 99999999
+
 /* Send output direct to console, or buffer it? */
 static volatile bool debugtrace_send_to_console;
 
 struct debugtrace_data {
     unsigned long prd;   /* Producer index. */
+    unsigned long wrap_cnt;
     char          buf[];
 };
 
@@ -72,6 +75,7 @@ static void debugtrace_dump_buffer(struct debugtrace_data 
*data,
     /* Print youngest portion of the ring. */
     data->buf[data->prd] = '\0';
     console_serial_puts(&data->buf[0], data->prd);
+    printk("wrap: %lu\n", data->wrap_cnt);
 
     memset(data->buf, '\0', debugtrace_bytes);
     data->prd = 0;
@@ -153,9 +157,9 @@ void debugtrace_printk(const char *fmt, ...)
 {
     static char buf[1024], last_buf[1024];
     static unsigned int count, last_count, last_cpu;
-    static unsigned long last_prd;
+    static unsigned long last_prd, wrap_cnt;
 
-    char          cntbuf[24];
+    char          cntbuf[50];
     va_list       args;
     unsigned long flags;
     unsigned int nr;
@@ -173,10 +177,23 @@ void debugtrace_printk(const char *fmt, ...)
     nr = vsnprintf(buf, sizeof(buf), fmt, args);
     va_end(args);
 
+    if ( count == DEBUGTRACE_COUNT_WRAP )
+    {
+        count = 0;
+        wrap_cnt++;
+    }
+
     if ( debugtrace_send_to_console )
     {
-        unsigned int n = scnprintf(cntbuf, sizeof(cntbuf), "%u ", ++count);
+        unsigned int n;
+
+        if ( count == 0 )
+        {
+            n = scnprintf(cntbuf, sizeof(cntbuf), "wrap: %lu\n", wrap_cnt);
+            console_serial_puts(cntbuf, n);
+        }
 
+        n = scnprintf(cntbuf, sizeof(cntbuf), "%u ", ++count);
         console_serial_puts(cntbuf, n);
         console_serial_puts(buf, nr);
     }
@@ -184,8 +201,16 @@ void debugtrace_printk(const char *fmt, ...)
     {
         unsigned int cpu = debugtrace_per_cpu ? smp_processor_id() : 0;
 
-        if ( debugtrace_buf_empty || cpu != last_cpu || strcmp(buf, last_buf) )
+        if ( debugtrace_buf_empty || cpu != last_cpu ||
+             wrap_cnt != data->wrap_cnt || strcmp(buf, last_buf) )
         {
+            if ( wrap_cnt != data->wrap_cnt )
+            {
+                snprintf(cntbuf, sizeof(cntbuf), "wrap: %lu->%lu\n",
+                         data->wrap_cnt, wrap_cnt);
+                debugtrace_add_to_buf(cntbuf);
+                data->wrap_cnt = wrap_cnt;
+            }
             debugtrace_buf_empty = false;
             last_prd = data->prd;
             last_count = ++count;
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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