[PATCH v2 0/2] xen: some debug trace enhancements

[PATCH v2 0/2] xen: some debug trace enhancements

[Juergen Gross]

While doing some scheduler work I used debug trace for diagnosis of
problems during dom0 boot. This small series is the result of adapting
debug trace to my needs.

Juergen Gross (2):
  xen/debug: make debugtrace configurable via Kconfig
  xen/debug: make debugtrace more clever regarding repeating entries

 xen/Kconfig.debug          |  7 +++++++
 xen/drivers/char/console.c | 44 ++++++++++++++++++++++++++++++++------------
 xen/include/xen/lib.h      |  3 +--
 3 files changed, 40 insertions(+), 14 deletions(-)

-- 
2.16.4


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[PATCH v2 1/2] xen/debug: make debugtrace configurable via Kconfig

[Juergen Gross]

Instead of having to edit include/xen/lib.h for making debugtrace
available make it configurable via Kconfig.

Default is off, it is available only in expert mode or in debug builds.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
---
 xen/Kconfig.debug          | 7 +++++++
 xen/drivers/char/console.c | 2 +-
 xen/include/xen/lib.h      | 3 +--
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/xen/Kconfig.debug b/xen/Kconfig.debug
index 4d5d7f87cb..daacf85141 100644
--- a/xen/Kconfig.debug
+++ b/xen/Kconfig.debug
@@ -98,6 +98,13 @@ config UBSAN
 
 	  If unsure, say N here.
 
+config DEBUG_TRACE
+	bool "Debug trace support"
+	---help---
+	  Debug trace enables to record debug trace messages which are printed
+	  either directly to the console or are printed to console in case of
+	  a system crash.
+
 endif # DEBUG || EXPERT
 
 endmenu
diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 4315588f05..41ec13ce52 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -1157,7 +1157,7 @@ int printk_ratelimit(void)
  * **************************************************************
  */
 
-#ifdef DEBUG_TRACE_DUMP
+#ifdef CONFIG_DEBUG_TRACE
 
 /* Send output direct to console, or buffer it? */
 static volatile int debugtrace_send_to_console;
diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h
index 89939f43c8..e0b7bcb6b7 100644
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -86,8 +86,7 @@ int parse_boolean(const char *name, const char *s, const char *e);
  */
 int cmdline_strcmp(const char *frag, const char *name);
 
-/*#define DEBUG_TRACE_DUMP*/
-#ifdef DEBUG_TRACE_DUMP
+#ifdef CONFIG_DEBUG_TRACE
 extern void debugtrace_dump(void);
 extern void debugtrace_printk(const char *fmt, ...)
     __attribute__ ((format (printf, 1, 2)));
-- 
2.16.4


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[PATCH v2 2/2] xen/debug: make debugtrace more clever regarding repeating entries

[Juergen Gross]

In case debugtrace is writing to memory and the last entry is repeated
don't fill up the trace buffer, but modify the count prefix to "x-y "
style instead.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 xen/drivers/char/console.c | 42 +++++++++++++++++++++++++++++++-----------
 1 file changed, 31 insertions(+), 11 deletions(-)

diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 41ec13ce52..f41b689847 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -1225,13 +1225,26 @@ void debugtrace_dump(void)
     watchdog_enable();
 }
 
+static void debugtrace_add_to_buf(char *buf)
+{
+    char *p;
+
+    for ( p = buf; *p != '\0'; p++ )
+    {
+        debugtrace_buf[debugtrace_prd++] = *p;
+        /* Always leave a nul byte at the end of the buffer. */
+        if ( debugtrace_prd == (debugtrace_bytes - 1) )
+            debugtrace_prd = 0;
+    }
+}
+
 void debugtrace_printk(const char *fmt, ...)
 {
-    static char    buf[1024];
-    static u32 count;
+    static char buf[1024], last_buf[1024];
+    static unsigned int count, last_count, last_prd;
 
+    char          cntbuf[24];
     va_list       args;
-    char         *p;
     unsigned long flags;
 
     if ( debugtrace_bytes == 0 )
@@ -1243,25 +1256,32 @@ void debugtrace_printk(const char *fmt, ...)
 
     ASSERT(debugtrace_buf[debugtrace_bytes - 1] == 0);
 
-    snprintf(buf, sizeof(buf), "%u ", ++count);
-
     va_start(args, fmt);
-    (void)vsnprintf(buf + strlen(buf), sizeof(buf) - strlen(buf), fmt, args);
+    vsnprintf(buf, sizeof(buf), fmt, args);
     va_end(args);
 
     if ( debugtrace_send_to_console )
     {
+        snprintf(cntbuf, sizeof(cntbuf), "%u ", ++count);
+        serial_puts(sercon_handle, cntbuf);
         serial_puts(sercon_handle, buf);
     }
     else
     {
-        for ( p = buf; *p != '\0'; p++ )
+        if ( strcmp(buf, last_buf) )
+        {
+            last_prd = debugtrace_prd;
+            last_count = ++count;
+            safe_strcpy(last_buf, buf);
+            snprintf(cntbuf, sizeof(cntbuf), "%u ", count);
+        }
+        else
         {
-            debugtrace_buf[debugtrace_prd++] = *p;            
-            /* Always leave a nul byte at the end of the buffer. */
-            if ( debugtrace_prd == (debugtrace_bytes - 1) )
-                debugtrace_prd = 0;
+            debugtrace_prd = last_prd;
+            snprintf(cntbuf, sizeof(cntbuf), "%u-%u ", last_count, ++count);
         }
+        debugtrace_add_to_buf(cntbuf);
+        debugtrace_add_to_buf(buf);
     }
 
     spin_unlock_irqrestore(&debugtrace_lock, flags);
-- 
2.16.4


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Re: [PATCH v2 2/2] xen/debug: make debugtrace more clever regarding repeating entries

[Wei Liu]

On Fri, Mar 15, 2019 at 07:35:57AM +0100, Juergen Gross wrote:
> In case debugtrace is writing to memory and the last entry is repeated
> don't fill up the trace buffer, but modify the count prefix to "x-y "
> style instead.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Acked-by: Wei Liu <wei.liu2@citrix.com>

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