xen: fix debugtrace clearing

After dumping the debugtrace buffer it is cleared. This results in some
entries not being printed in case the buffer is dumped again before
having wrapped.

While at it remove the trailing zero byte in the buffer as it is no
longer needed. Commit b5e6e1ee8da59f introduced passing the number of
chars to be printed in the related interfaces, so the trailing 0 byte
is no longer required.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index f49c6f29a8cc06a4d2dc2b7abaa906db8b49c6e8..3783618c1745f8b3975a9314df9b1d29072971cc 100644 (file)
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -1173,6 +1173,7 @@ static char        *debugtrace_buf; /* Debug-trace buffer */
 static unsigned int debugtrace_prd; /* Producer index     */
 static unsigned int debugtrace_kilobytes = 128, debugtrace_bytes;
 static unsigned int debugtrace_used;
+static bool debugtrace_buf_empty = true;
 static DEFINE_SPINLOCK(debugtrace_lock);
 integer_param("debugtrace", debugtrace_kilobytes);
 
@@ -1184,16 +1185,17 @@ static void debugtrace_dump_worker(void)
     printk("debugtrace_dump() starting\n");
 
     /* Print oldest portion of the ring. */
-    ASSERT(debugtrace_buf[debugtrace_bytes - 1] == 0);
     if ( debugtrace_buf[debugtrace_prd] != '\0' )
         console_serial_puts(&debugtrace_buf[debugtrace_prd],
-                            debugtrace_bytes - debugtrace_prd - 1);
+                            debugtrace_bytes - debugtrace_prd);
 
     /* Print youngest portion of the ring. */
     debugtrace_buf[debugtrace_prd] = '\0';
     console_serial_puts(&debugtrace_buf[0], debugtrace_prd);
 
     memset(debugtrace_buf, '\0', debugtrace_bytes);
+    debugtrace_prd = 0;
+    debugtrace_buf_empty = true;
 
     printk("debugtrace_dump() finished\n");
 }
@@ -1241,8 +1243,7 @@ static void debugtrace_add_to_buf(char *buf)
     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) )
+        if ( debugtrace_prd == debugtrace_bytes )
             debugtrace_prd = 0;
     }
 }
@@ -1264,8 +1265,6 @@ void debugtrace_printk(const char *fmt, ...)
 
     spin_lock_irqsave(&debugtrace_lock, flags);
 
-    ASSERT(debugtrace_buf[debugtrace_bytes - 1] == 0);
-
     va_start(args, fmt);
     nr = vscnprintf(buf, sizeof(buf), fmt, args);
     va_end(args);
@@ -1279,8 +1278,9 @@ void debugtrace_printk(const char *fmt, ...)
     }
     else
     {
-        if ( strcmp(buf, last_buf) )
+        if ( debugtrace_buf_empty || strcmp(buf, last_buf) )
         {
+            debugtrace_buf_empty = false;
             last_prd = debugtrace_prd;
             last_count = ++count;
             safe_strcpy(last_buf, buf);