xentrace: Fix bug in logic for bytes_to_wrap in trace buffer.

Admittedly, the bug could only be manifest with much larger trace
records than are currently allowed (or equivalently, much smaller
trace buffers), but the old code was harder to read, and thus hid the
logic bug well, too.

Signed-off-by: Michael A Fetterman <Michael.Fetterman@cl.cam.ac.uk>

diff --git a/xen/common/trace.c b/xen/common/trace.c
index 9af70798bb25d7223651f16ed4623e940cbab774..d2f8fceeaea3029b20ab106a4f60f71eea5cac96 100644 (file)
--- a/xen/common/trace.c
+++ b/xen/common/trace.c
@@ -425,25 +425,18 @@ void __trace_var(u32 event, int cycles, int extra, unsigned char *extra_data)
             total_size += bytes_to_wrap;
             bytes_to_wrap = data_size;
         } 
-        else
-        {
-            bytes_to_wrap -= LOST_REC_SIZE;
-            if ( bytes_to_wrap == 0 )
-                bytes_to_wrap = data_size;
-        }
         total_size += LOST_REC_SIZE;
+        bytes_to_wrap -= LOST_REC_SIZE;
+
+        /* LOST_REC might line up perfectly with the buffer wrap */
+        if ( bytes_to_wrap == 0 )
+            bytes_to_wrap = data_size;
     }
 
     if ( rec_size > bytes_to_wrap )
     {
         total_size += bytes_to_wrap;
-        bytes_to_wrap = data_size;
     } 
-    else
-    {
-        bytes_to_wrap -= rec_size;
-    }
-
     total_size += rec_size;
 
     /* Do we have enough space for everything? */
@@ -466,14 +459,12 @@ void __trace_var(u32 event, int cycles, int extra, unsigned char *extra_data)
             insert_wrap_record(buf, LOST_REC_SIZE);
             bytes_to_wrap = data_size;
         } 
-        else
-        {
-            bytes_to_wrap -= LOST_REC_SIZE;
-            /* LOST_REC might line up perfectly with the buffer wrap */
-            if ( bytes_to_wrap == 0 )
-                bytes_to_wrap = data_size;
-        }
         insert_lost_records(buf);
+        bytes_to_wrap -= LOST_REC_SIZE;
+
+        /* LOST_REC might line up perfectly with the buffer wrap */
+        if ( bytes_to_wrap == 0 )
+            bytes_to_wrap = data_size;
     }
 
     if ( rec_size > bytes_to_wrap )