From patchwork Tue May 25 10:24:11 2010
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Subject: [2/7] trace: Support disabled events in trace-events
Date: Tue, 25 May 2010 00:24:11 -0000
From: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
X-Patchwork-Id: 53526
Message-Id: <1274783056-14759-3-git-send-email-stefanha@linux.vnet.ibm.com>
To: <qemu-devel@nongnu.org>, <kvm@vger.kernel.org>
Cc: Jan Kiszka <jan.kiszka@siemens.com>,
 Anthony Liguori <aliguori@us.ibm.com>, Avi Kivity <avi@redhat.com>,
 Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, 
 Prerna Saxena <prerna@linux.vnet.ibm.com>

Sometimes it is useful to disable a trace event.  Removing the event
from trace-events is not enough since source code will call the
trace_*() function for the event.

This patch makes it easy to build without specific trace events by
marking them disabled in trace-events:

disable multiwrite_cb(void *mcb, int ret) "mcb %p ret %d"

This builds without the multiwrite_cb trace event.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

---
v2:
 * This patch is new in v2

 trace-events |    4 +++-
 tracetool    |   10 ++++++++--
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/trace-events b/trace-events
index a37d3cc..5efaa86 100644
--- a/trace-events
+++ b/trace-events
@@ -12,10 +12,12 @@
 #
 # Format of a trace event:
 #
-# <name>(<type1> <arg1>[, <type2> <arg2>] ...) "<format-string>"
+# [disable] <name>(<type1> <arg1>[, <type2> <arg2>] ...) "<format-string>"
 #
 # Example: qemu_malloc(size_t size) "size %zu"
 #
+# The "disable" keyword will build without the trace event.
+#
 # The <name> must be a valid as a C function name.
 #
 # Types should be standard C types.  Use void * for pointers because the trace
diff --git a/tracetool b/tracetool
index 766a9ba..53d3612 100755
--- a/tracetool
+++ b/tracetool
@@ -110,7 +110,7 @@ linetoc_end_nop()
 # Process stdin by calling begin, line, and end functions for the backend
 convert()
 {
-    local begin process_line end
+    local begin process_line end str disable
     begin="lineto$1_begin_$backend"
     process_line="lineto$1_$backend"
     end="lineto$1_end_$backend"
@@ -123,8 +123,14 @@ convert()
         str=${str%%#*}
         test -z "$str" && continue
 
+        # Process the line.  The nop backend handles disabled lines.
+        disable=${str%%disable*}
         echo
-        "$process_line" "$str"
+        if test -z "$disable"; then
+            "lineto$1_nop" "${str##disable}"
+        else
+            "$process_line" "$str"
+        fi
     done
 
     echo