trace: Support disabled events in trace-events

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>

trace: Allow bulk enabling/disabling of trace events at compile time

For 'simple' trace backend, allow bulk enabling/disabling of trace
events at compile time.  Trace events that are preceded by 'disable'
keyword are compiled in, but turned off by default. These can
individually be turned on using the monitor.  All other trace events are
enabled by default.

TODO :
This could be enhanced when the trace-event namespace is partitioned into a
group and an ID within that group. In such a case, marking a group as enabled
would automatically enable all trace-events listed under it.

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

2 files changed, 45 insertions, 6 deletions

diff --git a/trace-events b/trace-events
index a37d3cc6e3..2a986ecd29 100644
--- a/trace-events
+++ b/trace-events
@@ -12,10 +12,15 @@
 #
 # 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.
+# In case of 'simple' trace backend, it will allow the trace event to be
+# compiled, but this would be turned off by default. It can be toggled on via
+# the monitor.
+#
 # 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 2e2e37dbd3..8aeac4870b 100755
--- a/tracetool
+++ b/tracetool
@@ -87,6 +87,20 @@ get_fmt()
     echo "$fmt"
 }
 
+# Get the state of a trace event
+get_state()
+{
+    local str disable state
+    str=$(get_name "$1")
+    disable=${str##disable }
+    if [ "$disable" = "$str" ] ; then
+        state=1
+    else
+        state=0
+    fi
+    echo "$state"
+}
+
 linetoh_begin_nop()
 {
     return
@@ -146,10 +160,14 @@ cast_args_to_uint64_t()
 
 linetoh_simple()
 {
-    local name args argc trace_args
+    local name args argc trace_args state
     name=$(get_name "$1")
     args=$(get_args "$1")
     argc=$(get_argc "$1")
+    state=$(get_state "$1")
+    if [ "$state" = "0" ]; then
+        name=${name##disable }
+    fi
 
     trace_args="$simple_event_num"
     if [ "$argc" -gt 0 ]
@@ -188,10 +206,14 @@ EOF
 
 linetoc_simple()
 {
-    local name
+    local name state
     name=$(get_name "$1")
+    state=$(get_state "$1")
+    if [ "$state" = "0" ] ; then
+        name=${name##disable }
+    fi
     cat <<EOF
-{.tp_name = "$name", .state=0},
+{.tp_name = "$name", .state=$state},
 EOF
     simple_event_num=$((simple_event_num + 1))
 }
@@ -206,7 +228,7 @@ EOF
 # 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"
@@ -218,8 +240,20 @@ 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
+            # Pass the disabled state as an arg to lineto$1_simple().
+            # For all other cases, call lineto$1_nop()
+            if [ $backend = "simple" ]; then
+                "$process_line" "$str"
+            else
+                "lineto$1_nop" "${str##disable }"
+            fi
+        else
+            "$process_line" "$str"
+        fi
     done
 
     echo