[Qemu-devel] [RFC v2] [PATCH 3/3] Toggle tracepoint state

[Prerna Saxena]

This patch adds support for dynamically enabling/disabling of tracepoints.
Monitor commands added :
1) info tracepoints             : to view all available tracepoints and 
                                  their state.
2) tracepoint NAME on|off       : to enable/disable data logging from a 
                                  given tracepoint.
                                  Eg, tracepoint paio_submit off 
                                        disables logging of data when 
                                        paio_submit is hit.

For now it is a simple comparison, I'm exploring optimizations that can 
be employed to make this faster.

Signed-off-by: Prerna Saxena <address@hidden>
---
 monitor.c       |   16 +++++++++++++++-
 qemu-monitor.hx |   18 ++++++++++++++++++
 simpletrace.c   |   53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 tracetool       |   30 ++++++++++++++++++++++++++----
 vl.c            |    6 ++++++
 5 files changed, 118 insertions(+), 5 deletions(-)

diff --git a/monitor.c b/monitor.c
index 8b60830..e4c7bef 100644
--- a/monitor.c
+++ b/monitor.c
@@ -547,7 +547,14 @@ static void do_commit(Monitor *mon, const QDict *qdict)
         bdrv_commit(dinfo->bdrv);
     }
 }
-
+#ifdef CONFIG_SIMPLE_TRACE
+static void do_change_tracepoint_state(Monitor *mon, const QDict *qdict)
+{
+    const char *tp_name = qdict_get_str(qdict, "name");
+    bool new_state = qdict_get_bool(qdict, "option");
+    change_tracepoint_state(tp_name, new_state);
+}
+#endif
 static void user_monitor_complete(void *opaque, QObject *ret_data)
 {
     MonitorCompletionData *data = (MonitorCompletionData *)opaque; 
@@ -2791,6 +2798,13 @@ static const mon_cmd_t info_cmds[] = {
         .help       = "show current contents of trace buffer",
         .mhandler.info = do_info_trace,
     },
+    {
+        .name       = "tracepoints",
+        .args_type  = "",
+        .params     = "",
+        .help       = "show available tracepoints & their state",
+        .mhandler.info = do_info_all_tracepoints,
+    },
 #endif
     {
         .name       = NULL,
diff --git a/qemu-monitor.hx b/qemu-monitor.hx
index 766c30f..8540b8f 100644
--- a/qemu-monitor.hx
+++ b/qemu-monitor.hx
@@ -117,6 +117,8 @@ show device tree
 #ifdef CONFIG_SIMPLE_TRACE
 @item info trace
 show contents of trace buffer
address@hidden info tracepoints
+show available tracepoints and their state
 #endif
 @end table
 ETEXI
@@ -225,6 +227,22 @@ STEXI
 @item logfile @var{filename}
 @findex logfile
 Output logs to @var{filename}.
+#ifdef CONFIG_SIMPLE_TRACE
+ETEXI
+
+    {
+        .name       = "tracepoint",
+        .args_type  = "name:s,option:b",
+        .params     = "name on|off",
+        .help       = "changes status of a specific tracepoint",
+        .mhandler.cmd = do_change_tracepoint_state,
+    },
+
+STEXI
address@hidden tracepoint
address@hidden tracepoint
+changes status of a tracepoint
+#endif
 ETEXI
 
     {
diff --git a/simpletrace.c b/simpletrace.c
index 00df45a..b601d24 100644
--- a/simpletrace.c
+++ b/simpletrace.c
@@ -3,6 +3,12 @@
 #include "trace.h"
 
 typedef struct {
+    char *tp_name;
+    bool state;
+    unsigned int hash;
+} Tracepoint;
+
+typedef struct {
     unsigned long event;
     unsigned long x1;
     unsigned long x2;
@@ -18,10 +24,24 @@ enum {
 static TraceRecord trace_buf[TRACE_BUF_LEN];
 static unsigned int trace_idx;
 static FILE *trace_fp;
+static Tracepoint trace_list[NR_TRACEPOINTS];
+
+void init_tracepoint(const char *tname, TraceEvent tevent) {
+    if (!tname || tevent > NR_TRACEPOINTS)
+        return;
+
+    trace_list[tevent].tp_name = (char*)qemu_malloc(strlen(tname)+1);
+    strncpy(trace_list[tevent].tp_name, tname, strlen(tname));
+    trace_list[tevent].hash = tdb_hash(tname);
+    trace_list[tevent].state = 1; /* Enable all by default */
+    return;
+}
 
 static void trace(TraceEvent event, unsigned long x1,
                   unsigned long x2, unsigned long x3,
                   unsigned long x4, unsigned long x5) {
+    if (!trace_list[event].state)
+        return;
     TraceRecord *rec = &trace_buf[trace_idx];
     rec->event = event;
     rec->x1 = x1;
@@ -74,3 +94,36 @@ void do_info_trace(Monitor *mon)
                           trace_buf[i].event, trace_buf[i].x1, trace_buf[i].x2,
                             trace_buf[i].x3, trace_buf[i].x4, trace_buf[i].x5);
 }
+
+void do_info_all_tracepoints(Monitor *mon)
+{
+    unsigned int i;
+    for (i=0; i<NR_TRACEPOINTS; i++)
+        monitor_printf(mon, "%s [Event ID %u] : state %u\n",
+                                trace_list[i].tp_name, i, trace_list[i].state);
+}
+
+static int find_tracepoint_by_name(const char *tname)
+{
+    unsigned int i, name_hash;
+
+    if (!tname)
+        return -1;
+
+    name_hash = tdb_hash(tname);
+
+    for (i=0; i<NR_TRACEPOINTS; i++)
+        if (trace_list[i].hash == name_hash &&
+                         !strncmp(trace_list[i].tp_name, tname, strlen(tname)))
+            return i;
+    return -1; /* indicates end of list reached without a match */
+}
+
+void change_tracepoint_state(const char *tname, bool tstate)
+{
+    int i;
+
+    i = find_tracepoint_by_name(tname);
+    if (i >= 0)
+        trace_list[i].state = tstate;
+}
diff --git a/tracetool b/tracetool
index 2c73bab..00af205 100755
--- a/tracetool
+++ b/tracetool
@@ -123,14 +123,20 @@ linetoc_end_nop()
 linetoh_begin_simple()
 {
     cat <<EOF
+#include <stdbool.h>
+
 typedef unsigned int TraceEvent;
 
+void init_tracepoint_table(void);
+void init_tracepoint(const char *tname, TraceEvent tevent);
 void trace1(TraceEvent event, unsigned long x1);
 void trace2(TraceEvent event, unsigned long x1, unsigned long x2);
 void trace3(TraceEvent event, unsigned long x1, unsigned long x2, unsigned 
long x3);
 void trace4(TraceEvent event, unsigned long x1, unsigned long x2, unsigned 
long x3, unsigned long x4);
 void trace5(TraceEvent event, unsigned long x1, unsigned long x2, unsigned 
long x3, unsigned long x4, unsigned long x5);
 void do_info_trace(Monitor *mon);
+void do_info_all_tracepoints(Monitor *mon);
+void change_tracepoint_state(const char *tname, bool tstate);
 EOF
 
     simple_event_num=0
@@ -163,22 +169,38 @@ EOF
 
 linetoh_end_simple()
 {
-    return
+    cat <<EOF
+#define NR_TRACEPOINTS $simple_event_num
+EOF
 }
 
 linetoc_begin_simple()
 {
-    return
+    cat <<EOF
+#include "trace.h"
+
+void init_tracepoint_table(void) {
+EOF
+    simple_event_num=0
+
 }
 
 linetoc_simple()
 {
-    return
+    local name
+    name=$(get_name "$1")
+    cat <<EOF
+init_tracepoint("$name", $simple_event_num);
+EOF
+    simple_event_num=$((simple_event_num + 1))
 }
 
 linetoc_end_simple()
 {
-    return
+    cat <<EOF
+return;
+}
+EOF
 }
 
 linetoh_begin_ust()
diff --git a/vl.c b/vl.c
index 328395e..dd07904 100644
--- a/vl.c
+++ b/vl.c
@@ -163,6 +163,9 @@ int main(int argc, char **argv)
 #include "cpus.h"
 #include "arch_init.h"
 
+#ifdef CONFIG_SIMPLE_TRACE
+#include "trace.h"
+#endif
 //#define DEBUG_NET
 //#define DEBUG_SLIRP
 
@@ -3604,6 +3607,9 @@ int main(int argc, char **argv, char **envp)
     if (net_init_clients() < 0) {
         exit(1);
     }
+#ifdef CONFIG_SIMPLE_TRACE
+    init_tracepoint_table();
+#endif
 
     /* init the bluetooth world */
     if (foreach_device_config(DEV_BT, bt_parse))
-- 
1.6.2.5



-- 
Prerna Saxena

Linux Technology Centre,
IBM Systems and Technology Lab,
Bangalore, India