Re: [Qemu-devel] [PATCH 3/3] Toggle tracepoint state

[Luiz Capitulino <lcapitulino@redhat.com>]

On Tue, 8 Jun 2010 12:38:58 +0530
Prerna Saxena <prerna@linux.vnet.ibm.com> wrote:

> 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.
> 
> At present this is done with a simple comparison -- there is scope 
> for optimizations that can be employed here to speed this up.
> 
> Signed-off-by: Prerna Saxena <prerna@linux.vnet.ibm.com>
> ---
>  monitor.c       |   21 +++++++++++++++++++++
>  qemu-monitor.hx |   16 ++++++++++++++++
>  simpletrace.c   |   55 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  tracetool       |   30 ++++++++++++++++++++++++++----
>  vl.c            |    6 ++++++
>  5 files changed, 123 insertions(+), 5 deletions(-)
> 
> diff --git a/monitor.c b/monitor.c
> index fda29aa..1e05b38 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -547,7 +547,19 @@ 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");
> +    const char *tp_state = qdict_get_str(qdict, "option");
>  
> +    if (!strncmp(tp_state, "on", 2))
> +	change_tracepoint_state(tp_name, 1);
> +    if (!strncmp(tp_state, "off", 3))
> +	change_tracepoint_state(tp_name, 0);

 Monitor has a bool type, please take a look in do_set_link().

> +    return;

 Not needed, also true for other functions in this patch, suggest reading
CODING_STYLE for other style related issues in this series.

> +}
> +#endif
>  static void user_monitor_complete(void *opaque, QObject *ret_data)
>  {
>      MonitorCompletionData *data = (MonitorCompletionData *)opaque; 
> @@ -2783,6 +2795,15 @@ static const mon_cmd_t info_cmds[] = {
>          .help       = "show roms",
>          .mhandler.info = do_info_roms,
>      },
> +#ifdef CONFIG_SIMPLE_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 c604aec..36481ea 100644
> --- a/qemu-monitor.hx
> +++ b/qemu-monitor.hx
> @@ -114,6 +114,8 @@ show migration status
>  show balloon information
>  @item info qtree
>  show device tree
> +@item info tracepoints
> +show available tracepoints and their state
>  @end table
>  ETEXI
>  
> @@ -236,6 +238,20 @@ STEXI
>  @item trace
>  @findex trace
>  show contents of trace buffer
> +ETEXI
> +
> +    {
> +        .name       = "tracepoint",
> +        .args_type  = "name:s,option:s",
> +        .params     = "name on|off",
> +        .help       = "changes status of a specific tracepoint",
> +        .mhandler.cmd = do_change_tracepoint_state,
> +    },
> +
> +STEXI
> +@item tracepoint
> +@findex tracepoint
> +changes status of a tracepoint
>  #endif
>  ETEXI
>  
> diff --git a/simpletrace.c b/simpletrace.c
> index 8f33a81..75d2fca 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;
> @@ -64,7 +84,7 @@ void trace5(TraceEvent event, unsigned long x1, unsigned long x2, unsigned long
>  }
>  
>  void do_info_trace(Monitor *mon) {
> -    static unsigned int i, max_idx;
> +    unsigned int i, max_idx;
>  
>      if (trace_idx)
>          max_idx = trace_idx;
> @@ -77,3 +97,36 @@ void do_info_trace(Monitor *mon) {
>  	trace_buf[i].x3, trace_buf[i].x4, trace_buf[i].x5);
>      return;
>  }
> +
> +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);
> +    return;
> +}
> +
> +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);
> +    /* TODO : This update might need to be protected by a memory barrier */
> +    if (i >= 0)
> +	trace_list[i].state = tstate;
> +    return;
> +}
> diff --git a/tracetool b/tracetool
> index 6c15154..cc2b22c 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))