Re: [PATCH] trace:add "gfp_t" support in synthetic_events

[Tom Zanussi]

Hi Zhengjun,

On Thu, 2019-07-04 at 10:55 +0800, Zhengjun Xing wrote:
> Add "gfp_t" support in synthetic_events, then the "gfp_t" type
> parameter in some functions can be traced.
> 
> Signed-off-by: Zhengjun Xing <zhengjun.xing@xxxxxxxxxxxxxxx>
> ---
>  kernel/trace/trace_events_hist.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/trace/trace_events_hist.c
> b/kernel/trace/trace_events_hist.c
> index ca6b0dff60c5..0d3ab01b7cb5 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -752,6 +752,8 @@ static int synth_field_size(char *type)
>  		size = sizeof(unsigned long);
>  	else if (strcmp(type, "pid_t") == 0)
>  		size = sizeof(pid_t);
> +	else if (strcmp(type, "gfp_t") == 0)
> +		size = sizeof(gfp_t);
>  	else if (synth_field_is_string(type))
>  		size = synth_field_string_size(type);
>  
> @@ -792,6 +794,8 @@ static const char *synth_field_fmt(char *type)
>  		fmt = "%lu";
>  	else if (strcmp(type, "pid_t") == 0)
>  		fmt = "%d";
> +	else if (strcmp(type, "gfp_t") == 0)
> +		fmt = "%u";
>  	else if (synth_field_is_string(type))
>  		fmt = "%s";
>  

This will work, but I think it would be better to display as hex, and
also show the flags in human-readable form.

How about adding something like this on top of your patch?:


[PATCH] tracing: Add verbose gfp_flag printing to synthetic events

Add on top of 'trace:add "gfp_t" support in synthetic_events'.

Prints the gfp flags as hex in addition to the human-readable flag
string.  Example output:

  whoopsie-630 [000] ...1 78.969452: testevent: bar=b20 (GFP_ATOMIC|__GFP_ZERO)
    rcuc/0-11  [000] ...1 81.097555: testevent: bar=a20 (GFP_ATOMIC)
    rcuc/0-11  [000] ...1 81.583123: testevent: bar=a20 (GFP_ATOMIC)

Signed-off-by: Tom Zanussi <zanussi@xxxxxxxxxx>
---
 kernel/trace/trace_events_hist.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 0d3ab01..aeb4449 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -13,6 +13,10 @@
 #include <linux/rculist.h>
 #include <linux/tracefs.h>
 
+/* for gfp flag names */
+#include <linux/trace_events.h>
+#include <trace/events/mmflags.h>
+
 #include "tracing_map.h"
 #include "trace.h"
 #include "trace_dynevent.h"
@@ -795,7 +799,7 @@ static const char *synth_field_fmt(char *type)
 	else if (strcmp(type, "pid_t") == 0)
 		fmt = "%d";
 	else if (strcmp(type, "gfp_t") == 0)
-		fmt = "%u";
+		fmt = "%x";
 	else if (synth_field_is_string(type))
 		fmt = "%s";
 
@@ -838,9 +842,20 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter,
 					 i == se->n_fields - 1 ? "" : " ");
 			n_u64 += STR_VAR_LEN_MAX / sizeof(u64);
 		} else {
+			struct trace_print_flags __flags[] =
+				{ __def_gfpflag_names, { -1, NULL }};
+
 			trace_seq_printf(s, print_fmt, se->fields[i]->name,
 					 entry->fields[n_u64],
 					 i == se->n_fields - 1 ? "" : " ");
+
+			if (strcmp(se->fields[i]->type, "gfp_t") == 0) {
+				trace_seq_puts(s, " (");
+				trace_print_flags_seq(s, "|",
+						      entry->fields[n_u64],
+						      __flags);
+				trace_seq_putc(s, ')');
+			}
 			n_u64++;
 		}
 	}
-- 
2.7.4