[PATCH 16/18] tracing: Add NULL to skip args for function based events

[Steven Rostedt]

From: "Steven Rostedt (VMware)" 

If args are to be skipped (only care about second, third or later arguments)
then add a NULL to ignore them. For example, if one only wants to record the
third argument of a function, they can perform:

 echo foo(NULL, NULL, u32 arg3) > function_events

Then only the third argument is saved in the function based event.

Signed-off-by: Steven Rostedt (VMware) 
---
 Documentation/trace/function-based-events.rst | 28 +-
 kernel/trace/trace_event_ftrace.c | 34 ++-
 2 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/Documentation/trace/function-based-events.rst 
b/Documentation/trace/function-based-events.rst
index 6c643ea749e7..b90b52b7061d 100644
--- a/Documentation/trace/function-based-events.rst
+++ b/Documentation/trace/function-based-events.rst
@@ -91,7 +91,7 @@ as follows:
 
  ARGS := ARG | ARG ',' ARGS | ''
 
- ARG := TYPE FIELD | TYPE  '=' ADDR | TYPE ADDR | ARG '|' ARG
+ ARG := TYPE FIELD | TYPE  '=' ADDR | TYPE ADDR | ARG '|' ARG | 'NULL'
 
  TYPE := ATOM | ATOM '['  ']' | 'unsigned' TYPE
 
@@ -359,3 +359,29 @@ it will be truncated.
  # echo 'link_path_walk(string name)' > function_events
 
 Gives the same result as above, but does not waste buffer space.
+
+
+NULL arguments
+==
+
+If you are only interested in the second, or later parameter of a function,
+you do not have to record the previous parameters. Just set them as NULL and
+they will not be recorded.
+
+If we only wanted the perm_addr of the net_device of ip_rcv() and not the
+sk_buff, we put a NULL into the first parameter when created the function
+based event.
+
+  # echo 'ip_rcv(NULL, x8[6] perm_addr+558)' > function_events
+
+  # echo 1 > events/functions/ip_rcv/enable
+  # cat trace
+-0 [003] ..s3   165.617114: 
__netif_receive_skb_core->ip_rcv(perm_addr=b4,b5,2f,ce,18,65)
+-0 [003] ..s3   165.617133: 
__netif_receive_skb_core->ip_rcv(perm_addr=b4,b5,2f,ce,18,65)
+-0 [003] ..s3   166.412277: 
__netif_receive_skb_core->ip_rcv(perm_addr=b4,b5,2f,ce,18,65)
+-0 [003] ..s3   166.412797: 
__netif_receive_skb_core->ip_rcv(perm_addr=b4,b5,2f,ce,18,65)
+
+
+NULL can appear in any argument, to have them ignored. Note, skipping arguments
+does not give you access to later arguments if they are not supported by the
+architecture. The architecture only supplies the first set of arguments.
diff --git a/kernel/trace/trace_event_ftrace.c 
b/kernel/trace/trace_event_ftrace.c
index 273c5838a8e2..22bcb67ad184 100644
--- a/kernel/trace/trace_event_ftrace.c
+++ b/kernel/trace/trace_event_ftrace.c
@@ -75,6 +75,7 @@ enum func_states {
FUNC_STATE_ARRAY_END,
FUNC_STATE_VAR,
FUNC_STATE_COMMA,
+   FUNC_STATE_NULL,
FUNC_STATE_END,
FUNC_STATE_ERROR,
 };
@@ -117,6 +118,7 @@ static struct func_type {
int sign;
 } func_types[] = {
FUNC_TYPES,
+   { "NULL",   0,  0 },
{ NULL, 0,  0 }
 };
 
@@ -125,6 +127,7 @@ static struct func_type {
 
 enum {
FUNC_TYPES,
+   FUNC_TYPE_NULL,
FUNC_TYPE_MAX
 };
 
@@ -364,6 +367,8 @@ process_event(struct func_event *fevent, const char *token, 
enum func_states sta
fevent->arg_cnt++;
update_arg = false;
case FUNC_STATE_PIPE:
+   if (strcmp(token, "NULL") == 0)
+   return FUNC_STATE_NULL;
if (strcmp(token, "unsigned") == 0) {
unsign = 2;
return FUNC_STATE_UNSIGNED;
@@ -513,6 +518,19 @@ process_event(struct func_event *fevent, const char 
*token, enum func_states sta
fevent->last_arg->indirect = INDIRECT_FLAG;
return FUNC_STATE_ADDR;
 
+   case FUNC_STATE_NULL:
+   ret = add_arg(fevent, FUNC_TYPE_NULL, 0);
+   if (ret < 0)
+   break;
+   switch (token[0]) {
+   case ')':
+   goto end;
+   case ',':
+   update_arg = true;
+   return FUNC_STATE_COMMA;
+   }
+   break;
+
default:
break;
}
@@ -689,6 +707,8 @@ static void func_event_trace(struct trace_event_file 
*trace_file,
entry->parent_ip = parent_ip;
 
list_for_each_entry(arg, _event->args, list) {
+   if (arg->func_type == FUNC_TYPE_NULL)
+   continue;
if (arg->arg < nr_args)
val = get_arg(arg, args);
else
@@ -811,6 +831,8 @@ func_event_print(struct trace_iterator *iter, int flags,
trace_seq_printf(s, "%ps->%ps(",
 (void *)entry->parent_ip, (void *)entry->ip);
list_for_each_entry(arg, _event->args, list) {
+   if (arg->func_type == FUNC_TYPE_NULL)
+  

[PATCH 16/18] tracing: Add NULL to skip args for function based events

[Steven Rostedt]

From: "Steven Rostedt (VMware)" 

If args are to be skipped (only care about second, third or later arguments)
then add a NULL to ignore them. For example, if one only wants to record the
third argument of a function, they can perform:

 echo foo(NULL, NULL, u32 arg3) > function_events

Then only the third argument is saved in the function based event.

Signed-off-by: Steven Rostedt (VMware) 
---
 Documentation/trace/function-based-events.rst | 28 +-
 kernel/trace/trace_event_ftrace.c | 34 ++-
 2 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/Documentation/trace/function-based-events.rst 
b/Documentation/trace/function-based-events.rst
index 6c643ea749e7..b90b52b7061d 100644
--- a/Documentation/trace/function-based-events.rst
+++ b/Documentation/trace/function-based-events.rst
@@ -91,7 +91,7 @@ as follows:
 
  ARGS := ARG | ARG ',' ARGS | ''
 
- ARG := TYPE FIELD | TYPE  '=' ADDR | TYPE ADDR | ARG '|' ARG
+ ARG := TYPE FIELD | TYPE  '=' ADDR | TYPE ADDR | ARG '|' ARG | 'NULL'
 
  TYPE := ATOM | ATOM '['  ']' | 'unsigned' TYPE
 
@@ -359,3 +359,29 @@ it will be truncated.
  # echo 'link_path_walk(string name)' > function_events
 
 Gives the same result as above, but does not waste buffer space.
+
+
+NULL arguments
+==
+
+If you are only interested in the second, or later parameter of a function,
+you do not have to record the previous parameters. Just set them as NULL and
+they will not be recorded.
+
+If we only wanted the perm_addr of the net_device of ip_rcv() and not the
+sk_buff, we put a NULL into the first parameter when created the function
+based event.
+
+  # echo 'ip_rcv(NULL, x8[6] perm_addr+558)' > function_events
+
+  # echo 1 > events/functions/ip_rcv/enable
+  # cat trace
+-0 [003] ..s3   165.617114: 
__netif_receive_skb_core->ip_rcv(perm_addr=b4,b5,2f,ce,18,65)
+-0 [003] ..s3   165.617133: 
__netif_receive_skb_core->ip_rcv(perm_addr=b4,b5,2f,ce,18,65)
+-0 [003] ..s3   166.412277: 
__netif_receive_skb_core->ip_rcv(perm_addr=b4,b5,2f,ce,18,65)
+-0 [003] ..s3   166.412797: 
__netif_receive_skb_core->ip_rcv(perm_addr=b4,b5,2f,ce,18,65)
+
+
+NULL can appear in any argument, to have them ignored. Note, skipping arguments
+does not give you access to later arguments if they are not supported by the
+architecture. The architecture only supplies the first set of arguments.
diff --git a/kernel/trace/trace_event_ftrace.c 
b/kernel/trace/trace_event_ftrace.c
index 273c5838a8e2..22bcb67ad184 100644
--- a/kernel/trace/trace_event_ftrace.c
+++ b/kernel/trace/trace_event_ftrace.c
@@ -75,6 +75,7 @@ enum func_states {
FUNC_STATE_ARRAY_END,
FUNC_STATE_VAR,
FUNC_STATE_COMMA,
+   FUNC_STATE_NULL,
FUNC_STATE_END,
FUNC_STATE_ERROR,
 };
@@ -117,6 +118,7 @@ static struct func_type {
int sign;
 } func_types[] = {
FUNC_TYPES,
+   { "NULL",   0,  0 },
{ NULL, 0,  0 }
 };
 
@@ -125,6 +127,7 @@ static struct func_type {
 
 enum {
FUNC_TYPES,
+   FUNC_TYPE_NULL,
FUNC_TYPE_MAX
 };
 
@@ -364,6 +367,8 @@ process_event(struct func_event *fevent, const char *token, 
enum func_states sta
fevent->arg_cnt++;
update_arg = false;
case FUNC_STATE_PIPE:
+   if (strcmp(token, "NULL") == 0)
+   return FUNC_STATE_NULL;
if (strcmp(token, "unsigned") == 0) {
unsign = 2;
return FUNC_STATE_UNSIGNED;
@@ -513,6 +518,19 @@ process_event(struct func_event *fevent, const char 
*token, enum func_states sta
fevent->last_arg->indirect = INDIRECT_FLAG;
return FUNC_STATE_ADDR;
 
+   case FUNC_STATE_NULL:
+   ret = add_arg(fevent, FUNC_TYPE_NULL, 0);
+   if (ret < 0)
+   break;
+   switch (token[0]) {
+   case ')':
+   goto end;
+   case ',':
+   update_arg = true;
+   return FUNC_STATE_COMMA;
+   }
+   break;
+
default:
break;
}
@@ -689,6 +707,8 @@ static void func_event_trace(struct trace_event_file 
*trace_file,
entry->parent_ip = parent_ip;
 
list_for_each_entry(arg, _event->args, list) {
+   if (arg->func_type == FUNC_TYPE_NULL)
+   continue;
if (arg->arg < nr_args)
val = get_arg(arg, args);
else
@@ -811,6 +831,8 @@ func_event_print(struct trace_iterator *iter, int flags,
trace_seq_printf(s, "%ps->%ps(",
 (void *)entry->parent_ip, (void *)entry->ip);
list_for_each_entry(arg, _event->args, list) {
+   if (arg->func_type == FUNC_TYPE_NULL)
+   continue;
if