Add an 'onmatch(matching.event).<synthetic_event_name>(param list)'
hist trigger action which is invoked with the set of variables or
event fields named in the 'param list'.  The result is the generation
of a synthetic event that consists of the values contained in those
variables and/or fields at the time the invoking event was hit.

As an example the below defines a simple synthetic event using a
variable defined on the sched_wakeup_new event, and shows the event
definition with unresolved fields, since the sched_wakeup_new event
with the testpid variable hasn't been defined yet:

    # echo 'wakeup_new_test pid_t pid; int prio' >> \
      /sys/kernel/debug/tracing/synthetic_events

    # cat /sys/kernel/debug/tracing/synthetic_events
      wakeup_new_test pid_t pid; int prio

The following hist trigger both defines a testpid variable and
specifies an onmatch() trace action that uses that variable along with
a non-variable field to generate a wakeup_new_test synthetic event
whenever a sched_wakeup_new event occurs, which because of the 'if
comm == "cyclictest"' filter only happens when the executable is
cyclictest:

    # echo 'hist:keys=testpid=pid:\
      onmatch(sched.sched_wakeup_new).wakeup_new_test($testpid, prio) \
        if comm=="cyclictest"' >> \
      /sys/kernel/debug/tracing/events/sched/sched_wakeup_new/trigger

Creating and displaying a histogram based on those events is now just
a matter of using the fields and new synthetic event in the
tracing/events/synthetic directory, as usual:

    # echo 'hist:keys=pid,prio:sort=pid,prio' >> \
      /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/trigger

Signed-off-by: Tom Zanussi <tom.zanu...@linux.intel.com>
---
 kernel/trace/trace_events_hist.c | 955 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 940 insertions(+), 15 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index e11b3a3..b1f859c 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -59,6 +59,7 @@ struct hist_field {
        unsigned int                    size;
        unsigned int                    offset;
        unsigned int                    is_signed;
+       const char                      *type;
        struct hist_field               *operands[HIST_FIELD_OPERANDS_MAX];
        struct hist_trigger_data        *hist_data;
        struct hist_var                 var;
@@ -243,6 +244,16 @@ struct hist_trigger_attrs {
        unsigned int    n_actions;
 };
 
+struct field_var {
+       struct hist_field       *var;
+       struct hist_field       *val;
+};
+
+struct field_var_hist {
+       struct hist_trigger_data        *hist_data;
+       char                            *cmd;
+};
+
 struct hist_trigger_data {
        struct hist_field               *fields[HIST_FIELDS_MAX];
        unsigned int                    n_vals;
@@ -263,6 +274,14 @@ struct hist_trigger_data {
 
        struct action_data              *actions[HIST_ACTIONS_MAX];
        unsigned int                    n_actions;
+
+       struct hist_field               *synth_var_refs[SYNTH_FIELDS_MAX];
+       unsigned int                    n_synth_var_refs;
+       struct field_var                *field_vars[SYNTH_FIELDS_MAX];
+       unsigned int                    n_field_vars;
+       unsigned int                    n_field_var_str;
+       struct field_var_hist           *field_var_hists[SYNTH_FIELDS_MAX];
+       unsigned int                    n_field_var_hists;
 };
 
 struct synth_field {
@@ -291,7 +310,14 @@ typedef void (*action_fn_t) (struct hist_trigger_data 
*hist_data,
 
 struct action_data {
        action_fn_t             fn;
+       unsigned int            n_params;
+       char                    *params[SYNTH_FIELDS_MAX];
+
        unsigned int            var_ref_idx;
+       char                    *match_event;
+       char                    *match_event_system;
+       char                    *synth_event_name;
+       struct synth_event      *synth_event;
 };
 
 static LIST_HEAD(synth_event_list);
@@ -802,6 +828,50 @@ static struct synth_event *alloc_synth_event(char 
*event_name, int n_fields,
        return event;
 }
 
+static void action_trace(struct hist_trigger_data *hist_data,
+                        struct tracing_map_elt *elt, void *rec,
+                        struct ring_buffer_event *rbe,
+                        struct action_data *data, u64 *var_ref_vals)
+{
+       struct synth_event *event = data->synth_event;
+
+       trace_synth(event, var_ref_vals, data->var_ref_idx);
+}
+
+static bool check_hist_action_refs(struct hist_trigger_data *hist_data,
+                                  struct synth_event *event)
+{
+       unsigned int i;
+
+       for (i = 0; i < hist_data->n_actions; i++) {
+               struct action_data *data = hist_data->actions[i];
+
+               if (data->fn == action_trace && data->synth_event == event)
+                       return true;
+       }
+
+       return false;
+}
+
+static LIST_HEAD(hist_action_list);
+static LIST_HEAD(hist_var_list);
+
+struct hist_var_data {
+       struct list_head list;
+       struct hist_trigger_data *hist_data;
+};
+
+static bool check_synth_action_refs(struct synth_event *event)
+{
+       struct hist_var_data *var_data;
+
+       list_for_each_entry(var_data, &hist_action_list, list)
+               if (check_hist_action_refs(var_data->hist_data, event))
+                       return true;
+
+       return false;
+}
+
 static int create_synth_event(int argc, char **argv)
 {
        struct synth_field *fields[SYNTH_FIELDS_MAX];
@@ -832,15 +902,17 @@ static int create_synth_event(int argc, char **argv)
        event = find_synth_event(name);
        if (event) {
                if (delete_event) {
+                       if (check_synth_action_refs(event)) {
+                               ret = -EBUSY;
+                               goto out;
+                       }
                        remove_synth_event(event);
                        goto err;
                } else
                        ret = -EEXIST;
                goto out;
-       } else if (delete_event) {
-               ret = -EINVAL;
+       } else if (delete_event)
                goto out;
-       }
 
        if (argc < 2) {
                ret = -EINVAL;
@@ -891,11 +963,18 @@ static int release_all_synth_events(void)
 
        mutex_lock(&synth_event_mutex);
 
+       list_for_each_entry(event, &synth_event_list, list) {
+               if (check_synth_action_refs(event)) {
+                       ret = -EBUSY;
+                       goto out;
+               }
+       }
+
        list_for_each_entry_safe(event, e, &synth_event_list, list) {
                remove_synth_event(event);
                free_synth_event(event);
        }
-
+ out:
        mutex_unlock(&synth_event_mutex);
 
        return ret;
@@ -992,13 +1071,6 @@ static u64 hist_field_timestamp(struct hist_field 
*hist_field,
        return ts;
 }
 
-static LIST_HEAD(hist_var_list);
-
-struct hist_var_data {
-       struct list_head list;
-       struct hist_trigger_data *hist_data;
-};
-
 static struct hist_field *check_var_ref(struct hist_field *hist_field,
                                        struct hist_trigger_data *var_data,
                                        unsigned int var_idx)
@@ -1248,6 +1320,7 @@ static struct hist_field *find_event_var(const char 
*system,
 struct hist_elt_data {
        char *comm;
        u64 *var_ref_vals;
+       char *field_var_str[SYNTH_FIELDS_MAX];
 };
 
 static u64 hist_field_var_ref(struct hist_field *hist_field,
@@ -1415,11 +1488,21 @@ static void destroy_hist_trigger_attrs(struct 
hist_trigger_attrs *attrs)
 
 static int parse_action(char *str, struct hist_trigger_attrs *attrs)
 {
-       int ret = 0;
+       int ret = -EINVAL;
 
        if (attrs->n_actions >= HIST_ACTIONS_MAX)
                return ret;
 
+       if ((strncmp(str, "onmatch(", strlen("onmatch(")) == 0)) {
+               attrs->action_str[attrs->n_actions] = kstrdup(str, GFP_KERNEL);
+               if (!attrs->action_str[attrs->n_actions]) {
+                       ret = -ENOMEM;
+                       return ret;
+               }
+               attrs->n_actions++;
+               ret = 0;
+       }
+
        return ret;
 }
 
@@ -1525,7 +1608,14 @@ static inline void save_comm(char *comm, struct 
task_struct *task)
 
 static void hist_trigger_elt_data_free(struct tracing_map_elt *elt)
 {
+       struct hist_trigger_data *hist_data = elt->map->private_data;
        struct hist_elt_data *private_data = elt->private_data;
+       unsigned int i, n_str;
+
+       n_str = hist_data->n_field_var_str;
+
+       for (i = 0; i < n_str; i++)
+               kfree(private_data->field_var_str[i]);
 
        kfree(private_data->comm);
        kfree(private_data);
@@ -1537,7 +1627,7 @@ static int hist_trigger_elt_data_alloc(struct 
tracing_map_elt *elt)
        unsigned int size = TASK_COMM_LEN + 1;
        struct hist_elt_data *elt_data;
        struct hist_field *key_field;
-       unsigned int i;
+       unsigned int i, n_str;
 
        elt->private_data = elt_data = kzalloc(sizeof(*elt_data), GFP_KERNEL);
        if (!elt_data)
@@ -1557,6 +1647,16 @@ static int hist_trigger_elt_data_alloc(struct 
tracing_map_elt *elt)
                }
        }
 
+       n_str = hist_data->n_field_var_str;
+
+       for (i = 0; i < n_str; i++) {
+               elt_data->field_var_str[i] = kzalloc(size, GFP_KERNEL);
+               if (!elt_data->field_var_str[i]) {
+                       hist_trigger_elt_data_free(elt);
+                       return -ENOMEM;
+               }
+       }
+
        return 0;
 }
 
@@ -1674,6 +1774,7 @@ static void destroy_hist_field(struct hist_field 
*hist_field,
 
        kfree(hist_field->var.name);
        kfree(hist_field->name);
+       kfree(hist_field->type);
 
        kfree(hist_field);
 }
@@ -1704,6 +1805,10 @@ static struct hist_field *create_hist_field(struct 
hist_trigger_data *hist_data,
 
        if (flags & HIST_FIELD_FL_HITCOUNT) {
                hist_field->fn = hist_field_counter;
+               hist_field->size = sizeof(u64);
+               hist_field->type = kstrdup("u64", GFP_KERNEL);
+               if (!hist_field->type)
+                       goto free;
                goto out;
        }
 
@@ -1717,12 +1822,18 @@ static struct hist_field *create_hist_field(struct 
hist_trigger_data *hist_data,
                hist_field->fn = hist_field_log2;
                hist_field->operands[0] = create_hist_field(hist_data, field, 
fl, NULL);
                hist_field->size = hist_field->operands[0]->size;
+               hist_field->type = kstrdup(hist_field->operands[0]->type, 
GFP_KERNEL);
+               if (!hist_field->type)
+                       goto free;
                goto out;
        }
 
        if (flags & HIST_FIELD_FL_TIMESTAMP) {
                hist_field->fn = hist_field_timestamp;
                hist_field->size = sizeof(u64);
+               hist_field->type = kstrdup("u64", GFP_KERNEL);
+               if (!hist_field->type)
+                       goto free;
                goto out;
        }
 
@@ -1731,6 +1842,10 @@ static struct hist_field *create_hist_field(struct 
hist_trigger_data *hist_data,
 
        if (is_string_field(field)) {
                flags |= HIST_FIELD_FL_STRING;
+               hist_field->size = MAX_FILTER_STR_VAL;
+               hist_field->type = kstrdup(field->type, GFP_KERNEL);
+               if (!hist_field->type)
+                       goto free;
 
                if (field->filter_type == FILTER_STATIC_STRING)
                        hist_field->fn = hist_field_string;
@@ -1739,6 +1854,12 @@ static struct hist_field *create_hist_field(struct 
hist_trigger_data *hist_data,
                else
                        hist_field->fn = hist_field_pstring;
        } else {
+               hist_field->size = field->size;
+               hist_field->is_signed = field->is_signed;
+               hist_field->type = kstrdup(field->type, GFP_KERNEL);
+               if (!hist_field->type)
+                       goto free;
+
                hist_field->fn = select_value_fn(field->size,
                                                 field->is_signed);
                if (!hist_field->fn) {
@@ -1786,7 +1907,10 @@ static struct hist_field *create_var_ref(struct 
hist_field *var_field)
                ref_field->size = var_field->size;
                ref_field->is_signed = var_field->is_signed;
                ref_field->name = kstrdup(var_field->var.name, GFP_KERNEL);
-               if (!ref_field->name) {
+               ref_field->type = kstrdup(var_field->type, GFP_KERNEL);
+               if (!ref_field->name || !ref_field->type) {
+                       kfree(ref_field->name);
+                       kfree(ref_field->type);
                        destroy_hist_field(ref_field, 0);
                        return NULL;
                }
@@ -1970,6 +2094,11 @@ static struct hist_field *parse_unary(struct 
hist_trigger_data *hist_data,
        expr->operands[0] = operand1;
        expr->operator = FIELD_OP_UNARY_MINUS;
        expr->name = expr_str(expr, 0);
+       expr->type = kstrdup(operand1->type, GFP_KERNEL);
+       if (!expr->type) {
+               ret = -ENOMEM;
+               goto free;
+       }
 
        return expr;
  free:
@@ -2053,6 +2182,11 @@ static struct hist_field *parse_expr(struct 
hist_trigger_data *hist_data,
        expr->operands[1] = operand2;
        expr->operator = field_op;
        expr->name = expr_str(expr, 0);
+       expr->type = kstrdup(operand1->type, GFP_KERNEL);
+       if (!expr->type) {
+               ret = -ENOMEM;
+               goto free;
+       }
 
        switch (field_op) {
        case FIELD_OP_MINUS:
@@ -2074,6 +2208,718 @@ static struct hist_field *parse_expr(struct 
hist_trigger_data *hist_data,
        return ERR_PTR(ret);
 }
 
+static struct hist_var_data *find_actions(struct hist_trigger_data *hist_data)
+{
+       struct hist_var_data *var_data, *found = NULL;
+
+       list_for_each_entry(var_data, &hist_action_list, list) {
+               if (var_data->hist_data == hist_data) {
+                       found = var_data;
+                       break;
+               }
+       }
+
+       return found;
+}
+
+static int save_hist_actions(struct hist_trigger_data *hist_data)
+{
+       struct hist_var_data *var_data;
+
+       var_data = find_actions(hist_data);
+       if (var_data)
+               return 0;
+
+       var_data = kzalloc(sizeof(*var_data), GFP_KERNEL);
+       if (!var_data)
+               return -ENOMEM;
+
+       var_data->hist_data = hist_data;
+       list_add(&var_data->list, &hist_action_list);
+
+       return 0;
+}
+
+static void remove_hist_actions(struct hist_trigger_data *hist_data)
+{
+       struct hist_var_data *var_data;
+
+       var_data = find_actions(hist_data);
+       if (!var_data)
+               return;
+
+       list_del(&var_data->list);
+
+       kfree(var_data);
+}
+
+static char *find_trigger_filter(struct hist_trigger_data *hist_data,
+                                struct trace_event_file *file)
+{
+       struct event_trigger_data *test;
+
+       list_for_each_entry_rcu(test, &file->triggers, list) {
+               if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+                       if (test->private_data == hist_data)
+                               return test->filter_str;
+               }
+       }
+
+       return NULL;
+}
+
+static struct event_command trigger_hist_cmd;
+static int event_hist_trigger_func(struct event_command *cmd_ops,
+                                  struct trace_event_file *file,
+                                  char *glob, char *cmd, char *param);
+
+static bool compatible_keys(struct hist_trigger_data *target_hist_data,
+                           struct hist_trigger_data *hist_data,
+                           unsigned int n_keys)
+{
+       struct hist_field *target_hist_field, *hist_field;
+       unsigned int n, i, j;
+
+       if (hist_data->n_fields - hist_data->n_vals != n_keys)
+               return false;
+
+       i = hist_data->n_vals;
+       j = target_hist_data->n_vals;
+
+       for (n = 0; n < n_keys; n++) {
+               hist_field = hist_data->fields[i + n];
+               target_hist_field = hist_data->fields[j + n];
+
+               if (strcmp(hist_field->type, target_hist_field->type) != 0)
+                       return false;
+               if (hist_field->size != target_hist_field->size)
+                       return false;
+               if (hist_field->is_signed != target_hist_field->is_signed)
+                       return false;
+       }
+
+       return true;
+}
+
+static struct hist_trigger_data *
+find_compatible_hist(struct hist_trigger_data *target_hist_data,
+                    struct trace_event_file *file)
+{
+       struct hist_trigger_data *hist_data;
+       struct event_trigger_data *test;
+       unsigned int n_keys;
+
+       n_keys = target_hist_data->n_fields - target_hist_data->n_vals;
+
+       list_for_each_entry_rcu(test, &file->triggers, list) {
+               if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+                       hist_data = test->private_data;
+
+                       if (compatible_keys(target_hist_data, hist_data, 
n_keys))
+                               return hist_data;
+               }
+       }
+
+       return NULL;
+}
+
+static struct trace_event_file *event_file(char *system, char *event_name)
+{
+       struct trace_event_file *file;
+       struct trace_array *tr;
+
+       tr = top_trace_array();
+       if (!tr)
+               return ERR_PTR(-ENODEV);
+
+       file = find_event_file(tr, system, event_name);
+       if (!file)
+               return ERR_PTR(-EINVAL);
+
+       return file;
+}
+
+static struct hist_field *
+create_field_var_hist(struct hist_trigger_data *target_hist_data,
+                     char *system, char *event_name, char *field_name)
+{
+       struct hist_field *event_var = ERR_PTR(-EINVAL);
+       struct hist_trigger_data *hist_data;
+       unsigned int i, n, first = true;
+       struct field_var_hist *var_hist;
+       struct trace_event_file *file;
+       struct hist_field *key_field;
+       struct trace_array *tr;
+       char *saved_filter;
+       char *cmd;
+       int ret;
+
+       if (target_hist_data->n_field_var_hists >= SYNTH_FIELDS_MAX)
+               return ERR_PTR(-EINVAL);
+
+       tr = top_trace_array();
+       if (!tr)
+               return ERR_PTR(-ENODEV);
+
+       file = event_file(system, event_name);
+       if (IS_ERR(file)) {
+               ret = PTR_ERR(file);
+               return ERR_PTR(ret);
+       }
+
+       hist_data = find_compatible_hist(target_hist_data, file);
+       if (!hist_data)
+               return ERR_PTR(-EINVAL);
+
+       var_hist = kzalloc(sizeof(*var_hist), GFP_KERNEL);
+       if (!var_hist)
+               return ERR_PTR(-ENOMEM);
+
+       cmd = kzalloc(MAX_FILTER_STR_VAL, GFP_KERNEL);
+       if (!cmd) {
+               kfree(var_hist);
+               return ERR_PTR(-ENOMEM);
+       }
+
+       strcat(cmd, "keys=");
+
+       for_each_hist_key_field(i, hist_data) {
+               key_field = hist_data->fields[i];
+               if (!first)
+                       strcat(cmd, ",");
+               strcat(cmd, key_field->field->name);
+               first = false;
+       }
+
+       strcat(cmd, ":synthetic_");
+       strcat(cmd, field_name);
+       strcat(cmd, "=");
+       strcat(cmd, field_name);
+
+       saved_filter = find_trigger_filter(hist_data, file);
+       if (saved_filter) {
+               strcat(cmd, " if ");
+               strcat(cmd, saved_filter);
+       }
+
+       var_hist->cmd = kstrdup(cmd, GFP_KERNEL);
+       if (!var_hist->cmd) {
+               kfree(cmd);
+               kfree(var_hist);
+               return ERR_PTR(-ENOMEM);
+       }
+
+       var_hist->hist_data = hist_data;
+
+       ret = event_hist_trigger_func(&trigger_hist_cmd, file,
+                                     "", "hist", cmd);
+       if (ret) {
+               kfree(cmd);
+               kfree(var_hist->cmd);
+               kfree(var_hist);
+               return ERR_PTR(ret);
+       }
+
+       strcpy(cmd, "synthetic_");
+       strcat(cmd, field_name);
+
+       event_var = find_event_var(system, event_name, cmd);
+       if (!event_var) {
+               kfree(cmd);
+               kfree(var_hist->cmd);
+               kfree(var_hist);
+               return ERR_PTR(-EINVAL);
+       }
+
+       n = target_hist_data->n_field_var_hists;
+       target_hist_data->field_var_hists[n] = var_hist;
+       target_hist_data->n_field_var_hists++;
+
+       return event_var;
+}
+
+static struct hist_field *
+find_target_event_var(struct hist_trigger_data *hist_data,
+                     char *system, char *event_name, char *var_name)
+{
+       struct trace_event_file *file = hist_data->event_file;
+       struct hist_field *hist_field = NULL;
+
+       if (system) {
+               struct trace_event_call *call;
+
+               if (!event_name)
+                       return NULL;
+
+               call = file->event_call;
+
+               if (strcmp(system, call->class->system) != 0)
+                       return NULL;
+
+               if (strcmp(event_name, trace_event_name(call)) != 0)
+                       return NULL;
+       }
+
+       hist_field = find_var_field(hist_data, var_name);
+
+       return hist_field;
+}
+
+static inline void __update_field_vars(struct tracing_map_elt *elt,
+                                      struct ring_buffer_event *rbe,
+                                      void *rec,
+                                      struct field_var **field_vars,
+                                      unsigned int n_field_vars,
+                                      unsigned int field_var_str_start)
+{
+       struct hist_elt_data *elt_data = elt->private_data;
+       unsigned int i, j, var_idx;
+       u64 var_val;
+
+       for (i = 0, j = field_var_str_start; i < n_field_vars; i++) {
+               struct field_var *field_var = field_vars[i];
+               struct hist_field *var = field_var->var;
+               struct hist_field *val = field_var->val;
+
+               var_val = val->fn(val, elt, rbe, rec);
+               var_idx = var->var.idx;
+
+               if (val->flags & HIST_FIELD_FL_STRING) {
+                       char *str = elt_data->field_var_str[j++];
+
+                       memcpy(str, (char *)(uintptr_t)var_val,
+                              TASK_COMM_LEN + 1);
+                       var_val = (u64)(uintptr_t)str;
+               }
+               tracing_map_set_var(elt, var_idx, var_val);
+       }
+}
+
+static void update_field_vars(struct hist_trigger_data *hist_data,
+                             struct tracing_map_elt *elt,
+                             struct ring_buffer_event *rbe,
+                             void *rec)
+{
+       __update_field_vars(elt, rbe, rec, hist_data->field_vars,
+                           hist_data->n_field_vars, 0);
+}
+
+static struct hist_field *create_var(struct hist_trigger_data *hist_data,
+                                    struct trace_event_file *file,
+                                    char *name, int size, const char *type)
+{
+       struct hist_field *var;
+       int idx;
+
+       if (find_var(file, name) && !hist_data->remove) {
+               var = ERR_PTR(-EINVAL);
+               goto out;
+       }
+
+       var = kzalloc(sizeof(struct hist_field), GFP_KERNEL);
+       if (!var) {
+               var = ERR_PTR(-ENOMEM);
+               goto out;
+       }
+
+       idx = tracing_map_add_var(hist_data->map);
+       if (idx < 0) {
+               kfree(var);
+               var = ERR_PTR(-EINVAL);
+               goto out;
+       }
+
+       var->flags = HIST_FIELD_FL_VAR;
+       var->var.idx = idx;
+       var->var.hist_data = var->hist_data = hist_data;
+       var->size = size;
+       var->var.name = kstrdup(name, GFP_KERNEL);
+       var->type = kstrdup(type, GFP_KERNEL);
+       if (!var->var.name || !var->type) {
+               kfree(var->var.name);
+               kfree(var->type);
+               kfree(var);
+               var = ERR_PTR(-ENOMEM);
+       }
+ out:
+       return var;
+}
+
+static struct field_var *create_field_var(struct hist_trigger_data *hist_data,
+                                         struct trace_event_file *file,
+                                         char *field_name)
+{
+       struct hist_field *val = NULL, *var = NULL;
+       unsigned long flags = HIST_FIELD_FL_VAR;
+       struct field_var *field_var;
+       int ret = 0;
+
+       if (hist_data->n_field_vars >= SYNTH_FIELDS_MAX) {
+               ret = -EINVAL;
+               goto err;
+       }
+
+       val = parse_atom(hist_data, file, field_name, &flags, NULL);
+       if (IS_ERR(val)) {
+               ret = PTR_ERR(val);
+               goto err;
+       }
+
+       var = create_var(hist_data, file, field_name, val->size, val->type);
+       if (IS_ERR(var)) {
+               kfree(val);
+               ret = PTR_ERR(var);
+               goto err;
+       }
+
+       field_var = kzalloc(sizeof(struct field_var), GFP_KERNEL);
+       if (!field_var) {
+               kfree(val);
+               kfree(var);
+               ret =  -ENOMEM;
+               goto err;
+       }
+
+       field_var->var = var;
+       field_var->val = val;
+ out:
+       return field_var;
+ err:
+       field_var = ERR_PTR(ret);
+       goto out;
+}
+
+static struct field_var *
+create_target_field_var(struct hist_trigger_data *hist_data,
+                       char *system, char *event_name, char *var_name)
+{
+       struct trace_event_file *file = hist_data->event_file;
+
+       if (system) {
+               struct trace_event_call *call;
+
+               if (!event_name)
+                       return NULL;
+
+               call = file->event_call;
+
+               if (strcmp(system, call->class->system) != 0)
+                       return NULL;
+
+               if (strcmp(event_name, trace_event_name(call)) != 0)
+                       return NULL;
+       }
+
+       return create_field_var(hist_data, file, var_name);
+}
+
+static void onmatch_destroy(struct action_data *data)
+{
+       unsigned int i;
+
+       kfree(data->match_event);
+       kfree(data->match_event_system);
+       kfree(data->synth_event_name);
+
+       for (i = 0; i < data->n_params; i++)
+               kfree(data->params[i]);
+
+       kfree(data);
+}
+
+static void destroy_field_var(struct field_var *field_var)
+{
+       if (!field_var)
+               return;
+
+       destroy_hist_field(field_var->var, 0);
+       destroy_hist_field(field_var->val, 0);
+
+       kfree(field_var);
+}
+
+static void destroy_field_vars(struct hist_trigger_data *hist_data)
+{
+       unsigned int i;
+
+       for (i = 0; i < hist_data->n_field_vars; i++)
+               destroy_field_var(hist_data->field_vars[i]);
+}
+
+static void save_field_var(struct hist_trigger_data *hist_data,
+                          struct field_var *field_var)
+{
+       hist_data->field_vars[hist_data->n_field_vars++] = field_var;
+
+       if (field_var->val->flags & HIST_FIELD_FL_STRING)
+               hist_data->n_field_var_str++;
+}
+
+static void destroy_synth_var_refs(struct hist_trigger_data *hist_data)
+{
+       unsigned int i;
+
+       for (i = 0; i < hist_data->n_synth_var_refs; i++)
+               destroy_hist_field(hist_data->synth_var_refs[i], 0);
+}
+
+static void save_synth_var_ref(struct hist_trigger_data *hist_data,
+                        struct hist_field *var_ref)
+{
+       hist_data->synth_var_refs[hist_data->n_synth_var_refs++] = var_ref;
+
+       hist_data->var_refs[hist_data->n_var_refs] = var_ref;
+       var_ref->var_ref_idx = hist_data->n_var_refs++;
+}
+
+static int check_synth_field(struct synth_event *event,
+                            struct hist_field *hist_field,
+                            unsigned int field_pos)
+{
+       struct synth_field *field;
+
+       if (field_pos >= event->n_fields)
+               return -EINVAL;
+
+       field = event->fields[field_pos];
+
+       if (strcmp(field->type, hist_field->type) != 0)
+               return -EINVAL;
+
+       return 0;
+}
+
+static int parse_action_params(char *params, struct action_data *data)
+{
+       char *param, *saved_param;
+       int ret = 0;
+
+       while (params) {
+               if (data->n_params >= SYNTH_FIELDS_MAX)
+                       goto out;
+
+               param = strsep(&params, ",");
+               if (!param)
+                       goto out;
+
+               param = strstrip(param);
+               if (strlen(param) < 2) {
+                       ret = -EINVAL;
+                       goto out;
+               }
+
+               saved_param = kstrdup(param, GFP_KERNEL);
+               if (!saved_param) {
+                       ret = -ENOMEM;
+                       goto out;
+               }
+
+               data->params[data->n_params++] = saved_param;
+       }
+ out:
+       return ret;
+}
+
+static struct hist_field *
+onmatch_find_var(struct hist_trigger_data *hist_data, struct action_data *data,
+                char *system, char *event, char *var)
+{
+       struct hist_field *hist_field;
+
+       var++; /* skip '$' */
+
+       hist_field = find_target_event_var(hist_data, system, event, var);
+       if (!hist_field) {
+               if (!system) {
+                       system = data->match_event_system;
+                       event = data->match_event;
+               }
+
+               hist_field = find_event_var(system, event, var);
+       }
+
+       return hist_field;
+}
+
+static struct hist_field *
+onmatch_create_field_var(struct hist_trigger_data *hist_data,
+                        struct action_data *data, char *system,
+                        char *event, char *var)
+{
+       struct hist_field *hist_field = NULL;
+       struct field_var *field_var;
+
+       field_var = create_target_field_var(hist_data, system, event, var);
+       if (IS_ERR(field_var))
+               goto out;
+
+       if (field_var) {
+               save_field_var(hist_data, field_var);
+               hist_field = field_var->var;
+       } else {
+               if (!system) {
+                       system = data->match_event_system;
+                       event = data->match_event;
+               }
+
+               hist_field = create_field_var_hist(hist_data, system, event, 
var);
+               if (IS_ERR(hist_field))
+                       goto free;
+       }
+ out:
+       return hist_field;
+ free:
+       destroy_field_var(field_var);
+       hist_field = NULL;
+       goto out;
+}
+
+static int onmatch_create(struct hist_trigger_data *hist_data,
+                         struct trace_event_file *file,
+                         struct action_data *data)
+{
+       char *event_name, *param, *system = NULL;
+       struct hist_field *hist_field, *var_ref;
+       unsigned int i, var_ref_idx;
+       unsigned int field_pos = 0;
+       struct synth_event *event;
+       int ret = 0;
+
+       mutex_lock(&synth_event_mutex);
+
+       event = find_synth_event(data->synth_event_name);
+       if (!event) {
+               ret = -EINVAL;
+               goto out;
+       }
+
+       var_ref_idx = hist_data->n_var_refs;
+
+       for (i = 0; i < data->n_params; i++) {
+               char *p;
+
+               p = param = kstrdup(data->params[i], GFP_KERNEL);
+               if (!param)
+                       goto out;
+
+               system = strsep(&param, ".");
+               if (!param) {
+                       param = (char *)system;
+                       system = event_name = NULL;
+               } else {
+                       event_name = strsep(&param, ".");
+                       if (!param) {
+                               kfree(p);
+                               ret = -EINVAL;
+                               goto out;
+                       }
+               }
+
+               if (param[0] == '$')
+                       hist_field = onmatch_find_var(hist_data, data, system,
+                                                     event_name, param);
+               else
+                       hist_field = onmatch_create_field_var(hist_data, data,
+                                                             system,
+                                                             event_name,
+                                                             param);
+
+               if (!hist_field) {
+                       kfree(p);
+                       ret = -EINVAL;
+                       goto out;
+               }
+
+               if (check_synth_field(event, hist_field, field_pos) == 0) {
+                       var_ref = create_var_ref(hist_field);
+                       if (!var_ref) {
+                               kfree(p);
+                               ret = -ENOMEM;
+                               goto out;
+                       }
+
+                       save_synth_var_ref(hist_data, var_ref);
+                       field_pos++;
+                       kfree(p);
+                       continue;
+               }
+
+               kfree(p);
+               ret = -EINVAL;
+               goto out;
+       }
+
+       if (field_pos != event->n_fields) {
+               ret = -EINVAL;
+               goto out;
+       }
+
+       data->fn = action_trace;
+       data->synth_event = event;
+       data->var_ref_idx = var_ref_idx;
+       hist_data->actions[hist_data->n_actions++] = data;
+       save_hist_actions(hist_data);
+ out:
+       mutex_unlock(&synth_event_mutex);
+
+       return ret;
+}
+
+static struct action_data *onmatch_parse(char *str)
+{
+       char *match_event, *match_event_system;
+       char *synth_event_name, *params;
+       struct action_data *data;
+       int ret = -EINVAL;
+
+       data = kzalloc(sizeof(*data), GFP_KERNEL);
+       if (!data)
+               return ERR_PTR(-ENOMEM);
+
+       match_event = strsep(&str, ")");
+       if (!match_event || !str)
+               goto free;
+
+       match_event_system = strsep(&match_event, ".");
+       if (!match_event)
+               goto free;
+
+       if (IS_ERR(event_file(match_event_system, match_event)))
+               goto free;
+
+       data->match_event = kstrdup(match_event, GFP_KERNEL);
+       data->match_event_system = kstrdup(match_event_system, GFP_KERNEL);
+
+       strsep(&str, ".");
+       if (!str)
+               goto free;
+
+       synth_event_name = strsep(&str, "(");
+       if (!synth_event_name || !str)
+               goto free;
+       data->synth_event_name = kstrdup(synth_event_name, GFP_KERNEL);
+
+       params = strsep(&str, ")");
+       if (!params || !str || (str && strlen(str)))
+               goto free;
+
+       ret = parse_action_params(params, data);
+       if (ret)
+               goto free;
+
+       if (!data->match_event_system || !data->match_event ||
+           !data->synth_event_name) {
+               ret = -ENOMEM;
+               goto free;
+       }
+ out:
+       return data;
+ free:
+       onmatch_destroy(data);
+       data = ERR_PTR(ret);
+       goto out;
+}
+
 static int create_hitcount_val(struct hist_trigger_data *hist_data)
 {
        hist_data->fields[HITCOUNT_IDX] =
@@ -2465,19 +3311,37 @@ static void destroy_actions(struct hist_trigger_data 
*hist_data)
        for (i = 0; i < hist_data->n_actions; i++) {
                struct action_data *data = hist_data->actions[i];
 
-               kfree(data);
+               if (data->fn == action_trace)
+                       onmatch_destroy(data);
+               else
+                       kfree(data);
        }
 }
 
 static int create_actions(struct hist_trigger_data *hist_data,
                          struct trace_event_file *file)
 {
+       struct action_data *data;
        unsigned int i;
        int ret = 0;
        char *str;
 
        for (i = 0; i < hist_data->attrs->n_actions; i++) {
                str = hist_data->attrs->action_str[i];
+
+               if (strncmp(str, "onmatch(", strlen("onmatch(")) == 0) {
+                       char *action_str = str + strlen("onmatch(");
+
+                       data = onmatch_parse(action_str);
+                       if (IS_ERR(data))
+                               return PTR_ERR(data);
+
+                       ret = onmatch_create(hist_data, file, data);
+                       if (ret) {
+                               onmatch_destroy(data);
+                               return ret;
+                       }
+               }
        }
 
        return ret;
@@ -2494,6 +3358,26 @@ static void print_actions(struct seq_file *m,
        }
 }
 
+static void print_onmatch_spec(struct seq_file *m,
+                              struct hist_trigger_data *hist_data,
+                              struct action_data *data)
+{
+       unsigned int i;
+
+       seq_printf(m, ":onmatch(%s.%s).", data->match_event_system,
+                  data->match_event);
+
+       seq_printf(m, "%s(", data->synth_event->name);
+
+       for (i = 0; i < data->n_params; i++) {
+               if (i)
+                       seq_puts(m, ",");
+               seq_printf(m, "%s", data->params[i]);
+       }
+
+       seq_puts(m, ")");
+}
+
 static void print_actions_spec(struct seq_file *m,
                               struct hist_trigger_data *hist_data)
 {
@@ -2501,6 +3385,19 @@ static void print_actions_spec(struct seq_file *m,
 
        for (i = 0; i < hist_data->n_actions; i++) {
                struct action_data *data = hist_data->actions[i];
+
+               if (data->fn == action_trace)
+                       print_onmatch_spec(m, hist_data, data);
+       }
+}
+
+static void destroy_field_var_hists(struct hist_trigger_data *hist_data)
+{
+       unsigned int i;
+
+       for (i = 0; i < hist_data->n_field_var_hists; i++) {
+               kfree(hist_data->field_var_hists[i]->cmd);
+               kfree(hist_data->field_var_hists[i]);
        }
 }
 
@@ -2514,6 +3411,9 @@ static void destroy_hist_data(struct hist_trigger_data 
*hist_data)
        tracing_map_destroy(hist_data->map);
 
        destroy_actions(hist_data);
+       destroy_field_vars(hist_data);
+       destroy_field_var_hists(hist_data);
+       destroy_synth_var_refs(hist_data);
 
        kfree(hist_data);
 }
@@ -2648,6 +3548,8 @@ static void hist_trigger_elt_update(struct 
hist_trigger_data *hist_data,
                        tracing_map_set_var(elt, var_idx, hist_val);
                }
        }
+
+       update_field_vars(hist_data, elt, rbe, rec);
 }
 
 static inline void add_to_key(char *compound_key, void *key,
@@ -2861,6 +3763,8 @@ static void hist_trigger_stacktrace_print(struct seq_file 
*m,
                }
        }
 
+       print_actions(m, hist_data, elt);
+
        seq_puts(m, "\n");
 }
 
@@ -3128,6 +4032,8 @@ static void event_hist_trigger_free(struct 
event_trigger_ops *ops,
 
                remove_hist_vars(hist_data);
 
+               remove_hist_actions(hist_data);
+
                destroy_hist_data(hist_data);
        }
 }
@@ -3390,6 +4296,21 @@ static bool hist_trigger_check_refs(struct 
event_trigger_data *data,
        return false;
 }
 
+static void unregister_field_var_hists(struct hist_trigger_data *hist_data)
+{
+       struct trace_event_file *file;
+       unsigned int i;
+       char *cmd;
+       int ret;
+
+       for (i = 0; i < hist_data->n_field_var_hists; i++) {
+               file = hist_data->field_var_hists[i]->hist_data->event_file;
+               cmd = hist_data->field_var_hists[i]->cmd;
+               ret = event_hist_trigger_func(&trigger_hist_cmd, file,
+                                             "!hist", "hist", cmd);
+       }
+}
+
 static void hist_unregister_trigger(char *glob, struct event_trigger_ops *ops,
                                    struct event_trigger_data *data,
                                    struct trace_event_file *file)
@@ -3405,6 +4326,7 @@ static void hist_unregister_trigger(char *glob, struct 
event_trigger_ops *ops,
                if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
                        if (!hist_trigger_match(data, test, named_data, false))
                                continue;
+                       unregister_field_var_hists(test->private_data);
                        unregistered = true;
                        list_del_rcu(&test->list);
                        trace_event_trigger_enable_disable(file, 0);
@@ -3448,6 +4370,7 @@ static void hist_unreg_all(struct trace_event_file *file)
 
        list_for_each_entry_safe(test, n, &file->triggers, list) {
                if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+                       unregister_field_var_hists(test->private_data);
                        list_del_rcu(&test->list);
                        trace_event_trigger_enable_disable(file, 0);
                        update_cond_flag(file);
@@ -3571,6 +4494,8 @@ static int event_hist_trigger_func(struct event_command 
*cmd_ops,
 
        remove_hist_vars(hist_data);
 
+       remove_hist_actions(hist_data);
+
        kfree(trigger_data);
        destroy_hist_data(hist_data);
 
-- 
1.9.3

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