tracing: Allow triggers to filter for CPU ids and process names

By extending the filter rules by more generic fields
we can write triggers filters like

  echo 'stacktrace if cpu == 1' > \
	/sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger

or

  echo 'stacktrace if comm == sshd'  > \
	/sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger

CPU and COMM are not part of struct trace_entry. We could add the two
new fields to ftrace_common_field list and fix up all depending
sides. But that looks pretty ugly. Another thing I would like to
avoid that the 'format' file contents changes.

All this can be avoided by introducing another list which contains
non field members of struct trace_entry.

Link: http://lkml.kernel.org/r/1439210146-24707-1-git-send-email-daniel.wagner@bmw-carit.de

Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 77 insertions, 2 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 404a372ad85a..7ca09cdc20c2 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -30,6 +30,7 @@
 DEFINE_MUTEX(event_mutex);
 
 LIST_HEAD(ftrace_events);
+static LIST_HEAD(ftrace_generic_fields);
 static LIST_HEAD(ftrace_common_fields);
 
 #define GFP_TRACE (GFP_KERNEL | __GFP_ZERO)
@@ -94,6 +95,10 @@ trace_find_event_field(struct trace_event_call *call, char *name)
         struct ftrace_event_field *field;
         struct list_head *head;
 
+        field = __find_event_field(&ftrace_generic_fields, name);
+        if (field)
+                return field;
+
         field = __find_event_field(&ftrace_common_fields, name);
         if (field)
                 return field;
@@ -144,6 +149,13 @@ int trace_define_field(struct trace_event_call *call, const char *type,
 }
 EXPORT_SYMBOL_GPL(trace_define_field);
 
+#define __generic_field(type, item, filter_type)                        \
+        ret = __trace_define_field(&ftrace_generic_fields, #type,       \
+                                   #item, 0, 0, is_signed_type(type),   \
+                                   filter_type);                        \
+        if (ret)                                                        \
+                return ret;
+
 #define __common_field(type, item)                                      \
         ret = __trace_define_field(&ftrace_common_fields, #type,        \
                                    "common_" #item,                     \
@@ -153,6 +165,16 @@ EXPORT_SYMBOL_GPL(trace_define_field);
         if (ret)                                                        \
                 return ret;
 
+static int trace_define_generic_fields(void)
+{
+        int ret;
+
+        __generic_field(int, cpu, FILTER_OTHER);
+        __generic_field(char *, comm, FILTER_PTR_STRING);
+
+        return ret;
+}
+
 static int trace_define_common_fields(void)
 {
         int ret;
@@ -2671,6 +2693,9 @@ static __init int event_trace_init(void)
         if (!entry)
                 pr_warn("Could not create tracefs 'available_events' entry\n");
 
+        if (trace_define_generic_fields())
+                pr_warn("tracing: Failed to allocated generic fields");
+
         if (trace_define_common_fields())
                 pr_warn("tracing: Failed to allocate common fields");
 
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index d81d6f302b14..bd1bf184c5c9 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -252,6 +252,50 @@ static int filter_pred_strloc(struct filter_pred *pred, void *event)
         return match;
 }
 
+/* Filter predicate for CPUs. */
+static int filter_pred_cpu(struct filter_pred *pred, void *event)
+{
+        int cpu, cmp;
+        int match = 0;
+
+        cpu = raw_smp_processor_id();
+        cmp = pred->val;
+
+        switch (pred->op) {
+        case OP_EQ:
+                match = cpu == cmp;
+                break;
+        case OP_LT:
+                match = cpu < cmp;
+                break;
+        case OP_LE:
+                match = cpu <= cmp;
+                break;
+        case OP_GT:
+                match = cpu > cmp;
+                break;
+        case OP_GE:
+                match = cpu >= cmp;
+                break;
+        default:
+                break;
+        }
+
+        return !!match == !pred->not;
+}
+
+/* Filter predicate for COMM. */
+static int filter_pred_comm(struct filter_pred *pred, void *event)
+{
+        int cmp, match;
+
+        cmp = pred->regex.match(current->comm, &pred->regex,
+                                pred->regex.field_len);
+        match = cmp ^ pred->not;
+
+        return match;
+}
+
 static int filter_pred_none(struct filter_pred *pred, void *event)
 {
         return 0;
@@ -1002,7 +1046,10 @@ static int init_pred(struct filter_parse_state *ps,
         if (is_string_field(field)) {
                 filter_build_regex(pred);
 
-                if (field->filter_type == FILTER_STATIC_STRING) {
+                if (!strcmp(field->name, "comm")) {
+                        fn = filter_pred_comm;
+                        pred->regex.field_len = TASK_COMM_LEN;
+                } else if (field->filter_type == FILTER_STATIC_STRING) {
                         fn = filter_pred_string;
                         pred->regex.field_len = field->size;
                 } else if (field->filter_type == FILTER_DYN_STRING)
@@ -1025,7 +1072,10 @@ static int init_pred(struct filter_parse_state *ps,
                 }
                 pred->val = val;
 
-                fn = select_comparison_fn(pred->op, field->size,
+                if (!strcmp(field->name, "cpu"))
+                        fn = filter_pred_cpu;
+                else
+                        fn = select_comparison_fn(pred->op, field->size,
                                           field->is_signed);
                 if (!fn) {
                         parse_error(ps, FILT_ERR_INVALID_OP, 0);