tools/kvm_stat: fix fields filter for child events

The fields filter would not work with child fields, as the respective
parents would not be included. No parents displayed == no childs displayed.
To reproduce, run on s390 (would work on other platforms, too, but would
require a different filter name):
- Run 'kvm_stat -d'
- Press 'f'
- Enter 'instruct'
Notice that events like instruction_diag_44 or instruction_diag_500 are not
displayed - the output remains empty.
With this patch, we will filter by matching events and their parents.
However, consider the following example where we filter by
instruction_diag_44:

  kvm statistics - summary
                   regex filter: instruction_diag_44
   Event                                         Total %Total CurAvg/s
   exit_instruction                                276  100.0       12
     instruction_diag_44                           256   92.8       11
   Total                                           276              12

Note that the parent ('exit_instruction') displays the total events, but
the childs listed do not match its total (256 instead of 276). This is
intended (since we're filtering all but one child), but might be confusing
on first sight.
Signed-off-by: Stefan Raspl <raspl@linux.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/kvm/kvm_stat/kvm_stat

@@ -575,8 +575,12 @@ class TracepointProvider(Provider):
     def update_fields(self, fields_filter):
         """Refresh fields, applying fields_filter"""
         self.fields = [field for field in self._get_available_fields()
-                       if self.is_field_wanted(fields_filter, field) or
-                       ARCH.tracepoint_is_child(field)]
+                       if self.is_field_wanted(fields_filter, field)]
+        # add parents for child fields - otherwise we won't see any output!
+        for field in self._fields:
+            parent = ARCH.tracepoint_is_child(field)
+            if (parent and parent not in self._fields):
+                self.fields.append(parent)
 
     @staticmethod
     def _get_online_cpus():
@@ -735,8 +739,12 @@ class DebugfsProvider(Provider):
     def update_fields(self, fields_filter):
         """Refresh fields, applying fields_filter"""
         self._fields = [field for field in self._get_available_fields()
-                        if self.is_field_wanted(fields_filter, field) or
-                        ARCH.debugfs_is_child(field)]
+                        if self.is_field_wanted(fields_filter, field)]
+        # add parents for child fields - otherwise we won't see any output!
+        for field in self._fields:
+            parent = ARCH.debugfs_is_child(field)
+            if (parent and parent not in self._fields):
+                self.fields.append(parent)
 
     @property
     def fields(self):

tools/kvm/kvm_stat/kvm_stat.txt

@@ -34,6 +34,8 @@ INTERACTIVE COMMANDS
 *c*::	clear filter
 
 *f*::	filter by regular expression
+ ::     *Note*: Child events pull in their parents, and parents' stats summarize
+                all child events, not just the filtered ones
 
 *g*::	filter by guest name/PID