Filter: Making the filter state thread local.

While having the filter code still reentrant if we really need,
the compiler can now do constant propagation and address the
thread local storage directly to save some computation time.

filter/filter.c

@@ -51,14 +51,19 @@
 #include "filter/data.h"
 
 /* Internal filter state, to be allocated on stack when executing filters */
-struct filter_state {
+_Thread_local struct filter_state {
+  /* The route we are processing. This may be NULL to indicate no route available. */
   struct rte **rte;
+
+  /* The old rta to be freed after filters are done. */
   struct rta *old_rta;
+
+  /* Cached pointer to ea_list */
   struct ea_list **eattrs;
   struct linpool *pool;
   struct buffer buf;
   int flags;
-};
+} filter_state;
 
 void (*bt_assert_hook)(int result, const struct f_line_item *assert);
 
@@ -239,7 +244,7 @@ interpret(struct filter_state *fs, const struct f_line *line, struct f_val *val)
  * copied).
  *
  * The returned rte may reuse the (possibly cached, cloned) rta, or
- * (if rta was modificied) contains a modified uncached rta, which
+ * (if rta was modified) contains a modified uncached rta, which
  * uses parts allocated from @tmp_pool and parts shared from original
  * rta. There is one exception - if @rte is rw but contains a cached
  * rta and that is modified, rta in returned rte is also cached.
@@ -261,38 +266,47 @@ f_run(const struct filter *filter, struct rte **rte, struct linpool *tmp_pool, i
   int rte_cow = ((*rte)->flags & REF_COW);
   DBG( "Running filter `%s'...", filter->name );
 
-  struct filter_state fs = {
+  /* Initialize the filter state */
+  filter_state = (struct filter_state) {
     .rte = rte,
     .pool = tmp_pool,
     .flags = flags,
   };
 
-  LOG_BUFFER_INIT(fs.buf);
+  LOG_BUFFER_INIT(filter_state.buf);
 
-  enum filter_return fret = interpret(&fs, filter->root, NULL);
+  /* Run the interpreter itself */
+  enum filter_return fret = interpret(&filter_state, filter->root, NULL);
 
-  if (fs.old_rta) {
+  if (filter_state.old_rta) {
     /*
-     * Cached rta was modified and fs->rte contains now an uncached one,
+     * Cached rta was modified and filter_state->rte contains now an uncached one,
      * sharing some part with the cached one. The cached rta should
-     * be freed (if rte was originally COW, fs->old_rta is a clone
+     * be freed (if rte was originally COW, filter_state->old_rta is a clone
      * obtained during rte_cow()).
      *
      * This also implements the exception mentioned in f_run()
      * description. The reason for this is that rta reuses parts of
-     * fs->old_rta, and these may be freed during rta_free(fs->old_rta).
+     * filter_state->old_rta, and these may be freed during rta_free(filter_state->old_rta).
      * This is not the problem if rte was COW, because original rte
      * also holds the same rta.
      */
-    if (!rte_cow)
-      (*fs.rte)->attrs = rta_lookup((*fs.rte)->attrs);
+    if (!rte_cow) {
+      /* Cache the new attrs */
+      (*filter_state.rte)->attrs = rta_lookup((*filter_state.rte)->attrs);
 
-    rta_free(fs.old_rta);
+      /* Drop cached ea_list pointer */
+      filter_state.eattrs = NULL;
+    }
+
+    /* Uncache the old attrs and drop the pointer as it is invalid now. */
+    rta_free(filter_state.old_rta);
+    filter_state.old_rta = NULL;
   }
 
-
+  /* Process the filter output, log it and return */
   if (fret < F_ACCEPT) {
-    if (!(fs.flags & FF_SILENT))
+    if (!(filter_state.flags & FF_SILENT))
       log_rl(&rl_runtime_err, L_ERR "Filter %s did not return accept nor reject. Make up your mind", filter_name(filter));
     return F_ERROR;
   }
@@ -300,49 +314,72 @@ f_run(const struct filter *filter, struct rte **rte, struct linpool *tmp_pool, i
   return fret;
 }
 
-/* TODO: perhaps we could integrate f_eval(), f_eval_rte() and f_run() */
+/**
+ * f_eval_rte – run a filter line for an uncached route
+ * @expr: filter line to run
+ * @rte: route being filtered, may be modified
+ * @tmp_pool: all filter allocations go from this pool
+ *
+ * This specific filter entry point runs the given filter line
+ * (which must not have any arguments) on the given route.
+ *
+ * The route MUST NOT have REF_COW set and its attributes MUST NOT
+ * be cached by rta_lookup().
+ */
 
 enum filter_return
 f_eval_rte(const struct f_line *expr, struct rte **rte, struct linpool *tmp_pool)
 {
-
-  struct filter_state fs = {
+  filter_state = (struct filter_state) {
     .rte = rte,
     .pool = tmp_pool,
   };
 
-  LOG_BUFFER_INIT(fs.buf);
+  LOG_BUFFER_INIT(filter_state.buf);
 
-  /* Note that in this function we assume that rte->attrs is private / uncached */
-  return interpret(&fs, expr, NULL);
+  ASSERT(!((*rte)->flags & REF_COW));
+  ASSERT(!rta_is_cached((*rte)->attrs));
+
+  return interpret(&filter_state, expr, NULL);
 }
 
+/*
+ * f_eval – get a value of a term
+ * @expr: filter line containing the term
+ * @tmp_pool: long data may get allocated from this pool
+ * @pres: here the output will be stored
+ */
 enum filter_return
 f_eval(const struct f_line *expr, struct linpool *tmp_pool, struct f_val *pres)
 {
-  struct filter_state fs = {
+  filter_state = (struct filter_state) {
     .pool = tmp_pool,
   };
 
-  LOG_BUFFER_INIT(fs.buf);
+  LOG_BUFFER_INIT(filter_state.buf);
 
-  enum filter_return fret = interpret(&fs, expr, pres);
+  enum filter_return fret = interpret(&filter_state, expr, pres);
   return fret;
 }
 
+/*
+ * f_eval_int – get an integer value of a term 
+ * Called internally from the config parser, uses its internal memory pool
+ * for allocations. Do not call in other cases.
+ */
 uint
 f_eval_int(const struct f_line *expr)
 {
   /* Called independently in parse-time to eval expressions */
-  struct filter_state fs = {
+  filter_state = (struct filter_state) {
     .pool = cfg_mem,
   };
 
   struct f_val val;
 
-  LOG_BUFFER_INIT(fs.buf);
+  LOG_BUFFER_INIT(filter_state.buf);
 
-  if (interpret(&fs, expr, &val) > F_RETURN)
+  if (interpret(&filter_state, expr, &val) > F_RETURN)
     cf_error("Runtime error while evaluating expression");
 
   if (val.type != T_INT)
@@ -351,6 +388,9 @@ f_eval_int(const struct f_line *expr)
   return val.val.i;
 }
 
+/*
+ * f_eval_buf – get a value of a term and print it to the supplied buffer
+ */
 enum filter_return
 f_eval_buf(const struct f_line *expr, struct linpool *tmp_pool, buffer *buf)
 {