fix get_table_offline for percpu hash table

Use get_value() instead of lookup() as the value as in the case of
percpu tables the ValueType is an std::vector that has to be resized
before performing the lookup function.

Add also some testing for it.

Solves https://github.com/iovisor/bcc/issues/1860Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>

src/cc/api/BPFTable.h

@@ -232,11 +232,14 @@ class BPFHashTable : public BPFTableBase<KeyType, ValueType> {
     KeyType cur;
     ValueType value;
 
+    StatusTuple r(0);
+
     if (!this->first(&cur))
       return res;
 
     while (true) {
-      if (!this->lookup(&cur, &value))
+      r = get_value(cur, value);
+      if (r.code() != 0)
         break;
       res.emplace_back(cur, value);
       if (!this->next(&cur, &cur))

tests/cc/test_hash_table.cc

@@ -84,6 +84,10 @@ TEST_CASE("test hash table", "[hash_table]") {
       REQUIRE(pair.first % 3 == 0);
       REQUIRE(pair.first / 3 == pair.second);
     }
+
+    // clear table
+    t.clear_table_non_atomic();
+    REQUIRE(t.get_table_offline().size() == 0);
   }
 }
 
@@ -156,5 +160,34 @@ TEST_CASE("percpu hash table", "[percpu_hash_table]") {
     res = t.get_value(k, v2);
     REQUIRE(res.code() != 0);
   }
+
+  SECTION("walk table") {
+    std::vector<uint64_t> v(ncpus);
+
+    for (int k = 3; k <= 30; k+=3) {
+      for (size_t cpu = 0; cpu < ncpus; cpu++) {
+        v[cpu] = k * cpu;
+      }
+      res = t.update_value(k, v);
+      REQUIRE(res.code() == 0);
+    }
+
+    // get whole table
+    auto offline = t.get_table_offline();
+    REQUIRE(offline.size() == 10);
+    for (int i = 0; i < 10; i++) {
+      // check the key
+      REQUIRE(offline.at(i).first % 3 == 0);
+
+      // check value
+      for (size_t cpu = 0; cpu < ncpus; cpu++) {
+        REQUIRE(offline.at(i).second.at(cpu) == cpu * offline.at(i).first);
+      }
+    }
+
+    // clear table
+    t.clear_table_non_atomic();
+    REQUIRE(t.get_table_offline().size() == 0);
+  }
 }
 #endif