map.insert bcc helper to expose the BPF_NOEXIST flag (#1085)

Inserts element in map only if it does not already exist. Throws a
warning during rewriter step if used on a BPF array.

docs/reference_guide.md

@@ -375,7 +375,7 @@ Syntax: ```BPF_TABLE(_table_type, _key_type, _leaf_type, _name, _max_entries)```
 
 Creates a map named ```_name```. Most of the time this will be used via higher-level macros, like BPF_HASH, BPF_HIST, etc.
 
-Methods (covered later): map.lookup(), map.lookup_or_init(), map.delete(), map.update(), map.increment().
+Methods (covered later): map.lookup(), map.lookup_or_init(), map.delete(), map.update(), map.insert(), map.increment().
 
 Examples in situ:
 [search /examples](https://github.com/iovisor/bcc/search?q=BPF_TABLE+path%3Aexamples&type=Code),
@@ -397,7 +397,7 @@ BPF_HASH(start, struct request *);
 
 This creates a hash named ```start``` where the key is a ```struct request *```, and the value defaults to u64. This hash is used by the disksnoop.py example for saving timestamps for each I/O request, where the key is the pointer to struct request, and the value is the timestamp.
 
-Methods (covered later): map.lookup(), map.lookup_or_init(), map.delete(), map.update(), map.increment().
+Methods (covered later): map.lookup(), map.lookup_or_init(), map.delete(), map.update(), map.insert(), map.increment().
 
 Examples in situ:
 [search /examples](https://github.com/iovisor/bcc/search?q=BPF_HASH+path%3Aexamples&type=Code),
@@ -530,7 +530,16 @@ Examples in situ:
 [search /examples](https://github.com/iovisor/bcc/search?q=update+path%3Aexamples&type=Code),
 [search /tools](https://github.com/iovisor/bcc/search?q=update+path%3Atools&type=Code)
 
-### 11. map.increment()
+### 11. map.insert()
+
+Syntax: ```map.insert(&key, &val)```
+
+Associate the value in the second argument to the key, only if there was no previous value.
+
+Examples in situ:
+[search /examples](https://github.com/iovisor/bcc/search?q=insert+path%3Aexamples&type=Code)
+
+### 12. map.increment()
 
 Syntax: ```map.increment(key)```
 
@@ -540,7 +549,7 @@ Examples in situ:
 [search /examples](https://github.com/iovisor/bcc/search?q=increment+path%3Aexamples&type=Code),
 [search /tools](https://github.com/iovisor/bcc/search?q=increment+path%3Atools&type=Code)
 
-### 12. map.get_stackid()
+### 13. map.get_stackid()
 
 Syntax: ```int map.get_stackid(void *ctx, u64 flags)```
 
@@ -550,7 +559,7 @@ Examples in situ:
 [search /examples](https://github.com/iovisor/bcc/search?q=get_stackid+path%3Aexamples&type=Code),
 [search /tools](https://github.com/iovisor/bcc/search?q=get_stackid+path%3Atools&type=Code)
 
-### 13. map.perf_read()
+### 14. map.perf_read()
 
 Syntax: ```u64 map.perf_read(u32 cpu)```
 

examples/networking/neighbor_sharing/tc_neighbor_sharing.c

@@ -57,7 +57,7 @@ int classify_neighbor(struct __sk_buff *skb) {
     u32 sip = ip->src;
     struct ipkey key = {.client_ip=sip};
     int val = 1;
-    learned_ips.update(&key, &val);
+    learned_ips.insert(&key, &val);
     goto EOP;
   }
 EOP:

src/cc/export/helpers.h

@@ -45,6 +45,7 @@ struct _name##_table_t { \
   _leaf_type * (*lookup) (_key_type *); \
   _leaf_type * (*lookup_or_init) (_key_type *, _leaf_type *); \
   int (*update) (_key_type *, _leaf_type *); \
+  int (*insert) (_key_type *, _leaf_type *); \
   int (*delete) (_key_type *); \
   void (*call) (void *, int index); \
   void (*increment) (_key_type); \

src/cc/frontends/clang/b_frontend_action.cc

@@ -369,12 +369,10 @@ bool BTypeVisitor::VisitCallExpr(CallExpr *Call) {
         }
         string fd = to_string(table_it->fd);
         string prefix, suffix;
-        string map_update_policy = "BPF_ANY";
         string txt;
         auto rewrite_start = Call->getLocStart();
         auto rewrite_end = Call->getLocEnd();
         if (memb_name == "lookup_or_init") {
-          map_update_policy = "BPF_NOEXIST";
           string name = Ref->getDecl()->getName();
           string arg0 = rewriter_.getRewrittenText(expansionRange(Call->getArg(0)->getSourceRange()));
           string arg1 = rewriter_.getRewrittenText(expansionRange(Call->getArg(1)->getSourceRange()));
@@ -382,7 +380,7 @@ bool BTypeVisitor::VisitCallExpr(CallExpr *Call) {
           string update = "bpf_map_update_elem_(bpf_pseudo_fd(1, " + fd + ")";
           txt  = "({typeof(" + name + ".leaf) *leaf = " + lookup + ", " + arg0 + "); ";
           txt += "if (!leaf) {";
-          txt += " " + update + ", " + arg0 + ", " + arg1 + ", " + map_update_policy + ");";
+          txt += " " + update + ", " + arg0 + ", " + arg1 + ", BPF_NOEXIST);";
           txt += " leaf = " + lookup + ", " + arg0 + ");";
           txt += " if (!leaf) return 0;";
           txt += "}";
@@ -433,7 +431,13 @@ bool BTypeVisitor::VisitCallExpr(CallExpr *Call) {
             suffix = ")";
           } else if (memb_name == "update") {
             prefix = "bpf_map_update_elem";
-            suffix = ", " + map_update_policy + ")";
+            suffix = ", BPF_ANY)";
+          } else if (memb_name == "insert") {
+            if (table_it->type == BPF_MAP_TYPE_ARRAY) {
+              warning(Call->getLocStart(), "all element of an array already exist; insert() will have no effect");
+            }
+            prefix = "bpf_map_update_elem";
+            suffix = ", BPF_NOEXIST)";
           } else if (memb_name == "delete") {
             prefix = "bpf_map_delete_elem";
             suffix = ")";

tests/python/test_clang.py

@@ -3,7 +3,7 @@
 # Licensed under the Apache License, Version 2.0 (the "License")
 
 from bcc import BPF
-import ctypes
+import ctypes as ct
 from unittest import main, TestCase
 import os
 import sys
@@ -113,7 +113,7 @@ BPF_HASH(stats, int, struct { u32 a[3]; u32 b; }, 10);
         t = b.get_table("stats")
         s1 = t.key_sprintf(t.Key(2))
         self.assertEqual(s1, b"0x2")
-        s2 = t.leaf_sprintf(t.Leaf((ctypes.c_uint * 3)(1,2,3), 4))
+        s2 = t.leaf_sprintf(t.Leaf((ct.c_uint * 3)(1,2,3), 4))
         self.assertEqual(s2, b"{ [ 0x1 0x2 0x3 ] 0x4 }")
         l = t.leaf_scanf(s2)
         self.assertEqual(l.a[0], 1)
@@ -330,8 +330,7 @@ BPF_ARRAY(t2, struct list *, 1);
 BPF_ARRAY(t3, union emptyu, 1);
 """
         b = BPF(text=text)
-        import ctypes
-        self.assertEqual(ctypes.sizeof(b["t3"].Leaf), 8)
+        self.assertEqual(ct.sizeof(b["t3"].Leaf), 8)
 
     def test_cflags(self):
         text = """
@@ -485,5 +484,25 @@ int trace_entry(struct pt_regs *ctx) {
         self.assertIn(expectedWarn, output)
         r.close()
 
+    def test_map_insert(self):
+        text = """
+BPF_HASH(dummy);
+void do_trace(struct pt_regs *ctx) {
+    u64 key = 0, val = 2;
+    dummy.insert(&key, &val);
+    key = 1;
+    dummy.update(&key, &val);
+}
+"""
+        b = BPF(text=text)
+        c_val = ct.c_ulong(1)
+        b["dummy"][ct.c_ulong(0)] = c_val
+        b["dummy"][ct.c_ulong(1)] = c_val
+        b.attach_kprobe(event="sys_sync", fn_name="do_trace")
+        libc = ct.CDLL("libc.so.6")
+        libc.sync()
+        self.assertEqual(1, b["dummy"][ct.c_ulong(0)].value)
+        self.assertEqual(2, b["dummy"][ct.c_ulong(1)].value)
+
 if __name__ == "__main__":
     main()