commit bbb549957ac97e8b14c53775041a8189bfce3119
author Maciej Żenczykowski <maze@google.com> Thu Aug 29 18:15:30 2024 -0700
committer Maciej Żenczykowski <maze@google.com> Wed Sep 04 18:58:29 2024 -0700
tree a74b73be2da9bdd2052fd2e7963cc1e895655a64
parent 5e7247d92236a4ef078a1469eff261e824e3edf5

dscpPolicy: assume cache lookup always succeeds (though it might miss)

By construction it cannot actually fail, since
  per_cpu_array[cookie % nr_entries_per_cpu]
is always a valid array item...

This allows us to do direct per-cpu write into the cache
instead of going via bpf map update helper function

Test: TreeHugger, atest CtsNetTestCases:android.net.cts.DscpPolicyTest^C
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I8a70ae341b21202db88877856522288149a54f31

bpf/progs/dscpPolicy.c

diff --git a/bpf/progs/dscpPolicy.c b/bpf/progs/dscpPolicy.c
index 39f2961..4084933 100644
--- a/bpf/progs/dscpPolicy.c
+++ b/bpf/progs/dscpPolicy.c
@@ -113,8 +113,9 @@
     // this array lookup cannot actually fail
     RuleEntry* existing_rule = bpf_socket_policy_cache_map_lookup_elem(&cacheid);
 
-    if (existing_rule &&
-        v6_equal(src_ip, existing_rule->src_ip) &&
+    if (!existing_rule) return; // impossible
+
+    if (v6_equal(src_ip, existing_rule->src_ip) &&
         v6_equal(dst_ip, existing_rule->dst_ip) &&
         skb->ifindex == existing_rule->ifindex &&
         sport == existing_rule->src_port &&
@@ -187,7 +188,8 @@
         }
     }
 
-    RuleEntry value = {
+    // Update cache with found policy.
+    *existing_rule = (RuleEntry){
         .src_ip = src_ip,
         .dst_ip = dst_ip,
         .ifindex = skb->ifindex,
@@ -197,9 +199,6 @@
         .dscp_val = new_dscp,
     };
 
-    // Update cache with found policy.
-    bpf_socket_policy_cache_map_update_elem(&cacheid, &value, BPF_ANY);
-
     if (new_dscp < 0) return;
 
     // Need to store bytes after updating map or program will not load.