bpf: fix prepend_name unit tests for new buffer length

Signed-off-by: Mahe Tardy <mahe.tardy@gmail.com>

Makefile

@@ -264,8 +264,10 @@ test: tester-progs tetragon-bpf ## Run Go tests.
 tester-progs: ## Compile helper programs for unit testing.
 	$(MAKE) -C $(TESTER_PROGS_DIR)
 
+## bpf-test: ## run BPF tests.
+## bpf-test BPFGOTESTFLAGS="-v": ## run BPF tests with verbose.
 .PHONY: bpf-test
-bpf-test: ## Run BPF tests.
+bpf-test:
 	$(MAKE) -C ./bpf run-test
 
 .PHONY: verify

bpf/tests/prepend_name_test.c

@@ -13,7 +13,7 @@
 
 char _license[] __attribute__((section("license"), used)) = "Dual BSD/GPL";
 
-#define TEST_MAX_BUF_LEN 256
+#define TEST_MAX_BUF_LEN 4096
 #define NAME_MAX	 255
 
 struct test_prepend_name_state_map_value {

bpf/tests/prepend_name_test.go

@@ -18,7 +18,7 @@ import (
 
 const (
 	// those constants must be synchronized with the BPF code
-	MAX_BUF_LEN                 = 256
+	MAX_BUF_LEN                 = 4096
 	NAME_MAX                    = 255
 	testPrependNameStateMapName = "test_prepend_name_state_map"
 	programName                 = "test_prepend_name"
@@ -232,44 +232,67 @@ func Test_PrependName(t *testing.T) {
 		assert.Equal(t, "sr/bin/cat", state.BufferToString())
 	})
 
-	SetupLongDentry := func() string {
-		// length is 239
-		const longDentry = "pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil"
+	// length is 239
+	const longDentry = "pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil_pizza_tomato_mozzarella_basil"
+
+	t.Run("MaxSizeBufMedium", func(t *testing.T) {
+		const bufsize = 256
+		state.ResetStateWithBuflen(bufsize)
 
 		err = state.UpdateDentry(longDentry)
 		assert.NoError(t, err)
 		code := runPrependName()
 		assert.Equal(t, 0, code)
 		assert.Equal(t, "/"+longDentry, state.BufferToString())
-		return longDentry
-	}
-
-	t.Run("MaxSizeBufFull", func(t *testing.T) {
-		state.ResetStateWithBuflen(MAX_BUF_LEN)
-
-		longDentry := SetupLongDentry()
 
 		// length is 15, so 239 + 15 + 2 slash chars = 256
 		err = state.UpdateDentry("favorite_recipe")
 		assert.NoError(t, err)
-		code := runPrependName()
+		code = runPrependName()
 		assert.Equal(t, 0, code)
 		assert.Equal(t, "/favorite_recipe"+"/"+longDentry, state.BufferToString())
-		assert.Equal(t, MAX_BUF_LEN, len(state.BufferToString()))
+		assert.Equal(t, bufsize, len(state.BufferToString()))
 	})
 
-	t.Run("MaxSizeBufTooSmall", func(t *testing.T) {
+	t.Run("MaxSizeBufFull", func(t *testing.T) {
+		maxDentry := strings.Repeat("a", NAME_MAX)
 		state.ResetStateWithBuflen(MAX_BUF_LEN)
 
-		longDentry := SetupLongDentry()
+		var expectedState string
+		// (len("/") + 255) * 16 = 4096
+		for range 16 {
+			err = state.UpdateDentry(maxDentry)
+			assert.NoError(t, err)
+			code := runPrependName()
+			assert.Equal(t, 0, code)
+			expectedState += "/" + maxDentry
+			assert.Equal(t, expectedState, state.BufferToString())
+		}
+	})
+
+	t.Run("MaxSizeBufTooSmall", func(t *testing.T) {
+		largeDentry := strings.Repeat("a", 240)
+		state.ResetStateWithBuflen(MAX_BUF_LEN)
 
-		// length is 16 with the "s" of "recipes", so 240 + 15 + 2 slash chars = 257
-		err = state.UpdateDentry("favorite_recipes")
+		var expectedState string
+		// (len("/") + 240) * 16 = 3856
+		for range 16 {
+			err = state.UpdateDentry(largeDentry)
+			assert.NoError(t, err)
+			code := runPrependName()
+			assert.Equal(t, 0, code)
+			expectedState = "/" + largeDentry + expectedState
+			assert.Equal(t, expectedState, state.BufferToString())
+		}
+		// at this stage, there should be 240 chars left in the buf which leaves
+		// no space for the remaining root slash character
+		err = state.UpdateDentry(largeDentry)
 		assert.NoError(t, err)
 		code := runPrependName()
 		assert.Equal(t, -int(unix.ENAMETOOLONG), code)
-		assert.Equal(t, "favorite_recipes"+"/"+longDentry, state.BufferToString())
-		assert.Equal(t, MAX_BUF_LEN, len(state.BufferToString()))
+		// note that I intentionally don't add the '/' char
+		expectedState = largeDentry + expectedState
+		assert.Equal(t, expectedState, state.BufferToString())
 	})
 
 	t.Run("MaxSizeBufNormalUse", func(t *testing.T) {