NetBpfLoad: log on non-LTS or too old LTS kernel version

minimum versions chosen to match:
  //system/netd/tests/kernel_test.cpp
  //kernel/tests/net/test/kernel_feature_test.py

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ife6900333d97181765460c16676172bf05f8fd5f

netbpfload/NetBpfLoad.cpp

@@ -226,6 +226,11 @@ static int logTetheringApexVersion(void) {
     return 0;
 }
 
+static bool isGSI() {
+    // From //system/gsid/libgsi.cpp IsGsiRunning()
+    return !access("/metadata/gsi/dsu/booted", F_OK);
+}
+
 static int main(char** argv, char * const envp[]) {
     base::InitLogging(argv, &base::KernelLogger);
 
@@ -281,6 +286,34 @@ static int main(char** argv, char * const envp[]) {
         return 1;
     }
 
+    if (isAtLeastV) {
+        bool bad = false;
+
+        if (!isLtsKernel()) {
+            ALOGW("Android V only supports LTS kernels.");
+            bad = true;
+        }
+
+#define REQUIRE(maj, min, sub) \
+        if (isKernelVersion(maj, min) && !isAtLeastKernelVersion(maj, min, sub)) { \
+            ALOGW("Android V requires %d.%d kernel to be %d.%d.%d+.", maj, min, maj, min, sub); \
+            bad = true; \
+        }
+
+        REQUIRE(4, 19, 236)
+        REQUIRE(5, 4, 186)
+        REQUIRE(5, 10, 199)
+        REQUIRE(5, 15, 136)
+        REQUIRE(6, 1, 57)
+        REQUIRE(6, 6, 0)
+
+#undef REQUIRE
+
+        if (bad && !isGSI()) {
+            ALOGE("Unsupported kernel version (%07x).", kernelVersion());
+        }
+    }
+
     if (isUserspace32bit() && isAtLeastKernelVersion(6, 2, 0)) {
         /* Android 14/U should only launch on 64-bit kernels
          *   T launches on 5.10/5.15