commit 914c4b39c3ddae6e75cfe11894d4e51532d196f0
author Maciej Żenczykowski <maze@google.com> Wed Mar 18 22:32:43 2020 -0700
committer Maciej Żenczykowski <maze@google.com> Wed Mar 18 23:36:01 2020 -0700
tree 8fb3af89ab4af559526e1b94839ab2b292ea9ec9
parent 6161ff246f648c1375e3a7fd2a271ee18dbc8b43

getBpfSupportLevel - make 4.14+ kernel trump ro.product.first_api_level

Devices launching with Android 'X' must have one of the following kernels:
  O: 3.18 4.4  4.9
  P: 4.4  4.9  4.14
  Q: 4.9  4.14 4.19
  R: 4.14 4.19 5.4

You can see this by looking at:
  https://android.googlesource.com/kernel/configs/+/refs/heads/master
where the main directory is currently R (api level 30) and the subdirs for:
  O (26), O-MR1 (27), P (28), and Q (29)

As such running a 'Y' kernel is proof of being at least Android 'X':
  4.9  is O+
  4.14 is P+
  4.19 is Q+
  5.4  is R+

And we know Android P VINTF has always required eBPF support from its
kernels.  As such we can reorder the checks, to check kernel prior
to checking first_api_level.

This is *theoretically* a no-op.

But of course in practice it will actually fix a number of issues:
- Devices which launched on O with a 4.9 kernel but have been upgraded
  to a 4.14-Q kernel and thus now support ebpf and don't support xt_qtaguid,
  this will hopefully eliminate the need for test waivers...
- Devices during turn up where they're on a 4.19 kernel, targetting R,
  and yet somehow still erroneously reporting a first_api_level of 26 (O),
  this will hopefully eliminate some crash bugs.

Test: atest
Bug: 151753987
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I7eaca016d0f77e5f320b499ac428987e23a6d184

libbpf_android/BpfUtils.cpp

diff --git a/libbpf_android/BpfUtils.cpp b/libbpf_android/BpfUtils.cpp
index c7c56d5..cf10449 100644
--- a/libbpf_android/BpfUtils.cpp
+++ b/libbpf_android/BpfUtils.cpp
@@ -117,9 +117,9 @@
 std::string BpfLevelToString(BpfLevel bpfLevel) {
     switch (bpfLevel) {
         case BpfLevel::NONE:
-            return "None [pre-4.9]";
+            return "None [pre-4.9 or pre-P]";
         case BpfLevel::BASIC_4_9:
-            return "Basic [4.9]";
+            return "Basic [4.9 P+]";
         case BpfLevel::EXTENDED_4_14:
             return "Extended [4.14]";
         case BpfLevel::EXTENDED_4_19:
@@ -132,6 +132,12 @@
 }
 
 static BpfLevel getUncachedBpfSupportLevel() {
+    unsigned kver = kernelVersion();
+
+    if (kver >= KVER(5, 4, 0)) return BpfLevel::EXTENDED_5_4;
+    if (kver >= KVER(4, 19, 0)) return BpfLevel::EXTENDED_4_19;
+    if (kver >= KVER(4, 14, 0)) return BpfLevel::EXTENDED_4_14;
+
     uint64_t api_level = GetUintProperty<uint64_t>("ro.product.first_api_level", 0);
     if (api_level == 0) {
         ALOGE("Cannot determine initial API level of the device");
@@ -141,11 +147,6 @@
     // Check if the device is shipped originally with android P.
     if (api_level < MINIMUM_API_REQUIRED) return BpfLevel::NONE;
 
-    unsigned kver = kernelVersion();
-
-    if (kver >= KVER(5, 4, 0)) return BpfLevel::EXTENDED_5_4;
-    if (kver >= KVER(4, 19, 0)) return BpfLevel::EXTENDED_4_19;
-    if (kver >= KVER(4, 14, 0)) return BpfLevel::EXTENDED_4_14;
     if (kver >= KVER(4, 9, 0)) return BpfLevel::BASIC_4_9;
 
     return BpfLevel::NONE;