bpfloader: auto-demote DEVMAP/DEVMAP_HASH map types on too old kernels am: cb358de067
Original change: https://android-review.googlesource.com/c/platform/system/bpf/+/1619223
MUST ONLY BE SUBMITTED BY AUTOMERGER
Change-Id: I30a799d8beb4784baa0820d3fbad16d9b7e88464
diff --git a/libbpf_android/Loader.cpp b/libbpf_android/Loader.cpp
index e0d56e4..dbd198d 100644
--- a/libbpf_android/Loader.cpp
+++ b/libbpf_android/Loader.cpp
@@ -446,7 +446,28 @@
ALOGD("bpf_create_map reusing map %s, ret: %d\n", mapNames[i].c_str(), fd.get());
reuse = true;
} else {
- fd.reset(bpf_create_map(md[i].type, mapNames[i].c_str(), md[i].key_size, md[i].value_size,
+ enum bpf_map_type type = md[i].type;
+ if (type == BPF_MAP_TYPE_DEVMAP && !isAtLeastKernelVersion(4, 14, 0)) {
+ // On Linux Kernels older than 4.14 this map type doesn't exist, but it can kind
+ // of be approximated: ARRAY has the same userspace api, though it is not usable
+ // by the same ebpf programs. However, that's okay because the bpf_redirect_map()
+ // helper doesn't exist on 4.9 anyway (so the bpf program would fail to load,
+ // and thus needs to be tagged as 4.14+ either way), so there's nothing useful you
+ // could do with a DEVMAP anyway (that isn't already provided by an ARRAY)...
+ // Hence using an ARRAY instead of a DEVMAP simply makes life easier for userspace.
+ type = BPF_MAP_TYPE_ARRAY;
+ }
+ if (type == BPF_MAP_TYPE_DEVMAP_HASH && !isAtLeastKernelVersion(5, 4, 0)) {
+ // On Linux Kernels older than 5.4 this map type doesn't exist, but it can kind
+ // of be approximated: HASH has the same userspace visible api.
+ // However it cannot be used by ebpf programs in the same way.
+ // Since bpf_redirect_map() only requires 4.14, a program using a DEVMAP_HASH map
+ // would fail to load (due to trying to redirect to a HASH instead of DEVMAP_HASH).
+ // One must thus tag any BPF_MAP_TYPE_DEVMAP_HASH + bpf_redirect_map() using
+ // programs as being 5.4+...
+ type = BPF_MAP_TYPE_HASH;
+ }
+ fd.reset(bpf_create_map(type, mapNames[i].c_str(), md[i].key_size, md[i].value_size,
md[i].max_entries, md[i].map_flags));
saved_errno = errno;
ALOGD("bpf_create_map name %s, ret: %d\n", mapNames[i].c_str(), fd.get());