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bpfloader: auto-demote DEVMAP/DEVMAP_HASH map types on too old kernels am: cb358de067 am: 76f565a3f1 am: 3aa8ecefd5

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Original change: https://android-review.googlesource.com/c/platform/system/bpf/+/1619223

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I7dc2b7da56ee348f87cded9c1fb858a240e3776b
This commit is contained in:
Maciej Żenczykowski 2021-03-05 07:27:32 +00:00 committed by Automerger Merge Worker
commit ade234047b
1 changed files with 22 additions and 1 deletions
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23
libbpf_android/Loader.cpp
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@ -446,7 +446,28 @@ static int createMaps(const char* elfPath, ifstream& elfFile, vector<unique_fd>&
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());