From dfd941f0fd4bfab63d3b2509b5321711368a3248 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maciej=20=C5=BBenczykowski?= <maze@google.com>
Date: Mon, 20 Jan 2020 03:18:26 -0800
Subject: [PATCH] BpfMap - add pinned path based constructors
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(and remove the old straight from fd constructor)

Note that BpfMapRO is not yet truly compile time read-only,
since it still has methods that can modify things (although those
modifications will of course fail due to the map fd being r/o).

Test: build, atest with followup fixes
Bug: 129773125
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I70b511e3f0a62cd4d9d5a923e658b1086337ec4c
---
 libbpf_android/include/bpf/BpfMap.h | 32 +++++++++++++++--------------
 1 file changed, 17 insertions(+), 15 deletions(-)

diff --git a/libbpf_android/include/bpf/BpfMap.h b/libbpf_android/include/bpf/BpfMap.h
index 31efd58..4b941a8 100644
--- a/libbpf_android/include/bpf/BpfMap.h
+++ b/libbpf_android/include/bpf/BpfMap.h
@@ -46,25 +46,20 @@ template <class Key, class Value>
 class BpfMap {
   public:
     BpfMap<Key, Value>() {};
-    explicit BpfMap<Key, Value>(int fd) : mMapFd(fd){};
 
-    // We could technically implement this constructor either with
-    //   : mMapFd(dup(fd)) {}        // fd valid in caller, we have our own local copy
-    // or
-    //   : mMapFd(fd.release()) {}   // fd no longer valid in caller, we 'stole' it
-    //
-    // However, I think we're much better off with a compile time failure, since
-    // it's better for whoever passes in a unique_fd to think twice about whether
-    // they're trying to pass in ownership or not.
-    explicit BpfMap<Key, Value>(base::unique_fd fd) = delete;
+  protected:
+    // flag must be within BPF_OBJ_FLAG_MASK, ie. 0, BPF_F_RDONLY, BPF_F_WRONLY
+    BpfMap<Key, Value>(const char* pathname, uint32_t flags) {
+        int map_fd = mapRetrieve(pathname, flags);
+        if (map_fd >= 0) mMapFd.reset(map_fd);
+    }
+
+  public:
+    explicit BpfMap<Key, Value>(const char* pathname) : BpfMap<Key, Value>(pathname, 0) {}
 
     BpfMap<Key, Value>(bpf_map_type map_type, uint32_t max_entries, uint32_t map_flags) {
         int map_fd = createMap(map_type, sizeof(Key), sizeof(Value), max_entries, map_flags);
-        if (map_fd < 0) {
-            mMapFd.reset(-1);
-        } else {
-            mMapFd.reset(map_fd);
-        }
+        if (map_fd >= 0) mMapFd.reset(map_fd);
     }
 
     base::Result<Key> getFirstKey() const {
@@ -246,6 +241,13 @@ base::Result<void> BpfMap<Key, Value>::iterateWithValue(
     return curKey.error();
 }
 
+template <class Key, class Value>
+class BpfMapRO : public BpfMap<Key, Value> {
+  public:
+    explicit BpfMapRO<Key, Value>(const char* pathname)
+        : BpfMap<Key, Value>(pathname, BPF_F_RDONLY) {}
+};
+
 }  // namespace bpf
 }  // namespace android