Load library using file handle.

* This patch enables dlopen by file descriptor
   instead of path/name.

Bug: 15984217
Change-Id: Ib39051e00567fb97070bf96d8ce63993877c0a01

libc/include/android/dlext.h

@@ -49,11 +49,17 @@ enum {
    */
   ANDROID_DLEXT_USE_RELRO             = 0x8,
 
+  /* Instruct dlopen to use library_fd instead of opening file by name.
+   * The filename parameter is still used to identify the library.
+   */
+  ANDROID_DLEXT_USE_LIBRARY_FD        = 0x10,
+
   /* Mask of valid bits */
   ANDROID_DLEXT_VALID_FLAG_BITS       = ANDROID_DLEXT_RESERVED_ADDRESS |
                                         ANDROID_DLEXT_RESERVED_ADDRESS_HINT |
                                         ANDROID_DLEXT_WRITE_RELRO |
-                                        ANDROID_DLEXT_USE_RELRO,
+                                        ANDROID_DLEXT_USE_RELRO |
+                                        ANDROID_DLEXT_USE_LIBRARY_FD,
 };
 
 typedef struct {
@@ -61,6 +67,7 @@ typedef struct {
   void*   reserved_addr;
   size_t  reserved_size;
   int     relro_fd;
+  int     library_fd;
 } android_dlextinfo;
 
 extern void* android_dlopen_ext(const char* filename, int flag, const android_dlextinfo* extinfo);

libc/private/ScopedFd.h

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2009 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef SCOPED_FD_H
+#define SCOPED_FD_H
+
+#include <unistd.h>
+#include "bionic_macros.h"
+
+// A smart pointer that closes the given fd on going out of scope.
+// Use this when the fd is incidental to the purpose of your function,
+// but needs to be cleaned up on exit.
+class ScopedFd {
+public:
+    explicit ScopedFd(int fd) : fd(fd) {
+    }
+
+    ~ScopedFd() {
+      reset();
+    }
+
+    int get() const {
+        return fd;
+    }
+
+    int release() __attribute__((warn_unused_result)) {
+        int localFd = fd;
+        fd = -1;
+        return localFd;
+    }
+
+    void reset(int new_fd = -1) {
+      if (fd != -1) {
+          TEMP_FAILURE_RETRY(close(fd));
+      }
+      fd = new_fd;
+    }
+
+private:
+    int fd;
+
+    // Disallow copy and assignment.
+    DISALLOW_COPY_AND_ASSIGN(ScopedFd);
+};
+
+#endif  // SCOPED_FD_H