4 files changed, 187 insertions, 0 deletions
diff --git a/base/Android.bp b/base/Android.bp
index daa820ab4..741664bb9 100644
--- a/base/Android.bp
+++ b/base/Android.bp
@@ -47,6 +47,7 @@ cc_defaults {
         "chrono_utils.cpp",
         "file.cpp",
         "logging.cpp",
+        "mapped_file.cpp",
         "parsenetaddress.cpp",
         "properties.cpp",
         "quick_exit.cpp",
@@ -124,6 +125,7 @@ cc_test {
         "file_test.cpp",
         "logging_test.cpp",
         "macros_test.cpp",
+        "mapped_file_test.cpp",
         "parsedouble_test.cpp",
         "parseint_test.cpp",
         "parsenetaddress_test.cpp",
diff --git a/base/include/android-base/mapped_file.h b/base/include/android-base/mapped_file.h
new file mode 100644
index 000000000..52d11eda9
--- /dev/null
+++ b/base/include/android-base/mapped_file.h
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2018 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.
+ */
+
+#pragma once
+
+#include "android-base/macros.h"
+
+#include <sys/types.h>
+
+#include <memory>
+
+#if defined(_WIN32)
+#include <windows.h>
+#define PROT_READ 1
+#define PROT_WRITE 2
+#else
+#include <sys/mman.h>
+#endif
+
+namespace android {
+namespace base {
+
+/**
+ * A region of a file mapped into memory.
+ */
+class MappedFile {
+ public:
+  /**
+   * Creates a new mapping of the file pointed to by `fd`. Unlike the underlying OS primitives,
+   * `offset` does not need to be page-aligned. If `PROT_WRITE` is set in `prot`, the mapping
+   * will be writable, otherwise it will be read-only. Mappings are always `MAP_SHARED`.
+   */
+  static std::unique_ptr<MappedFile> FromFd(int fd, off64_t offset, size_t length, int prot);
+
+  /**
+   * Removes the mapping.
+   */
+  ~MappedFile();
+
+  char* data() { return base_ + offset_; }
+  size_t size() { return size_; }
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(MappedFile);
+
+  char* base_;
+  size_t size_;
+
+  size_t offset_;
+
+#if defined(_WIN32)
+  MappedFile(char* base, size_t size, size_t offset, HANDLE handle)
+      : base_(base), size_(size), offset_(offset), handle_(handle) {}
+  HANDLE handle_;
+#else
+  MappedFile(char* base, size_t size, size_t offset) : base_(base), size_(size), offset_(offset) {}
+#endif
+};
+
+}  // namespace base
+}  // namespace android
diff --git a/base/mapped_file.cpp b/base/mapped_file.cpp
new file mode 100644
index 000000000..f7901afa4
--- /dev/null
+++ b/base/mapped_file.cpp
@@ -0,0 +1,71 @@
+/*
+ * Copyright (C) 2018 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.
+ */
+
+#include "android-base/mapped_file.h"
+
+namespace android {
+namespace base {
+
+static off64_t InitPageSize() {
+#if defined(_WIN32)
+  SYSTEM_INFO si;
+  GetSystemInfo(&si);
+  return si.dwAllocationGranularity;
+#else
+  return sysconf(_SC_PAGE_SIZE);
+#endif
+}
+
+std::unique_ptr<MappedFile> MappedFile::FromFd(int fd, off64_t offset, size_t length, int prot) {
+  static off64_t page_size = InitPageSize();
+  size_t slop = offset % page_size;
+  off64_t file_offset = offset - slop;
+  off64_t file_length = length + slop;
+
+#if defined(_WIN32)
+  HANDLE handle =
+      CreateFileMapping(reinterpret_cast<HANDLE>(_get_osfhandle(fd)), nullptr,
+                        (prot & PROT_WRITE) ? PAGE_READWRITE : PAGE_READONLY, 0, 0, nullptr);
+  if (handle == nullptr) return nullptr;
+  void* base = MapViewOfFile(handle, (prot & PROT_WRITE) ? FILE_MAP_ALL_ACCESS : FILE_MAP_READ, 0,
+                             file_offset, file_length);
+  if (base == nullptr) {
+    CloseHandle(handle);
+    return nullptr;
+  }
+  return std::unique_ptr<MappedFile>(
+      new MappedFile{static_cast<char*>(base), length, slop, handle});
+#else
+  void* base = mmap(nullptr, file_length, prot, MAP_SHARED, fd, file_offset);
+  if (base == MAP_FAILED) return nullptr;
+  return std::unique_ptr<MappedFile>(new MappedFile{static_cast<char*>(base), length, slop});
+#endif
+}
+
+MappedFile::~MappedFile() {
+#if defined(_WIN32)
+  if (base_ != nullptr) UnmapViewOfFile(base_);
+  if (handle_ != nullptr) CloseHandle(handle_);
+#else
+  if (base_ != nullptr) munmap(base_, size_);
+#endif
+
+  base_ = nullptr;
+  offset_ = size_ = 0;
+}
+
+}  // namespace base
+}  // namespace android
diff --git a/base/mapped_file_test.cpp b/base/mapped_file_test.cpp
new file mode 100644
index 000000000..57fde6f45
--- /dev/null
+++ b/base/mapped_file_test.cpp
@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2018 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.
+ */
+
+#include "android-base/mapped_file.h"
+
+#include <gtest/gtest.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <string>
+
+#include "android-base/file.h"
+#include "android-base/test_utils.h"
+#include "android-base/unique_fd.h"
+
+TEST(mapped_file, smoke) {
+  TemporaryFile tf;
+  ASSERT_TRUE(tf.fd != -1);
+  ASSERT_TRUE(android::base::WriteStringToFd("hello world", tf.fd));
+
+  auto m = android::base::MappedFile::FromFd(tf.fd, 3, 2, PROT_READ);
+  ASSERT_EQ(2u, m->size());
+  ASSERT_EQ('l', m->data()[0]);
+  ASSERT_EQ('o', m->data()[1]);
+}