Revert mmap loader changes (pytorch#11928)

### Summary
Revert pytorch#11654 and
pytorch#11858 due to Meta-internal
build breakage. I will re-land these (preserving attribution).

Author: GregoryComer

extension/data_loader/mmap_data_loader.cpp

@@ -150,10 +150,10 @@ void MunmapSegment(void* context, void* data, size_t size) {
 }
 } // namespace
 
-/**
- * Validates that file read range is within bounds.
- */
-Error MmapDataLoader::validate_input(size_t offset, size_t size) const {
+Result<FreeableBuffer> MmapDataLoader::load(
+    size_t offset,
+    size_t size,
+    ET_UNUSED const DataLoader::SegmentInfo& segment_info) const {
   ET_CHECK_OR_RETURN_ERROR(
       // Probably had its value moved to another instance.
       fd_ >= 0,
@@ -173,18 +173,6 @@ Error MmapDataLoader::validate_input(size_t offset, size_t size) const {
       InvalidArgument,
       "Offset %zu too large for off_t",
       offset);
-  return Error::Ok;
-}
-
-Result<FreeableBuffer> MmapDataLoader::load(
-    size_t offset,
-    size_t size,
-    ET_UNUSED const DataLoader::SegmentInfo& segment_info) const {
-  // Ensure read range is valid.
-  auto validation_err = validate_input(offset, size);
-  if (validation_err != Error::Ok) {
-    return validation_err;
-  }
 
   // mmap() will fail if the size is zero.
   if (size == 0) {
@@ -279,69 +267,5 @@ Result<size_t> MmapDataLoader::size() const {
   return file_size_;
 }
 
-Error MmapDataLoader::load_into(
-    size_t offset,
-    size_t size,
-    ET_UNUSED const SegmentInfo& segment_info,
-    void* buffer) const {
-  ET_CHECK_OR_RETURN_ERROR(
-      buffer != nullptr, InvalidArgument, "Buffer is null");
-
-  // Ensure read range is valid.
-  auto err = validate_input(offset, size);
-  if (err != Error::Ok) {
-    return err;
-  }
-
-  // Nothing to copy.
-  if (size == 0) {
-    return Error::Ok;
-  }
-
-  // Find the range of pages that covers the requested region.
-  Range range =
-      get_overlapping_pages(static_cast<uintptr_t>(offset), size, page_size_);
-
-  size_t map_size = range.size;
-  if (range.start + map_size > file_size_) {
-    // Clamp to the end of the file.
-    //
-    // The Windows implementation of mmap uses CreateFileMapping which returns
-    // error STATUS_SECTION_TOO_BIG (0xc0000040) if we try to map past the end
-    // of the last page of a file mapped in as read-only.
-    map_size = file_size_ - range.start;
-  }
-
-  // Map the pages read-only. MAP_PRIVATE vs. MAP_SHARED doesn't matter since
-  // the data is read-only, but use PRIVATE just to further avoid accidentally
-  // modifying the file.
-  void* pages = ::mmap(
-      nullptr,
-      map_size,
-      PROT_READ,
-      MAP_PRIVATE,
-      fd_,
-      static_cast<off_t>(range.start));
-  ET_CHECK_OR_RETURN_ERROR(
-      pages != MAP_FAILED,
-      AccessFailed,
-      "Failed to map %s: mmap(..., size=%zd, ..., fd=%d, offset=0x%zx)",
-      file_name_,
-      range.size,
-      fd_,
-      range.start);
-
-  // Offset into mapped region.
-  const size_t map_delta = offset - range.start;
-
-  // Copy data into caller's buffer.
-  std::memcpy(buffer, static_cast<uint8_t*>(pages) + map_delta, size);
-
-  // Unmap mapped region.
-  ::munmap(pages, map_size);
-
-  return Error::Ok;
-}
-
 } // namespace extension
 } // namespace executorch

extension/data_loader/mmap_data_loader.h

@@ -95,13 +95,6 @@ class MmapDataLoader final : public executorch::runtime::DataLoader {
 
   ET_NODISCARD executorch::runtime::Result<size_t> size() const override;
 
-  ET_NODISCARD
-  executorch::runtime::Error load_into(
-      size_t offset,
-      size_t size,
-      ET_UNUSED const SegmentInfo& segment_info,
-      void* buffer) const override;
-
  private:
   MmapDataLoader(
       int fd,
@@ -120,10 +113,6 @@ class MmapDataLoader final : public executorch::runtime::DataLoader {
   MmapDataLoader& operator=(const MmapDataLoader&) = delete;
   MmapDataLoader& operator=(MmapDataLoader&&) = delete;
 
-  ET_NODISCARD executorch::runtime::Error validate_input(
-      size_t offset,
-      size_t size) const;
-
   const char* const file_name_; // String data is owned by the instance.
   const size_t file_size_;
   const size_t page_size_;

extension/data_loader/test/mmap_data_loader_test.cpp

@@ -376,56 +376,3 @@ TEST_F(MmapDataLoaderTest, DEPRECATEDFrom) {
   ASSERT_EQ(total_size.error(), Error::Ok);
   EXPECT_EQ(*total_size, contents_size);
 }
-
-// Tests that load_into copies bytes correctly.
-TEST_F(MmapDataLoaderTest, LoadIntoCopiesCorrectly) {
-  // Create a test string.
-  const char* test_text = "FILE_CONTENTS";
-  const size_t text_size = std::strlen(test_text);
-  TempFile tf(test_text);
-
-  // Wrap it in a loader.
-  Result<MmapDataLoader> mdl = MmapDataLoader::from(tf.path().c_str());
-  ASSERT_EQ(mdl.error(), Error::Ok);
-
-  // Destination buffer.
-  std::vector<uint8_t> dst(text_size);
-
-  // Call load_into()
-  Error err = mdl->load_into(
-      /*offset=*/0,
-      /*size=*/text_size,
-      DataLoader::SegmentInfo(DataLoader::SegmentInfo::Type::Program),
-      dst.data());
-  ASSERT_EQ(err, Error::Ok);
-
-  // Verify memory copied correctly.
-  EXPECT_EQ(0, std::memcmp(dst.data(), test_text, text_size));
-}
-
-// Tests that load_into copies offset slice correctly.
-TEST_F(MmapDataLoaderTest, LoadIntoCopiesOffsetCorrectly) {
-  // Create a test string.
-  const char* contents = "ABCDEFGH";
-  TempFile tf(contents);
-
-  // Wrap it in a loader.
-  Result<MmapDataLoader> mdl = MmapDataLoader::from(tf.path().c_str());
-  ASSERT_EQ(mdl.error(), Error::Ok);
-
-  // Copying 3 bytes starting at offset 2 = "CDE"
-  const size_t offset = 2;
-  const size_t size = 3;
-  uint8_t dst[size];
-
-  // Call load_into()
-  Error err = mdl->load_into(
-      offset,
-      size,
-      DataLoader::SegmentInfo(DataLoader::SegmentInfo::Type::Program),
-      dst);
-  ASSERT_EQ(err, Error::Ok);
-
-  // Verify memory copied correctly.
-  EXPECT_EQ(0, std::memcmp(dst, contents + offset, size));
-}