Add a PartialPreReadImage function to file_util (on Windows).

base/file_util_win.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/file_util.h"
 
 #include <windows.h>
 #include <propvarutil.h>
 #include <psapi.h>
 #include <shellapi.h>
 #include <shlobj.h>
 #include <time.h>
 
+#include <algorithm>
 #include <limits>
 #include <string>
 
 #include "base/file_path.h"
 #include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/metrics/histogram.h"
 #include "base/string_number_conversions.h"
 #include "base/string_util.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/time.h"
 #include "base/utf_string_conversions.h"
 #include "base/win/pe_image.h"
 #include "base/win/scoped_comptr.h"
 #include "base/win/scoped_handle.h"
 #include "base/win/win_util.h"
@@ skipping 1069 matching lines @@
   bool success = false;
   HANDLE cp = GetCurrentProcess();
   if (::GetMappedFileNameW(cp, file_view, mapped_file_path, kMaxPathLength)) {
     *nt_path = FilePath(mapped_file_path);
     success = true;
   }
   ::UnmapViewOfFile(file_view);
   return success;
 }
 
+namespace {
+
+// The PE file headers usually fit into a single 1KB page, and a PE file must
+// at least contain the initial page with the headers. That said, as long as
+// we expect at least sizeof(IMAGE_DOS_HEADER) bytes, we're ok.

[Evan Martin, 2012/01/27 20:13:58]

This comment is about PE files, but it doesn't describe what the variable it's
heading is for.

[Roger McFarlane (Google), 2012/01/27 21:25:54]

Fixed the comments and chose a better name for the constant.

+const size_t kMinPreReadBufferSize = 0x400;
+
+// A handy symbolic constant.
+const size_t kOneHundredPercent = 100;
+
+void StaticAssertions() {
+  COMPILE_ASSERT(kMinPreReadBufferSize >= sizeof(IMAGE_DOS_HEADER),
+                 min_pre_read_buffer_size_must_be_bigger_than_dos_header);
+}
+
+// This struct provides a deallocation functor for use with scoped_ptr<T>
+// allocated with ::VirtualAlloc().
+struct ScopedPtrVirtualFree {
+  void operator() (void* ptr) {
+    ::VirtualFree(ptr, 0, MEM_RELEASE);
+  }
+};
+
+// A wrapper for the Win32 ::SetFilePointer() function with some error checking.
+bool SetFilePointer(HANDLE file_handle, size_t position) {
+  return position <= std::numeric_limits<LONG>::max() &&
+      ::SetFilePointer(file_handle,
+                       static_cast<LONG>(position),
+                       NULL,
+                       FILE_BEGIN) != INVALID_SET_FILE_POINTER;
+}
+
+// A helper function to read the next @p bytes_to_read bytes from the file
+// given by @p file_handle into @p buffer.
+bool ReadNextBytes(HANDLE file_handle, void* buffer, size_t bytes_to_read) {
+  DCHECK(file_handle != INVALID_HANDLE_VALUE);
+  DCHECK(buffer != NULL);
+  DCHECK(bytes_to_read > 0);
+
+  DWORD bytes_read = 0;
+  return bytes_to_read <= std::numeric_limits<DWORD>::max() &&
+      ::ReadFile(file_handle,
+                 buffer,
+                 static_cast<DWORD>(bytes_to_read),
+                 &bytes_read,
+                 NULL) &&
+      bytes_read == bytes_to_read;
+}
+
+// A helper function to extend the @p current_buffer of bytes such that it
+// contains @p desired_length bytes read from @p file.
+// @pre It is assumed that file has been used to sequentially populate
+//     @p current_buffer thus far and is already positioned at the
+//     appropriate read position.
+bool ReadMissingBytes(HANDLE file_handle,
+                      std::vector<uint8>* current_buffer,
+                      size_t desired_length) {
+  DCHECK(file_handle != INVALID_HANDLE_VALUE);
+  DCHECK(current_buffer != NULL);
+
+  size_t current_length = current_buffer->size();
+  if (current_length >= desired_length)
+    return true;
+
+  size_t bytes_to_read = desired_length - current_length;
+  current_buffer->resize(desired_length);
+  return ReadNextBytes(file_handle,
+                       &((*current_buffer)[current_length]),
+                       bytes_to_read);
+}
+
+// Return a @p percentage of the number of initialized bytes in the given
+// @p section.
+//
+// This returns a percentage of the lesser of the size of the raw data in
+// the section and the virtual size of the section.
+//
+// Note that sections can have their tails implicitly initialized to zero
+// (i.e., their virtual size is larger than the raw size) and that raw data
+// is padded to the PE page size if the entire section is initialized (i.e.,
+// their raw data size will be larger than the virtual size).
+//
+// Any data after the initialized portion of the section will be soft-faulted
+// in (very quickly) as needed, so we don't need to include it in the returned
+// length.
+size_t GetPercentageOfSectionLength(const IMAGE_SECTION_HEADER* section,
+                                    size_t percentage) {
+  DCHECK(section != NULL);
+  DCHECK_GT(percentage, 0);
+  DCHECK_LE(percentage, kOneHundredPercent);
+
+  size_t initialized_length = std::min(section->SizeOfRawData,
+                                       section->Misc.VirtualSize);
+
+  if (initialized_length == 0)
+    return 0;
+
+  size_t length = (initialized_length * percentage) / kOneHundredPercent;
+
+  return std::max<size_t>(length, 1);
+}
+
+// Helper function to read through a @p percentage of the given @p section
+// of the file given by @p file_handle. The @p temp_buffer is (re)used as
+// a transient storage area as the section is read in chunks of
+// @p temp_buffer_size bytes.
+bool ReadThroughSection(HANDLE file_handle,
+                        const IMAGE_SECTION_HEADER* section,
+                        size_t percentage,
+                        void* temp_buffer,
+                        size_t temp_buffer_size) {
+  DCHECK(file_handle != INVALID_HANDLE_VALUE);
+  DCHECK(section != NULL);
+  DCHECK_LE(percentage, kOneHundredPercent);
+  DCHECK(temp_buffer != NULL);
+  DCHECK_GE(temp_buffer_size,  kMinPreReadBufferSize);
+
+  size_t bytes_to_read = GetPercentageOfSectionLength(section, percentage);
+  if (bytes_to_read == 0)
+    return true;
+
+  if (!SetFilePointer(file_handle, section->PointerToRawData))
+    return false;
+
+  // Read all chunks except the last one.
+  size_t max_chunk_size = temp_buffer_size;
+  while (bytes_to_read > max_chunk_size) {
+    if (!ReadNextBytes(file_handle, temp_buffer, max_chunk_size))
+      return false;
+    bytes_to_read -= max_chunk_size;
+  }
+
+  // Read the last (possibly partial) chunk and return.
+  return ReadNextBytes(file_handle, temp_buffer, bytes_to_read);
+}
+
+// A helper function to touch all pages in the range
+// [base_addr, base_addr + length).
+void TouchPagesInRange(void* base_addr, size_t length) {
+  DCHECK(base_addr != NULL);
+  DCHECK(length > 0);
+
+  // Get the system info so we know the page size.
+  SYSTEM_INFO system_info;
+  GetSystemInfo(&system_info);
+
+  // We don't want to read outside the byte range (which could trigger an
+  // access violation), so let's figure out the exact locations of the first
+  // and final bytes we want to read.
+  volatile uint8* touch_ptr = reinterpret_cast<uint8*>(base_addr);
+  volatile uint8* final_touch_ptr = touch_ptr + length - 1;
+
+  // Read the memory in the range [touch_ptr, final_touch_ptr] with a stride
+  // of the system page size, to ensure that it's been paged in.
+  uint8 dummy;
+  while (touch_ptr < final_touch_ptr) {
+    dummy = *touch_ptr;
+    touch_ptr += system_info.dwPageSize;
+  }
+  dummy = *final_touch_ptr;
+}
+
+}  // namespace
+
+namespace internal {
+
+BASE_EXPORT bool PartialPreReadImageOnDisk(const wchar_t* file_path,
+                                           size_t percentage,
+                                           size_t max_chunk_size) {
+  // TODO(rogerm): change this to have the number of bytes pre-read per
+  //     section be driven by a static table within the PE file (defaulting to
+  //     full read if it's not there?) that's initialized by the optimization
+  //     toolchain.
+  DCHECK(file_path != NULL);
+
+  if (percentage == 0)
+    return true;
+
+  if (percentage > kOneHundredPercent)
+    percentage = kOneHundredPercent;
+
+  // Validate/setup max_chunk_size, imposing a 1MB minimum on the chunk size.
+  const size_t kMinChunkSize = 1024 * 1024;
+  max_chunk_size = std::max(max_chunk_size, kMinChunkSize);
+
+  // Open the file.
+  base::win::ScopedHandle file(
+      CreateFile(file_path,
+                 GENERIC_READ,
+                 FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
+                 NULL,
+                 OPEN_EXISTING,
+                 FILE_FLAG_SEQUENTIAL_SCAN,
+                 NULL));
+
+  if (!file.IsValid())
+    return false;
+
+  // Allocate a resizable buffer for the headers. We initially reserve as much
+  // space as we typically see as the header size for chrome.dll and other
+  // PE images.
+  std::vector<uint8> headers;
+  headers.reserve(kMinPreReadBufferSize);
+
+  // Read, hopefully, all of the headers.
+  if (!ReadMissingBytes(file, &headers, kMinPreReadBufferSize))
+    return false;
+
+  // The DOS header starts at offset 0 and allows us to get the offset of the
+  // NT headers. Let's ensure we've read enough to capture the NT headers.
+  size_t nt_headers_start =
+      reinterpret_cast<IMAGE_DOS_HEADER*>(&headers[0])->e_lfanew;
+  size_t nt_headers_end = nt_headers_start + sizeof(IMAGE_NT_HEADERS);
+  if (!ReadMissingBytes(file, &headers, nt_headers_end))
+    return false;
+
+  // Now that we've got the NT headers we can get the total header size,
+  // including all of the section headers. Let's ensure we've read enough
+  // to capture all of the header data.
+  size_t size_of_headers = reinterpret_cast<IMAGE_NT_HEADERS*>(
+      &headers[nt_headers_start])->OptionalHeader.SizeOfHeaders;
+  if (!ReadMissingBytes(file, &headers, size_of_headers))
+    return false;
+
+  // Now we have all of the headers. This is enough to let us use the PEImage
+  // wrapper to query the structure of the image.
+  base::win::PEImage pe_image(reinterpret_cast<HMODULE>(&headers[0]));
+  CHECK(pe_image.VerifyMagic());
+
+  // Allocate a buffer to hold the pre-read bytes.
+  scoped_ptr_malloc<uint8, ScopedPtrVirtualFree> buffer(
+      reinterpret_cast<uint8*>(
+          ::VirtualAlloc(NULL, max_chunk_size, MEM_COMMIT, PAGE_READWRITE)));
+  if (buffer.get() == NULL)
+    return false;
+
+  // Iterate over each section, reading in a percentage of each.
+  const IMAGE_SECTION_HEADER* section = NULL;
+  for (UINT i = 0; (section = pe_image.GetSectionHeader(i)) != NULL; ++i) {
+    CHECK_LE(reinterpret_cast<const uint8*>(section + 1),
+             &headers[0] + headers.size());
+    if (!ReadThroughSection(
+            file, section, percentage, buffer.get(), max_chunk_size))
+      return false;
+  }
+
+  // We're done.
+  return true;
+}
+
+BASE_EXPORT bool PartialPreReadImageInMemory(const wchar_t* file_path,
+                                             size_t percentage) {
+  // TODO(rogerm): change this to have the number of bytes pre-read per
+  //     section be driven by a static table within the PE file (defaulting to
+  //     full read if it's not there?) that's initialized by the optimization
+  //     toolchain.
+  DCHECK(file_path != NULL);
+
+  if (percentage == 0)
+    return true;
+
+  if (percentage > kOneHundredPercent)
+    percentage = kOneHundredPercent;
+
+  HMODULE dll_module = ::LoadLibraryExW(
+      file_path,
+      NULL,
+      LOAD_WITH_ALTERED_SEARCH_PATH | DONT_RESOLVE_DLL_REFERENCES);
+
+  if (!dll_module)
+    return false;
+
+  base::win::PEImage pe_image(dll_module);
+  CHECK(pe_image.VerifyMagic());
+
+  // Iterate over each section, stepping through a percentage of each to page
+  // it in off the disk.
+  const IMAGE_SECTION_HEADER* section = NULL;
+  for (UINT i = 0; (section = pe_image.GetSectionHeader(i)) != NULL; ++i) {
+    // Get the extent we want to touch.
+    size_t length = GetPercentageOfSectionLength(section, percentage);
+    if (length == 0)
+      continue;
+    uint8* start =
+        static_cast<uint8*>(pe_image.RVAToAddr(section->VirtualAddress));
+
+    // Verify that the extent we're going to touch falls inside the section
+    // we expect it to (and by implication, inside the pe_image).
+    CHECK_EQ(section,
+             pe_image.GetImageSectionFromAddr(start));
+    CHECK_EQ(section,
+             pe_image.GetImageSectionFromAddr(start + length - 1));
+
+    // Page in the section range.
+    TouchPagesInRange(start, length);
+  }
+
+  FreeLibrary(dll_module);
+
+  return true;
+}
+
+}  // namespace file_util::internal
+
 bool PreReadImage(const wchar_t* file_path, size_t size_to_read,
                   size_t step_size) {
   base::ThreadRestrictions::AssertIOAllowed();
   if (base::win::GetVersion() > base::win::VERSION_XP) {
     // Vista+ branch. On these OSes, the forced reads through the DLL actually
     // slows warm starts. The solution is to sequentially read file contents
     // with an optional cap on total amount to read.
     base::win::ScopedHandle file(
         CreateFile(file_path,
                    GENERIC_READ,
@@ skipping 21 matching lines @@
     size_t total_read = 0;
     while (::ReadFile(file, buffer, actual_step_size, &len, NULL) &&
            len > 0 &&
            (size_to_read ? total_read < size_to_read : true)) {
       total_read += static_cast<size_t>(len);
     }
     ::VirtualFree(buffer, 0, MEM_RELEASE);
   } else {
     // WinXP branch. Here, reading the DLL from disk doesn't do
     // what we want so instead we pull the pages into memory by loading
-    // the DLL and touching pages at a stride.
+    // the DLL and touching pages at a stride. We use the system's page
+    // size as the stride, ignoring the passed in step_size, to make sure
+    // each page in the range is touched.
     HMODULE dll_module = ::LoadLibraryExW(
         file_path,
         NULL,
         LOAD_WITH_ALTERED_SEARCH_PATH | DONT_RESOLVE_DLL_REFERENCES);
 
     if (!dll_module)
       return false;
 
     base::win::PEImage pe_image(dll_module);
+    CHECK(pe_image.VerifyMagic());
+
+    // We don't want to read past the end of the module (which could trigger
+    // an access violation), so make sure to check the image size.
     PIMAGE_NT_HEADERS nt_headers = pe_image.GetNTHeaders();
-    size_t actual_size_to_read = size_to_read ? size_to_read :
-                                 nt_headers->OptionalHeader.SizeOfImage;
-    volatile uint8* touch = reinterpret_cast<uint8*>(dll_module);
-    size_t offset = 0;
-    while (offset < actual_size_to_read) {
-      uint8 unused = *(touch + offset);
-      offset += step_size;
-    }
+    size_t dll_module_length = std::min(
+        size_to_read ? size_to_read : ~0,
+        static_cast<size_t>(nt_headers->OptionalHeader.SizeOfImage));
+
+    // Page in then release the module.
+    TouchPagesInRange(dll_module, dll_module_length);
     FreeLibrary(dll_module);
   }
 
   return true;
 }
 
+bool PartialPreReadImage(const wchar_t* file_path,
+                         size_t percentage,
+                         size_t max_chunk_size) {
+  base::ThreadRestrictions::AssertIOAllowed();
+
+  if (percentage >= kOneHundredPercent) {
+    // If we're reading the whole image, we don't need to parse headers and
+    // navigate sections, the basic PreReadImage() can be used to just step
+    // blindly through the entire file / address-space.
+    return PreReadImage(file_path, 0, max_chunk_size);
+  }
+
+  using internal::PartialPreReadImageInMemory;
+  using internal::PartialPreReadImageOnDisk;
+
+  if (base::win::GetVersion() > base::win::VERSION_XP) {
+    // Vista+ branch. On these OSes, we warm up the Image by reading its
+    // file off the disk.
+    return PartialPreReadImageOnDisk(file_path, percentage, max_chunk_size);
+  }
+
+  // WinXP branch. For XP, reading the image from disk doesn't do what we want
+  // so instead we pull the pages into memory by loading the DLL and touching
+  // initialized pages at a stride.
+  return PartialPreReadImageInMemory(file_path, percentage);
+}
+
 }  // namespace file_util