media: VideoFrame: add offset for shared memory buffers

content/common/gpu/media/gpu_video_encode_accelerator.cc

Index: content/common/gpu/media/gpu_video_encode_accelerator.cc
diff --git a/content/common/gpu/media/gpu_video_encode_accelerator.cc b/content/common/gpu/media/gpu_video_encode_accelerator.cc
index df16d97839ac9b14e8a407ce06d25622df1e873b..98d0406b2359e89bd7e12dedcaf8eadbb0afb6d4 100644
--- a/content/common/gpu/media/gpu_video_encode_accelerator.cc
+++ b/content/common/gpu/media/gpu_video_encode_accelerator.cc
@@ -9,6 +9,8 @@
 #include "base/logging.h"
 #include "base/memory/shared_memory.h"
 #include "base/message_loop/message_loop_proxy.h"
+#include "base/numerics/safe_math.h"
+#include "base/sys_info.h"
 #include "build/build_config.h"
 #include "content/common/gpu/gpu_channel.h"
 #include "content/common/gpu/gpu_messages.h"
@@ -245,6 +247,7 @@ GpuVideoEncodeAccelerator::CreateAndroidVEA() {
 
 void GpuVideoEncodeAccelerator::OnEncode(int32 frame_id,
                                          base::SharedMemoryHandle buffer_handle,
+                                         uint32 buffer_offset,
                                          uint32 buffer_size,
                                          bool force_keyframe) {
   DVLOG(3) << "GpuVideoEncodeAccelerator::OnEncode(): frame_id=" << frame_id
@@ -259,16 +262,36 @@ void GpuVideoEncodeAccelerator::OnEncode(int32 frame_id,
     return;
   }
 
+  base::CheckedNumeric<off_t> map_offset = buffer_offset;
+  map_offset -= (buffer_offset % base::SysInfo::VMAllocationGranularity());
+  if (!map_offset.IsValid()) {
+    DLOG(ERROR) << "GpuVideoEncodeAccelerator::OnEncode():"
+                << " invalid buffer_offset=" << buffer_offset;
+    NotifyError(media::VideoEncodeAccelerator::kPlatformFailureError);
+    return;
+  }
+  base::CheckedNumeric<size_t> map_size = buffer_size;
+  map_size += (static_cast<off_t>(buffer_offset) -
+               static_cast<off_t>(map_offset.ValueOrDie()));

[dcheng, 2015/02/06 21:39:47]

Let's avoid casting if we don't have to. It makes it harder to be sure if
something is going to overflow at some point.

How about this?

uint32 aligned_offset = buffer_offset %
base::SysInfo::VMAllocationGranularity();
base::CheckedNumeric<off_t> map_offset = buffer_offset;
map_offset -= aligned_offset;
base::CheckedNumeric<size_t> map_size = buffer_size;
map_size += aligned_offset;

if (!map_offset.IsValid() || !map_size.IsValid()) {
  // error handling here...
}

[llandwerlin-old, 2015/02/09 14:48:47]

Done.

+  if (!map_size.IsValid()) {
+    DLOG(ERROR) << "GpuVideoEncodeAccelerator::OnEncode():"
+                << " invalid buffer_offset=" << buffer_offset
+                << " buffer_size=" << buffer_size;
+    NotifyError(media::VideoEncodeAccelerator::kPlatformFailureError);
+    return;
+  }
+
   scoped_ptr<base::SharedMemory> shm(
       new base::SharedMemory(buffer_handle, true));
-  if (!shm->Map(buffer_size)) {
+  if (!shm->MapAt(map_offset.ValueOrDie(), map_size.ValueOrDie())) {
     DLOG(ERROR) << "GpuVideoEncodeAccelerator::OnEncode(): "
                    "could not map frame_id=" << frame_id;
     NotifyError(media::VideoEncodeAccelerator::kPlatformFailureError);
     return;
   }
 
-  uint8* shm_memory = reinterpret_cast<uint8*>(shm->memory());
+  uint8* shm_memory = reinterpret_cast<uint8*>(shm->memory()) +
+                      (buffer_offset - map_offset.ValueOrDie());
   scoped_refptr<media::VideoFrame> frame =
       media::VideoFrame::WrapExternalPackedMemory(
           input_format_,
@@ -278,6 +301,7 @@ void GpuVideoEncodeAccelerator::OnEncode(int32 frame_id,
           shm_memory,
           buffer_size,
           buffer_handle,
+          buffer_offset,
           base::TimeDelta(),
           // It's turtles all the way down...
           base::Bind(base::IgnoreResult(&base::MessageLoopProxy::PostTask),