Linux Video Capture: Add V4L2VideoCaptureDelegate{Single,Multi}Plane.

media/video/capture/linux/v4l2_video_capture_delegate.cc

Index: media/video/capture/linux/v4l2_video_capture_delegate.cc
diff --git a/media/video/capture/linux/v4l2_video_capture_delegate.cc b/media/video/capture/linux/v4l2_video_capture_delegate.cc
new file mode 100644
index 0000000000000000000000000000000000000000..3ba1113d338cb6e69dddcb65bee4a97d58c68bdb
--- /dev/null
+++ b/media/video/capture/linux/v4l2_video_capture_delegate.cc
@@ -0,0 +1,605 @@
+// Copyright 2015 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 "media/video/capture/linux/v4l2_video_capture_delegate.h"
+
+#include <poll.h>
+#include <sys/fcntl.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+
+#include "base/bind.h"
+#include "base/files/file_enumerator.h"
+#include "base/posix/eintr_wrapper.h"
+#include "base/strings/stringprintf.h"
+#include "media/base/bind_to_current_loop.h"
+#include "media/video/capture/linux/video_capture_device_linux.h"
+
+namespace media {
+
+// Max number of video buffers VideoCaptureDeviceLinux can allocate.
+const uint32_t kMaxVideoBuffers = 2;
+// Timeout in milliseconds v4l2_thread_ blocks waiting for a frame from the hw.
+const int kCaptureTimeoutMs = 200;
+// The number of continuous timeouts tolerated before treated as error.
+const int kContinuousTimeoutLimit = 10;
+// MJPEG is preferred if the requested width or height is larger than this.
+const int kMjpegWidth = 640;
+const int kMjpegHeight = 480;
+// Typical framerate, in fps
+const int kTypicalFramerate = 30;
+
+// V4L2 color formats supported by V4L2CaptureDelegateSinglePlane. This list is
+// ordered by precedence of use.
+static const uint32_t kSinglePlaneSupportedFormats[] = {
+    V4L2_PIX_FMT_YUV420,
+    V4L2_PIX_FMT_YUYV,
+    V4L2_PIX_FMT_UYVY,
+    // JPEG works as MJPEG on some gspca webcams from field reports.
+    V4L2_PIX_FMT_JPEG};
+
+// List of supported formats and their respective amount of sub-buffers for
+// V4L2CaptureDelegateMultiPlane.
+static const struct {
+  uint32_t fourcc;
+  size_t num_planes;
+} kMultiPlaneSupportedFormats[] = {
+    {V4L2_PIX_FMT_YUV420M, 3}
+    // TODO(mcasas): add V4L2_PIX_FMT_YVU420M when available in bots.
+};
+
+// Returns the input fourcc as a std::string four char representation.
+static std::string FourccToString(uint32_t fourcc) {
+  return base::StringPrintf("%c%c%c%c", fourcc & 0xFF, (fourcc >> 8) & 0xFF,
+                            (fourcc >> 16) & 0xFF, (fourcc >> 24) & 0xFF);
+}
+
+static std::list<uint32_t> GetListOfUsableFourCcsSinglePlane() {
+  return std::list<uint32_t>(
+      kSinglePlaneSupportedFormats,
+      kSinglePlaneSupportedFormats + arraysize(kSinglePlaneSupportedFormats));
+}
+
+static size_t GetNumPlanesForFourCc(uint32_t fourcc) {
+  for (const auto& fourcc_and_pixel_format : kMultiPlaneSupportedFormats) {
+    if (fourcc_and_pixel_format.fourcc == fourcc)
+      return fourcc_and_pixel_format.num_planes;
+  }
+  NOTREACHED() << "Unknown fourcc " << FourccToString(fourcc);
+  return 0;
+}
+
+static std::list<uint32_t> GetListOfUsableFourCcsMultiPlane() {
+  std::list<uint32_t> supported_formats;
+  for (const auto& i : kMultiPlaneSupportedFormats)
+    supported_formats.push_back(i.fourcc);
+  return supported_formats;
+}
+
+// V4L2 specifics for SPLANE API.
+class V4L2CaptureDelegateSinglePlane final : public V4L2VideoCaptureDelegate {
+ public:
+  V4L2CaptureDelegateSinglePlane(
+      const VideoCaptureDevice::Name& device_name,
+      const scoped_refptr<base::SingleThreadTaskRunner>& v4l2_task_runner,
+      int power_line_frequency)
+      : V4L2VideoCaptureDelegate(device_name,
+                                 v4l2_task_runner,
+                                 power_line_frequency) {}
+
+ private:
+  // BufferTracker derivation to implement construction semantics for SPLANE.
+  class BufferTrackerSPlane final : public BufferTracker {
+   public:
+    BufferTrackerSPlane(int fd, const v4l2_buffer& buffer);

[Pawel Osciak, 2015/03/06 10:43:54]

We need Initialize() methods as I mention elsewhere in order to return failures.

[mcasas, 2015/03/09 21:23:56]

Done.

+
+   private:
+    ~BufferTrackerSPlane() override {};
+  };
+
+  ~V4L2CaptureDelegateSinglePlane() override {};
+
+  // V4L2VideoCaptureDelegate virtual methods implementation.
+  scoped_refptr<BufferTracker> CreateBufferTracker(
+      int fd,
+      const v4l2_buffer& buffer) override;
+  void FillV4L2Format(v4l2_format* format,
+                      uint32_t width,
+                      uint32_t height,
+                      uint32_t pixelformat_fourcc) override;
+  void FinishFillingV4L2Buffer(v4l2_buffer* buffer) override {}
+  void SendBuffer(const v4l2_buffer& buffer) override;
+};
+
+// V4L2 specifics for MPLANE API.
+class V4L2CaptureDelegateMultiPlane final : public V4L2VideoCaptureDelegate {
+ public:
+  V4L2CaptureDelegateMultiPlane(
+      const VideoCaptureDevice::Name& device_name,
+      const scoped_refptr<base::SingleThreadTaskRunner>& v4l2_task_runner,
+      int power_line_frequency)
+      : V4L2VideoCaptureDelegate(device_name,
+                                 v4l2_task_runner,
+                                 power_line_frequency),
+        fourcc_(0),
+        num_planes_(0) {}
+
+ private:
+  // BufferTracker derivation to implement construction semantics for MPLANE.
+  class BufferTrackerMPlane final : public BufferTracker {
+   public:
+    BufferTrackerMPlane(int fd, const v4l2_buffer& buffer);
+
+   private:
+    ~BufferTrackerMPlane() override {};
+  };
+
+  ~V4L2CaptureDelegateMultiPlane() override {};
+
+  // V4L2VideoCaptureDelegate virtual methods implementation.
+  scoped_refptr<BufferTracker> CreateBufferTracker(
+      int fd,
+      const v4l2_buffer& buffer) override;
+  void FillV4L2Format(v4l2_format* format,
+                      uint32_t width,
+                      uint32_t height,
+                      uint32_t pixelformat_fourcc) override;
+  void FinishFillingV4L2Buffer(v4l2_buffer* buffer) override;
+  void SendBuffer(const v4l2_buffer& buffer) override;
+
+  // Actual pixel format and number of planes, known after FillV4L2Format().
+  uint32_t fourcc_;
+  size_t num_planes_;
+
+  // Scoped_ptr to allocate and track as many v4l2_plane structs as planes,
+  // needed inside v4l2_buffer.
+  scoped_ptr<struct v4l2_plane[]> v4l2_plane_;
+};
+
+// static
+scoped_refptr<V4L2VideoCaptureDelegate>
+V4L2VideoCaptureDelegate::CreateV4L2VideoCaptureDelegate(
+    const VideoCaptureDevice::Name& device_name,
+    const VideoPixelFormat pixel_format,
+    const scoped_refptr<base::SingleThreadTaskRunner>& v4l2_task_runner,
+    int power_line_frequency) {
+  switch (device_name.capture_api_type()) {
+    case VideoCaptureDevice::Name::V4L2_SINGLE_PLANE:
+      return make_scoped_refptr(new V4L2CaptureDelegateSinglePlane(
+          device_name, v4l2_task_runner, power_line_frequency));
+    case VideoCaptureDevice::Name::V4L2_MULTI_PLANE:
+      if (pixel_format != PIXEL_FORMAT_I420)

[Pawel Osciak, 2015/03/06 10:43:54]

This may bitrot. Please instead look up pixel_format in the supported formats
array above.

[mcasas, 2015/03/09 21:23:56]

I think this early-bail-out is not really needed
anymore. Best to leave this factory method to
create a V4L2 delegate of the appropriate API,
and, if the pixel format is not supported, fail
in AllocateAndStart() which is more orthodox, i.e.
follows other platform implementations modus
operandi.

[Pawel Osciak, 2015/03/13 09:52:52]

Acknowledged.

+        return scoped_refptr<V4L2VideoCaptureDelegate>();
+      return make_scoped_refptr(new V4L2CaptureDelegateMultiPlane(
+          device_name, v4l2_task_runner, power_line_frequency));
+    default:
+      NOTIMPLEMENTED() << "Unknown V4L2 capture API type";
+      return scoped_refptr<V4L2VideoCaptureDelegate>();
+  }
+}
+
+// static
+VideoPixelFormat V4L2VideoCaptureDelegate::V4l2FourCcToChromiumPixelFormat(
+    uint32_t v4l2_fourcc) {
+  const struct {
+    uint32_t fourcc;
+    VideoPixelFormat pixel_format;
+  } kFourCcAndChromiumPixelFormats[] = {
+      {V4L2_PIX_FMT_YUV420M, PIXEL_FORMAT_I420},
+      {V4L2_PIX_FMT_YUV420, PIXEL_FORMAT_I420},
+      {V4L2_PIX_FMT_YUYV, PIXEL_FORMAT_YUY2},
+      {V4L2_PIX_FMT_UYVY, PIXEL_FORMAT_UYVY},
+      {V4L2_PIX_FMT_MJPEG, PIXEL_FORMAT_MJPEG},
+      {V4L2_PIX_FMT_JPEG, PIXEL_FORMAT_MJPEG},
+  };
+  for (const auto& fourcc_and_pixel_format : kFourCcAndChromiumPixelFormats) {
+    if (fourcc_and_pixel_format.fourcc == v4l2_fourcc)
+      return fourcc_and_pixel_format.pixel_format;
+  }
+  DVLOG(1) << "Unsupported pixel format: " << FourccToString(v4l2_fourcc);
+  return PIXEL_FORMAT_UNKNOWN;
+}
+
+// static
+std::list<uint32_t> V4L2VideoCaptureDelegate::GetListOfUsableFourCss(

[emircan, 2015/03/04 02:47:47]

/s/FourCss/FourCcs/

[mcasas, 2015/03/09 21:23:56]

Done.

+    bool prefer_mjpeg) {
+  std::list<uint32_t> singleplane_formats = GetListOfUsableFourCcsSinglePlane();
+  std::list<uint32_t> multiplane_formats = GetListOfUsableFourCcsMultiPlane();
+  multiplane_formats.insert(multiplane_formats.end(),
+                            singleplane_formats.begin(),
+                            singleplane_formats.end());
+  // Add MJPEG to the front or the back of the list depending on |prefer_mjpeg|.
+  multiplane_formats.insert(

[Pawel Osciak, 2015/03/06 10:43:54]

if (prefer_mjpeg)
  multiplane_formats.push_front(MJPEG);
else
  multiplane_formats.push_back(MJPEG);

[mcasas, 2015/03/09 21:23:56]

Done.

+      (prefer_mjpeg ? multiplane_formats.begin() : multiplane_formats.end()),
+      V4L2_PIX_FMT_MJPEG);

[Pawel Osciak, 2015/03/06 10:43:55]

This is different from existing code, which always has JPEG last, MJPEG always
comes before JPEG.

[mcasas, 2015/03/09 21:23:56]

Done.

+  return multiplane_formats;
+}
+
+V4L2VideoCaptureDelegate::BufferTracker::BufferTracker(

[Pawel Osciak, 2015/03/06 10:43:55]

This is not needed?

[mcasas, 2015/03/09 21:23:56]

Needed due to:

[chromium-style] Complex class/struct needs an explicit out-of-line constructor.

But now, with an Init(...) method, it's not needed. Removed.

+    int fd,
+    const v4l2_buffer& buffer) {
+}
+
+V4L2VideoCaptureDelegate::BufferTracker::~BufferTracker() {
+  for (const auto& plane : planes_) {
+    if (plane->start == NULL)
+      continue;
+    const int result = munmap(plane->start, plane->length);
+    PLOG_IF(ERROR, result < 0) << "Error munmap()ing V4L2 buffer";
+  }
+}
+
+V4L2VideoCaptureDelegate::V4L2VideoCaptureDelegate(
+    const VideoCaptureDevice::Name& device_name,
+    const scoped_refptr<base::SingleThreadTaskRunner>& v4l2_task_runner,
+    int power_line_frequency)
+    : capture_type_((device_name.capture_api_type() ==
+                     VideoCaptureDevice::Name::V4L2_SINGLE_PLANE)
+                        ? V4L2_BUF_TYPE_VIDEO_CAPTURE
+                        : V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE),
+      v4l2_task_runner_(v4l2_task_runner),
+      device_name_(device_name),
+      power_line_frequency_(power_line_frequency),
+      is_capturing_(false),
+      timeout_count_(0),
+      rotation_(0) {
+}
+
+void V4L2VideoCaptureDelegate::AllocateAndStart(
+    int width,
+    int height,
+    float frame_rate,
+    scoped_ptr<VideoCaptureDevice::Client> client) {
+  DCHECK(v4l2_task_runner_->BelongsToCurrentThread());
+  DCHECK(client);
+  client_ = client.Pass();
+
+  // Need to open camera with O_RDWR after Linux kernel 3.3.
+  device_fd_.reset(HANDLE_EINTR(open(device_name_.id().c_str(), O_RDWR)));
+  if (!device_fd_.is_valid()) {
+    SetErrorState("Failed to open V4L2 device driver file.");
+    return;
+  }
+
+  v4l2_capability cap = {};
+  if (!((HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_QUERYCAP, &cap)) == 0) &&
+        ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE ||
+          cap.capabilities & V4L2_CAP_VIDEO_CAPTURE_MPLANE) &&
+         !(cap.capabilities & V4L2_CAP_VIDEO_OUTPUT) &&
+         !(cap.capabilities & V4L2_CAP_VIDEO_OUTPUT_MPLANE)))) {
+    device_fd_.reset();
+    SetErrorState("This is not a V4L2 video capture device");
+    return;
+  }
+
+  // Get supported video formats in preferred order.
+  // For large resolutions, favour mjpeg over raw formats.
+  const std::list<uint32_t>& desired_v4l2_formats =
+      GetListOfUsableFourCss(width > kMjpegWidth || height > kMjpegHeight);
+  std::list<uint32_t>::const_iterator best = desired_v4l2_formats.end();
+
+  v4l2_fmtdesc fmtdesc = {};
+  fmtdesc.type = capture_type_;
+  for (; HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_ENUM_FMT, &fmtdesc)) == 0;
+       ++fmtdesc.index) {
+    best = std::find(desired_v4l2_formats.begin(), best, fmtdesc.pixelformat);

[Pawel Osciak, 2015/03/06 10:43:55]

Maybe I'm missing something, but I think this will for example fail if we have
MJPEG at the front of desired_v4l2_formats and ENUM_FMT returns in order: MJPEG
and XYZ.

Then the first iteration will get best = desired_v4l2_formats.begin(), because
MJPEG is at beginning. Then second iteration will call an equivalent of best =
std::find(desired_v4l2_formats.begin(), desired_v4l2_formats.begin(),
fmtdesc.pixelformat), which is an empty list and will always fail. So best =
end() at the end and we will always fail, even though we should have matched
MJPEG?

[mcasas, 2015/03/09 21:23:56]

According to the fact that it works and the list
of possible equivalent implementations in [1],

Iterator a = foo.begin();
Iterator b = foo.begin();
std::find(a, b, bla) 

is |b|. 

So you could argue that the code as is, could do
several loop iterations after finding the best format.
emircan@ has a similar comment below.



[1] http://en.cppreference.com/w/cpp/algorithm/find

[Pawel Osciak, 2015/03/13 09:52:52]

Acknowledged and true. Sorry.

+  }

[emircan, 2015/03/04 02:47:47]

You can end the iteration when (best == desired_v4l2_formats.begin()).

[mcasas, 2015/03/09 21:23:56]

That would be an overoptimization, wouldn't it?

Meaning, let's say desired_v4l2_formats is 
{ 
V4L2_PIX_FMT_MJPEG, 
V4L2_PIX_FMT_UYVY
};
and the webcam only supports, say, UYVY. 

We would iterate two times and select UYVY at
the end. No early-exiting the for loop, since
the early formats are not the optimal.

(Conversely, if the webcam would support MJPEG,
then early exit would be beneficial).

Since this loop is only run once and during capture
startup phase, I'd say we leave it as is.

+  if (best == desired_v4l2_formats.end()) {
+    SetErrorState("Failed to find a supported camera format.");
+    return;
+  }
+
+  DVLOG(1) << "chosen pixel format is " << FourccToString(*best);
+
+  v4l2_format video_fmt = {};
+  video_fmt.type = capture_type_;
+  FillV4L2Format(&video_fmt, width, height, *best);
+  if (HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_S_FMT, &video_fmt)) < 0) {
+    SetErrorState("Failed to set video capture format");
+    return;
+  }
+
+  // Set capture framerate in the form of capture interval.
+  v4l2_streamparm streamparm = {};
+  streamparm.type = capture_type_;
+  // The following line checks that the driver knows about framerate get/set.
+  if (HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_G_PARM, &streamparm)) >= 0) {
+    // Now check if the device is able to accept a capture framerate set.
+    if (streamparm.parm.capture.capability & V4L2_CAP_TIMEPERFRAME) {
+      // |frame_rate| is float, approximate by a fraction.
+      streamparm.parm.capture.timeperframe.numerator =
+          media::kFrameRatePrecision;
+      streamparm.parm.capture.timeperframe.denominator =
+          (frame_rate) ? (frame_rate * media::kFrameRatePrecision)
+                       : (kTypicalFramerate * media::kFrameRatePrecision);
+
+      if (HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_S_PARM, &streamparm)) <
+          0) {
+        SetErrorState("Failed to set camera framerate");
+        return;
+      }
+      DVLOG(2) << "Actual camera driverframerate: "
+               << streamparm.parm.capture.timeperframe.denominator << "/"
+               << streamparm.parm.capture.timeperframe.numerator;
+    }
+  }
+  // TODO(mcasas): what should be done if the camera driver does not allow
+  // framerate configuration, or the actual one is different from the desired?
+
+  // Set anti-banding/anti-flicker to 50/60Hz. May fail due to not supported
+  // operation (|errno| == EINVAL in this case) or plain failure.
+  if ((power_line_frequency_ == V4L2_CID_POWER_LINE_FREQUENCY_50HZ) ||
+      (power_line_frequency_ == V4L2_CID_POWER_LINE_FREQUENCY_60HZ)) {
+    struct v4l2_control control = {};
+    control.id = V4L2_CID_POWER_LINE_FREQUENCY;
+    control.value = power_line_frequency_;
+    HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_S_CTRL, &control));
+  }
+
+  capture_format_.frame_size.SetSize(video_fmt.fmt.pix.width,
+                                     video_fmt.fmt.pix.height);
+  capture_format_.frame_rate = frame_rate;
+  capture_format_.pixel_format =
+      V4l2FourCcToChromiumPixelFormat(video_fmt.fmt.pix.pixelformat);

[Pawel Osciak, 2015/03/06 10:43:55]

This needs to be checked for success, we don't want to proceed with a bad
format.

[mcasas, 2015/03/09 21:23:56]

Done, but moved a bit farther above.

+
+  if (!AllocateVideoBuffers()) {
+    SetErrorState("Allocate buffer failed");
+    return;
+  }
+
+  if (HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_STREAMON, &capture_type_))
+      < 0) {
+    SetErrorState("VIDIOC_STREAMON failed");
+    return;
+  }
+
+  is_capturing_ = true;
+  // Post task to start fetching frames from v4l2.
+  v4l2_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&V4L2VideoCaptureDelegate::DoCapture, this));
+}
+
+void V4L2VideoCaptureDelegate::StopAndDeAllocate() {
+  DCHECK(v4l2_task_runner_->BelongsToCurrentThread());
+  // The order is important: stop streaming, clear |buffer_pool_|,
+  // thus munmap()ing the v4l2_buffers, and then return them to the OS.
+  if (HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_STREAMOFF, &capture_type_))
+      < 0) {
+    SetErrorState("VIDIOC_STREAMOFF failed");
+    return;
+  }
+
+  buffer_tracker_pool_.clear();
+
+  v4l2_requestbuffers r_buffer = {};
+  r_buffer.type = capture_type_;
+  r_buffer.memory = V4L2_MEMORY_MMAP;
+  r_buffer.count = 0;
+  if (HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_REQBUFS, &r_buffer)) < 0)
+    SetErrorState("Failed to VIDIOC_REQBUFS with count = 0");
+
+  // At this point we can close the device.
+  // This is also needed for correctly changing settings later via VIDIOC_S_FMT.
+  device_fd_.reset();
+  is_capturing_ = false;
+  client_.reset();
+}
+
+void V4L2VideoCaptureDelegate::SetRotation(int rotation) {
+  DCHECK(v4l2_task_runner_->BelongsToCurrentThread());
+  DCHECK(rotation >= 0 && rotation < 360 && rotation % 90 == 0);
+  rotation_ = rotation;
+}
+
+bool V4L2VideoCaptureDelegate::AllocateVideoBuffers() {
+  v4l2_requestbuffers r_buffer = {};
+  r_buffer.type = capture_type_;
+  r_buffer.memory = V4L2_MEMORY_MMAP;
+  r_buffer.count = kMaxVideoBuffers;
+  if (HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_REQBUFS, &r_buffer)) < 0) {
+    DLOG(ERROR) << "Error requesting MMAP buffers from V4L2";
+    return false;
+  }
+  DCHECK_EQ(r_buffer.count, kMaxVideoBuffers);
+  r_buffer.count = std::min(r_buffer.count, kMaxVideoBuffers);
+  for (unsigned int i = 0; i < r_buffer.count; ++i) {
+    v4l2_buffer buffer = {};
+    buffer.type = capture_type_;
+    buffer.memory = V4L2_MEMORY_MMAP;
+    buffer.index = i;
+    FinishFillingV4L2Buffer(&buffer);
+
+    if (HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_QUERYBUF, &buffer)) < 0) {
+      DLOG(ERROR) << "Error querying status of a MMAP V4L2 buffer";
+      return false;
+    }

[Pawel Osciak, 2015/03/06 10:43:54]

As described in h, this all could go to CreateBufferTracker please.

[mcasas, 2015/03/09 21:23:56]

Acknowledged.

+
+    buffer_tracker_pool_.push_back(CreateBufferTracker(device_fd_.get(),
+                                                       buffer));
+
+    // Enqueue the buffer in the drivers incoming queue.
+    if (HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_QBUF, &buffer)) < 0) {
+      DLOG(ERROR) << "Error enqueuing a V4L2 buffer back into the driver";
+      return false;
+    }
+  }
+  return true;
+}
+
+void V4L2VideoCaptureDelegate::DoCapture() {
+  DCHECK(v4l2_task_runner_->BelongsToCurrentThread());
+  if (!is_capturing_)
+    return;
+
+  pollfd device_pfd = {};
+  device_pfd.fd = device_fd_.get();
+  device_pfd.events = POLLIN;
+  const int result = HANDLE_EINTR(poll(&device_pfd, 1, kCaptureTimeoutMs));
+  if (result < 0) {
+    SetErrorState("Poll failed");
+    return;
+  }
+  // Check if poll() timed out; track the amount of times it did in a row and
+  // throw an error if it times out too many times.
+  if (result == 0) {
+    timeout_count_++;
+    if (timeout_count_ >= kContinuousTimeoutLimit) {
+      SetErrorState("Multiple continuous timeouts while read-polling.");
+      timeout_count_ = 0;
+      return;
+    }
+  } else {
+    timeout_count_ = 0;
+  }
+
+  // Deenqueue, send and reenqueue a buffer if the driver has filled one in.
+  if (device_pfd.revents & POLLIN) {
+    v4l2_buffer buffer = {};
+    buffer.type = capture_type_;
+    buffer.memory = V4L2_MEMORY_MMAP;
+    buffer.index = 0;
+    FinishFillingV4L2Buffer(&buffer);

[Pawel Osciak, 2015/03/06 10:43:54]

This would just be FillV4L2Buffer().

[mcasas, 2015/03/09 21:23:56]

Done.

+
+    if (HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_DQBUF, &buffer)) < 0) {
+      SetErrorState("Failed to dequeue capture buffer");
+      return;
+    }
+
+    SendBuffer(buffer);
+
+    if (HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_QBUF, &buffer)) < 0) {
+      SetErrorState("Failed to enqueue capture buffer");
+      return;
+    }
+  }
+
+  v4l2_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&V4L2VideoCaptureDelegate::DoCapture, this));
+}
+
+void V4L2VideoCaptureDelegate::SetErrorState(const std::string& reason) {
+  DCHECK(v4l2_task_runner_->BelongsToCurrentThread());
+  is_capturing_ = false;
+  client_->OnError(reason);
+}
+
+V4L2VideoCaptureDelegate::~V4L2VideoCaptureDelegate() {
+}
+
+scoped_refptr<V4L2VideoCaptureDelegate::BufferTracker>
+V4L2CaptureDelegateSinglePlane::CreateBufferTracker(int fd,
+                                                    const v4l2_buffer& buffer) {
+  return make_scoped_refptr(new BufferTrackerSPlane(fd, buffer));
+}
+
+void V4L2CaptureDelegateSinglePlane::FillV4L2Format(
+    v4l2_format* format,
+    uint32_t width,
+    uint32_t height,
+    uint32_t pixelformat_fourcc) {
+  format->fmt.pix.width = width;
+  format->fmt.pix.height = height;
+  format->fmt.pix.pixelformat = pixelformat_fourcc;
+}
+
+void V4L2CaptureDelegateSinglePlane::SendBuffer(const v4l2_buffer& buffer) {
+  BufferTrackerSPlane* const buffer_tracker =
+      reinterpret_cast<BufferTrackerSPlane*>(
+          buffer_tracker_pool()[buffer.index].get());
+  DCHECK_EQ(buffer_tracker->planes()[0]->length, buffer.length);
+  client()->OnIncomingCapturedData(
+      static_cast<uint8*>(buffer_tracker->planes()[0]->start),
+      buffer_tracker->planes()[0]->length,
+      capture_format(),
+      rotation(),
+      base::TimeTicks::Now());
+}
+
+V4L2CaptureDelegateSinglePlane::BufferTrackerSPlane::BufferTrackerSPlane(
+    int fd,
+    const v4l2_buffer& buffer)
+    : BufferTracker(fd, buffer) {
+  scoped_ptr<Plane> plane(new Plane());
+  // Some devices require mmap() to be called with both READ and WRITE.
+  // See http://crbug.com/178582.
+  plane->start = mmap(NULL, buffer.length, PROT_READ | PROT_WRITE, MAP_SHARED,
+                      fd, buffer.m.offset);
+  if (plane->start == MAP_FAILED) {
+    DLOG(ERROR) << "Error mmap()ing a V4L2 buffer into userspace";
+    return;
+  }
+  plane->length = buffer.length;
+  planes().push_back(plane.Pass());
+}
+
+scoped_refptr<V4L2VideoCaptureDelegate::BufferTracker>
+V4L2CaptureDelegateMultiPlane::CreateBufferTracker(int fd,
+                                                   const v4l2_buffer& buffer) {
+  DCHECK_LE(buffer.length, num_planes_);
+  return make_scoped_refptr(new BufferTrackerMPlane(fd, buffer));
+}
+
+void V4L2CaptureDelegateMultiPlane::FillV4L2Format(
+    v4l2_format* format,
+    uint32_t width,
+    uint32_t height,
+    uint32_t pixelformat_fourcc) {
+  format->fmt.pix_mp.width = width;
+  format->fmt.pix_mp.height = height;
+
+  fourcc_ = pixelformat_fourcc;
+  format->fmt.pix_mp.pixelformat = fourcc_;
+
+  num_planes_ = GetNumPlanesForFourCc(fourcc_);
+  DCHECK_GT(num_planes_, 0u);
+  DCHECK_LE(num_planes_, static_cast<unsigned long>(VIDEO_MAX_PLANES));
+  format->fmt.pix_mp.num_planes = num_planes_;
+
+  v4l2_plane_.reset(new v4l2_plane[num_planes_]);

[Pawel Osciak, 2015/03/06 10:43:55]

We still don't want to call new foo[0] if GetNumPlanesForFourCc fails, as per
standard:

"The effect of dereferencing a pointer returned as a request for zero size is
undefined."

[mcasas, 2015/03/09 21:23:56]

Done. I return a bool (false) if this goes south
and then on AllocateAndStart() is caught and
treated.

+}
+
+void V4L2CaptureDelegateMultiPlane::FinishFillingV4L2Buffer(
+    v4l2_buffer* buffer) {
+  buffer->length = num_planes_;
+  buffer->m.planes = v4l2_plane_.get();
+}
+
+void V4L2CaptureDelegateMultiPlane::SendBuffer(const v4l2_buffer& buffer) {
+  DCHECK_EQ(capture_format().pixel_format, PIXEL_FORMAT_I420);
+
+  BufferTrackerMPlane* const buffer_tracker =
+      reinterpret_cast<BufferTrackerMPlane*>(
+          buffer_tracker_pool()[buffer.index].get());
+
+  client()->OnIncomingCapturedYuvData(
+      static_cast<uint8*>(buffer_tracker->planes()[0]->start),
+      static_cast<uint8*>(buffer_tracker->planes()[1]->start),
+      static_cast<uint8*>(buffer_tracker->planes()[2]->start),
+      buffer_tracker->planes()[0]->length,
+      buffer_tracker->planes()[1]->length,
+      buffer_tracker->planes()[2]->length,
+      capture_format(),
+      rotation(),
+      base::TimeTicks::Now());
+}
+
+V4L2CaptureDelegateMultiPlane::BufferTrackerMPlane::BufferTrackerMPlane(
+    int fd,
+    const v4l2_buffer& buffer)
+    : BufferTracker(fd, buffer) {
+  for (size_t p = 0; p < buffer.length; ++p) {
+    scoped_ptr<Plane> plane(new Plane());
+    plane->start = mmap(NULL, buffer.m.planes[p].length, PROT_READ | PROT_WRITE,
+                        MAP_SHARED, fd, buffer.m.planes[p].m.mem_offset);
+    if (plane->start == MAP_FAILED) {
+      DLOG(ERROR) << "Error mmap()ing a V4L2 buffer into userspace";
+      return;

[Pawel Osciak, 2015/03/06 10:43:55]

This way you'd still use the plane as normal if this failed. You need an
Initialize() method.

Also, you can't leave plane->start = MAP_FAILED, MAP_FAILED is not NULL, so when
unmapping, we'll succeed plane->start == NULL test and we'll end up calling
munmap(MAP_FAILED, 0);

[mcasas, 2015/03/09 21:23:56]

Done.

+    }
+    plane->length = buffer.m.planes[p].length;
+    DVLOG(3) << "Mmap()ed plane #" << p << ", length " << plane->length << "B";
+    planes().push_back(plane.Pass());
+  }
+}
+
+}  // namespace media