ImageCapture v4l2: retry reading capabilities

media/capture/video/linux/v4l2_capture_delegate.cc

 // 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/capture/video/linux/v4l2_capture_delegate.h"
 
 #include <linux/version.h>
 #include <linux/videodev2.h>
 #include <poll.h>
 #include <sys/fcntl.h>
@@ skipping 104 matching lines @@
   request_buffer->memory = V4L2_MEMORY_MMAP;
   request_buffer->count = count;
 }
 
 // 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);
 }
 
-// Creates a mojom::RangePtr with the range of values (min, max, current) of the
-// user control associated with |control_id|. Returns an empty Range otherwise.
+// Running ioctl() on some devices, especially shortly after (re)opening the
+// device file descriptor or (re)starting streaming, can fail but works after
+// retrying (https://crbug.com/670262).
+// Returns false if the |request| ioctl fails too many times.
+static bool RunIoctl(int fd, int request, void* argp) {
+  int num_retries = 0;
+  for (; HANDLE_EINTR(ioctl(fd, request, argp)) < 0 &&
+         num_retries < kMaxIOCtrlRetries;
+       ++num_retries) {
+    DPLOG(WARNING) << "ioctl";
+  }
+  DPLOG_IF(ERROR, num_retries != kMaxIOCtrlRetries);
+  return num_retries != kMaxIOCtrlRetries;
+}
+
+// Creates a mojom::RangePtr with the (min, max, current, step) values of the
+// control associated with |control_id|. Returns an empty Range otherwise.
 static mojom::RangePtr RetrieveUserControlRange(int device_fd, int control_id) {
   mojom::RangePtr capability = mojom::Range::New();
 
   v4l2_queryctrl range = {};
   range.id = control_id;
   range.type = V4L2_CTRL_TYPE_INTEGER;
-  if (HANDLE_EINTR(ioctl(device_fd, VIDIOC_QUERYCTRL, &range)) < 0)
+  if (!RunIoctl(device_fd, VIDIOC_QUERYCTRL, &range))
     return mojom::Range::New();
   capability->max = range.maximum;
   capability->min = range.minimum;
   capability->step = range.step;
 
   v4l2_control current = {};
   current.id = control_id;
-  if (HANDLE_EINTR(ioctl(device_fd, VIDIOC_G_CTRL, &current)) < 0)
+  if (!RunIoctl(device_fd, VIDIOC_G_CTRL, &current))
     return mojom::Range::New();
   capability->current = current.value;
 
   return capability;
 }
 
 // Determines if |control_id| is special, i.e. controls another one's state.
 static bool IsSpecialControl(int control_id) {
   switch (control_id) {
     case V4L2_CID_AUTO_WHITE_BALANCE:
     case V4L2_CID_EXPOSURE_AUTO:
     case V4L2_CID_EXPOSURE_AUTO_PRIORITY:
     case V4L2_CID_FOCUS_AUTO:
       return true;
   }
   return false;
 }
 
 // Sets all user control to their default. Some controls are enabled by another
 // flag, usually having the word "auto" in the name, see IsSpecialControl().
 // These flags are preset beforehand, then set to their defaults individually
 // afterwards.
 static void ResetUserAndCameraControlsToDefault(int device_fd) {
   // Set V4L2_CID_AUTO_WHITE_BALANCE to false first.
   v4l2_control auto_white_balance = {};
   auto_white_balance.id = V4L2_CID_AUTO_WHITE_BALANCE;
   auto_white_balance.value = false;
-  int num_retries = 0;
-  // Setting up the first control right after stopping streaming seems
-  // not to the work the first time, so retry a few times.
-  for (; num_retries < kMaxIOCtrlRetries &&
-         HANDLE_EINTR(ioctl(device_fd, VIDIOC_S_CTRL, &auto_white_balance)) < 0;
-       ++num_retries) {
-    DPLOG(WARNING) << "VIDIOC_S_CTRL";
-  }
-  if (num_retries == kMaxIOCtrlRetries) {
-    DLOG(ERROR) << "Cannot access device controls";
+  if (!RunIoctl(device_fd, VIDIOC_S_CTRL, &auto_white_balance))
     return;
-  }
 
   std::vector<struct v4l2_ext_control> special_camera_controls;
   // Set V4L2_CID_EXPOSURE_AUTO to V4L2_EXPOSURE_MANUAL.
   v4l2_ext_control auto_exposure = {};
   auto_exposure.id = V4L2_CID_EXPOSURE_AUTO;
   auto_exposure.value = V4L2_EXPOSURE_MANUAL;
   special_camera_controls.push_back(auto_exposure);
   // Set V4L2_CID_EXPOSURE_AUTO_PRIORITY to false.
   v4l2_ext_control priority_auto_exposure = {};
   priority_auto_exposure.id = V4L2_CID_EXPOSURE_AUTO_PRIORITY;
@@ skipping 590 matching lines @@
     DLOG(ERROR) << "Error mmap()ing a V4L2 buffer into userspace";
     return false;
   }
   start_ = static_cast<uint8_t*>(start);
   length_ = buffer.length;
   payload_size_ = 0;
   return true;
 }
 
 }  // namespace media