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libv4l2.c

/*
#             (C) 2008 Hans de Goede <j.w.r.degoede@hhs.nl>

# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation; either version 2.1 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

/* MAKING CHANGES TO THIS FILE??   READ THIS FIRST!!!

   This file implements libv4l2, which offers v4l2_ prefixed versions of
   open/close/etc. The API is 100% the same as directly opening /dev/videoX
   using regular open/close/etc, the big difference is that format conversion
   is done if necessary when capturing. That is if you (try to) set a capture
   format which is not supported by the cam, but is supported by libv4lconvert,
   then the try_fmt / set_fmt will succeed as if the cam supports the format
   and on dqbuf / read the data will be converted for you and returned in
   the request format.

   Important note to people making changes to this file: All functions
   (v4l2_close, v4l2_ioctl, etc.) are designed to function as their regular
   counterpart when they get passed a fd that is not "registered" by libv4l2,
   there are 2 reasons for this:
   1) This allows us to get completely out of the way when dealing with non
      capture devices.
   2) libv4l2 is the base of the v4l2convert.so wrapper lib, which is a .so
      which can be LD_PRELOAD-ed and the overrules the libc's open/close/etc,
      and when opening /dev/videoX or /dev/v4l/ calls v4l2_open.  Because we
      behave as the regular counterpart when the fd is not known (instead of say
      throwing an error), v4l2convert.so can simply call the v4l2_ prefixed
      function for all wrapped functions (except for v4l2_open which will fail
      when not called on a v4l2 device). This way the wrapper does not have to
      keep track of which fd's are being handled by libv4l2, as libv4l2 already
      keeps track of this itself.

      This also means that libv4l2 may not use any of the regular functions
      it mimics, as for example open could be a symbol in v4l2convert.so, which
      in turn will call v4l2_open, so therefor v4l2_open (for example) may not
      use the regular open()!

   Another important note: libv4l2 does conversion for capture usage only, if
   any calls are made which are passed a v4l2_buffer or v4l2_format with a
   v4l2_buf_type which is different from V4L2_BUF_TYPE_VIDEO_CAPTURE, then
   the v4l2_ methods behave exactly the same as their regular counterparts.
   When modifications are made, one should be carefull that this behavior is
   preserved.
*/
#include <errno.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <syscall.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include "libv4l2.h"
#include "libv4l2-priv.h"

/* Note these flags are stored together with the flags passed to v4l2_fd_open()
   in v4l2_dev_info's flags member, so care should be taken that the do not
   use the same bits! */
#define V4L2_STREAMON               0x0100
#define V4L2_BUFFERS_REQUESTED_BY_READ    0x0200
#define V4L2_STREAM_CONTROLLED_BY_READ    0x0400
#define V4L2_SUPPORTS_READ          0x0800

#define V4L2_MMAP_OFFSET_MAGIC      0xABCDEF00u

static pthread_mutex_t v4l2_open_mutex = PTHREAD_MUTEX_INITIALIZER;
static struct v4l2_dev_info devices[V4L2_MAX_DEVICES] = { { .fd = -1 },
  { .fd = -1 }, { .fd = -1 }, { .fd = -1 }, { .fd = -1 }, { .fd = -1 },
  { .fd = -1 }, { .fd = -1 }, { .fd = -1 }, { .fd = -1 }, { .fd = -1 },
  { .fd = -1 }, { .fd = -1 }, { .fd = -1 }, { .fd = -1 }, { .fd = -1 }};
static int devices_used = 0;


static int v4l2_request_read_buffers(int index)
{
  int result;
  struct v4l2_requestbuffers req;

  /* Note we re-request the buffers if they are already requested as the format
     and thus the needed buffersize may have changed. */
  req.count = (devices[index].no_frames)? devices[index].no_frames:
                                devices[index].nreadbuffers;
  req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  req.memory = V4L2_MEMORY_MMAP;
  if ((result = syscall(SYS_ioctl, devices[index].fd, VIDIOC_REQBUFS, &req)) < 0){
    int saved_err = errno;
    V4L2_LOG_ERR("requesting %u buffers: %s\n", req.count, strerror(errno));
    errno = saved_err;
    return result;
  }

  if (!devices[index].no_frames && req.count)
    devices[index].flags |= V4L2_BUFFERS_REQUESTED_BY_READ;

  devices[index].no_frames = MIN(req.count, V4L2_MAX_NO_FRAMES);
  return 0;
}

static void v4l2_unrequest_read_buffers(int index)
{
  struct v4l2_requestbuffers req;

  if (!(devices[index].flags & V4L2_BUFFERS_REQUESTED_BY_READ) ||
      devices[index].no_frames == 0)
    return;

  /* (Un)Request buffers, note not all driver support this, and those
     who do not support it don't need it. */
  req.count = 0;
  req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  req.memory = V4L2_MEMORY_MMAP;
  if(syscall(SYS_ioctl, devices[index].fd, VIDIOC_REQBUFS, &req) < 0)
    return;

  devices[index].no_frames = MIN(req.count, V4L2_MAX_NO_FRAMES);
  if (devices[index].no_frames == 0)
    devices[index].flags &= ~V4L2_BUFFERS_REQUESTED_BY_READ;
}

static int v4l2_map_buffers(int index)
{
  int result = 0;
  unsigned int i;
  struct v4l2_buffer buf;

  for (i = 0; i < devices[index].no_frames; i++) {
    if (devices[index].frame_pointers[i] != MAP_FAILED)
      continue;

    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;
    buf.index = i;
    result = syscall(SYS_ioctl, devices[index].fd, VIDIOC_QUERYBUF, &buf);
    if (result) {
      int saved_err = errno;
      V4L2_LOG_ERR("querying buffer %u: %s\n", i, strerror(errno));
      errno = saved_err;
      break;
    }

    devices[index].frame_pointers[i] = (void *)syscall(SYS_mmap2, NULL,
      (size_t)buf.length, PROT_READ|PROT_WRITE, MAP_SHARED, devices[index].fd,
      (__off_t)(buf.m.offset >> MMAP2_PAGE_SHIFT));
    if (devices[index].frame_pointers[i] == MAP_FAILED) {
      int saved_err = errno;
      V4L2_LOG_ERR("mmapping buffer %u: %s\n", i, strerror(errno));
      errno = saved_err;
      result = -1;
      break;
    }
    V4L2_LOG("mapped buffer %u at %p\n", i,
      devices[index].frame_pointers[i]);

    devices[index].frame_sizes[i] = buf.length;
  }

  return result;
}

static void v4l2_unmap_buffers(int index)
{
  unsigned int i;

  /* unmap the buffers */
  for (i = 0; i < devices[index].no_frames; i++) {
    if (devices[index].frame_pointers[i] != MAP_FAILED) {
      syscall(SYS_munmap, devices[index].frame_pointers[i],
            devices[index].frame_sizes[i]);
      devices[index].frame_pointers[i] = MAP_FAILED;
      V4L2_LOG("unmapped buffer %u\n", i);
    }
  }
}

static int v4l2_streamon(int index)
{
  int result;
  enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

  if (!(devices[index].flags & V4L2_STREAMON)) {
    if ((result = syscall(SYS_ioctl, devices[index].fd, VIDIOC_STREAMON,
                    &type))) {
      int saved_err = errno;
      V4L2_LOG_ERR("turning on stream: %s\n", strerror(errno));
      errno = saved_err;
      return result;
    }
    devices[index].flags |= V4L2_STREAMON;
  }

  return 0;
}

static int v4l2_streamoff(int index)
{
  int result;
  enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

  if (devices[index].flags & V4L2_STREAMON) {
    if ((result = syscall(SYS_ioctl, devices[index].fd, VIDIOC_STREAMOFF,
                    &type))) {
      int saved_err = errno;
      V4L2_LOG_ERR("turning off stream: %s\n", strerror(errno));
      errno = saved_err;
      return result;
    }
    devices[index].flags &= ~V4L2_STREAMON;

    /* Stream off also unqueues all our buffers! */
    devices[index].frame_queued = 0;
  }

  return 0;
}

static int v4l2_queue_read_buffer(int index, int buffer_index)
{
  int result;
  struct v4l2_buffer buf;

  if (devices[index].frame_queued & (1 << buffer_index))
    return 0;

  memset(&buf, 0, sizeof(buf));
  buf.type   = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  buf.memory = V4L2_MEMORY_MMAP;
  buf.index  = buffer_index;
  if ((result = syscall(SYS_ioctl, devices[index].fd, VIDIOC_QBUF, &buf))) {
    int saved_err = errno;
    V4L2_LOG_ERR("queuing buf %d: %s\n", buffer_index, strerror(errno));
    errno = saved_err;
    return result;
  }

  devices[index].frame_queued |= 1 << buffer_index;
  return 0;
}

static int v4l2_dequeue_and_convert(int index, struct v4l2_buffer *buf,
  unsigned char *dest, int dest_size)
{
  const int max_tries = 10;
  int result, tries = max_tries;

  /* Make sure we have the real v4l2 buffers mapped */
  if ((result = v4l2_map_buffers(index)))
    return result;

  do {
    if ((result = syscall(SYS_ioctl, devices[index].fd, VIDIOC_DQBUF, buf))) {
      int saved_err = errno;
      V4L2_LOG_ERR("dequeuing buf: %s\n", strerror(errno));
      errno = saved_err;
      return result;
    }

    devices[index].frame_queued &= ~(1 << buf->index);

    result = v4lconvert_convert(devices[index].convert,
         &devices[index].src_fmt, &devices[index].dest_fmt,
         devices[index].frame_pointers[buf->index],
         buf->bytesused, dest ? dest : (devices[index].convert_mmap_buf +
           buf->index * V4L2_FRAME_BUF_SIZE), dest_size);

    if (result < 0) {
      int saved_err = errno;

      if(errno == EAGAIN)
      V4L2_LOG("warning error while converting frame data: %s\n",
        v4lconvert_get_error_message(devices[index].convert));
      else
      V4L2_LOG_ERR("converting / decoding frame data: %s\n",
        v4lconvert_get_error_message(devices[index].convert));

      v4l2_queue_read_buffer(index, buf->index);
      errno = saved_err;
    }
    tries--;
  } while (result < 0 && errno == EAGAIN && tries);

  if (result < 0 && errno == EAGAIN) {
    V4L2_LOG_ERR("got %d consecutive frame decode errors, last error: %s\n",
      max_tries, v4lconvert_get_error_message(devices[index].convert));
  }

  return result;
}

static int v4l2_queue_read_buffers(int index)
{
  unsigned int i;
  int last_error = EIO, queued = 0;

  for (i = 0; i < devices[index].no_frames; i++) {
    /* Don't queue unmapped buffers (should never happen) */
    if (devices[index].frame_pointers[i] != MAP_FAILED) {
      if (v4l2_queue_read_buffer(index, i)) {
      last_error = errno;
      continue;
      }
      queued++;
    }
  }

  if (!queued) {
    errno = last_error;
    return -1;
  }
  return 0;
}

static int v4l2_activate_read_stream(int index)
{
  int result;

  if ((result = v4l2_request_read_buffers(index)))
    return result;

  if ((result = v4l2_map_buffers(index)))
    return result;

  if ((result = v4l2_queue_read_buffers(index)))
    return result;

  devices[index].flags |= V4L2_STREAM_CONTROLLED_BY_READ;

  return result = v4l2_streamon(index);
}

static int v4l2_deactivate_read_stream(int index)
{
  int result;

  if ((result = v4l2_streamoff(index)))
    return result;

  /* No need to unqueue our buffers, streamoff does that for us */

  v4l2_unmap_buffers(index);

  v4l2_unrequest_read_buffers(index);

  devices[index].flags &= ~V4L2_STREAM_CONTROLLED_BY_READ;

  return 0;
}

static int v4l2_buffers_mapped(int index)
{
  unsigned int i;

  if (devices[index].src_fmt.fmt.pix.pixelformat ==
      devices[index].dest_fmt.fmt.pix.pixelformat) {
    /* Normal (no conversion) mode */
    struct v4l2_buffer buf;

    for (i = 0; i < devices[index].no_frames; i++) {
      buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
      buf.memory = V4L2_MEMORY_MMAP;
      buf.index = i;
      if (syscall(SYS_ioctl, devices[index].fd, VIDIOC_QUERYBUF, &buf)) {
      int saved_err = errno;
      V4L2_LOG_ERR("querying buffer %u: %s\n", i, strerror(errno));
      errno = saved_err;
      break;
      }
      if (buf.flags & V4L2_BUF_FLAG_MAPPED)
      break;
    }
  } else {
    /* Conversion mode */
    for (i = 0; i < devices[index].no_frames; i++)
      if (devices[index].frame_map_count[i])
      break;
  }

  if (i != devices[index].no_frames)
    V4L2_LOG("v4l2_buffers_mapped(): buffers still mapped\n");

  return i != devices[index].no_frames;
}


int v4l2_open (const char *file, int oflag, ...)
{
  int fd;

  /* original open code */
  if (oflag & O_CREAT)
  {
    va_list ap;
    mode_t mode;

    va_start (ap, oflag);
    mode = va_arg (ap, mode_t);

    fd = syscall(SYS_open, file, oflag, mode);

    va_end(ap);
  }
  else
    fd = syscall(SYS_open, file, oflag);
  /* end of original open code */

  if (fd == -1)
    return fd;

  if (v4l2_fd_open(fd, 0) == -1) {
    int saved_err = errno;
    syscall(SYS_close, fd);
    errno = saved_err;
    return -1;
  }

  return fd;
}

int v4l2_fd_open(int fd, int v4l2_flags)
{
  int i, index;
  char *lfname;
  struct v4l2_capability cap;
  struct v4l2_format fmt;
  struct v4lconvert_data *convert;

  /* If no log file was set by the app, see if one was specified through the
     environment */
  if (!v4l2_log_file && (lfname = getenv("LIBV4L2_LOG_FILENAME")))
    v4l2_log_file = fopen(lfname, "w");

  /* check that this is an v4l2 device */
  if (syscall(SYS_ioctl, fd, VIDIOC_QUERYCAP, &cap)) {
    int saved_err = errno;
    V4L2_LOG_ERR("getting capabilities: %s\n", strerror(errno));
    errno = saved_err;
    return -1;
  }

  /* we only add functionality for video capture devices, and we do not
     handle devices which don't do mmap */
  if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) ||
      !(cap.capabilities & V4L2_CAP_STREAMING))
    return fd;

  /* Get current cam format */
  fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  if (syscall(SYS_ioctl, fd, VIDIOC_G_FMT, &fmt)) {
    int saved_err = errno;
    V4L2_LOG_ERR("getting pixformat: %s\n", strerror(errno));
    errno = saved_err;
    return -1;
  }

  /* init libv4lconvert */
  if (!(convert = v4lconvert_create(fd)))
    return -1;

  /* So we have a v4l2 capture device, register it in our devices array */
  pthread_mutex_lock(&v4l2_open_mutex);
  for (index = 0; index < V4L2_MAX_DEVICES; index++)
    if(devices[index].fd == -1) {
      devices[index].fd = fd;
      break;
    }
  pthread_mutex_unlock(&v4l2_open_mutex);

  if (index == V4L2_MAX_DEVICES) {
    V4L2_LOG_ERR("attempting to open more then %d video devices\n",
      V4L2_MAX_DEVICES);
    errno = EBUSY;
    return -1;
  }

  devices[index].flags = v4l2_flags;
  if (cap.capabilities & V4L2_CAP_READWRITE)
    devices[index].flags |= V4L2_SUPPORTS_READ;
  devices[index].open_count = 1;
  devices[index].src_fmt = fmt;
  devices[index].dest_fmt = fmt;

  pthread_mutex_init(&devices[index].stream_lock, NULL);

  devices[index].no_frames = 0;
  devices[index].nreadbuffers = V4L2_DEFAULT_NREADBUFFERS;
  devices[index].convert = convert;
  devices[index].convert_mmap_buf = MAP_FAILED;
  for (i = 0; i < V4L2_MAX_NO_FRAMES; i++) {
    devices[index].frame_pointers[i] = MAP_FAILED;
    devices[index].frame_map_count[i] = 0;
  }
  devices[index].frame_queued = 0;

  if (index >= devices_used)
    devices_used = index + 1;

  V4L2_LOG("open: %d\n", fd);

  return fd;
}

/* Is this an fd for which we are emulating v4l1 ? */
static int v4l2_get_index(int fd)
{
  int index;

  /* We never handle fd -1 */
  if (fd == -1)
    return -1;

  for (index = 0; index < devices_used; index++)
    if (devices[index].fd == fd)
      break;

  if (index == devices_used)
    return -1;

  return index;
}


int v4l2_close(int fd)
{
  int index, result;

  if ((index = v4l2_get_index(fd)) == -1)
    return syscall(SYS_close, fd);

  /* Abuse stream_lock to stop 2 closes from racing and trying to free the
     resources twice */
  pthread_mutex_lock(&devices[index].stream_lock);
  devices[index].open_count--;
  result = devices[index].open_count != 0;
  pthread_mutex_unlock(&devices[index].stream_lock);

  if (result)
    return 0;

  /* Free resources */
  v4l2_unmap_buffers(index);
  v4lconvert_destroy(devices[index].convert);
  if (devices[index].convert_mmap_buf != MAP_FAILED) {
    if (v4l2_buffers_mapped(index))
      V4L2_LOG_WARN("v4l2 mmap buffers still mapped on close()\n");
    else
      syscall(SYS_munmap, devices[index].convert_mmap_buf,
            devices[index].no_frames * V4L2_FRAME_BUF_SIZE);
    devices[index].convert_mmap_buf = MAP_FAILED;
  }

  /* Remove the fd from our list of managed fds before closing it, because as
     soon as we've done the actual close the fd maybe returned by an open in
     another thread and we don't want to intercept calls to this new fd. */
  devices[index].fd = -1;

  /* Since we've marked the fd as no longer used, and freed the resources,
     redo the close in case it was interrupted */
  do {
    result = syscall(SYS_close, fd);
  } while (result == -1 && errno == EINTR);

  V4L2_LOG("close: %d\n", fd);

  return result;
}

int v4l2_dup(int fd)
{
  int index;

  if ((index = v4l2_get_index(fd)) == -1)
    return syscall(SYS_dup, fd);

  devices[index].open_count++;

  return fd;
}

static int v4l2_check_buffer_change_ok(int index)
{
  v4l2_unmap_buffers(index);

  /* Check if the app itself still is using the stream */
  if (v4l2_buffers_mapped(index) ||
       (!(devices[index].flags & V4L2_STREAM_CONTROLLED_BY_READ) &&
       ((devices[index].flags & V4L2_STREAMON) ||
         devices[index].frame_queued))) {
    V4L2_LOG("v4l2_check_buffer_change_ok(): stream busy\n");
    errno = EBUSY;
    return -1;
  }

  /* We may change from convert to non conversion mode and
     v4l2_unrequest_read_buffers may change the no_frames, so free the
     convert mmap buffer */
  syscall(SYS_munmap, devices[index].convert_mmap_buf,
    devices[index].no_frames * V4L2_FRAME_BUF_SIZE);
  devices[index].convert_mmap_buf = MAP_FAILED;

  if (devices[index].flags & V4L2_STREAM_CONTROLLED_BY_READ) {
    V4L2_LOG("deactivating read-stream for settings change\n");
    return v4l2_deactivate_read_stream(index);
  }

  return 0;
}

static int v4l2_pix_fmt_identical(struct v4l2_format *a, struct v4l2_format *b)
{
  if (a->fmt.pix.width == b->fmt.pix.width &&
      a->fmt.pix.height == b->fmt.pix.height &&
      a->fmt.pix.pixelformat == b->fmt.pix.pixelformat &&
      a->fmt.pix.field == b->fmt.pix.field)
    return 1;

  return 0;
}

static void v4l2_set_src_and_dest_format(int index,
  struct v4l2_format *src_fmt, struct v4l2_format *dest_fmt)
{
  /* Sigh some drivers (pwc) do not properly reflect what one really gets
     after a s_fmt in their try_fmt answer. So update dest format (which we
     report as result from s_fmt / g_fmt to the app) with all info from the src
     format not changed by conversion */
  dest_fmt->fmt.pix.field = src_fmt->fmt.pix.field;
  dest_fmt->fmt.pix.colorspace = src_fmt->fmt.pix.colorspace;
  /* When we're not converting use bytesperline and imagesize from src_fmt */
  if (v4l2_pix_fmt_identical(src_fmt, dest_fmt)) {
    dest_fmt->fmt.pix.bytesperline = src_fmt->fmt.pix.bytesperline;
    dest_fmt->fmt.pix.sizeimage = src_fmt->fmt.pix.sizeimage;
  }

  devices[index].src_fmt = *src_fmt;
  devices[index].dest_fmt = *dest_fmt;
}

int v4l2_ioctl (int fd, unsigned long int request, ...)
{
  void *arg;
  va_list ap;
  int result, converting, index, saved_err;
  int is_capture_request = 0, stream_needs_locking = 0;

  va_start (ap, request);
  arg = va_arg (ap, void *);
  va_end (ap);

  if ((index = v4l2_get_index(fd)) == -1)
    return syscall(SYS_ioctl, fd, request, arg);

  /* Appearantly the kernel and / or glibc ignore the 32 most significant bits
     when long = 64 bits, and some applications pass an int holding the req to
     ioctl, causing it to get sign extended, depending upon this behavior */
  request = (unsigned int)request;

  /* Is this a capture request and do we need to take the stream lock? */
  switch (request) {
    case VIDIOC_QUERYCAP:
      is_capture_request = 1;
      break;
    case VIDIOC_ENUM_FMT:
      if (((struct v4l2_fmtdesc *)arg)->type == V4L2_BUF_TYPE_VIDEO_CAPTURE &&
        (devices[index].flags & V4L2_ENABLE_ENUM_FMT_EMULATION))
      is_capture_request = 1;
      break;
    case VIDIOC_ENUM_FRAMESIZES:
    case VIDIOC_ENUM_FRAMEINTERVALS:
      if (devices[index].flags & V4L2_ENABLE_ENUM_FMT_EMULATION)
      is_capture_request = 1;
      break;
    case VIDIOC_TRY_FMT:
      if (((struct v4l2_format *)arg)->type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
      is_capture_request = 1;
      break;
    case VIDIOC_S_FMT:
    case VIDIOC_G_FMT:
      if (((struct v4l2_format *)arg)->type == V4L2_BUF_TYPE_VIDEO_CAPTURE) {
      is_capture_request = 1;
      stream_needs_locking = 1;
      }
      break;
    case VIDIOC_REQBUFS:
      if (((struct v4l2_requestbuffers *)arg)->type ==
        V4L2_BUF_TYPE_VIDEO_CAPTURE) {
      is_capture_request = 1;
      stream_needs_locking = 1;
      }
      break;
    case VIDIOC_QUERYBUF:
    case VIDIOC_QBUF:
    case VIDIOC_DQBUF:
      if (((struct v4l2_buffer *)arg)->type == V4L2_BUF_TYPE_VIDEO_CAPTURE) {
      is_capture_request = 1;
      stream_needs_locking = 1;
      }
      break;
    case VIDIOC_STREAMON:
    case VIDIOC_STREAMOFF:
      if (*((enum v4l2_buf_type *)arg) == V4L2_BUF_TYPE_VIDEO_CAPTURE) {
      is_capture_request = 1;
      stream_needs_locking = 1;
      }
  }

  if (!is_capture_request) {
    result = syscall(SYS_ioctl, fd, request, arg);
    saved_err = errno;
    v4l2_log_ioctl(request, arg, result);
    errno = saved_err;
    return result;
  }


  if (stream_needs_locking)
    pthread_mutex_lock(&devices[index].stream_lock);

  converting = v4lconvert_needs_conversion(devices[index].convert,
                   &devices[index].src_fmt, &devices[index].dest_fmt);

  switch (request) {
    case VIDIOC_QUERYCAP:
      {
      struct v4l2_capability *cap = arg;

      result = syscall(SYS_ioctl, devices[index].fd, VIDIOC_QUERYCAP, cap);
      if (result == 0)
        /* We always support read() as we fake it using mmap mode */
        cap->capabilities |= V4L2_CAP_READWRITE;
      }
      break;

    case VIDIOC_ENUM_FMT:
      result = v4lconvert_enum_fmt(devices[index].convert, arg);
      break;

    case VIDIOC_ENUM_FRAMESIZES:
      result = v4lconvert_enum_framesizes(devices[index].convert, arg);
      break;

    case VIDIOC_ENUM_FRAMEINTERVALS:
      result = v4lconvert_enum_frameintervals(devices[index].convert, arg);
      break;

    case VIDIOC_TRY_FMT:
      result = v4lconvert_try_format(devices[index].convert, arg, NULL);
      break;

    case VIDIOC_S_FMT:
      {
      struct v4l2_format src_fmt, *dest_fmt = arg;
      struct v4l2_pix_format req_pix_fmt;

      if (v4l2_pix_fmt_identical(&devices[index].dest_fmt, dest_fmt)) {
        *dest_fmt = devices[index].dest_fmt;
        result = 0;
        break;
      }

      if (v4l2_log_file) {
        int pixfmt = dest_fmt->fmt.pix.pixelformat;

        fprintf(v4l2_log_file, "VIDIOC_S_FMT app requesting: %c%c%c%c\n",
          pixfmt & 0xff,
          (pixfmt >> 8) & 0xff,
          (pixfmt >> 16) & 0xff,
          pixfmt >> 24);
      }

      if (devices[index].flags & V4L2_DISABLE_CONVERSION) {
        result = syscall(SYS_ioctl, devices[index].fd, VIDIOC_TRY_FMT,
                     dest_fmt);
        src_fmt = *dest_fmt;
      } else {
        result = v4lconvert_try_format(devices[index].convert, dest_fmt,
                               &src_fmt);
      }

      if (result)
        break;

      if (src_fmt.fmt.pix.pixelformat != dest_fmt->fmt.pix.pixelformat &&
          v4l2_log_file) {
        int pixfmt = src_fmt.fmt.pix.pixelformat;

        fprintf(v4l2_log_file, "VIDIOC_S_FMT converting from: %c%c%c%c\n",
          pixfmt & 0xff,
          (pixfmt >> 8) & 0xff,
          (pixfmt >> 16) & 0xff,
          pixfmt >> 24);
      }

      /* Maybe after try format has adjusted width/height etc, to whats
         available nothing has changed (on the cam side) ? */
      if (v4l2_pix_fmt_identical(&devices[index].src_fmt, &src_fmt)) {
        v4l2_set_src_and_dest_format(index, &devices[index].src_fmt,
                               dest_fmt);
        result = 0;
        break;
      }

      if ((result = v4l2_check_buffer_change_ok(index)))
        break;

      req_pix_fmt = src_fmt.fmt.pix;
      result = syscall(SYS_ioctl, devices[index].fd, VIDIOC_S_FMT, &src_fmt);
      if (result) {
        saved_err = errno;
        V4L2_LOG_ERR("setting pixformat: %s\n", strerror(errno));
        /* Report to the app dest_fmt has not changed */
        *dest_fmt = devices[index].dest_fmt;
        errno = saved_err;
        break;
      }
      /* See if we've gotten what try_fmt promised us
         (this check should never fail) */
      if (src_fmt.fmt.pix.width != req_pix_fmt.width ||
          src_fmt.fmt.pix.height != req_pix_fmt.height ||
          src_fmt.fmt.pix.pixelformat != req_pix_fmt.pixelformat) {
        V4L2_LOG_ERR("set_fmt gave us a different result then try_fmt!\n");
        /* Not what we expected / wanted, disable conversion */
        *dest_fmt = src_fmt;
      }

      v4l2_set_src_and_dest_format(index, &src_fmt, dest_fmt);
      }
      break;

    case VIDIOC_G_FMT:
      {
      struct v4l2_format* fmt = arg;

      *fmt = devices[index].dest_fmt;
      result = 0;
      }
      break;

    case VIDIOC_REQBUFS:
      {
      struct v4l2_requestbuffers *req = arg;

      /* IMPROVEME (maybe?) add support for userptr's? */
      if (req->memory != V4L2_MEMORY_MMAP) {
        errno = EINVAL;
        result = -1;
        break;
      }

      if ((result = v4l2_check_buffer_change_ok(index)))
        break;

      /* No more buffers then we can manage please */
      if (req->count > V4L2_MAX_NO_FRAMES)
        req->count = V4L2_MAX_NO_FRAMES;

      result = syscall(SYS_ioctl, devices[index].fd, VIDIOC_REQBUFS, req);
      if (result < 0)
        break;
      result = 0; /* some drivers return the number of buffers on success */

      devices[index].no_frames = MIN(req->count, V4L2_MAX_NO_FRAMES);
      devices[index].flags &= ~V4L2_BUFFERS_REQUESTED_BY_READ;
      }
      break;

    case VIDIOC_QUERYBUF:
      {
      struct v4l2_buffer *buf = arg;

      if (devices[index].flags & V4L2_STREAM_CONTROLLED_BY_READ)
        if ((result = v4l2_deactivate_read_stream(index)))
          break;

      /* Do a real query even when converting to let the driver fill in
         things like buf->field */
      result = syscall(SYS_ioctl, devices[index].fd, VIDIOC_QUERYBUF, buf);
      if (result || !converting)
        break;

      buf->m.offset = V4L2_MMAP_OFFSET_MAGIC | buf->index;
      buf->length = V4L2_FRAME_BUF_SIZE;
      if (devices[index].frame_map_count[buf->index])
        buf->flags |= V4L2_BUF_FLAG_MAPPED;
      else
        buf->flags &= ~V4L2_BUF_FLAG_MAPPED;
      }
      break;

    case VIDIOC_QBUF:
      if (devices[index].flags & V4L2_STREAM_CONTROLLED_BY_READ)
      if ((result = v4l2_deactivate_read_stream(index)))
        break;

      /* With some drivers the buffers must be mapped before queuing */
      if (converting)
      if ((result = v4l2_map_buffers(index)))
        break;

      result = syscall(SYS_ioctl, devices[index].fd, VIDIOC_QBUF, arg);
      break;

    case VIDIOC_DQBUF:
      {
      struct v4l2_buffer *buf = arg;

      if (devices[index].flags & V4L2_STREAM_CONTROLLED_BY_READ)
        if ((result = v4l2_deactivate_read_stream(index)))
          break;

      if (!converting) {
        result = syscall(SYS_ioctl, devices[index].fd, VIDIOC_DQBUF, buf);
        if (result) {
          int saved_err = errno;
          V4L2_LOG_ERR("dequeuing buf: %s\n", strerror(errno));
          errno = saved_err;
        }
        break;
      }

      /* An application can do a DQBUF before mmap-ing in the buffer,
         but we need the buffer _now_ to write our converted data
         to it! */
      if (devices[index].convert_mmap_buf == MAP_FAILED) {
        devices[index].convert_mmap_buf = (void *)syscall(SYS_mmap2,
                                       (size_t)(
                                         devices[index].no_frames *
                                         V4L2_FRAME_BUF_SIZE),
                                       PROT_READ|PROT_WRITE,
                                       MAP_ANONYMOUS|MAP_PRIVATE,
                                       -1, 0);
        if (devices[index].convert_mmap_buf == MAP_FAILED) {
          saved_err = errno;
          V4L2_LOG_ERR("allocating conversion buffer\n");
          errno = saved_err;
          result = -1;
          break;
        }
      }

      result = v4l2_dequeue_and_convert(index, buf, 0, V4L2_FRAME_BUF_SIZE);
      if (result < 0)
        break;

      buf->bytesused = result;
      buf->m.offset = V4L2_MMAP_OFFSET_MAGIC | buf->index;
      buf->length = V4L2_FRAME_BUF_SIZE;
      if (devices[index].frame_map_count[buf->index])
        buf->flags |= V4L2_BUF_FLAG_MAPPED;
      else
        buf->flags &= ~V4L2_BUF_FLAG_MAPPED;

      result = 0;
      }
      break;

    case VIDIOC_STREAMON:
    case VIDIOC_STREAMOFF:
      if (devices[index].flags & V4L2_STREAM_CONTROLLED_BY_READ)
      if ((result = v4l2_deactivate_read_stream(index)))
        break;

      if (request == VIDIOC_STREAMON)
      result = v4l2_streamon(index);
      else
      result = v4l2_streamoff(index);
      break;

    default:
      result = syscall(SYS_ioctl, fd, request, arg);
  }

  if (stream_needs_locking)
    pthread_mutex_unlock(&devices[index].stream_lock);

  saved_err = errno;
  v4l2_log_ioctl(request, arg, result);
  errno = saved_err;

  return result;
}


ssize_t v4l2_read (int fd, void* dest, size_t n)
{
  ssize_t result;
  int index;
  struct v4l2_buffer buf;

  if ((index = v4l2_get_index(fd)) == -1)
    return syscall(SYS_read, fd, dest, n);

  pthread_mutex_lock(&devices[index].stream_lock);

  /* When not converting and the device supports read let the kernel handle
     it */
  if ((devices[index].flags & V4L2_SUPPORTS_READ) &&
      !v4lconvert_needs_conversion(devices[index].convert,
               &devices[index].src_fmt, &devices[index].dest_fmt)) {
    result = syscall(SYS_read, fd, dest, n);
    goto leave;
  }

  if (!(devices[index].flags & V4L2_STREAM_CONTROLLED_BY_READ)) {
    if ((devices[index].flags & V4L2_STREAMON) ||
      devices[index].frame_queued) {
      errno = EBUSY;
      result = -1;
      goto leave;
    }
    if ((result = v4l2_activate_read_stream(index)))
      goto leave;
  }

  buf.type   = V4L2_BUF_TYPE_VIDEO_CAPTURE;
  buf.memory = V4L2_MEMORY_MMAP;
  result = v4l2_dequeue_and_convert(index, &buf, dest, n);

  if (result >= 0)
    v4l2_queue_read_buffer(index, buf.index);

leave:
  pthread_mutex_unlock(&devices[index].stream_lock);

  return result;
}

void *v4l2_mmap(void *start, size_t length, int prot, int flags, int fd,
  __off64_t offset)
{
  int index;
  unsigned int buffer_index;
  void *result;

  if ((index = v4l2_get_index(fd)) == -1 ||
      /* Check if the mmap data matches our answer to QUERY_BUF, if it doesn't
       let the kernel handle it (to allow for mmap based non capture use) */
      start || length != V4L2_FRAME_BUF_SIZE ||
      ((unsigned int)offset & ~0xFFu) != V4L2_MMAP_OFFSET_MAGIC) {
    if (index != -1)
      V4L2_LOG("Passing mmap(%p, %d, ..., %x, through to the driver\n",
      start, (int)length, (int)offset);

    if (offset & ((1 << MMAP2_PAGE_SHIFT) - 1)) {
      errno = EINVAL;
      return MAP_FAILED;
    }

    return (void *)syscall(SYS_mmap2, start, length, prot, flags, fd,
                     (__off_t)(offset >> MMAP2_PAGE_SHIFT));
  }

  pthread_mutex_lock(&devices[index].stream_lock);

  buffer_index = offset & 0xff;
  if (buffer_index >= devices[index].no_frames ||
      /* Got magic offset and not converting ?? */
      !v4lconvert_needs_conversion(devices[index].convert,
               &devices[index].src_fmt, &devices[index].dest_fmt)) {
    errno = EINVAL;
    result = MAP_FAILED;
    goto leave;
  }

  if (devices[index].convert_mmap_buf == MAP_FAILED) {
    devices[index].convert_mmap_buf = (void *)syscall(SYS_mmap2, NULL,
                                   (size_t)(
                                     devices[index].no_frames *
                                     V4L2_FRAME_BUF_SIZE),
                                   PROT_READ|PROT_WRITE,
                                   MAP_ANONYMOUS|MAP_PRIVATE,
                                   -1, 0);
    if (devices[index].convert_mmap_buf == MAP_FAILED) {
      int saved_err = errno;
      V4L2_LOG_ERR("allocating conversion buffer\n");
      errno = saved_err;
      result = MAP_FAILED;
      goto leave;
    }
  }

  devices[index].frame_map_count[buffer_index]++;

  result = devices[index].convert_mmap_buf +
    buffer_index * V4L2_FRAME_BUF_SIZE;

  V4L2_LOG("Fake (conversion) mmap buf %u, seen by app at: %p\n",
    buffer_index, result);

leave:
  pthread_mutex_unlock(&devices[index].stream_lock);

  return result;
}

int v4l2_munmap(void *_start, size_t length)
{
  int index;
  unsigned int buffer_index;
  unsigned char *start = _start;

  /* Is this memory ours? */
  if (start != MAP_FAILED && length == V4L2_FRAME_BUF_SIZE) {
    for (index = 0; index < devices_used; index++)
      if (devices[index].fd != -1 &&
        devices[index].convert_mmap_buf != MAP_FAILED &&
        start >= devices[index].convert_mmap_buf &&
        (start - devices[index].convert_mmap_buf) % length == 0)
      break;

    if (index != devices_used) {
      int unmapped = 0;

      pthread_mutex_lock(&devices[index].stream_lock);

      buffer_index = (start - devices[index].convert_mmap_buf) / length;

      /* Redo our checks now that we have the lock, things may have changed */
      if (devices[index].convert_mmap_buf != MAP_FAILED &&
        start >= devices[index].convert_mmap_buf &&
        (start - devices[index].convert_mmap_buf) % length == 0 &&
        buffer_index < devices[index].no_frames) {
      if (devices[index].frame_map_count[buffer_index] > 0)
        devices[index].frame_map_count[buffer_index]--;
      unmapped = 1;
      }

      pthread_mutex_unlock(&devices[index].stream_lock);

      if (unmapped) {
      V4L2_LOG("v4l2 fake buffer munmap %p, %d\n", start, (int)length);
      return 0;
      }
    }
  }

  V4L2_LOG("v4l2 unknown munmap %p, %d\n", start, (int)length);

  return syscall(SYS_munmap, _start, length);
}

/* Misc utility functions */
int v4l2_set_control(int fd, int cid, int value)
{
  struct v4l2_queryctrl qctrl = { .id = cid };
  struct v4l2_control ctrl = { .id = cid };
  int result;

  if ((result = syscall(SYS_ioctl, fd, VIDIOC_QUERYCTRL, &qctrl)))
    return result;

  if (!(qctrl.flags & V4L2_CTRL_FLAG_DISABLED) &&
      !(qctrl.flags & V4L2_CTRL_FLAG_GRABBED)) {
    if (qctrl.type == V4L2_CTRL_TYPE_BOOLEAN)
      ctrl.value = value? 1:0;
    else
      ctrl.value = (value * (qctrl.maximum - qctrl.minimum) + 32767) / 65535 +
               qctrl.minimum;

    result = syscall(SYS_ioctl, fd, VIDIOC_S_CTRL, &ctrl);
  }

  return result;
}

int v4l2_get_control(int fd, int cid)
{
  struct v4l2_queryctrl qctrl = { .id = cid };
  struct v4l2_control ctrl = { .id = cid };

  if (syscall(SYS_ioctl, fd, VIDIOC_QUERYCTRL, &qctrl))
    return 0;

  if (qctrl.flags & V4L2_CTRL_FLAG_DISABLED)
    return 0;

  if (syscall(SYS_ioctl, fd, VIDIOC_G_CTRL, &ctrl))
    return 0;

  return ((ctrl.value - qctrl.minimum) * 65535 +
        (qctrl.maximum - qctrl.minimum) / 2) /
       (qctrl.maximum - qctrl.minimum);
}

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