    /* V4L2 video picture grabber
       Copyright (C) 2009 Mauro Carvalho Chehab <mchehab@infradead.org>

       This program is free software; you can redistribute it and/or modify
       it under the terms of the GNU General Public License as published by
       the Free Software Foundation version 2 of the License.

       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 General Public License for more details.
     */

    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <fcntl.h>
    #include <errno.h>
    #include <sys/ioctl.h>
    #include <sys/types.h>
    #include <sys/time.h>
    #include <sys/mman.h>
    #include <linux/videodev2.h>
    #include "../libv4l/include/libv4l2.h"

    #define CLEAR(x) memset(&(x), 0, sizeof(x))

    struct buffer {
            void   *start;
            size_t length;
    };

    static void xioctl(int fh, int request, void *arg)
    {
            int r;

            do {
                    r = v4l2_ioctl(fh, request, arg);
            } while (r == -1 && ((errno == EINTR) || (errno == EAGAIN)));

            if (r == -1) {
                    fprintf(stderr, "error %d, %s\n", errno, strerror(errno));
                    exit(EXIT_FAILURE);
            }
    }

    int main(int argc, char **argv)
    {
            struct v4l2_format              fmt;
            struct v4l2_buffer              buf;
            struct v4l2_requestbuffers      req;
            enum v4l2_buf_type              type;
            fd_set                          fds;
            struct timeval                  tv;
            int                             r, fd = -1;
            unsigned int                    i, n_buffers;
            char                            *dev_name = "/dev/video0";
            char                            out_name[256];
            FILE                            *fout;
            struct buffer                   *buffers;

            fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0);
            if (fd < 0) {
                    perror("Cannot open device");
                    exit(EXIT_FAILURE);
            }

            CLEAR(fmt);
            fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
            fmt.fmt.pix.width       = 640;
            fmt.fmt.pix.height      = 480;
            fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_RGB24;
            fmt.fmt.pix.field       = V4L2_FIELD_INTERLACED;
            xioctl(fd, VIDIOC_S_FMT, &fmt);
            if (fmt.fmt.pix.pixelformat != V4L2_PIX_FMT_RGB24) {
                    printf("Libv4l didn't accept RGB24 format. Can't proceed.\n");
                    exit(EXIT_FAILURE);
            }
            if ((fmt.fmt.pix.width != 640) || (fmt.fmt.pix.height != 480))
                    printf("Warning: driver is sending image at %dx%d\n",
                            fmt.fmt.pix.width, fmt.fmt.pix.height);

            CLEAR(req);
            req.count = 2;
            req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
            req.memory = V4L2_MEMORY_MMAP;
            xioctl(fd, VIDIOC_REQBUFS, &req);

            buffers = calloc(req.count, sizeof(*buffers));
            for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
                    CLEAR(buf);

                    buf.type        = V4L2_BUF_TYPE_VIDEO_CAPTURE;
                    buf.memory      = V4L2_MEMORY_MMAP;
                    buf.index       = n_buffers;

                    xioctl(fd, VIDIOC_QUERYBUF, &buf);

                    buffers[n_buffers].length = buf.length;
                    buffers[n_buffers].start = v4l2_mmap(NULL, buf.length,
                                  PROT_READ | PROT_WRITE, MAP_SHARED,
                                  fd, buf.m.offset);

                    if (MAP_FAILED == buffers[n_buffers].start) {
                            perror("mmap");
                            exit(EXIT_FAILURE);
                    }
            }

            for (i = 0; i < n_buffers; ++i) {
                    CLEAR(buf);
                    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
                    buf.memory = V4L2_MEMORY_MMAP;
                    buf.index = i;
                    xioctl(fd, VIDIOC_QBUF, &buf);
            }
            type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

            xioctl(fd, VIDIOC_STREAMON, &type);
            for (i = 0; i < 20; i++) {
                    do {
                            FD_ZERO(&fds);
                            FD_SET(fd, &fds);

                            /* Timeout. */
                            tv.tv_sec = 2;
                            tv.tv_usec = 0;

                            r = select(fd + 1, &fds, NULL, NULL, &tv);
                    } while ((r == -1 && (errno = EINTR)));
                    if (r == -1) {
                            perror("select");
                            return errno;
                    }

                    CLEAR(buf);
                    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
                    buf.memory = V4L2_MEMORY_MMAP;
                    xioctl(fd, VIDIOC_DQBUF, &buf);

                    sprintf(out_name, "out%03d.ppm", i);
                    fout = fopen(out_name, "w");
                    if (!fout) {
                            perror("Cannot open image");
                            exit(EXIT_FAILURE);
                    }
                    fprintf(fout, "P6\n%d %d 255\n",
                            fmt.fmt.pix.width, fmt.fmt.pix.height);
                    fwrite(buffers[buf.index].start, buf.bytesused, 1, fout);
                    fclose(fout);

                    xioctl(fd, VIDIOC_QBUF, &buf);
            }

            type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
            xioctl(fd, VIDIOC_STREAMOFF, &type);
            for (i = 0; i < n_buffers; ++i)
                    v4l2_munmap(buffers[i].start, buffers[i].length);
            v4l2_close(fd);

            return 0;
    }