Re: libv4l2 woes

[Ronny Brendel <ronnybrendel@gmail.com>]

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I tried a bit further, and I came to the conclusion that this is likely a bug 
in libv4l2 ... I don't yet know what it is.

The strongest argument is ,that the capturing example taken from the specs of 
v4l, replaced with the respective v4l2_ calls (to utilize auto conversion), 
make the program throw out the exact same error.

Can anybody please guide me?
I am desperade ~.~ trying to get it to work.

regards
Ronny

attached: the modified v4l-example

On Monday 10 August 2009 19:29:58 Ronny Brendel wrote:
> Hi there,
>
> I am currently trying to read image data from my webcam.
> When I read raw data data by using open/read/close everything works just
> fine.
>
> Since I want to use the auto-conversion of libv4l2, I tried out reading
> using the v4l2_ counterparts,
> Unfortunately the library closes with an error message::
>
> libv4l2: error requesting 4 buffers: Device or resource busy
>
> Can some please give a suggestion what to do?
>
>
> The source of my tool is available at
> http://github.com/hydroo/videocapture/tree/master (CaptureDevice.{hpp,cpp}
>
> regards
> Ronny



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/*
 *  *  V4L2 video capture example
 *   *
 *    *  This program can be used and distributed without restrictions.
 *     */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include <getopt.h>             /* getopt_long() */

#include <fcntl.h>              /* low-level i/o */
#include <unistd.h>
#include <errno.h>
#include <malloc.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <libv4l2.h>

#include <asm/types.h>          /* for videodev2.h */

#include <linux/videodev2.h>

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

typedef enum {
    IO_METHOD_READ,
    IO_METHOD_MMAP,
    IO_METHOD_USERPTR,
} io_method;

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

static char *           dev_name        = NULL;
static io_method        io              = IO_METHOD_MMAP;
static int              fd              = -1;
struct buffer *         buffers         = NULL;
static unsigned int     n_buffers       = 0;

    static void
errno_exit                      (const char *           s)
{
    fprintf (stderr, "%s error %d, %s\n",
            s, errno, strerror (errno));

    exit (EXIT_FAILURE);
}

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

    do r = v4l2_ioctl (fd, request, arg);
    while (-1 == r && EINTR == errno);

    return r;
}

    static void
process_image                   (const void *           p)
{
    fputc ('.', stdout);
    fflush (stdout);
}

    static int
read_frame                      (void)
{
    struct v4l2_buffer buf;
    unsigned int i;

    switch (io) {
        case IO_METHOD_READ:
            if (-1 == v4l2_read (fd, buffers[0].start, buffers[0].length)) {
                switch (errno) {
                    case EAGAIN:
                        return 0;

                    case EIO:
                        /* Could ignore EIO, see spec. */

                        /* fall through */

                    default:
                        errno_exit ("read");
                }
            }

            process_image (buffers[0].start);

            break;

        case IO_METHOD_MMAP:
            CLEAR (buf);

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

            if (-1 == xioctl (fd, VIDIOC_DQBUF, &buf)) {
                switch (errno) {
                    case EAGAIN:
                        return 0;

                    case EIO:
                        /* Could ignore EIO, see spec. */

                        /* fall through */

                    default:
                        errno_exit ("VIDIOC_DQBUF");
                }
            }

            assert (buf.index < n_buffers);

            process_image (buffers[buf.index].start);

            if (-1 == xioctl (fd, VIDIOC_QBUF, &buf))
                errno_exit ("VIDIOC_QBUF");

            break;

        case IO_METHOD_USERPTR:
            CLEAR (buf);

            buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
            buf.memory = V4L2_MEMORY_USERPTR;

            if (-1 == xioctl (fd, VIDIOC_DQBUF, &buf)) {
                switch (errno) {
                    case EAGAIN:
                        return 0;

                    case EIO:
                        /* Could ignore EIO, see spec. */

                        /* fall through */

                    default:
                        errno_exit ("VIDIOC_DQBUF");
                }
            }

            for (i = 0; i < n_buffers; ++i)
                if (buf.m.userptr == (unsigned long) buffers[i].start
                        && buf.length == buffers[i].length)
                    break;

            assert (i < n_buffers);

            process_image ((void *) buf.m.userptr);

            if (-1 == xioctl (fd, VIDIOC_QBUF, &buf))
                errno_exit ("VIDIOC_QBUF");

            break;
    }

    return 1;
}

    static void
mainloop                        (void)
{
    unsigned int count;

    count = 100;

    while (count-- > 0) {
        for (;;) {
            fd_set fds;
            struct timeval tv;
            int r;

            FD_ZERO (&fds);
            FD_SET (fd, &fds);

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

            r = select (fd + 1, &fds, NULL, NULL, &tv);

            if (-1 == r) {
                if (EINTR == errno)
                    continue;

                errno_exit ("select");
            }

            if (0 == r) {
                fprintf (stderr, "select timeout\n");
                exit (EXIT_FAILURE);
            }

            if (read_frame ())
                break;

            /* EAGAIN - continue select loop. */
        }
    }
}

    static void
stop_capturing                  (void)
{
    enum v4l2_buf_type type;

    switch (io) {
        case IO_METHOD_READ:
            /* Nothing to do. */
            break;

        case IO_METHOD_MMAP:
        case IO_METHOD_USERPTR:
            type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

            if (-1 == xioctl (fd, VIDIOC_STREAMOFF, &type))
                errno_exit ("VIDIOC_STREAMOFF");

            break;
    }
}

    static void
start_capturing                 (void)
{
    unsigned int i;
    enum v4l2_buf_type type;

    switch (io) {
        case IO_METHOD_READ:
            /* Nothing to do. */
            break;

        case IO_METHOD_MMAP:
            for (i = 0; i < n_buffers; ++i) {
                struct v4l2_buffer buf;

                CLEAR (buf);

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

                if (-1 == xioctl (fd, VIDIOC_QBUF, &buf))
                    errno_exit ("VIDIOC_QBUF");
            }

            type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

            if (-1 == xioctl (fd, VIDIOC_STREAMON, &type))
                errno_exit ("VIDIOC_STREAMON");

            break;

        case IO_METHOD_USERPTR:
            for (i = 0; i < n_buffers; ++i) {
                struct v4l2_buffer buf;

                CLEAR (buf);

                buf.type        = V4L2_BUF_TYPE_VIDEO_CAPTURE;
                buf.memory      = V4L2_MEMORY_USERPTR;
                buf.index       = i;
                buf.m.userptr   = (unsigned long) buffers[i].start;
                buf.length      = buffers[i].length;

                if (-1 == xioctl (fd, VIDIOC_QBUF, &buf))
                    errno_exit ("VIDIOC_QBUF");
            }

            type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

            if (-1 == xioctl (fd, VIDIOC_STREAMON, &type))
                errno_exit ("VIDIOC_STREAMON");

            break;
    }
}

    static void
uninit_device                   (void)
{
    unsigned int i;

    switch (io) {
        case IO_METHOD_READ:
            free (buffers[0].start);
            break;

        case IO_METHOD_MMAP:
            for (i = 0; i < n_buffers; ++i)
                if (-1 == munmap (buffers[i].start, buffers[i].length))
                    errno_exit ("munmap");
            break;

        case IO_METHOD_USERPTR:
            for (i = 0; i < n_buffers; ++i)
                free (buffers[i].start);
            break;
    }

    free (buffers);
}

    static void
init_read                       (unsigned int           buffer_size)
{
    buffers = calloc (1, sizeof (*buffers));

    if (!buffers) {
        fprintf (stderr, "Out of memory\n");
        exit (EXIT_FAILURE);
    }

    buffers[0].length = buffer_size;
    buffers[0].start = malloc (buffer_size);

    if (!buffers[0].start) {
        fprintf (stderr, "Out of memory\n");
        exit (EXIT_FAILURE);
    }
}

    static void
init_mmap                       (void)
{
    struct v4l2_requestbuffers req;

    CLEAR (req);

    req.count               = 4;
    req.type                = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory              = V4L2_MEMORY_MMAP;

    if (-1 == xioctl (fd, VIDIOC_REQBUFS, &req)) {
        if (EINVAL == errno) {
            fprintf (stderr, "%s does not support "
                    "memory mapping\n", dev_name);
            exit (EXIT_FAILURE);
        } else {
            errno_exit ("VIDIOC_REQBUFS");
        }
    }

    if (req.count < 2) {
        fprintf (stderr, "Insufficient buffer memory on %s\n",
                dev_name);
        exit (EXIT_FAILURE);
    }

    buffers = calloc (req.count, sizeof (*buffers));

    if (!buffers) {
        fprintf (stderr, "Out of memory\n");
        exit (EXIT_FAILURE);
    }

    for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
        struct v4l2_buffer buf;

        CLEAR (buf);

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

        if (-1 == xioctl (fd, VIDIOC_QUERYBUF, &buf))
            errno_exit ("VIDIOC_QUERYBUF");

        buffers[n_buffers].length = buf.length;
        buffers[n_buffers].start =
            mmap (NULL /* start anywhere */,
                    buf.length,
                    PROT_READ | PROT_WRITE /* required */,
                    MAP_SHARED /* recommended */,
                    fd, buf.m.offset);

        if (MAP_FAILED == buffers[n_buffers].start)
            errno_exit ("mmap");
    }
}

    static void
init_userp                      (unsigned int           buffer_size)
{
    struct v4l2_requestbuffers req;
    unsigned int page_size;

    page_size = getpagesize ();
    buffer_size = (buffer_size + page_size - 1) & ~(page_size - 1);

    CLEAR (req);

    req.count               = 4;
    req.type                = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory              = V4L2_MEMORY_USERPTR;

    if (-1 == xioctl (fd, VIDIOC_REQBUFS, &req)) {
        if (EINVAL == errno) {
            fprintf (stderr, "%s does not support "
                    "user pointer i/o\n", dev_name);
            exit (EXIT_FAILURE);
        } else {
            errno_exit ("VIDIOC_REQBUFS");
        }
    }

    buffers = calloc (4, sizeof (*buffers));

    if (!buffers) {
        fprintf (stderr, "Out of memory\n");
        exit (EXIT_FAILURE);
    }

    for (n_buffers = 0; n_buffers < 4; ++n_buffers) {
        buffers[n_buffers].length = buffer_size;
        buffers[n_buffers].start = memalign (/* boundary */ page_size,
                buffer_size);

        if (!buffers[n_buffers].start) {
            fprintf (stderr, "Out of memory\n");
            exit (EXIT_FAILURE);
        }
    }
}

    static void
init_device                     (void)
{
    struct v4l2_capability cap;
    struct v4l2_cropcap cropcap;
    struct v4l2_crop crop;
    struct v4l2_format fmt;
    unsigned int min;

    if (-1 == xioctl (fd, VIDIOC_QUERYCAP, &cap)) {
        if (EINVAL == errno) {
            fprintf (stderr, "%s is no V4L2 device\n",
                    dev_name);
            exit (EXIT_FAILURE);
        } else {
            errno_exit ("VIDIOC_QUERYCAP");
        }
    }

    if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
        fprintf (stderr, "%s is no video capture device\n",
                dev_name);
        exit (EXIT_FAILURE);
    }

    switch (io) {
        case IO_METHOD_READ:
            if (!(cap.capabilities & V4L2_CAP_READWRITE)) {
                fprintf (stderr, "%s does not support read i/o\n",
                        dev_name);
                exit (EXIT_FAILURE);
            }

            break;

        case IO_METHOD_MMAP:
        case IO_METHOD_USERPTR:
            if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
                fprintf (stderr, "%s does not support streaming i/o\n",
                        dev_name);
                exit (EXIT_FAILURE);
            }

            break;
    }


    /* Select video input, video standard and tune here. */


    CLEAR (cropcap);

    cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    if (0 == xioctl (fd, VIDIOC_CROPCAP, &cropcap)) {
        crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        crop.c = cropcap.defrect; /* reset to default */

        if (-1 == xioctl (fd, VIDIOC_S_CROP, &crop)) {
            switch (errno) {
                case EINVAL:
                    /* Cropping not supported. */
                    break;
                default:
                    /* Errors ignored. */
                    break;
            }
        }
    } else {        
        /* Errors ignored. */
    }


    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;

    if (-1 == xioctl (fd, VIDIOC_S_FMT, &fmt))
        errno_exit ("VIDIOC_S_FMT");

    /* Note VIDIOC_S_FMT may change width and height. */

    /* Buggy driver paranoia. */
    min = fmt.fmt.pix.width * 2;
    if (fmt.fmt.pix.bytesperline < min)
        fmt.fmt.pix.bytesperline = min;
    min = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;
    if (fmt.fmt.pix.sizeimage < min)
        fmt.fmt.pix.sizeimage = min;

    switch (io) {
        case IO_METHOD_READ:
            init_read (fmt.fmt.pix.sizeimage);
            break;

        case IO_METHOD_MMAP:
            init_mmap ();
            break;

        case IO_METHOD_USERPTR:
            init_userp (fmt.fmt.pix.sizeimage);
            break;
    }
}

    static void
close_device                    (void)
{
    if (-1 == close (fd))
        errno_exit ("close");

    fd = -1;
}

    static void
open_device                     (void)
{
    struct stat st; 

    if (-1 == stat (dev_name, &st)) {
        fprintf (stderr, "Cannot identify '%s': %d, %s\n",
                dev_name, errno, strerror (errno));
        exit (EXIT_FAILURE);
    }

    if (!S_ISCHR (st.st_mode)) {
        fprintf (stderr, "%s is no device\n", dev_name);
        exit (EXIT_FAILURE);
    }

    fd = v4l2_open (dev_name, O_RDWR /* required */ | O_NONBLOCK, 0);

    if (-1 == fd) {
        fprintf (stderr, "Cannot open '%s': %d, %s\n",
                dev_name, errno, strerror (errno));
        exit (EXIT_FAILURE);
    }
}

    static void
usage                           (FILE *                 fp,
        int                    argc,
        char **                argv)
{
    fprintf (fp,
            "Usage: %s [options]\n\n"
            "Options:\n"
            "-d | --device name   Video device name [/dev/video]\n"
            "-h | --help          Print this message\n"
            "-m | --mmap          Use memory mapped buffers\n"
            "-r | --read          Use read() calls\n"
            "-u | --userp         Use application allocated buffers\n"
            "",
            argv[0]);
}

static const char short_options [] = "d:hmru";

static const struct option
long_options [] = {
    { "device",     required_argument,      NULL,           'd' },
    { "help",       no_argument,            NULL,           'h' },
    { "mmap",       no_argument,            NULL,           'm' },
    { "read",       no_argument,            NULL,           'r' },
    { "userp",      no_argument,            NULL,           'u' },
    { 0, 0, 0, 0 }
};

    int
main                            (int                    argc,
        char **                argv)
{
    dev_name = "/dev/video";

    for (;;) {
        int index;
        int c;

        c = getopt_long (argc, argv,
                short_options, long_options,
                &index);

        if (-1 == c)
            break;

        switch (c) {
            case 0: /* getopt_long() flag */
                break;

            case 'd':
                dev_name = optarg;
                break;

            case 'h':
                usage (stdout, argc, argv);
                exit (EXIT_SUCCESS);

            case 'm':
                io = IO_METHOD_MMAP;
                break;

            case 'r':
                io = IO_METHOD_READ;
                break;

            case 'u':
                io = IO_METHOD_USERPTR;
                break;

            default:
                usage (stderr, argc, argv);
                exit (EXIT_FAILURE);
        }
    }

    open_device ();

    init_device ();

    start_capturing ();

    mainloop ();

    stop_capturing ();

    uninit_device ();

    close_device ();

    exit (EXIT_SUCCESS);

    return 0;
}