[V4L] V4L2: VIDIOC_QUERYBUF returns invalid argument

[Gert Vervoort]

Hi,

In an attempt to see how V4L2 programming works, I try to write a little capture
program. The program below returns an invalid argument in the VIDIOC_QUERYBUF
ioctl:

[gert@viper v4l2]$ gcc -O2 v4l2_cap.c
[gert@viper v4l2]$ ./a.out 
image size: 152064
2 buffers granted
VIDIOC_QUERYBUF: Invalid argument
[gert@viper v4l2]$ 

What am I overlooking?

-- Gert


driver  : bttv-0.8.31
kernel  : 2.4.15
patches : 10_videodev-2.4.15-pre6.diff
          11_v4l2-2.4.15-pre6.diff
          12_userdma-2.4.15-pre6.diff


v4l2_cap.c:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/videodev.h>

#define HSIZE 352
#define VSIZE 288
#define NUM_BUFFERS 2

struct buffer {
        struct v4l2_buffer vidbuf;
        char* data;
        int length;
};

int main()
{
        struct v4l2_capability vidcap;
        struct v4l2_format fmt;
        struct v4l2_requestbuffers reqbufs;
        struct buffer cap_bufs[NUM_BUFFERS];

        int fd;
        int i;
        
        if((fd = open("/dev/video", O_RDWR)) < 0) {
                perror("open");
                exit(-1);
        }

        if(ioctl(fd,  VIDIOC_QUERYCAP, &vidcap) < 0) {
                perror("VIDIOC_QUERYCAP");
                exit(-1);
        }

        if (vidcap.type != V4L2_TYPE_CAPTURE) {
                fprintf(stderr, "Error, not a capture device\n");
                exit(-1);
        }
        if(!(vidcap.flags & V4L2_FLAG_STREAMING)) {
                fprintf(stderr, "Error, streaming capture not supported\n");
                exit(-1);
        }

        memset(&fmt, 0x0, sizeof(fmt));
        fmt.type =  V4L2_BUF_TYPE_CAPTURE;
        fmt.fmt.pix.pixelformat =  V4L2_PIX_FMT_YUV420;
        fmt.fmt.pix.flags = V4L2_FMT_FLAG_INTERLACED;
        fmt.fmt.pix.width = HSIZE;
        fmt.fmt.pix.height = VSIZE;
        if(ioctl(fd, VIDIOC_S_FMT, &fmt) < 0) {
                perror("VIDIOC_S_FMT");
                exit(-1);
        }
        printf("image size: %d\n", fmt.fmt.pix.sizeimage); 
                
        reqbufs.count = NUM_BUFFERS;
        reqbufs.type = V4L2_BUF_TYPE_CAPTURE;
        if(ioctl(fd, VIDIOC_REQBUFS, &reqbufs) < 0) {
                perror("VIDIOC_REQBUFS");
                exit(-1);
        }
        printf("%d buffers granted\n", reqbufs.count);
        
        for(i=0; i<reqbufs.count; i++) {
                struct v4l2_buffer *vidbuf = &cap_bufs[i].vidbuf;
                
                vidbuf->index = i;
                vidbuf->type = V4L2_BUF_TYPE_CAPTURE;
                if(ioctl(fd, VIDIOC_QUERYBUF, vidbuf) < 0) {
                        perror("VIDIOC_QUERYBUF");
                        exit(-1);
                }



        
        }       

        close(fd);
        return 0;
}



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