[question] v4l read() operation

[Dave Hylands]

Hi Ezequiel

2012/2/25 Ezequiel García <elezegarcia at gmail.com>:
> Hi,
>
> If I register a video device with this fops:
>
> static const struct v4l2_file_operations v4l2_fops = {
>        .owner      = THIS_MODULE,
>        .open        = xxx_open,
>        .unlocked_ioctl = xxx_unlocked_ioctl,
>        .poll           = xxx_poll,
>        .mmap      = xxx_mmap,
> };
>
> then if I "cat" the device
>
> $ cat /dev/video0
>
> Who is supporting read() ?
>
> I thought it could be v4l2_read(),
> however this function seems to return EINVAL:
>
> static ssize_t v4l2_read(struct file *filp, char __user *buf,
>                size_t sz, loff_t *off)
> {
>        struct video_device *vdev = video_devdata(filp);
>        int ret = -ENODEV;
>
>        if (!vdev->fops->read)
>                return -EINVAL;
>        if (vdev->lock && mutex_lock_interruptible(vdev->lock))
>                return -ERESTARTSYS;
>        if (video_is_registered(vdev))
>                ret = vdev->fops->read(filp, buf, sz, off);
>        if (vdev->lock)
>                mutex_unlock(vdev->lock);
>        return ret;
> }

I'm not all that familiar with v4l, but based on what you've posted,
you need to populate the read routine in your v4l2_fops structure to
support read.

-- 
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com