Re: [question] v4l read() operation
Hi Dave, 2012/2/25 Dave Hylands dhyla...@gmail.com: 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. My bad! You are totally right: I forgot about my webcam. When I did: $ cat /dev/video0 I was actually getting data from my webcam (which supports read), and not from the easycap device, which is /dev/video1. So, everything makes sense now: $ cat /dev/video1 ... open(/dev/video1, O_RDONLY|O_LARGEFILE) = 3 ... read(3, 0x8835000, 32768) = -1 EINVAL (Invalid argument) This is clearly shown by the piece of code mentioned before. Thanks and sorry for the noise, Ezequiel. -- To unsubscribe from this list: send the line unsubscribe linux-media in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [question] v4l read() operation
Hi Ezequiel
2012/2/25 Ezequiel García elezegar...@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
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Re: [question] v4l read() operation
Ezequiel García elezegar...@gmail.com wrote:
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;
}
Thanks,
Ezequiel.
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Please read the v4l2 specification. Drivers can support the read/write methods
or streaming IO methods (using mmap) or both.
Often it is the case that drivers for MPEG encoders or other chips that produce
container formats use read/write. Drivers for chips the provide raw frames
often use streaming IO.
Note that the videobuf2 framework can provide read/write method emulation for a
driver IIRC.
- Andy
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