And another thing that I found while implementing this in v4l2-ctl:
On 06/24/2014 01:54 AM, Laurent Pinchart wrote:
> The v4l2_pix_format structure has no reserved field. It is embedded in
> the v4l2_framebuffer structure which has no reserved fields either, and
> in the v4l2_format structure which has reserved fields that were not
> previously required to be zeroed out by applications.
>
> To allow extending v4l2_pix_format, inline it in the v4l2_framebuffer
> structure, and use the priv field as a magic value to indicate that the
> application has set all v4l2_pix_format extended fields and zeroed all
> reserved fields following the v4l2_pix_format field in the v4l2_format
> structure.
>
> The availability of this API extension is reported to userspace through
> the new V4L2_CAP_EXT_PIX_FORMAT capability flag. Just checking that the
> priv field is still set to the magic value at [GS]_FMT return wouldn't
> be enough, as older kernels don't zero the priv field on return.
>
> To simplify the internal API towards drivers zero the extended fields
> and set the priv field to the magic value for applications not aware of
> the extensions.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 16bffd8..01b4588 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -959,13 +959,48 @@ static int check_fmt(struct file *file, enum v4l2_buf_type type)
> return -EINVAL;
> }
>
> +static void v4l_sanitize_format(struct v4l2_format *fmt)
> +{
> + unsigned int offset;
> +
> + /*
> + * The v4l2_pix_format structure has been extended with fields that were
> + * not previously required to be set to zero by applications. The priv
> + * field, when set to a magic value, indicates the the extended fields
> + * are valid. Otherwise they will contain undefined values. To simplify
> + * the API towards drivers zero the extended fields and set the priv
> + * field to the magic value when the extended pixel format structure
> + * isn't used by applications.
> + */
> +
> + if (fmt->type != V4L2_BUF_TYPE_VIDEO_CAPTURE &&
> + fmt->type != V4L2_BUF_TYPE_VIDEO_OUTPUT)
> + return;
> +
> + if (fmt->fmt.pix.priv == V4L2_PIX_FMT_PRIV_MAGIC)
> + return;
> +
> + fmt->fmt.pix.priv = V4L2_PIX_FMT_PRIV_MAGIC;
> +
> + offset = offsetof(struct v4l2_pix_format, priv)
> + + sizeof(fmt->fmt.pix.priv);
> + memset(((void *)&fmt->fmt.pix) + offset, 0,
> + sizeof(fmt->fmt.pix) - offset);
> +}
> +
> static int v4l_querycap(const struct v4l2_ioctl_ops *ops,
> struct file *file, void *fh, void *arg)
> {
> struct v4l2_capability *cap = (struct v4l2_capability *)arg;
> + int ret;
>
> cap->version = LINUX_VERSION_CODE;
> - return ops->vidioc_querycap(file, fh, cap);
> +
> + ret = ops->vidioc_querycap(file, fh, cap);
> +
> + cap->capabilities |= V4L2_CAP_EXT_PIX_FORMAT;
It should be ORed to cap->device_caps as well.
> +
> + return ret;
Regards,
Hans
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