[vlc-devel] [PATCH] v4l2: check if kernel headers are recent enough

[Rémi Denis-Courmont]

On Wed, 18 Jan 2012 20:06:21 -0500, Rafaël Carré <funman at videolan.org>
wrote:
> V4L2_FIELD_INTERLACED_BT was introduced in v2.6.25-3581-g26d507f

Stictly speaking, VLC requires kernel header version 3.1, so that
V4L2_CTRL_TYPE_BITMASK is in enum v4l2_ctrl_type. Oh wait... it actually
depends on version 3.2 as enum v4l2_power_line_frequency was modified. This
can actually be a real problem: the compiler can perform optimization
assuming that only defined values are used in enums. This affects
switch/case blocks especially.

I do not feel like supporting pre-2.6.26. This is really old now. And
builders do ignore warnings. Next thing, they will come and complain that
v4l2:// stopped working silently. I'd rather have the build system explode
in their face really.

Furthermore I am not a fan of patching configure.ac as it is slow as hell.

> ---
>  configure.ac |   13 ++++++++++++-
>  1 files changed, 12 insertions(+), 1 deletions(-)
> 
> diff --git a/configure.ac b/configure.ac
> index 8489a90..557ffe1 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -1845,7 +1845,18 @@ AC_ARG_ENABLE(pvr,
[AS_HELP_STRING([--enable-pvr],
>    [support PVR V4L2 cards (default disabled)])])
>  have_v4l2="no"
>  AC_CHECK_HEADERS([linux/videodev2.h sys/videoio.h], [
> -  have_v4l2="yes"
> +  AC_PREPROC_IFELSE([
> +  #ifdef __linux__
> +  # include <linux/version.h>
> +  # if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,26)
> +  #  error Kernel headers too old
> +  # endif
> +  #endif
> +    ], [
> +      have_v4l2="yes"
> +      ], [
> +      AC_MSG_WARN([Kernel headers too old for V4L2 module. You need at
> least 2.6.22])

This    ^^^^^^ is inconsistent.

> +  ])
>  ])
>  AS_IF([test "$have_v4l2" = "yes"], [
>    AS_IF([test "${enable_libv4l2}" != "no"], [

-- 
Rémi Denis-Courmont
http://www.remlab.net/