Re: [PATCH libnetfilter_queue v2] src: examples: Use libnetfilter_queue cached linux headers throughout

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Tue, Jul 06, 2021 at 03:36:48PM +1000, Duncan Roe wrote:
> A user will typically copy nf-queue.c, make changes and compile: picking up
> /usr/include/linux/nfnetlink_queue.h rather than
> /usr/include/libnetfilter_queue/linux_nfnetlink_queue.h as is recommended.
> 
> libnetfilter_queue.h already includes linux_nfnetlink_queue.h so we only need
> to delete the errant line.
> 
> (Running `make nf-queue` from within libnetfilter_queue/examples will get
> the private cached version of nfnetlink_queue.h which is not distributed).
> 
> Signed-off-by: Duncan Roe <duncan_roe@optusnet.com.au>
> ---
> v2: Don't insert a new #include
>     Doesn't clash with other nearby patch
>  examples/nf-queue.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/examples/nf-queue.c b/examples/nf-queue.c
> index 3da2c24..e4b33b5 100644
> --- a/examples/nf-queue.c
> +++ b/examples/nf-queue.c
> @@ -11,7 +11,6 @@
>  #include <linux/netfilter/nfnetlink.h>
>  
>  #include <linux/types.h>
> -#include <linux/netfilter/nfnetlink_queue.h>

I remember now what the intention was.

This include is fine as is: new applications should cache a copy of
nfnetlink_queue.h in their own tree, that's the recommended way to go.
This is the approach that we follow in other existing userspace
netfilter codebase (ie. the userspace program caches the kernel UAPI
header in the tree). The linux_nfnetlink_queue.h header is a legacy
file only for backward compatibility, it should not be used for new
software. This is not documented, the use of this include in
examples/nf-queue.c was intentional.

This approach also allows to fall back to the UAPI kernel headers that
are installed in your system.

Thanks.