Re: [PATCH nft,v3 2/7] mnl: mnl_set_rcvbuffer() skips buffer size update if it is too small

[Phil Sutter <phil@nwl.cc>]

Hi Pablo,

On Thu, May 30, 2019 at 01:12:46PM +0200, Pablo Neira Ayuso wrote:
> Check for existing buffer size, if this is larger than the newer buffer
> size, skip this size update.
> 
> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
> ---
> v3: 'len' variable was not properly set.
> 
>  src/mnl.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/src/mnl.c b/src/mnl.c
> index 288a887df097..2270a084ad29 100644
> --- a/src/mnl.c
> +++ b/src/mnl.c
> @@ -235,8 +235,15 @@ static void mnl_set_sndbuffer(const struct mnl_socket *nl,
>  
>  static int mnl_set_rcvbuffer(const struct mnl_socket *nl, size_t bufsiz)
>  {
> +	unsigned int cur_bufsiz;
> +	socklen_t len = sizeof(cur_bufsiz);
>  	int ret;
>  
> +	ret = getsockopt(mnl_socket_get_fd(nl), SOL_SOCKET, SO_RCVBUF,
> +			 &cur_bufsiz, &len);
> +	if (cur_bufsiz > bufsiz)
> +		return 0;
> +

For mnl_set_sndbuffer(), there is simply a global static variable
holding the last set value. Can't we use that here as well? I think of
something like:

+ static unsigned int nlsndbufsiz;

 static int mnl_set_rcvbuffer(const struct mnl_socket *nl, size_t bufsiz)
 {
+	socklen_t len = sizeof(nlsndbufsiz);
 	int ret;
 
+	if (!nlsndbufsiz)
+		ret = getsockopt(mnl_socket_get_fd(nl), SOL_SOCKET, SO_RCVBUF,
+				 &nlsndbufsiz, &len);
+	if (nlsndbufsiz >= bufsiz)
+		return 0;

Cheers, Phil