linux-kernel - Re: [PATCH] AF_UNIX: Implement SO_TIMESTAMP and SO

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Date:	Mon, 04 Oct 2010 18:41:44 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alban Crequy <alban.crequy@...labora.co.uk>
Cc:	Lennart Poettering <lennart@...ttering.net>,
	"David S. Miller" <davem@...emloft.net>,
	Stephen Hemminger <shemminger@...tta.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] AF_UNIX: Implement SO_TIMESTAMP and SO_TIMETAMPNS on
 Unix sockets

Le lundi 04 octobre 2010 à 16:38 +0100, Alban Crequy a écrit :
> Userspace applications can already request to receive timestamps with:
> setsockopt(sockfd, SOL_SOCKET, SO_TIMESTAMP, ...)
> 
> Although setsockopt() returns zero (success), timestamps are not added to the
> ancillary data. This patch fixes that.
> 
> Signed-off-by: Alban Crequy <alban.crequy@...labora.co.uk>
> ---
>  net/unix/af_unix.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 617bea4..142ccea 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1697,6 +1697,8 @@ static int unix_dgram_recvmsg(struct kiocb *iocb, struct socket *sock,
>  	if (err)
>  		goto out_free;
>  
> +	sock_recv_timestamp(msg, sk, skb);
> +
>  	if (!siocb->scm) {
>  		siocb->scm = &tmp_scm;
>  		memset(&tmp_scm, 0, sizeof(tmp_scm));
> @@ -1877,6 +1879,8 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock,
>  		copied += chunk;
>  		size -= chunk;
>  
> +		sock_recv_timestamp(msg, sk, skb);
> +
>  		/* Mark read part of skb as used */
>  		if (!(flags & MSG_PEEK)) {
>  			skb_pull(skb, chunk);

Are you sure its needed for unix_stream case ?

We dont do this for TCP for example, only for datagrams.

As shown in the past, sock_recv_timestamp() is a bit expensive because
it takes care of many possible options.

It would be better to use in AF_UNIX case (only software timestamps) :

Solution 1) 
if (sock_flag(sk, SOCK_RCVTSTAMP))
	__sock_recv_timestamp(msg, sk, skb);

Solution 2) 
Or something already used elsewhere since 2.6.35 and commit
767dd03369ac1 (net: speedup sock_recv_ts_and_drops()) :

sock_recv_ts_and_drops(msg, sk, skb);


I would vote for the 1) solution


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