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Date: Sat, 5 Jul 2014 22:10:07 +0200
From: Richard Cochran <richardcochran@...il.com>
To: Willem de Bruijn <willemb@...gle.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net,
eric.dumazet@...il.com, richardcochran@...ail.com,
stephen@...workplumber.org
Subject: Re: [PATCH net-next v2 1/8] net-timestamp: explicit SO_TIMESTAMPING
ancillary data struct
On Thu, Jul 03, 2014 at 03:39:33PM -0400, Willem de Bruijn wrote:
> +/**
> + * struct scm_timestamping - timestamps exposed through cmsg
> + *
> + * The timestamping interfaces SO_TIMESTAMPING, MSG_TSTAMP_*
> + * communicate network timestamps by passing this struct in a cmsg with
> + * recvmsg(). See Documentation/networking/timestamping.txt for details.
> + */
> +struct scm_timestamping {
> + struct timespec ts[3];
> +};
> +
> +#define SCM_TSTAMP_SND 0x1 /* driver passed skb to NIC */
> +#define SCM_TSTAMP_ACK 0x2 /* transport layer saw ACK */
> +#define SCM_TSTAMP_ENQ 0x4 /* stack passed skb to TC layer */
> +#define SCM_TSTAMP_RCV 0x8 /* stack received skb */
> +#define SCM_TSTAMP_HWSYS 0x10 /* NIC tstamp in system format */
> +#define SCM_TSTAMP_HWRAW 0x20 /* NIC tstamp in native format */
> +
> +#define SCM_TSTAMP_OFF(n, ts) (ts << (10 * n))
Hm ...
> #endif /* _UAPI_LINUX_ERRQUEUE_H */
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index c1a3303..1bcd05d 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3521,6 +3521,7 @@ void skb_tstamp_tx(struct sk_buff *orig_skb,
> memset(serr, 0, sizeof(*serr));
> serr->ee.ee_errno = ENOMSG;
> serr->ee.ee_origin = SO_EE_ORIGIN_TIMESTAMPING;
> + serr->ee.ee_info = hwtstamps ? 0 : SCM_TSTAMP_SND;
>
> err = sock_queue_err_skb(sk, skb);
>
> diff --git a/net/socket.c b/net/socket.c
> index abf56b2..a31138d 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -106,6 +106,7 @@
> #include <linux/sockios.h>
> #include <linux/atalk.h>
> #include <net/busy_poll.h>
> +#include <linux/errqueue.h>
>
> #ifdef CONFIG_NET_RX_BUSY_POLL
> unsigned int sysctl_net_busy_read __read_mostly;
> @@ -696,9 +697,10 @@ EXPORT_SYMBOL(kernel_sendmsg);
> void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,
> struct sk_buff *skb)
> {
> + struct sock_exterr_skb *serr = SKB_EXT_ERR(skb);
> int need_software_tstamp = sock_flag(sk, SOCK_RCVTSTAMP);
> - struct timespec ts[3];
> - int empty = 1;
> + struct scm_timestamping tss;
> + int tstype = 0, is_tx = skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP;
> struct skb_shared_hwtstamps *shhwtstamps =
> skb_hwtstamps(skb);
>
> @@ -714,28 +716,31 @@ void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,
> put_cmsg(msg, SOL_SOCKET, SCM_TIMESTAMP,
> sizeof(tv), &tv);
> } else {
> - skb_get_timestampns(skb, &ts[0]);
> + struct timespec ts;
> + skb_get_timestampns(skb, &ts);
> put_cmsg(msg, SOL_SOCKET, SCM_TIMESTAMPNS,
> - sizeof(ts[0]), &ts[0]);
> + sizeof(ts), &ts);
> }
> }
>
> -
> - memset(ts, 0, sizeof(ts));
> + memset(&tss, 0, sizeof(tss));
> if (sock_flag(sk, SOCK_TIMESTAMPING_SOFTWARE) &&
> - ktime_to_timespec_cond(skb->tstamp, ts + 0))
> - empty = 0;
> + ktime_to_timespec_cond(skb->tstamp, tss.ts + 0))
> + tstype |= is_tx ? serr->ee.ee_info : SCM_TSTAMP_RCV;
> if (shhwtstamps) {
> if (sock_flag(sk, SOCK_TIMESTAMPING_SYS_HARDWARE) &&
> - ktime_to_timespec_cond(shhwtstamps->syststamp, ts + 1))
> - empty = 0;
> + ktime_to_timespec_cond(shhwtstamps->syststamp, tss.ts + 1))
> + tstype |= SCM_TSTAMP_OFF(1, SCM_TSTAMP_HWSYS);
> if (sock_flag(sk, SOCK_TIMESTAMPING_RAW_HARDWARE) &&
> - ktime_to_timespec_cond(shhwtstamps->hwtstamp, ts + 2))
> - empty = 0;
> + ktime_to_timespec_cond(shhwtstamps->hwtstamp, tss.ts + 2))
> + tstype |= SCM_TSTAMP_OFF(2, SCM_TSTAMP_HWRAW);
So you want ee_info to be a bit field like this?
| 10 bits | 10 bits | 10 bits | 2 bits |
|------------+------------+------------+--------|
| ts[0] type | ts[1] type | ts[2] type | rsv |
Why not simplify this into two fields:
1. the index ts[] that contains a time stamp
2. the type of the time stamp
The kernel never provides more than one value in ts[], and it is hard
to imagine that we will ever do this. The original so_timestamping
interface and documentation seem to suggest that multiple values are
possible, but there was never, ever any code that did this. As an end
user, I found that very confusing.
I would prefer making the extended interface simpler, rather than
giving the impression that multiple time stamps are possible when they
really are not.
Thanks,
Richard
> }
> - if (!empty)
> + if (tstype) {
> + if (is_tx)
> + serr->ee.ee_info = tstype;
> put_cmsg(msg, SOL_SOCKET,
> - SCM_TIMESTAMPING, sizeof(ts), &ts);
> + SCM_TIMESTAMPING, sizeof(tss), &tss);
> + }
> }
> EXPORT_SYMBOL_GPL(__sock_recv_timestamp);
>
> --
> 2.0.0.526.g5318336
>
> --
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