netdev - Re: [PATCH v2 5/5] io_uring/netcmd: add tx timestamping cmd support

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Message-ID: <b82bd278-1562-4901-971a-aa111c749747@kernel.dk>
Date: Wed, 4 Jun 2025 06:04:10 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
 Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Cc: netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
 Kuniyuki Iwashima <kuniyu@...zon.com>, Paolo Abeni <pabeni@...hat.com>,
 Willem de Bruijn <willemb@...gle.com>, "David S . Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
 Richard Cochran <richardcochran@...il.com>
Subject: Re: [PATCH v2 5/5] io_uring/netcmd: add tx timestamping cmd support

On 6/4/25 2:42 AM, Pavel Begunkov wrote:
> Add a new socket command which returns tx time stamps to the user. It
> provide an alternative to the existing error queue recvmsg interface.
> The command works in a polled multishot mode, which means io_uring will
> poll the socket and keep posting timestamps until the request is
> cancelled or fails in any other way (e.g. with no space in the CQ). It
> reuses the net infra and grabs timestamps from the socket's error queue.
> 
> The command requires IORING_SETUP_CQE32. All non-final CQEs (marked with
> IORING_CQE_F_MORE) have cqe->res set to the tskey, and the upper 16 bits
> of cqe->flags keep tstype (i.e. offset by IORING_CQE_BUFFER_SHIFT). The
> timevalue is store in the upper part of the extended CQE. The final
> completion won't have IORING_CQR_F_MORE and will have cqe->res storing
                         ^^

CQE_F_MORE

Minor nit below.

> +static bool io_process_timestamp_skb(struct io_uring_cmd *cmd, struct sock *sk,
> +				     struct sk_buff *skb, unsigned issue_flags)
> +{
> +	struct sock_exterr_skb *serr = SKB_EXT_ERR(skb);
> +	struct io_uring_cqe cqe[2];
> +	struct io_timespec *iots;
> +	struct timespec64 ts;
> +	u32 tskey;
> +
> +	BUILD_BUG_ON(sizeof(struct io_uring_cqe) != sizeof(struct io_timespec));
> +
> +	if (!skb_get_tx_timestamp(skb, sk, &ts))
> +		return false;
> +
> +	tskey = serr->ee.ee_data;
> +
> +	cqe->user_data = 0;
> +	cqe->res = tskey;
> +	cqe->flags = IORING_CQE_F_MORE;
> +	cqe->flags |= (u32)serr->ee.ee_info << IORING_CQE_BUFFER_SHIFT;

Get rid of the tskey variable? And I think this would be more easily
readable if it used:

	cqe[0].user_data = 0;

etc.

> +	iots = (struct io_timespec *)&cqe[1];
> +	iots->tv_sec = ts.tv_sec;
> +	iots->tv_nsec = ts.tv_nsec;
> +	return io_uring_cmd_post_mshot_cqe32(cmd, issue_flags, cqe);
> +}

A bit of a shame we can't just get the double CQE and fill it in, rather
than fill it on stack and copy it. But probably doesn't matter much.

-- 
Jens Axboe