Re: [PATCH v3 5/5] io_uring/netcmd: add tx timestamping cmd support

[Pavel Begunkov <asml.silence@gmail.com>]

On 6/12/25 15:12, Jens Axboe wrote:
> On 6/12/25 3:09 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
>                          ^^^^^^^^^^^^^^^^^
> 
> Pointed this out before, but this typo is still there.

Forgot about that one

> 
>> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
>> index cfd17e382082..5c89e6f6d624 100644
>> --- a/include/uapi/linux/io_uring.h
>> +++ b/include/uapi/linux/io_uring.h
>> @@ -968,6 +968,15 @@ enum io_uring_socket_op {
>>   	SOCKET_URING_OP_SIOCOUTQ,
>>   	SOCKET_URING_OP_GETSOCKOPT,
>>   	SOCKET_URING_OP_SETSOCKOPT,
>> +	SOCKET_URING_OP_TX_TIMESTAMP,
>> +};
>> +
>> +#define IORING_CQE_F_TIMESTAMP_HW	((__u32)1 << IORING_CQE_BUFFER_SHIFT)
>> +#define IORING_TIMESTAMP_TSTYPE_SHIFT	(IORING_CQE_BUFFER_SHIFT + 1)
> 
> Don't completely follow this, would at the very least need a comment.
> Whether it's a HW or SW timestamp is flagged in the upper 16 bits, just
> like a provided buffer ID. But since we don't use buffer IDs here, then
> it's up for grabs. Do we have other commands that use the upper flags
> space for command private flags?

Probably not, but the place is better than the lower half, which
has common flags like F_MORE, especially since the patch is already
using it to store the type.

> The above makes sense, but then what is IORING_TIMESTAMP_TSTYPE_SHIFT?

It's a shift for where the timestamp type is stored, HW vs SW is
not a timestamp type. I don't get the question.

-- 
Pavel Begunkov