Subject: Re: [PATCH iproute2-next] ss: Show zerocopy sendfile status of TLS sockets

From: Jakub Kicinski <[email-masked]>
Date: Tue, 31 May 2022 12:18:29 -0700

On Mon, 30 May 2022 11:17:45 -0700 Jakub Kicinski wrote:
> Also please send a patch to Documentation/, I forgot about that.

Actually let me take care of that on my own, I have some optimizations
to add, saves me a rebase ;)

Does this sound good?

Optional optimizations
----------------------

There are certain condition-specific optimizations the TLS ULP can make,
if requested. Those optimizations are either not universally beneficial
or may impact correctness, hence they require an opt-in.
All options are set per-socket using setsockopt(), and their
state can be checked using getsockopt() and via socket diag (``ss``).

TLS_INFO_ZC_SENDFILE
~~~~~~~~~~~~~~~~~~~~

For device offload only. Allow sendfile() data to be transmitted directly
to the NIC without making an in-kernel copy. This allows true zero-copy
behavior when device offload is enabled.

The application must make sure that the data is not modified between being
submitted and transmission completing. In other words this is mostly
applicable if the data sent on a socket via sendfile() is read-only.

Modifying the data may result in different versions of the data being used
for the original TCP transmission and TCP retransmissions. To the receiver
this will look like TLS records had been tampered with and will result
in record authentication failures.