Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <b6d8611a-714c-4fb0-5027-584884bb66a1@petrovitsch.priv.at>
Date:   Tue, 21 Jun 2022 09:02:38 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.10.0
Subject: Re: Networking Question
Content-Language: en-US
To:     "Ryan P. Nicholl" <rnicholl@protonmail.com>
References: <6_nVwntZEyEq2Gn0PYDz5w_yuD20E9Je_Bk2rJHsOersGq3v2x3_6hXnyjNm-X83-OTl1KKo4eLoHzyBVM_nzCcDrpPtz4dz3_71A3QezfI=@protonmail.com>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>
From:   Bernd Petrovitsch <bernd@petrovitsch.priv.at>
BIMI-Selector: v=BIMI1; s=default
In-Reply-To: <6_nVwntZEyEq2Gn0PYDz5w_yuD20E9Je_Bk2rJHsOersGq3v2x3_6hXnyjNm-X83-OTl1KKo4eLoHzyBVM_nzCcDrpPtz4dz3_71A3QezfI=@protonmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

Hi all!

On 21/06/2022 02:29, Ryan P. Nicholl wrote:
> I've been unable to find any Linux API for asynchronously waiting for the TCP send buffer to drain.
> 
> The problem I have, in a nutshell, is noted in this part of the documentation:
> 
>         If fildes refers to a socket, close() shall cause the socket to
>         be destroyed. If the socket is in connection-mode, and the

That's not really a Linux kernel question as such (because that should 
work that way on all TCP connections anywhere) but the shutdown() 
syscall is probably what you need:
- your side shuts down the sending part of the socket.
- the other side reads data and gets eventually EOF
- the other side call shutdown() for it's sending side when it's done.
- your side gets EOF.
And then your side knows that no data is in flight.
- finally, you clean up with close(). You can shutdown() the receiving
   side too but doesn't change anything.

[ deleted SO_LINGER stuff - that's for something completelly different ... ]

Kind regards,
	Bernd
-- 
Bernd Petrovitsch                  Email : bernd@petrovitsch.priv.at
      There is NO CLOUD, just other people's computers. - FSFE
                      LUGA : http://www.luga.at