netdev - Re: Add a SOCK_DESTROY operation to close sockets from userspace

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Date:	Thu, 19 Nov 2015 14:14:58 -0800
From:	Tom Herbert <tom@...bertland.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	zenczykowski <zenczykowski@...il.com>,
	Lorenzo Colitti <lorenzo@...gle.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>, Erik Kline <ek@...gle.com>,
	Dmitry Torokhov <dtor@...gle.com>
Subject: Re: Add a SOCK_DESTROY operation to close sockets from userspace

On Thu, Nov 19, 2015 at 2:07 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Thu, 2015-11-19 at 13:53 -0800, Tom Herbert wrote:
>
>> That covers the case where the local address is removed, but the not
>> the case where the network manager is informed of an error in the path
>> and wants to signal the application. My understanding was that
>> SIOCKILLADDR would work for the first case, but this patch was need to
>> cover the second case.
>>
>> btw, instead of closing the TCP socket can we just report an error and
>> wake up the application without affecting the connection? That is this
>> just becomes an error on the socket. The response by the application
>> will be the same in any case, porbablly just close the socket and try
>> to reestablish the connection.
>
> I thought this was the patch intent ?
>
> Application gets a EPOLLIN|EPOLLOUT|POLLERR notification (if it is
> willing to receive it, or blocked in a socket syscall) and closes the
> socket.
>
>          sk->sk_err = ETIMEDOUT;
>          sk->sk_error_report(sk);
>          tcp_done(sk);
>
The tcp_done is not needed here. This is the difference between the
application having the connection closed underneath them, versus the
application performing a close to terminate the connection. The latter
behavior preserves the semantics that only the stack or the
application owning the socket can initiate a state change on the
connection.
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