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

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Date:	Thu, 3 Dec 2015 00:18:10 +0900
From:	Lorenzo Colitti <lorenzo@...gle.com>
To:	Tom Herbert <tom@...bertland.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Erik Kline <ek@...gle.com>,
	Maciej Żenczykowski <zenczykowski@...il.com>
Subject: Re: Add a SOCK_DESTROY operation to close sockets from userspace

On Tue, Dec 1, 2015 at 11:53 AM, Tom Herbert <tom@...bertland.com> wrote:
> This is awesome! The only thing I would suggest is to make
> sock_destroy a proto_op so that it can be called from within the
> kernel. This should be preferred to externally calling tcp_done
> (hopefully we can unexport that symbol then).

I'm not sure there is value in making it a proto op. The sock_diag
code that finds the socket based on the netlink diag request is
specific to both the protocol family (e.g., the sock_diag structures
for inet and unix differ) and protocol (e.g., TCP, UDPv4 and UDPv6 use
different hash tables).

So even if we add a proto_op (or struct proto function pointer) to
destroy a socket, we can't just have a generic function (or even an
inet-specific function) that just finds a socket and does "return
sk->sk_prot->diag_destroy(sk)" regardless of what protocol that socket
is.

The code does look better if the protocol-specific code is moved to a
new tcp_abort function that just takes a pointer to the sk.
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