From 1fbe13cf4b16ebf899f031c1c41e89c555dfe3e8 Mon Sep 17 00:00:00 2001
From: "Jonathan T. Looney" <jtl@FreeBSD.org>
Date: Fri, 8 Jun 2018 19:35:24 +0000
Subject: [PATCH] Add a socket destructor callback.  This allows kernel
 providers to set callbacks to perform additional cleanup actions at the time
 a socket is closed.

Michio Honda presented a use for this at BSDCan 2018.
(See https://www.bsdcan.org/2018/schedule/events/965.en.html .)

Submitted by:	Michio Honda <micchie at sfc.wide.ad.jp> (previous version)
Reviewed by:	lstewart (previous version)
Differential Revision:	https://reviews.freebsd.org/D15706
---
 share/man/man9/socket.9 | 14 +++++++++++++-
 sys/kern/uipc_socket.c  | 13 +++++++++++++
 sys/sys/socketvar.h     |  3 +++
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/share/man/man9/socket.9 b/share/man/man9/socket.9
index 4b3e2cbd4669..a4eb98275ec6 100644
--- a/share/man/man9/socket.9
+++ b/share/man/man9/socket.9
@@ -26,7 +26,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd May 26, 2014
+.Dd June 8, 2018
 .Dt SOCKET 9
 .Os
 .Sh NAME
@@ -54,6 +54,11 @@
 .Fc
 .Ft int
 .Fn sodisconnect "struct socket *so"
+.Ft void
+.Fo sodtor_set
+.Fa "struct socket *so" 
+.Fa "void (*func)(struct socket *)"
+.Fc
 .Ft struct  sockaddr *
 .Fn sodupsockaddr "const struct sockaddr *sa" "int mflags"
 .Ft void
@@ -369,6 +374,13 @@ be cleared, with
 .Dv SO_RCV
 or
 .Dv SO_SND .
+.Ss Socket Destructor Callback
+A kernel system can use the
+.Fn sodtor_set
+function to set a destructor for a socket.
+The destructor is called when the socket is closed.
+The destructor is called after the protocol close routine has completed.
+The destructor can serve as a callback to initiate additional cleanup actions.
 .Ss Socket I/O
 The
 .Fn soreceive
diff --git a/sys/kern/uipc_socket.c b/sys/kern/uipc_socket.c
index 1dd52489c76b..cc3013ec3252 100644
--- a/sys/kern/uipc_socket.c
+++ b/sys/kern/uipc_socket.c
@@ -1101,6 +1101,8 @@ soclose(struct socket *so)
 drop:
 	if (so->so_proto->pr_usrreqs->pru_close != NULL)
 		(*so->so_proto->pr_usrreqs->pru_close)(so);
+	if (so->so_dtor != NULL)
+		so->so_dtor(so);
 
 	SOCK_LOCK(so);
 	if ((listening = (so->so_options & SO_ACCEPTCONN))) {
@@ -3812,6 +3814,17 @@ sodupsockaddr(const struct sockaddr *sa, int mflags)
 	return sa2;
 }
 
+/*
+ * Register per-socket destructor.
+ */
+void
+sodtor_set(struct socket *so, so_dtor_t *func)
+{
+
+	SOCK_LOCK_ASSERT(so);
+	so->so_dtor = func;
+}
+
 /*
  * Register per-socket buffer upcalls.
  */
diff --git a/sys/sys/socketvar.h b/sys/sys/socketvar.h
index 546939fcf2b3..187aa57dc97d 100644
--- a/sys/sys/socketvar.h
+++ b/sys/sys/socketvar.h
@@ -63,6 +63,7 @@ struct vnet;
  * private data and error information.
  */
 typedef	int so_upcall_t(struct socket *, void *, int);
+typedef	void so_dtor_t(struct socket *);
 
 struct socket;
 
@@ -99,6 +100,7 @@ struct socket {
 	/* NB: generation count must not be first. */
 	so_gen_t so_gencnt;		/* (h) generation count */
 	void	*so_emuldata;		/* (b) private data for emulators */
+	so_dtor_t *so_dtor;		/* (b) optional destructor */
 	struct	osd	osd;		/* Object Specific extensions */
 	/*
 	 * so_fibnum, so_user_cookie and friends can be used to attach
@@ -397,6 +399,7 @@ int	soconnect2(struct socket *so1, struct socket *so2);
 int	socreate(int dom, struct socket **aso, int type, int proto,
 	    struct ucred *cred, struct thread *td);
 int	sodisconnect(struct socket *so);
+void	sodtor_set(struct socket *, so_dtor_t *);
 struct	sockaddr *sodupsockaddr(const struct sockaddr *sa, int mflags);
 void	sofree(struct socket *so);
 void	sohasoutofband(struct socket *so);