xref: /freebsd/sys/kern/uipc_usrreq.c (revision 69a2875821ed9404a95f41bbeeb561908e3c38dc)

/*-
 * Copyright (c) 1982, 1986, 1989, 1991, 1993
 *	The Regents of the University of California.
 * Copyright (c) 2004-2009 Robert N. M. Watson
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	From: @(#)uipc_usrreq.c	8.3 (Berkeley) 1/4/94
 */

/*
 * UNIX Domain (Local) Sockets
 *
 * This is an implementation of UNIX (local) domain sockets.  Each socket has
 * an associated struct unpcb (UNIX protocol control block).  Stream sockets
 * may be connected to 0 or 1 other socket.  Datagram sockets may be
 * connected to 0, 1, or many other sockets.  Sockets may be created and
 * connected in pairs (socketpair(2)), or bound/connected to using the file
 * system name space.  For most purposes, only the receive socket buffer is
 * used, as sending on one socket delivers directly to the receive socket
 * buffer of a second socket.
 *
 * The implementation is substantially complicated by the fact that
 * "ancillary data", such as file descriptors or credentials, may be passed
 * across UNIX domain sockets.  The potential for passing UNIX domain sockets
 * over other UNIX domain sockets requires the implementation of a simple
 * garbage collector to find and tear down cycles of disconnected sockets.
 *
 * TODO:
 *	RDM
 *	rethink name space problems
 *	need a proper out-of-band
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_ddb.h"

#include <sys/param.h>
#include <sys/capsicum.h>
#include <sys/domain.h>
#include <sys/fcntl.h>
#include <sys/malloc.h>		/* XXX must be before <sys/file.h> */
#include <sys/eventhandler.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mbuf.h>
#include <sys/mount.h>
#include <sys/mutex.h>
#include <sys/namei.h>
#include <sys/proc.h>
#include <sys/protosw.h>
#include <sys/queue.h>
#include <sys/resourcevar.h>
#include <sys/rwlock.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/signalvar.h>
#include <sys/stat.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/taskqueue.h>
#include <sys/un.h>
#include <sys/unpcb.h>
#include <sys/vnode.h>

#include <net/vnet.h>

#ifdef DDB
#include <ddb/ddb.h>
#endif

#include <security/mac/mac_framework.h>

#include <vm/uma.h>

MALLOC_DECLARE(M_FILECAPS);

/*
 * Locking key:
 * (l)	Locked using list lock
 * (g)	Locked using linkage lock
 */

static uma_zone_t	unp_zone;
static unp_gen_t	unp_gencnt;	/* (l) */
static u_int		unp_count;	/* (l) Count of local sockets. */
static ino_t		unp_ino;	/* Prototype for fake inode numbers. */
static int		unp_rights;	/* (g) File descriptors in flight. */
static struct unp_head	unp_shead;	/* (l) List of stream sockets. */
static struct unp_head	unp_dhead;	/* (l) List of datagram sockets. */
static struct unp_head	unp_sphead;	/* (l) List of seqpacket sockets. */

struct unp_defer {
	SLIST_ENTRY(unp_defer) ud_link;
	struct file *ud_fp;
};
static SLIST_HEAD(, unp_defer) unp_defers;
static int unp_defers_count;

static const struct sockaddr	sun_noname = { sizeof(sun_noname), AF_LOCAL };

/*
 * Garbage collection of cyclic file descriptor/socket references occurs
 * asynchronously in a taskqueue context in order to avoid recursion and
 * reentrance in the UNIX domain socket, file descriptor, and socket layer
 * code.  See unp_gc() for a full description.
 */
static struct timeout_task unp_gc_task;

/*
 * The close of unix domain sockets attached as SCM_RIGHTS is
 * postponed to the taskqueue, to avoid arbitrary recursion depth.
 * The attached sockets might have another sockets attached.
 */
static struct task	unp_defer_task;

/*
 * Both send and receive buffers are allocated PIPSIZ bytes of buffering for
 * stream sockets, although the total for sender and receiver is actually
 * only PIPSIZ.
 *
 * Datagram sockets really use the sendspace as the maximum datagram size,
 * and don't really want to reserve the sendspace.  Their recvspace should be
 * large enough for at least one max-size datagram plus address.
 */
#ifndef PIPSIZ
#define	PIPSIZ	8192
#endif
static u_long	unpst_sendspace = PIPSIZ;
static u_long	unpst_recvspace = PIPSIZ;
static u_long	unpdg_sendspace = 2*1024;	/* really max datagram size */
static u_long	unpdg_recvspace = 4*1024;
static u_long	unpsp_sendspace = PIPSIZ;	/* really max datagram size */
static u_long	unpsp_recvspace = PIPSIZ;

static SYSCTL_NODE(_net, PF_LOCAL, local, CTLFLAG_RW, 0, "Local domain");
static SYSCTL_NODE(_net_local, SOCK_STREAM, stream, CTLFLAG_RW, 0,
    "SOCK_STREAM");
static SYSCTL_NODE(_net_local, SOCK_DGRAM, dgram, CTLFLAG_RW, 0, "SOCK_DGRAM");
static SYSCTL_NODE(_net_local, SOCK_SEQPACKET, seqpacket, CTLFLAG_RW, 0,
    "SOCK_SEQPACKET");

SYSCTL_ULONG(_net_local_stream, OID_AUTO, sendspace, CTLFLAG_RW,
	   &unpst_sendspace, 0, "Default stream send space.");
SYSCTL_ULONG(_net_local_stream, OID_AUTO, recvspace, CTLFLAG_RW,
	   &unpst_recvspace, 0, "Default stream receive space.");
SYSCTL_ULONG(_net_local_dgram, OID_AUTO, maxdgram, CTLFLAG_RW,
	   &unpdg_sendspace, 0, "Default datagram send space.");
SYSCTL_ULONG(_net_local_dgram, OID_AUTO, recvspace, CTLFLAG_RW,
	   &unpdg_recvspace, 0, "Default datagram receive space.");
SYSCTL_ULONG(_net_local_seqpacket, OID_AUTO, maxseqpacket, CTLFLAG_RW,
	   &unpsp_sendspace, 0, "Default seqpacket send space.");
SYSCTL_ULONG(_net_local_seqpacket, OID_AUTO, recvspace, CTLFLAG_RW,
	   &unpsp_recvspace, 0, "Default seqpacket receive space.");
SYSCTL_INT(_net_local, OID_AUTO, inflight, CTLFLAG_RD, &unp_rights, 0,
    "File descriptors in flight.");
SYSCTL_INT(_net_local, OID_AUTO, deferred, CTLFLAG_RD,
    &unp_defers_count, 0,
    "File descriptors deferred to taskqueue for close.");

/*
 * Locking and synchronization:
 *
 * Three types of locks exit in the local domain socket implementation: a
 * global list mutex, a global linkage rwlock, and per-unpcb mutexes.  Of the
 * global locks, the list lock protects the socket count, global generation
 * number, and stream/datagram global lists.  The linkage lock protects the
 * interconnection of unpcbs, the v_socket and unp_vnode pointers, and can be
 * held exclusively over the acquisition of multiple unpcb locks to prevent
 * deadlock.
 *
 * UNIX domain sockets each have an unpcb hung off of their so_pcb pointer,
 * allocated in pru_attach() and freed in pru_detach().  The validity of that
 * pointer is an invariant, so no lock is required to dereference the so_pcb
 * pointer if a valid socket reference is held by the caller.  In practice,
 * this is always true during operations performed on a socket.  Each unpcb
 * has a back-pointer to its socket, unp_socket, which will be stable under
 * the same circumstances.
 *
 * This pointer may only be safely dereferenced as long as a valid reference
 * to the unpcb is held.  Typically, this reference will be from the socket,
 * or from another unpcb when the referring unpcb's lock is held (in order
 * that the reference not be invalidated during use).  For example, to follow
 * unp->unp_conn->unp_socket, you need unlock the lock on unp, not unp_conn,
 * as unp_socket remains valid as long as the reference to unp_conn is valid.
 *
 * Fields of unpcbss are locked using a per-unpcb lock, unp_mtx.  Individual
 * atomic reads without the lock may be performed "lockless", but more
 * complex reads and read-modify-writes require the mutex to be held.  No
 * lock order is defined between unpcb locks -- multiple unpcb locks may be
 * acquired at the same time only when holding the linkage rwlock
 * exclusively, which prevents deadlocks.
 *
 * Blocking with UNIX domain sockets is a tricky issue: unlike most network
 * protocols, bind() is a non-atomic operation, and connect() requires
 * potential sleeping in the protocol, due to potentially waiting on local or
 * distributed file systems.  We try to separate "lookup" operations, which
 * may sleep, and the IPC operations themselves, which typically can occur
 * with relative atomicity as locks can be held over the entire operation.
 *
 * Another tricky issue is simultaneous multi-threaded or multi-process
 * access to a single UNIX domain socket.  These are handled by the flags
 * UNP_CONNECTING and UNP_BINDING, which prevent concurrent connecting or
 * binding, both of which involve dropping UNIX domain socket locks in order
 * to perform namei() and other file system operations.
 */
static struct rwlock	unp_link_rwlock;
static struct mtx	unp_list_lock;
static struct mtx	unp_defers_lock;

#define	UNP_LINK_LOCK_INIT()		rw_init(&unp_link_rwlock,	\
					    "unp_link_rwlock")

#define	UNP_LINK_LOCK_ASSERT()	rw_assert(&unp_link_rwlock,	\
					    RA_LOCKED)
#define	UNP_LINK_UNLOCK_ASSERT()	rw_assert(&unp_link_rwlock,	\
					    RA_UNLOCKED)

#define	UNP_LINK_RLOCK()		rw_rlock(&unp_link_rwlock)
#define	UNP_LINK_RUNLOCK()		rw_runlock(&unp_link_rwlock)
#define	UNP_LINK_WLOCK()		rw_wlock(&unp_link_rwlock)
#define	UNP_LINK_WUNLOCK()		rw_wunlock(&unp_link_rwlock)
#define	UNP_LINK_WLOCK_ASSERT()		rw_assert(&unp_link_rwlock,	\
					    RA_WLOCKED)

#define	UNP_LIST_LOCK_INIT()		mtx_init(&unp_list_lock,	\
					    "unp_list_lock", NULL, MTX_DEF)
#define	UNP_LIST_LOCK()			mtx_lock(&unp_list_lock)
#define	UNP_LIST_UNLOCK()		mtx_unlock(&unp_list_lock)

#define	UNP_DEFERRED_LOCK_INIT()	mtx_init(&unp_defers_lock, \
					    "unp_defer", NULL, MTX_DEF)
#define	UNP_DEFERRED_LOCK()		mtx_lock(&unp_defers_lock)
#define	UNP_DEFERRED_UNLOCK()		mtx_unlock(&unp_defers_lock)

#define UNP_PCB_LOCK_INIT(unp)		mtx_init(&(unp)->unp_mtx,	\
					    "unp_mtx", "unp_mtx",	\
					    MTX_DUPOK|MTX_DEF|MTX_RECURSE)
#define	UNP_PCB_LOCK_DESTROY(unp)	mtx_destroy(&(unp)->unp_mtx)
#define	UNP_PCB_LOCK(unp)		mtx_lock(&(unp)->unp_mtx)
#define	UNP_PCB_UNLOCK(unp)		mtx_unlock(&(unp)->unp_mtx)
#define	UNP_PCB_LOCK_ASSERT(unp)	mtx_assert(&(unp)->unp_mtx, MA_OWNED)

static int	uipc_connect2(struct socket *, struct socket *);
static int	uipc_ctloutput(struct socket *, struct sockopt *);
static int	unp_connect(struct socket *, struct sockaddr *,
		    struct thread *);
static int	unp_connectat(int, struct socket *, struct sockaddr *,
		    struct thread *);
static int	unp_connect2(struct socket *so, struct socket *so2, int);
static void	unp_disconnect(struct unpcb *unp, struct unpcb *unp2);
static void	unp_dispose(struct socket *so);
static void	unp_dispose_mbuf(struct mbuf *);
static void	unp_shutdown(struct unpcb *);
static void	unp_drop(struct unpcb *);
static void	unp_gc(__unused void *, int);
static void	unp_scan(struct mbuf *, void (*)(struct filedescent **, int));
static void	unp_discard(struct file *);
static void	unp_freerights(struct filedescent **, int);
static void	unp_init(void);
static int	unp_internalize(struct mbuf **, struct thread *);
static void	unp_internalize_fp(struct file *);
static int	unp_externalize(struct mbuf *, struct mbuf **, int);
static int	unp_externalize_fp(struct file *);
static struct mbuf	*unp_addsockcred(struct thread *, struct mbuf *);
static void	unp_process_defers(void * __unused, int);

/*
 * Definitions of protocols supported in the LOCAL domain.
 */
static struct domain localdomain;
static struct pr_usrreqs uipc_usrreqs_dgram, uipc_usrreqs_stream;
static struct pr_usrreqs uipc_usrreqs_seqpacket;
static struct protosw localsw[] = {
{
	.pr_type =		SOCK_STREAM,
	.pr_domain =		&localdomain,
	.pr_flags =		PR_CONNREQUIRED|PR_WANTRCVD|PR_RIGHTS,
	.pr_ctloutput =		&uipc_ctloutput,
	.pr_usrreqs =		&uipc_usrreqs_stream
},
{
	.pr_type =		SOCK_DGRAM,
	.pr_domain =		&localdomain,
	.pr_flags =		PR_ATOMIC|PR_ADDR|PR_RIGHTS,
	.pr_ctloutput =		&uipc_ctloutput,
	.pr_usrreqs =		&uipc_usrreqs_dgram
},
{
	.pr_type =		SOCK_SEQPACKET,
	.pr_domain =		&localdomain,

	/*
	 * XXXRW: For now, PR_ADDR because soreceive will bump into them
	 * due to our use of sbappendaddr.  A new sbappend variants is needed
	 * that supports both atomic record writes and control data.
	 */
	.pr_flags =		PR_ADDR|PR_ATOMIC|PR_CONNREQUIRED|PR_WANTRCVD|
				    PR_RIGHTS,
	.pr_ctloutput =		&uipc_ctloutput,
	.pr_usrreqs =		&uipc_usrreqs_seqpacket,
},
};

static struct domain localdomain = {
	.dom_family =		AF_LOCAL,
	.dom_name =		"local",
	.dom_init =		unp_init,
	.dom_externalize =	unp_externalize,
	.dom_dispose =		unp_dispose,
	.dom_protosw =		localsw,
	.dom_protoswNPROTOSW =	&localsw[nitems(localsw)]
};
DOMAIN_SET(local);

static void
uipc_abort(struct socket *so)
{
	struct unpcb *unp, *unp2;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("uipc_abort: unp == NULL"));

	UNP_LINK_WLOCK();
	UNP_PCB_LOCK(unp);
	unp2 = unp->unp_conn;
	if (unp2 != NULL) {
		UNP_PCB_LOCK(unp2);
		unp_drop(unp2);
		UNP_PCB_UNLOCK(unp2);
	}
	UNP_PCB_UNLOCK(unp);
	UNP_LINK_WUNLOCK();
}

static int
uipc_accept(struct socket *so, struct sockaddr **nam)
{
	struct unpcb *unp, *unp2;
	const struct sockaddr *sa;

	/*
	 * Pass back name of connected socket, if it was bound and we are
	 * still connected (our peer may have closed already!).
	 */
	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("uipc_accept: unp == NULL"));

	*nam = malloc(sizeof(struct sockaddr_un), M_SONAME, M_WAITOK);
	UNP_LINK_RLOCK();
	unp2 = unp->unp_conn;
	if (unp2 != NULL && unp2->unp_addr != NULL) {
		UNP_PCB_LOCK(unp2);
		sa = (struct sockaddr *) unp2->unp_addr;
		bcopy(sa, *nam, sa->sa_len);
		UNP_PCB_UNLOCK(unp2);
	} else {
		sa = &sun_noname;
		bcopy(sa, *nam, sa->sa_len);
	}
	UNP_LINK_RUNLOCK();
	return (0);
}

static int
uipc_attach(struct socket *so, int proto, struct thread *td)
{
	u_long sendspace, recvspace;
	struct unpcb *unp;
	int error;

	KASSERT(so->so_pcb == NULL, ("uipc_attach: so_pcb != NULL"));
	if (so->so_snd.sb_hiwat == 0 || so->so_rcv.sb_hiwat == 0) {
		switch (so->so_type) {
		case SOCK_STREAM:
			sendspace = unpst_sendspace;
			recvspace = unpst_recvspace;
			break;

		case SOCK_DGRAM:
			sendspace = unpdg_sendspace;
			recvspace = unpdg_recvspace;
			break;

		case SOCK_SEQPACKET:
			sendspace = unpsp_sendspace;
			recvspace = unpsp_recvspace;
			break;

		default:
			panic("uipc_attach");
		}
		error = soreserve(so, sendspace, recvspace);
		if (error)
			return (error);
	}
	unp = uma_zalloc(unp_zone, M_NOWAIT | M_ZERO);
	if (unp == NULL)
		return (ENOBUFS);
	LIST_INIT(&unp->unp_refs);
	UNP_PCB_LOCK_INIT(unp);
	unp->unp_socket = so;
	so->so_pcb = unp;
	unp->unp_refcount = 1;
	if (so->so_head != NULL)
		unp->unp_flags |= UNP_NASCENT;

	UNP_LIST_LOCK();
	unp->unp_gencnt = ++unp_gencnt;
	unp_count++;
	switch (so->so_type) {
	case SOCK_STREAM:
		LIST_INSERT_HEAD(&unp_shead, unp, unp_link);
		break;

	case SOCK_DGRAM:
		LIST_INSERT_HEAD(&unp_dhead, unp, unp_link);
		break;

	case SOCK_SEQPACKET:
		LIST_INSERT_HEAD(&unp_sphead, unp, unp_link);
		break;

	default:
		panic("uipc_attach");
	}
	UNP_LIST_UNLOCK();

	return (0);
}

static int
uipc_bindat(int fd, struct socket *so, struct sockaddr *nam, struct thread *td)
{
	struct sockaddr_un *soun = (struct sockaddr_un *)nam;
	struct vattr vattr;
	int error, namelen;
	struct nameidata nd;
	struct unpcb *unp;
	struct vnode *vp;
	struct mount *mp;
	cap_rights_t rights;
	char *buf;

	if (nam->sa_family != AF_UNIX)
		return (EAFNOSUPPORT);

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("uipc_bind: unp == NULL"));

	if (soun->sun_len > sizeof(struct sockaddr_un))
		return (EINVAL);
	namelen = soun->sun_len - offsetof(struct sockaddr_un, sun_path);
	if (namelen <= 0)
		return (EINVAL);

	/*
	 * We don't allow simultaneous bind() calls on a single UNIX domain
	 * socket, so flag in-progress operations, and return an error if an
	 * operation is already in progress.
	 *
	 * Historically, we have not allowed a socket to be rebound, so this
	 * also returns an error.  Not allowing re-binding simplifies the
	 * implementation and avoids a great many possible failure modes.
	 */
	UNP_PCB_LOCK(unp);
	if (unp->unp_vnode != NULL) {
		UNP_PCB_UNLOCK(unp);
		return (EINVAL);
	}
	if (unp->unp_flags & UNP_BINDING) {
		UNP_PCB_UNLOCK(unp);
		return (EALREADY);
	}
	unp->unp_flags |= UNP_BINDING;
	UNP_PCB_UNLOCK(unp);

	buf = malloc(namelen + 1, M_TEMP, M_WAITOK);
	bcopy(soun->sun_path, buf, namelen);
	buf[namelen] = 0;

restart:
	NDINIT_ATRIGHTS(&nd, CREATE, NOFOLLOW | LOCKPARENT | SAVENAME | NOCACHE,
	    UIO_SYSSPACE, buf, fd, cap_rights_init(&rights, CAP_BINDAT), td);
/* SHOULD BE ABLE TO ADOPT EXISTING AND wakeup() ALA FIFO's */
	error = namei(&nd);
	if (error)
		goto error;
	vp = nd.ni_vp;
	if (vp != NULL || vn_start_write(nd.ni_dvp, &mp, V_NOWAIT) != 0) {
		NDFREE(&nd, NDF_ONLY_PNBUF);
		if (nd.ni_dvp == vp)
			vrele(nd.ni_dvp);
		else
			vput(nd.ni_dvp);
		if (vp != NULL) {
			vrele(vp);
			error = EADDRINUSE;
			goto error;
		}
		error = vn_start_write(NULL, &mp, V_XSLEEP | PCATCH);
		if (error)
			goto error;
		goto restart;
	}
	VATTR_NULL(&vattr);
	vattr.va_type = VSOCK;
	vattr.va_mode = (ACCESSPERMS & ~td->td_proc->p_fd->fd_cmask);
#ifdef MAC
	error = mac_vnode_check_create(td->td_ucred, nd.ni_dvp, &nd.ni_cnd,
	    &vattr);
#endif
	if (error == 0)
		error = VOP_CREATE(nd.ni_dvp, &nd.ni_vp, &nd.ni_cnd, &vattr);
	NDFREE(&nd, NDF_ONLY_PNBUF);
	vput(nd.ni_dvp);
	if (error) {
		vn_finished_write(mp);
		goto error;
	}
	vp = nd.ni_vp;
	ASSERT_VOP_ELOCKED(vp, "uipc_bind");
	soun = (struct sockaddr_un *)sodupsockaddr(nam, M_WAITOK);

	UNP_LINK_WLOCK();
	UNP_PCB_LOCK(unp);
	VOP_UNP_BIND(vp, unp->unp_socket);
	unp->unp_vnode = vp;
	unp->unp_addr = soun;
	unp->unp_flags &= ~UNP_BINDING;
	UNP_PCB_UNLOCK(unp);
	UNP_LINK_WUNLOCK();
	VOP_UNLOCK(vp, 0);
	vn_finished_write(mp);
	free(buf, M_TEMP);
	return (0);

error:
	UNP_PCB_LOCK(unp);
	unp->unp_flags &= ~UNP_BINDING;
	UNP_PCB_UNLOCK(unp);
	free(buf, M_TEMP);
	return (error);
}

static int
uipc_bind(struct socket *so, struct sockaddr *nam, struct thread *td)
{

	return (uipc_bindat(AT_FDCWD, so, nam, td));
}

static int
uipc_connect(struct socket *so, struct sockaddr *nam, struct thread *td)
{
	int error;

	KASSERT(td == curthread, ("uipc_connect: td != curthread"));
	UNP_LINK_WLOCK();
	error = unp_connect(so, nam, td);
	UNP_LINK_WUNLOCK();
	return (error);
}

static int
uipc_connectat(int fd, struct socket *so, struct sockaddr *nam,
    struct thread *td)
{
	int error;

	KASSERT(td == curthread, ("uipc_connectat: td != curthread"));
	UNP_LINK_WLOCK();
	error = unp_connectat(fd, so, nam, td);
	UNP_LINK_WUNLOCK();
	return (error);
}

static void
uipc_close(struct socket *so)
{
	struct unpcb *unp, *unp2;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("uipc_close: unp == NULL"));

	UNP_LINK_WLOCK();
	UNP_PCB_LOCK(unp);
	unp2 = unp->unp_conn;
	if (unp2 != NULL) {
		UNP_PCB_LOCK(unp2);
		unp_disconnect(unp, unp2);
		UNP_PCB_UNLOCK(unp2);
	}
	UNP_PCB_UNLOCK(unp);
	UNP_LINK_WUNLOCK();
}

static int
uipc_connect2(struct socket *so1, struct socket *so2)
{
	struct unpcb *unp, *unp2;
	int error;

	UNP_LINK_WLOCK();
	unp = so1->so_pcb;
	KASSERT(unp != NULL, ("uipc_connect2: unp == NULL"));
	UNP_PCB_LOCK(unp);
	unp2 = so2->so_pcb;
	KASSERT(unp2 != NULL, ("uipc_connect2: unp2 == NULL"));
	UNP_PCB_LOCK(unp2);
	error = unp_connect2(so1, so2, PRU_CONNECT2);
	UNP_PCB_UNLOCK(unp2);
	UNP_PCB_UNLOCK(unp);
	UNP_LINK_WUNLOCK();
	return (error);
}

static void
uipc_detach(struct socket *so)
{
	struct unpcb *unp, *unp2;
	struct sockaddr_un *saved_unp_addr;
	struct vnode *vp;
	int freeunp, local_unp_rights;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("uipc_detach: unp == NULL"));

	vp = NULL;
	local_unp_rights = 0;

	UNP_LIST_LOCK();
	LIST_REMOVE(unp, unp_link);
	unp->unp_gencnt = ++unp_gencnt;
	--unp_count;
	UNP_LIST_UNLOCK();

	if ((unp->unp_flags & UNP_NASCENT) != 0) {
		UNP_PCB_LOCK(unp);
		goto teardown;
	}
	UNP_LINK_WLOCK();
	UNP_PCB_LOCK(unp);

	/*
	 * XXXRW: Should assert vp->v_socket == so.
	 */
	if ((vp = unp->unp_vnode) != NULL) {
		VOP_UNP_DETACH(vp);
		unp->unp_vnode = NULL;
	}
	unp2 = unp->unp_conn;
	if (unp2 != NULL) {
		UNP_PCB_LOCK(unp2);
		unp_disconnect(unp, unp2);
		UNP_PCB_UNLOCK(unp2);
	}

	/*
	 * We hold the linkage lock exclusively, so it's OK to acquire
	 * multiple pcb locks at a time.
	 */
	while (!LIST_EMPTY(&unp->unp_refs)) {
		struct unpcb *ref = LIST_FIRST(&unp->unp_refs);

		UNP_PCB_LOCK(ref);
		unp_drop(ref);
		UNP_PCB_UNLOCK(ref);
	}
	local_unp_rights = unp_rights;
	UNP_LINK_WUNLOCK();
teardown:
	unp->unp_socket->so_pcb = NULL;
	saved_unp_addr = unp->unp_addr;
	unp->unp_addr = NULL;
	unp->unp_refcount--;
	freeunp = (unp->unp_refcount == 0);
	if (saved_unp_addr != NULL)
		free(saved_unp_addr, M_SONAME);
	if (freeunp) {
		UNP_PCB_LOCK_DESTROY(unp);
		uma_zfree(unp_zone, unp);
	} else
		UNP_PCB_UNLOCK(unp);
	if (vp)
		vrele(vp);
	if (local_unp_rights)
		taskqueue_enqueue_timeout(taskqueue_thread, &unp_gc_task, -1);
}

static int
uipc_disconnect(struct socket *so)
{
	struct unpcb *unp, *unp2;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("uipc_disconnect: unp == NULL"));

	UNP_LINK_WLOCK();
	UNP_PCB_LOCK(unp);
	unp2 = unp->unp_conn;
	if (unp2 != NULL) {
		UNP_PCB_LOCK(unp2);
		unp_disconnect(unp, unp2);
		UNP_PCB_UNLOCK(unp2);
	}
	UNP_PCB_UNLOCK(unp);
	UNP_LINK_WUNLOCK();
	return (0);
}

static int
uipc_listen(struct socket *so, int backlog, struct thread *td)
{
	struct unpcb *unp;
	int error;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("uipc_listen: unp == NULL"));

	UNP_PCB_LOCK(unp);
	if (unp->unp_vnode == NULL) {
		/* Already connected or not bound to an address. */
		error = unp->unp_conn != NULL ? EINVAL : EDESTADDRREQ;
		UNP_PCB_UNLOCK(unp);
		return (error);
	}

	SOCK_LOCK(so);
	error = solisten_proto_check(so);
	if (error == 0) {
		cru2x(td->td_ucred, &unp->unp_peercred);
		unp->unp_flags |= UNP_HAVEPCCACHED;
		solisten_proto(so, backlog);
	}
	SOCK_UNLOCK(so);
	UNP_PCB_UNLOCK(unp);
	return (error);
}

static int
uipc_peeraddr(struct socket *so, struct sockaddr **nam)
{
	struct unpcb *unp, *unp2;
	const struct sockaddr *sa;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("uipc_peeraddr: unp == NULL"));

	*nam = malloc(sizeof(struct sockaddr_un), M_SONAME, M_WAITOK);
	UNP_LINK_RLOCK();
	/*
	 * XXX: It seems that this test always fails even when connection is
	 * established.  So, this else clause is added as workaround to
	 * return PF_LOCAL sockaddr.
	 */
	unp2 = unp->unp_conn;
	if (unp2 != NULL) {
		UNP_PCB_LOCK(unp2);
		if (unp2->unp_addr != NULL)
			sa = (struct sockaddr *) unp2->unp_addr;
		else
			sa = &sun_noname;
		bcopy(sa, *nam, sa->sa_len);
		UNP_PCB_UNLOCK(unp2);
	} else {
		sa = &sun_noname;
		bcopy(sa, *nam, sa->sa_len);
	}
	UNP_LINK_RUNLOCK();
	return (0);
}

static int
uipc_rcvd(struct socket *so, int flags)
{
	struct unpcb *unp, *unp2;
	struct socket *so2;
	u_int mbcnt, sbcc;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("%s: unp == NULL", __func__));
	KASSERT(so->so_type == SOCK_STREAM || so->so_type == SOCK_SEQPACKET,
	    ("%s: socktype %d", __func__, so->so_type));

	/*
	 * Adjust backpressure on sender and wakeup any waiting to write.
	 *
	 * The unp lock is acquired to maintain the validity of the unp_conn
	 * pointer; no lock on unp2 is required as unp2->unp_socket will be
	 * static as long as we don't permit unp2 to disconnect from unp,
	 * which is prevented by the lock on unp.  We cache values from
	 * so_rcv to avoid holding the so_rcv lock over the entire
	 * transaction on the remote so_snd.
	 */
	SOCKBUF_LOCK(&so->so_rcv);
	mbcnt = so->so_rcv.sb_mbcnt;
	sbcc = sbavail(&so->so_rcv);
	SOCKBUF_UNLOCK(&so->so_rcv);
	/*
	 * There is a benign race condition at this point.  If we're planning to
	 * clear SB_STOP, but uipc_send is called on the connected socket at
	 * this instant, it might add data to the sockbuf and set SB_STOP.  Then
	 * we would erroneously clear SB_STOP below, even though the sockbuf is
	 * full.  The race is benign because the only ill effect is to allow the
	 * sockbuf to exceed its size limit, and the size limits are not
	 * strictly guaranteed anyway.
	 */
	UNP_PCB_LOCK(unp);
	unp2 = unp->unp_conn;
	if (unp2 == NULL) {
		UNP_PCB_UNLOCK(unp);
		return (0);
	}
	so2 = unp2->unp_socket;
	SOCKBUF_LOCK(&so2->so_snd);
	if (sbcc < so2->so_snd.sb_hiwat && mbcnt < so2->so_snd.sb_mbmax)
		so2->so_snd.sb_flags &= ~SB_STOP;
	sowwakeup_locked(so2);
	UNP_PCB_UNLOCK(unp);
	return (0);
}

static int
uipc_send(struct socket *so, int flags, struct mbuf *m, struct sockaddr *nam,
    struct mbuf *control, struct thread *td)
{
	struct unpcb *unp, *unp2;
	struct socket *so2;
	u_int mbcnt, sbcc;
	int error = 0;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("%s: unp == NULL", __func__));
	KASSERT(so->so_type == SOCK_STREAM || so->so_type == SOCK_DGRAM ||
	    so->so_type == SOCK_SEQPACKET,
	    ("%s: socktype %d", __func__, so->so_type));

	if (flags & PRUS_OOB) {
		error = EOPNOTSUPP;
		goto release;
	}
	if (control != NULL && (error = unp_internalize(&control, td)))
		goto release;
	if ((nam != NULL) || (flags & PRUS_EOF))
		UNP_LINK_WLOCK();
	else
		UNP_LINK_RLOCK();
	switch (so->so_type) {
	case SOCK_DGRAM:
	{
		const struct sockaddr *from;

		unp2 = unp->unp_conn;
		if (nam != NULL) {
			UNP_LINK_WLOCK_ASSERT();
			if (unp2 != NULL) {
				error = EISCONN;
				break;
			}
			error = unp_connect(so, nam, td);
			if (error)
				break;
			unp2 = unp->unp_conn;
		}

		/*
		 * Because connect() and send() are non-atomic in a sendto()
		 * with a target address, it's possible that the socket will
		 * have disconnected before the send() can run.  In that case
		 * return the slightly counter-intuitive but otherwise
		 * correct error that the socket is not connected.
		 */
		if (unp2 == NULL) {
			error = ENOTCONN;
			break;
		}
		/* Lockless read. */
		if (unp2->unp_flags & UNP_WANTCRED)
			control = unp_addsockcred(td, control);
		UNP_PCB_LOCK(unp);
		if (unp->unp_addr != NULL)
			from = (struct sockaddr *)unp->unp_addr;
		else
			from = &sun_noname;
		so2 = unp2->unp_socket;
		SOCKBUF_LOCK(&so2->so_rcv);
		if (sbappendaddr_locked(&so2->so_rcv, from, m,
		    control)) {
			sorwakeup_locked(so2);
			m = NULL;
			control = NULL;
		} else {
			SOCKBUF_UNLOCK(&so2->so_rcv);
			error = ENOBUFS;
		}
		if (nam != NULL) {
			UNP_LINK_WLOCK_ASSERT();
			UNP_PCB_LOCK(unp2);
			unp_disconnect(unp, unp2);
			UNP_PCB_UNLOCK(unp2);
		}
		UNP_PCB_UNLOCK(unp);
		break;
	}

	case SOCK_SEQPACKET:
	case SOCK_STREAM:
		if ((so->so_state & SS_ISCONNECTED) == 0) {
			if (nam != NULL) {
				UNP_LINK_WLOCK_ASSERT();
				error = unp_connect(so, nam, td);
				if (error)
					break;	/* XXX */
			} else {
				error = ENOTCONN;
				break;
			}
		}

		/* Lockless read. */
		if (so->so_snd.sb_state & SBS_CANTSENDMORE) {
			error = EPIPE;
			break;
		}

		/*
		 * Because connect() and send() are non-atomic in a sendto()
		 * with a target address, it's possible that the socket will
		 * have disconnected before the send() can run.  In that case
		 * return the slightly counter-intuitive but otherwise
		 * correct error that the socket is not connected.
		 *
		 * Locking here must be done carefully: the linkage lock
		 * prevents interconnections between unpcbs from changing, so
		 * we can traverse from unp to unp2 without acquiring unp's
		 * lock.  Socket buffer locks follow unpcb locks, so we can
		 * acquire both remote and lock socket buffer locks.
		 */
		unp2 = unp->unp_conn;
		if (unp2 == NULL) {
			error = ENOTCONN;
			break;
		}
		so2 = unp2->unp_socket;
		UNP_PCB_LOCK(unp2);
		SOCKBUF_LOCK(&so2->so_rcv);
		if (unp2->unp_flags & UNP_WANTCRED) {
			/*
			 * Credentials are passed only once on SOCK_STREAM
			 * and SOCK_SEQPACKET.
			 */
			unp2->unp_flags &= ~UNP_WANTCRED;
			control = unp_addsockcred(td, control);
		}
		/*
		 * Send to paired receive port, and then reduce send buffer
		 * hiwater marks to maintain backpressure.  Wake up readers.
		 */
		switch (so->so_type) {
		case SOCK_STREAM:
			if (control != NULL) {
				if (sbappendcontrol_locked(&so2->so_rcv, m,
				    control))
					control = NULL;
			} else
				sbappend_locked(&so2->so_rcv, m, flags);
			break;

		case SOCK_SEQPACKET: {
			const struct sockaddr *from;

			from = &sun_noname;
			/*
			 * Don't check for space available in so2->so_rcv.
			 * Unix domain sockets only check for space in the
			 * sending sockbuf, and that check is performed one
			 * level up the stack.
			 */
			if (sbappendaddr_nospacecheck_locked(&so2->so_rcv,
				from, m, control))
				control = NULL;
			break;
			}
		}

		mbcnt = so2->so_rcv.sb_mbcnt;
		sbcc = sbavail(&so2->so_rcv);
		if (sbcc)
			sorwakeup_locked(so2);
		else
			SOCKBUF_UNLOCK(&so2->so_rcv);

		/*
		 * The PCB lock on unp2 protects the SB_STOP flag.  Without it,
		 * it would be possible for uipc_rcvd to be called at this
		 * point, drain the receiving sockbuf, clear SB_STOP, and then
		 * we would set SB_STOP below.  That could lead to an empty
		 * sockbuf having SB_STOP set
		 */
		SOCKBUF_LOCK(&so->so_snd);
		if (sbcc >= so->so_snd.sb_hiwat || mbcnt >= so->so_snd.sb_mbmax)
			so->so_snd.sb_flags |= SB_STOP;
		SOCKBUF_UNLOCK(&so->so_snd);
		UNP_PCB_UNLOCK(unp2);
		m = NULL;
		break;
	}

	/*
	 * PRUS_EOF is equivalent to pru_send followed by pru_shutdown.
	 */
	if (flags & PRUS_EOF) {
		UNP_PCB_LOCK(unp);
		socantsendmore(so);
		unp_shutdown(unp);
		UNP_PCB_UNLOCK(unp);
	}

	if ((nam != NULL) || (flags & PRUS_EOF))
		UNP_LINK_WUNLOCK();
	else
		UNP_LINK_RUNLOCK();

	if (control != NULL && error != 0)
		unp_dispose_mbuf(control);

release:
	if (control != NULL)
		m_freem(control);
	if (m != NULL)
		m_freem(m);
	return (error);
}

static int
uipc_ready(struct socket *so, struct mbuf *m, int count)
{
	struct unpcb *unp, *unp2;
	struct socket *so2;
	int error;

	unp = sotounpcb(so);

	UNP_LINK_RLOCK();
	unp2 = unp->unp_conn;
	UNP_PCB_LOCK(unp2);
	so2 = unp2->unp_socket;

	SOCKBUF_LOCK(&so2->so_rcv);
	if ((error = sbready(&so2->so_rcv, m, count)) == 0)
		sorwakeup_locked(so2);
	else
		SOCKBUF_UNLOCK(&so2->so_rcv);

	UNP_PCB_UNLOCK(unp2);
	UNP_LINK_RUNLOCK();

	return (error);
}

static int
uipc_sense(struct socket *so, struct stat *sb)
{
	struct unpcb *unp;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("uipc_sense: unp == NULL"));

	sb->st_blksize = so->so_snd.sb_hiwat;
	UNP_PCB_LOCK(unp);
	sb->st_dev = NODEV;
	if (unp->unp_ino == 0)
		unp->unp_ino = (++unp_ino == 0) ? ++unp_ino : unp_ino;
	sb->st_ino = unp->unp_ino;
	UNP_PCB_UNLOCK(unp);
	return (0);
}

static int
uipc_shutdown(struct socket *so)
{
	struct unpcb *unp;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("uipc_shutdown: unp == NULL"));

	UNP_LINK_WLOCK();
	UNP_PCB_LOCK(unp);
	socantsendmore(so);
	unp_shutdown(unp);
	UNP_PCB_UNLOCK(unp);
	UNP_LINK_WUNLOCK();
	return (0);
}

static int
uipc_sockaddr(struct socket *so, struct sockaddr **nam)
{
	struct unpcb *unp;
	const struct sockaddr *sa;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("uipc_sockaddr: unp == NULL"));

	*nam = malloc(sizeof(struct sockaddr_un), M_SONAME, M_WAITOK);
	UNP_PCB_LOCK(unp);
	if (unp->unp_addr != NULL)
		sa = (struct sockaddr *) unp->unp_addr;
	else
		sa = &sun_noname;
	bcopy(sa, *nam, sa->sa_len);
	UNP_PCB_UNLOCK(unp);
	return (0);
}

static struct pr_usrreqs uipc_usrreqs_dgram = {
	.pru_abort = 		uipc_abort,
	.pru_accept =		uipc_accept,
	.pru_attach =		uipc_attach,
	.pru_bind =		uipc_bind,
	.pru_bindat =		uipc_bindat,
	.pru_connect =		uipc_connect,
	.pru_connectat =	uipc_connectat,
	.pru_connect2 =		uipc_connect2,
	.pru_detach =		uipc_detach,
	.pru_disconnect =	uipc_disconnect,
	.pru_listen =		uipc_listen,
	.pru_peeraddr =		uipc_peeraddr,
	.pru_rcvd =		uipc_rcvd,
	.pru_send =		uipc_send,
	.pru_sense =		uipc_sense,
	.pru_shutdown =		uipc_shutdown,
	.pru_sockaddr =		uipc_sockaddr,
	.pru_soreceive =	soreceive_dgram,
	.pru_close =		uipc_close,
};

static struct pr_usrreqs uipc_usrreqs_seqpacket = {
	.pru_abort =		uipc_abort,
	.pru_accept =		uipc_accept,
	.pru_attach =		uipc_attach,
	.pru_bind =		uipc_bind,
	.pru_bindat =		uipc_bindat,
	.pru_connect =		uipc_connect,
	.pru_connectat =	uipc_connectat,
	.pru_connect2 =		uipc_connect2,
	.pru_detach =		uipc_detach,
	.pru_disconnect =	uipc_disconnect,
	.pru_listen =		uipc_listen,
	.pru_peeraddr =		uipc_peeraddr,
	.pru_rcvd =		uipc_rcvd,
	.pru_send =		uipc_send,
	.pru_sense =		uipc_sense,
	.pru_shutdown =		uipc_shutdown,
	.pru_sockaddr =		uipc_sockaddr,
	.pru_soreceive =	soreceive_generic,	/* XXX: or...? */
	.pru_close =		uipc_close,
};

static struct pr_usrreqs uipc_usrreqs_stream = {
	.pru_abort = 		uipc_abort,
	.pru_accept =		uipc_accept,
	.pru_attach =		uipc_attach,
	.pru_bind =		uipc_bind,
	.pru_bindat =		uipc_bindat,
	.pru_connect =		uipc_connect,
	.pru_connectat =	uipc_connectat,
	.pru_connect2 =		uipc_connect2,
	.pru_detach =		uipc_detach,
	.pru_disconnect =	uipc_disconnect,
	.pru_listen =		uipc_listen,
	.pru_peeraddr =		uipc_peeraddr,
	.pru_rcvd =		uipc_rcvd,
	.pru_send =		uipc_send,
	.pru_ready =		uipc_ready,
	.pru_sense =		uipc_sense,
	.pru_shutdown =		uipc_shutdown,
	.pru_sockaddr =		uipc_sockaddr,
	.pru_soreceive =	soreceive_generic,
	.pru_close =		uipc_close,
};

static int
uipc_ctloutput(struct socket *so, struct sockopt *sopt)
{
	struct unpcb *unp;
	struct xucred xu;
	int error, optval;

	if (sopt->sopt_level != 0)
		return (EINVAL);

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("uipc_ctloutput: unp == NULL"));
	error = 0;
	switch (sopt->sopt_dir) {
	case SOPT_GET:
		switch (sopt->sopt_name) {
		case LOCAL_PEERCRED:
			UNP_PCB_LOCK(unp);
			if (unp->unp_flags & UNP_HAVEPC)
				xu = unp->unp_peercred;
			else {
				if (so->so_type == SOCK_STREAM)
					error = ENOTCONN;
				else
					error = EINVAL;
			}
			UNP_PCB_UNLOCK(unp);
			if (error == 0)
				error = sooptcopyout(sopt, &xu, sizeof(xu));
			break;

		case LOCAL_CREDS:
			/* Unlocked read. */
			optval = unp->unp_flags & UNP_WANTCRED ? 1 : 0;
			error = sooptcopyout(sopt, &optval, sizeof(optval));
			break;

		case LOCAL_CONNWAIT:
			/* Unlocked read. */
			optval = unp->unp_flags & UNP_CONNWAIT ? 1 : 0;
			error = sooptcopyout(sopt, &optval, sizeof(optval));
			break;

		default:
			error = EOPNOTSUPP;
			break;
		}
		break;

	case SOPT_SET:
		switch (sopt->sopt_name) {
		case LOCAL_CREDS:
		case LOCAL_CONNWAIT:
			error = sooptcopyin(sopt, &optval, sizeof(optval),
					    sizeof(optval));
			if (error)
				break;

#define	OPTSET(bit) do {						\
	UNP_PCB_LOCK(unp);						\
	if (optval)							\
		unp->unp_flags |= bit;					\
	else								\
		unp->unp_flags &= ~bit;					\
	UNP_PCB_UNLOCK(unp);						\
} while (0)

			switch (sopt->sopt_name) {
			case LOCAL_CREDS:
				OPTSET(UNP_WANTCRED);
				break;

			case LOCAL_CONNWAIT:
				OPTSET(UNP_CONNWAIT);
				break;

			default:
				break;
			}
			break;
#undef	OPTSET
		default:
			error = ENOPROTOOPT;
			break;
		}
		break;

	default:
		error = EOPNOTSUPP;
		break;
	}
	return (error);
}

static int
unp_connect(struct socket *so, struct sockaddr *nam, struct thread *td)
{

	return (unp_connectat(AT_FDCWD, so, nam, td));
}

static int
unp_connectat(int fd, struct socket *so, struct sockaddr *nam,
    struct thread *td)
{
	struct sockaddr_un *soun = (struct sockaddr_un *)nam;
	struct vnode *vp;
	struct socket *so2, *so3;
	struct unpcb *unp, *unp2, *unp3;
	struct nameidata nd;
	char buf[SOCK_MAXADDRLEN];
	struct sockaddr *sa;
	cap_rights_t rights;
	int error, len;

	if (nam->sa_family != AF_UNIX)
		return (EAFNOSUPPORT);

	UNP_LINK_WLOCK_ASSERT();

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("unp_connect: unp == NULL"));

	if (nam->sa_len > sizeof(struct sockaddr_un))
		return (EINVAL);
	len = nam->sa_len - offsetof(struct sockaddr_un, sun_path);
	if (len <= 0)
		return (EINVAL);
	bcopy(soun->sun_path, buf, len);
	buf[len] = 0;

	UNP_PCB_LOCK(unp);
	if (unp->unp_flags & UNP_CONNECTING) {
		UNP_PCB_UNLOCK(unp);
		return (EALREADY);
	}
	UNP_LINK_WUNLOCK();
	unp->unp_flags |= UNP_CONNECTING;
	UNP_PCB_UNLOCK(unp);

	sa = malloc(sizeof(struct sockaddr_un), M_SONAME, M_WAITOK);
	NDINIT_ATRIGHTS(&nd, LOOKUP, FOLLOW | LOCKSHARED | LOCKLEAF,
	    UIO_SYSSPACE, buf, fd, cap_rights_init(&rights, CAP_CONNECTAT), td);
	error = namei(&nd);
	if (error)
		vp = NULL;
	else
		vp = nd.ni_vp;
	ASSERT_VOP_LOCKED(vp, "unp_connect");
	NDFREE(&nd, NDF_ONLY_PNBUF);
	if (error)
		goto bad;

	if (vp->v_type != VSOCK) {
		error = ENOTSOCK;
		goto bad;
	}
#ifdef MAC
	error = mac_vnode_check_open(td->td_ucred, vp, VWRITE | VREAD);
	if (error)
		goto bad;
#endif
	error = VOP_ACCESS(vp, VWRITE, td->td_ucred, td);
	if (error)
		goto bad;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("unp_connect: unp == NULL"));

	/*
	 * Lock linkage lock for two reasons: make sure v_socket is stable,
	 * and to protect simultaneous locking of multiple pcbs.
	 */
	UNP_LINK_WLOCK();
	VOP_UNP_CONNECT(vp, &so2);
	if (so2 == NULL) {
		error = ECONNREFUSED;
		goto bad2;
	}
	if (so->so_type != so2->so_type) {
		error = EPROTOTYPE;
		goto bad2;
	}
	if (so->so_proto->pr_flags & PR_CONNREQUIRED) {
		if (so2->so_options & SO_ACCEPTCONN) {
			CURVNET_SET(so2->so_vnet);
			so3 = sonewconn(so2, 0);
			CURVNET_RESTORE();
		} else
			so3 = NULL;
		if (so3 == NULL) {
			error = ECONNREFUSED;
			goto bad2;
		}
		unp = sotounpcb(so);
		unp2 = sotounpcb(so2);
		unp3 = sotounpcb(so3);
		UNP_PCB_LOCK(unp);
		UNP_PCB_LOCK(unp2);
		UNP_PCB_LOCK(unp3);
		if (unp2->unp_addr != NULL) {
			bcopy(unp2->unp_addr, sa, unp2->unp_addr->sun_len);
			unp3->unp_addr = (struct sockaddr_un *) sa;
			sa = NULL;
		}

		/*
		 * The connector's (client's) credentials are copied from its
		 * process structure at the time of connect() (which is now).
		 */
		cru2x(td->td_ucred, &unp3->unp_peercred);
		unp3->unp_flags |= UNP_HAVEPC;

		/*
		 * The receiver's (server's) credentials are copied from the
		 * unp_peercred member of socket on which the former called
		 * listen(); uipc_listen() cached that process's credentials
		 * at that time so we can use them now.
		 */
		KASSERT(unp2->unp_flags & UNP_HAVEPCCACHED,
		    ("unp_connect: listener without cached peercred"));
		memcpy(&unp->unp_peercred, &unp2->unp_peercred,
		    sizeof(unp->unp_peercred));
		unp->unp_flags |= UNP_HAVEPC;
		if (unp2->unp_flags & UNP_WANTCRED)
			unp3->unp_flags |= UNP_WANTCRED;
		UNP_PCB_UNLOCK(unp3);
		UNP_PCB_UNLOCK(unp2);
		UNP_PCB_UNLOCK(unp);
#ifdef MAC
		mac_socketpeer_set_from_socket(so, so3);
		mac_socketpeer_set_from_socket(so3, so);
#endif

		so2 = so3;
	}
	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("unp_connect: unp == NULL"));
	unp2 = sotounpcb(so2);
	KASSERT(unp2 != NULL, ("unp_connect: unp2 == NULL"));
	UNP_PCB_LOCK(unp);
	UNP_PCB_LOCK(unp2);
	error = unp_connect2(so, so2, PRU_CONNECT);
	UNP_PCB_UNLOCK(unp2);
	UNP_PCB_UNLOCK(unp);
bad2:
	UNP_LINK_WUNLOCK();
bad:
	if (vp != NULL)
		vput(vp);
	free(sa, M_SONAME);
	UNP_LINK_WLOCK();
	UNP_PCB_LOCK(unp);
	unp->unp_flags &= ~UNP_CONNECTING;
	UNP_PCB_UNLOCK(unp);
	return (error);
}

static int
unp_connect2(struct socket *so, struct socket *so2, int req)
{
	struct unpcb *unp;
	struct unpcb *unp2;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("unp_connect2: unp == NULL"));
	unp2 = sotounpcb(so2);
	KASSERT(unp2 != NULL, ("unp_connect2: unp2 == NULL"));

	UNP_LINK_WLOCK_ASSERT();
	UNP_PCB_LOCK_ASSERT(unp);
	UNP_PCB_LOCK_ASSERT(unp2);

	if (so2->so_type != so->so_type)
		return (EPROTOTYPE);
	unp2->unp_flags &= ~UNP_NASCENT;
	unp->unp_conn = unp2;

	switch (so->so_type) {
	case SOCK_DGRAM:
		LIST_INSERT_HEAD(&unp2->unp_refs, unp, unp_reflink);
		soisconnected(so);
		break;

	case SOCK_STREAM:
	case SOCK_SEQPACKET:
		unp2->unp_conn = unp;
		if (req == PRU_CONNECT &&
		    ((unp->unp_flags | unp2->unp_flags) & UNP_CONNWAIT))
			soisconnecting(so);
		else
			soisconnected(so);
		soisconnected(so2);
		break;

	default:
		panic("unp_connect2");
	}
	return (0);
}

static void
unp_disconnect(struct unpcb *unp, struct unpcb *unp2)
{
	struct socket *so;

	KASSERT(unp2 != NULL, ("unp_disconnect: unp2 == NULL"));

	UNP_LINK_WLOCK_ASSERT();
	UNP_PCB_LOCK_ASSERT(unp);
	UNP_PCB_LOCK_ASSERT(unp2);

	unp->unp_conn = NULL;
	switch (unp->unp_socket->so_type) {
	case SOCK_DGRAM:
		LIST_REMOVE(unp, unp_reflink);
		so = unp->unp_socket;
		SOCK_LOCK(so);
		so->so_state &= ~SS_ISCONNECTED;
		SOCK_UNLOCK(so);
		break;

	case SOCK_STREAM:
	case SOCK_SEQPACKET:
		soisdisconnected(unp->unp_socket);
		unp2->unp_conn = NULL;
		soisdisconnected(unp2->unp_socket);
		break;
	}
}

/*
 * unp_pcblist() walks the global list of struct unpcb's to generate a
 * pointer list, bumping the refcount on each unpcb.  It then copies them out
 * sequentially, validating the generation number on each to see if it has
 * been detached.  All of this is necessary because copyout() may sleep on
 * disk I/O.
 */
static int
unp_pcblist(SYSCTL_HANDLER_ARGS)
{
	int error, i, n;
	int freeunp;
	struct unpcb *unp, **unp_list;
	unp_gen_t gencnt;
	struct xunpgen *xug;
	struct unp_head *head;
	struct xunpcb *xu;

	switch ((intptr_t)arg1) {
	case SOCK_STREAM:
		head = &unp_shead;
		break;

	case SOCK_DGRAM:
		head = &unp_dhead;
		break;

	case SOCK_SEQPACKET:
		head = &unp_sphead;
		break;

	default:
		panic("unp_pcblist: arg1 %d", (int)(intptr_t)arg1);
	}

	/*
	 * The process of preparing the PCB list is too time-consuming and
	 * resource-intensive to repeat twice on every request.
	 */
	if (req->oldptr == NULL) {
		n = unp_count;
		req->oldidx = 2 * (sizeof *xug)
			+ (n + n/8) * sizeof(struct xunpcb);
		return (0);
	}

	if (req->newptr != NULL)
		return (EPERM);

	/*
	 * OK, now we're committed to doing something.
	 */
	xug = malloc(sizeof(*xug), M_TEMP, M_WAITOK);
	UNP_LIST_LOCK();
	gencnt = unp_gencnt;
	n = unp_count;
	UNP_LIST_UNLOCK();

	xug->xug_len = sizeof *xug;
	xug->xug_count = n;
	xug->xug_gen = gencnt;
	xug->xug_sogen = so_gencnt;
	error = SYSCTL_OUT(req, xug, sizeof *xug);
	if (error) {
		free(xug, M_TEMP);
		return (error);
	}

	unp_list = malloc(n * sizeof *unp_list, M_TEMP, M_WAITOK);

	UNP_LIST_LOCK();
	for (unp = LIST_FIRST(head), i = 0; unp && i < n;
	     unp = LIST_NEXT(unp, unp_link)) {
		UNP_PCB_LOCK(unp);
		if (unp->unp_gencnt <= gencnt) {
			if (cr_cansee(req->td->td_ucred,
			    unp->unp_socket->so_cred)) {
				UNP_PCB_UNLOCK(unp);
				continue;
			}
			unp_list[i++] = unp;
			unp->unp_refcount++;
		}
		UNP_PCB_UNLOCK(unp);
	}
	UNP_LIST_UNLOCK();
	n = i;			/* In case we lost some during malloc. */

	error = 0;
	xu = malloc(sizeof(*xu), M_TEMP, M_WAITOK | M_ZERO);
	for (i = 0; i < n; i++) {
		unp = unp_list[i];
		UNP_PCB_LOCK(unp);
		unp->unp_refcount--;
	        if (unp->unp_refcount != 0 && unp->unp_gencnt <= gencnt) {
			xu->xu_len = sizeof *xu;
			xu->xu_unpp = unp;
			/*
			 * XXX - need more locking here to protect against
			 * connect/disconnect races for SMP.
			 */
			if (unp->unp_addr != NULL)
				bcopy(unp->unp_addr, &xu->xu_addr,
				      unp->unp_addr->sun_len);
			if (unp->unp_conn != NULL &&
			    unp->unp_conn->unp_addr != NULL)
				bcopy(unp->unp_conn->unp_addr,
				      &xu->xu_caddr,
				      unp->unp_conn->unp_addr->sun_len);
			bcopy(unp, &xu->xu_unp, sizeof *unp);
			sotoxsocket(unp->unp_socket, &xu->xu_socket);
			UNP_PCB_UNLOCK(unp);
			error = SYSCTL_OUT(req, xu, sizeof *xu);
		} else {
			freeunp = (unp->unp_refcount == 0);
			UNP_PCB_UNLOCK(unp);
			if (freeunp) {
				UNP_PCB_LOCK_DESTROY(unp);
				uma_zfree(unp_zone, unp);
			}
		}
	}
	free(xu, M_TEMP);
	if (!error) {
		/*
		 * Give the user an updated idea of our state.  If the
		 * generation differs from what we told her before, she knows
		 * that something happened while we were processing this
		 * request, and it might be necessary to retry.
		 */
		xug->xug_gen = unp_gencnt;
		xug->xug_sogen = so_gencnt;
		xug->xug_count = unp_count;
		error = SYSCTL_OUT(req, xug, sizeof *xug);
	}
	free(unp_list, M_TEMP);
	free(xug, M_TEMP);
	return (error);
}

SYSCTL_PROC(_net_local_dgram, OID_AUTO, pcblist, CTLTYPE_OPAQUE | CTLFLAG_RD,
    (void *)(intptr_t)SOCK_DGRAM, 0, unp_pcblist, "S,xunpcb",
    "List of active local datagram sockets");
SYSCTL_PROC(_net_local_stream, OID_AUTO, pcblist, CTLTYPE_OPAQUE | CTLFLAG_RD,
    (void *)(intptr_t)SOCK_STREAM, 0, unp_pcblist, "S,xunpcb",
    "List of active local stream sockets");
SYSCTL_PROC(_net_local_seqpacket, OID_AUTO, pcblist,
    CTLTYPE_OPAQUE | CTLFLAG_RD,
    (void *)(intptr_t)SOCK_SEQPACKET, 0, unp_pcblist, "S,xunpcb",
    "List of active local seqpacket sockets");

static void
unp_shutdown(struct unpcb *unp)
{
	struct unpcb *unp2;
	struct socket *so;

	UNP_LINK_WLOCK_ASSERT();
	UNP_PCB_LOCK_ASSERT(unp);

	unp2 = unp->unp_conn;
	if ((unp->unp_socket->so_type == SOCK_STREAM ||
	    (unp->unp_socket->so_type == SOCK_SEQPACKET)) && unp2 != NULL) {
		so = unp2->unp_socket;
		if (so != NULL)
			socantrcvmore(so);
	}
}

static void
unp_drop(struct unpcb *unp)
{
	struct socket *so = unp->unp_socket;
	struct unpcb *unp2;

	UNP_LINK_WLOCK_ASSERT();
	UNP_PCB_LOCK_ASSERT(unp);

	/*
	 * Regardless of whether the socket's peer dropped the connection
	 * with this socket by aborting or disconnecting, POSIX requires
	 * that ECONNRESET is returned.
	 */
	so->so_error = ECONNRESET;
	unp2 = unp->unp_conn;
	if (unp2 == NULL)
		return;
	UNP_PCB_LOCK(unp2);
	unp_disconnect(unp, unp2);
	UNP_PCB_UNLOCK(unp2);
}

static void
unp_freerights(struct filedescent **fdep, int fdcount)
{
	struct file *fp;
	int i;

	KASSERT(fdcount > 0, ("%s: fdcount %d", __func__, fdcount));

	for (i = 0; i < fdcount; i++) {
		fp = fdep[i]->fde_file;
		filecaps_free(&fdep[i]->fde_caps);
		unp_discard(fp);
	}
	free(fdep[0], M_FILECAPS);
}

static int
unp_externalize(struct mbuf *control, struct mbuf **controlp, int flags)
{
	struct thread *td = curthread;		/* XXX */
	struct cmsghdr *cm = mtod(control, struct cmsghdr *);
	int i;
	int *fdp;
	struct filedesc *fdesc = td->td_proc->p_fd;
	struct filedescent **fdep;
	void *data;
	socklen_t clen = control->m_len, datalen;
	int error, newfds;
	u_int newlen;

	UNP_LINK_UNLOCK_ASSERT();

	error = 0;
	if (controlp != NULL) /* controlp == NULL => free control messages */
		*controlp = NULL;
	while (cm != NULL) {
		if (sizeof(*cm) > clen || cm->cmsg_len > clen) {
			error = EINVAL;
			break;
		}
		data = CMSG_DATA(cm);
		datalen = (caddr_t)cm + cm->cmsg_len - (caddr_t)data;
		if (cm->cmsg_level == SOL_SOCKET
		    && cm->cmsg_type == SCM_RIGHTS) {
			newfds = datalen / sizeof(*fdep);
			if (newfds == 0)
				goto next;
			fdep = data;

			/* If we're not outputting the descriptors free them. */
			if (error || controlp == NULL) {
				unp_freerights(fdep, newfds);
				goto next;
			}
			FILEDESC_XLOCK(fdesc);

			/*
			 * Now change each pointer to an fd in the global
			 * table to an integer that is the index to the local
			 * fd table entry that we set up to point to the
			 * global one we are transferring.
			 */
			newlen = newfds * sizeof(int);
			*controlp = sbcreatecontrol(NULL, newlen,
			    SCM_RIGHTS, SOL_SOCKET);
			if (*controlp == NULL) {
				FILEDESC_XUNLOCK(fdesc);
				error = E2BIG;
				unp_freerights(fdep, newfds);
				goto next;
			}

			fdp = (int *)
			    CMSG_DATA(mtod(*controlp, struct cmsghdr *));
			if (fdallocn(td, 0, fdp, newfds) != 0) {
				FILEDESC_XUNLOCK(fdesc);
				error = EMSGSIZE;
				unp_freerights(fdep, newfds);
				m_freem(*controlp);
				*controlp = NULL;
				goto next;
			}
			for (i = 0; i < newfds; i++, fdp++) {
				_finstall(fdesc, fdep[i]->fde_file, *fdp,
				    (flags & MSG_CMSG_CLOEXEC) != 0 ? UF_EXCLOSE : 0,
				    &fdep[i]->fde_caps);
				unp_externalize_fp(fdep[i]->fde_file);
			}
			FILEDESC_XUNLOCK(fdesc);
			free(fdep[0], M_FILECAPS);
		} else {
			/* We can just copy anything else across. */
			if (error || controlp == NULL)
				goto next;
			*controlp = sbcreatecontrol(NULL, datalen,
			    cm->cmsg_type, cm->cmsg_level);
			if (*controlp == NULL) {
				error = ENOBUFS;
				goto next;
			}
			bcopy(data,
			    CMSG_DATA(mtod(*controlp, struct cmsghdr *)),
			    datalen);
		}
		controlp = &(*controlp)->m_next;

next:
		if (CMSG_SPACE(datalen) < clen) {
			clen -= CMSG_SPACE(datalen);
			cm = (struct cmsghdr *)
			    ((caddr_t)cm + CMSG_SPACE(datalen));
		} else {
			clen = 0;
			cm = NULL;
		}
	}

	m_freem(control);
	return (error);
}

static void
unp_zone_change(void *tag)
{

	uma_zone_set_max(unp_zone, maxsockets);
}

static void
unp_init(void)
{

#ifdef VIMAGE
	if (!IS_DEFAULT_VNET(curvnet))
		return;
#endif
	unp_zone = uma_zcreate("unpcb", sizeof(struct unpcb), NULL, NULL,
	    NULL, NULL, UMA_ALIGN_PTR, 0);
	if (unp_zone == NULL)
		panic("unp_init");
	uma_zone_set_max(unp_zone, maxsockets);
	uma_zone_set_warning(unp_zone, "kern.ipc.maxsockets limit reached");
	EVENTHANDLER_REGISTER(maxsockets_change, unp_zone_change,
	    NULL, EVENTHANDLER_PRI_ANY);
	LIST_INIT(&unp_dhead);
	LIST_INIT(&unp_shead);
	LIST_INIT(&unp_sphead);
	SLIST_INIT(&unp_defers);
	TIMEOUT_TASK_INIT(taskqueue_thread, &unp_gc_task, 0, unp_gc, NULL);
	TASK_INIT(&unp_defer_task, 0, unp_process_defers, NULL);
	UNP_LINK_LOCK_INIT();
	UNP_LIST_LOCK_INIT();
	UNP_DEFERRED_LOCK_INIT();
}

static int
unp_internalize(struct mbuf **controlp, struct thread *td)
{
	struct mbuf *control = *controlp;
	struct proc *p = td->td_proc;
	struct filedesc *fdesc = p->p_fd;
	struct bintime *bt;
	struct cmsghdr *cm = mtod(control, struct cmsghdr *);
	struct cmsgcred *cmcred;
	struct filedescent *fde, **fdep, *fdev;
	struct file *fp;
	struct timeval *tv;
	int i, *fdp;
	void *data;
	socklen_t clen = control->m_len, datalen;
	int error, oldfds;
	u_int newlen;

	UNP_LINK_UNLOCK_ASSERT();

	error = 0;
	*controlp = NULL;
	while (cm != NULL) {
		if (sizeof(*cm) > clen || cm->cmsg_level != SOL_SOCKET
		    || cm->cmsg_len > clen || cm->cmsg_len < sizeof(*cm)) {
			error = EINVAL;
			goto out;
		}
		data = CMSG_DATA(cm);
		datalen = (caddr_t)cm + cm->cmsg_len - (caddr_t)data;

		switch (cm->cmsg_type) {
		/*
		 * Fill in credential information.
		 */
		case SCM_CREDS:
			*controlp = sbcreatecontrol(NULL, sizeof(*cmcred),
			    SCM_CREDS, SOL_SOCKET);
			if (*controlp == NULL) {
				error = ENOBUFS;
				goto out;
			}
			cmcred = (struct cmsgcred *)
			    CMSG_DATA(mtod(*controlp, struct cmsghdr *));
			cmcred->cmcred_pid = p->p_pid;
			cmcred->cmcred_uid = td->td_ucred->cr_ruid;
			cmcred->cmcred_gid = td->td_ucred->cr_rgid;
			cmcred->cmcred_euid = td->td_ucred->cr_uid;
			cmcred->cmcred_ngroups = MIN(td->td_ucred->cr_ngroups,
			    CMGROUP_MAX);
			for (i = 0; i < cmcred->cmcred_ngroups; i++)
				cmcred->cmcred_groups[i] =
				    td->td_ucred->cr_groups[i];
			break;

		case SCM_RIGHTS:
			oldfds = datalen / sizeof (int);
			if (oldfds == 0)
				break;
			/*
			 * Check that all the FDs passed in refer to legal
			 * files.  If not, reject the entire operation.
			 */
			fdp = data;
			FILEDESC_SLOCK(fdesc);
			for (i = 0; i < oldfds; i++, fdp++) {
				fp = fget_locked(fdesc, *fdp);
				if (fp == NULL) {
					FILEDESC_SUNLOCK(fdesc);
					error = EBADF;
					goto out;
				}
				if (!(fp->f_ops->fo_flags & DFLAG_PASSABLE)) {
					FILEDESC_SUNLOCK(fdesc);
					error = EOPNOTSUPP;
					goto out;
				}

			}

			/*
			 * Now replace the integer FDs with pointers to the
			 * file structure and capability rights.
			 */
			newlen = oldfds * sizeof(fdep[0]);
			*controlp = sbcreatecontrol(NULL, newlen,
			    SCM_RIGHTS, SOL_SOCKET);
			if (*controlp == NULL) {
				FILEDESC_SUNLOCK(fdesc);
				error = E2BIG;
				goto out;
			}
			fdp = data;
			fdep = (struct filedescent **)
			    CMSG_DATA(mtod(*controlp, struct cmsghdr *));
			fdev = malloc(sizeof(*fdev) * oldfds, M_FILECAPS,
			    M_WAITOK);
			for (i = 0; i < oldfds; i++, fdev++, fdp++) {
				fde = &fdesc->fd_ofiles[*fdp];
				fdep[i] = fdev;
				fdep[i]->fde_file = fde->fde_file;
				filecaps_copy(&fde->fde_caps,
				    &fdep[i]->fde_caps, true);
				unp_internalize_fp(fdep[i]->fde_file);
			}
			FILEDESC_SUNLOCK(fdesc);
			break;

		case SCM_TIMESTAMP:
			*controlp = sbcreatecontrol(NULL, sizeof(*tv),
			    SCM_TIMESTAMP, SOL_SOCKET);
			if (*controlp == NULL) {
				error = ENOBUFS;
				goto out;
			}
			tv = (struct timeval *)
			    CMSG_DATA(mtod(*controlp, struct cmsghdr *));
			microtime(tv);
			break;

		case SCM_BINTIME:
			*controlp = sbcreatecontrol(NULL, sizeof(*bt),
			    SCM_BINTIME, SOL_SOCKET);
			if (*controlp == NULL) {
				error = ENOBUFS;
				goto out;
			}
			bt = (struct bintime *)
			    CMSG_DATA(mtod(*controlp, struct cmsghdr *));
			bintime(bt);
			break;

		default:
			error = EINVAL;
			goto out;
		}

		controlp = &(*controlp)->m_next;
		if (CMSG_SPACE(datalen) < clen) {
			clen -= CMSG_SPACE(datalen);
			cm = (struct cmsghdr *)
			    ((caddr_t)cm + CMSG_SPACE(datalen));
		} else {
			clen = 0;
			cm = NULL;
		}
	}

out:
	m_freem(control);
	return (error);
}

static struct mbuf *
unp_addsockcred(struct thread *td, struct mbuf *control)
{
	struct mbuf *m, *n, *n_prev;
	struct sockcred *sc;
	const struct cmsghdr *cm;
	int ngroups;
	int i;

	ngroups = MIN(td->td_ucred->cr_ngroups, CMGROUP_MAX);
	m = sbcreatecontrol(NULL, SOCKCREDSIZE(ngroups), SCM_CREDS, SOL_SOCKET);
	if (m == NULL)
		return (control);

	sc = (struct sockcred *) CMSG_DATA(mtod(m, struct cmsghdr *));
	sc->sc_uid = td->td_ucred->cr_ruid;
	sc->sc_euid = td->td_ucred->cr_uid;
	sc->sc_gid = td->td_ucred->cr_rgid;
	sc->sc_egid = td->td_ucred->cr_gid;
	sc->sc_ngroups = ngroups;
	for (i = 0; i < sc->sc_ngroups; i++)
		sc->sc_groups[i] = td->td_ucred->cr_groups[i];

	/*
	 * Unlink SCM_CREDS control messages (struct cmsgcred), since just
	 * created SCM_CREDS control message (struct sockcred) has another
	 * format.
	 */
	if (control != NULL)
		for (n = control, n_prev = NULL; n != NULL;) {
			cm = mtod(n, struct cmsghdr *);
    			if (cm->cmsg_level == SOL_SOCKET &&
			    cm->cmsg_type == SCM_CREDS) {
    				if (n_prev == NULL)
					control = n->m_next;
				else
					n_prev->m_next = n->m_next;
				n = m_free(n);
			} else {
				n_prev = n;
				n = n->m_next;
			}
		}

	/* Prepend it to the head. */
	m->m_next = control;
	return (m);
}

static struct unpcb *
fptounp(struct file *fp)
{
	struct socket *so;

	if (fp->f_type != DTYPE_SOCKET)
		return (NULL);
	if ((so = fp->f_data) == NULL)
		return (NULL);
	if (so->so_proto->pr_domain != &localdomain)
		return (NULL);
	return sotounpcb(so);
}

static void
unp_discard(struct file *fp)
{
	struct unp_defer *dr;

	if (unp_externalize_fp(fp)) {
		dr = malloc(sizeof(*dr), M_TEMP, M_WAITOK);
		dr->ud_fp = fp;
		UNP_DEFERRED_LOCK();
		SLIST_INSERT_HEAD(&unp_defers, dr, ud_link);
		UNP_DEFERRED_UNLOCK();
		atomic_add_int(&unp_defers_count, 1);
		taskqueue_enqueue(taskqueue_thread, &unp_defer_task);
	} else
		(void) closef(fp, (struct thread *)NULL);
}

static void
unp_process_defers(void *arg __unused, int pending)
{
	struct unp_defer *dr;
	SLIST_HEAD(, unp_defer) drl;
	int count;

	SLIST_INIT(&drl);
	for (;;) {
		UNP_DEFERRED_LOCK();
		if (SLIST_FIRST(&unp_defers) == NULL) {
			UNP_DEFERRED_UNLOCK();
			break;
		}
		SLIST_SWAP(&unp_defers, &drl, unp_defer);
		UNP_DEFERRED_UNLOCK();
		count = 0;
		while ((dr = SLIST_FIRST(&drl)) != NULL) {
			SLIST_REMOVE_HEAD(&drl, ud_link);
			closef(dr->ud_fp, NULL);
			free(dr, M_TEMP);
			count++;
		}
		atomic_add_int(&unp_defers_count, -count);
	}
}

static void
unp_internalize_fp(struct file *fp)
{
	struct unpcb *unp;

	UNP_LINK_WLOCK();
	if ((unp = fptounp(fp)) != NULL) {
		unp->unp_file = fp;
		unp->unp_msgcount++;
	}
	fhold(fp);
	unp_rights++;
	UNP_LINK_WUNLOCK();
}

static int
unp_externalize_fp(struct file *fp)
{
	struct unpcb *unp;
	int ret;

	UNP_LINK_WLOCK();
	if ((unp = fptounp(fp)) != NULL) {
		unp->unp_msgcount--;
		ret = 1;
	} else
		ret = 0;
	unp_rights--;
	UNP_LINK_WUNLOCK();
	return (ret);
}

/*
 * unp_defer indicates whether additional work has been defered for a future
 * pass through unp_gc().  It is thread local and does not require explicit
 * synchronization.
 */
static int	unp_marked;
static int	unp_unreachable;

static void
unp_accessable(struct filedescent **fdep, int fdcount)
{
	struct unpcb *unp;
	struct file *fp;
	int i;

	for (i = 0; i < fdcount; i++) {
		fp = fdep[i]->fde_file;
		if ((unp = fptounp(fp)) == NULL)
			continue;
		if (unp->unp_gcflag & UNPGC_REF)
			continue;
		unp->unp_gcflag &= ~UNPGC_DEAD;
		unp->unp_gcflag |= UNPGC_REF;
		unp_marked++;
	}
}

static void
unp_gc_process(struct unpcb *unp)
{
	struct socket *soa;
	struct socket *so;
	struct file *fp;

	/* Already processed. */
	if (unp->unp_gcflag & UNPGC_SCANNED)
		return;
	fp = unp->unp_file;

	/*
	 * Check for a socket potentially in a cycle.  It must be in a
	 * queue as indicated by msgcount, and this must equal the file
	 * reference count.  Note that when msgcount is 0 the file is NULL.
	 */
	if ((unp->unp_gcflag & UNPGC_REF) == 0 && fp &&
	    unp->unp_msgcount != 0 && fp->f_count == unp->unp_msgcount) {
		unp->unp_gcflag |= UNPGC_DEAD;
		unp_unreachable++;
		return;
	}

	/*
	 * Mark all sockets we reference with RIGHTS.
	 */
	so = unp->unp_socket;
	if ((unp->unp_gcflag & UNPGC_IGNORE_RIGHTS) == 0) {
		SOCKBUF_LOCK(&so->so_rcv);
		unp_scan(so->so_rcv.sb_mb, unp_accessable);
		SOCKBUF_UNLOCK(&so->so_rcv);
	}

	/*
	 * Mark all sockets in our accept queue.
	 */
	ACCEPT_LOCK();
	TAILQ_FOREACH(soa, &so->so_comp, so_list) {
		if ((sotounpcb(soa)->unp_gcflag & UNPGC_IGNORE_RIGHTS) != 0)
			continue;
		SOCKBUF_LOCK(&soa->so_rcv);
		unp_scan(soa->so_rcv.sb_mb, unp_accessable);
		SOCKBUF_UNLOCK(&soa->so_rcv);
	}
	ACCEPT_UNLOCK();
	unp->unp_gcflag |= UNPGC_SCANNED;
}

static int unp_recycled;
SYSCTL_INT(_net_local, OID_AUTO, recycled, CTLFLAG_RD, &unp_recycled, 0,
    "Number of unreachable sockets claimed by the garbage collector.");

static int unp_taskcount;
SYSCTL_INT(_net_local, OID_AUTO, taskcount, CTLFLAG_RD, &unp_taskcount, 0,
    "Number of times the garbage collector has run.");

static void
unp_gc(__unused void *arg, int pending)
{
	struct unp_head *heads[] = { &unp_dhead, &unp_shead, &unp_sphead,
				    NULL };
	struct unp_head **head;
	struct file *f, **unref;
	struct unpcb *unp;
	int i, total;

	unp_taskcount++;
	UNP_LIST_LOCK();
	/*
	 * First clear all gc flags from previous runs, apart from
	 * UNPGC_IGNORE_RIGHTS.
	 */
	for (head = heads; *head != NULL; head++)
		LIST_FOREACH(unp, *head, unp_link)
			unp->unp_gcflag =
			    (unp->unp_gcflag & UNPGC_IGNORE_RIGHTS);

	/*
	 * Scan marking all reachable sockets with UNPGC_REF.  Once a socket
	 * is reachable all of the sockets it references are reachable.
	 * Stop the scan once we do a complete loop without discovering
	 * a new reachable socket.
	 */
	do {
		unp_unreachable = 0;
		unp_marked = 0;
		for (head = heads; *head != NULL; head++)
			LIST_FOREACH(unp, *head, unp_link)
				unp_gc_process(unp);
	} while (unp_marked);
	UNP_LIST_UNLOCK();
	if (unp_unreachable == 0)
		return;

	/*
	 * Allocate space for a local list of dead unpcbs.
	 */
	unref = malloc(unp_unreachable * sizeof(struct file *),
	    M_TEMP, M_WAITOK);

	/*
	 * Iterate looking for sockets which have been specifically marked
	 * as as unreachable and store them locally.
	 */
	UNP_LINK_RLOCK();
	UNP_LIST_LOCK();
	for (total = 0, head = heads; *head != NULL; head++)
		LIST_FOREACH(unp, *head, unp_link)
			if ((unp->unp_gcflag & UNPGC_DEAD) != 0) {
				f = unp->unp_file;
				if (unp->unp_msgcount == 0 || f == NULL ||
				    f->f_count != unp->unp_msgcount)
					continue;
				unref[total++] = f;
				fhold(f);
				KASSERT(total <= unp_unreachable,
				    ("unp_gc: incorrect unreachable count."));
			}
	UNP_LIST_UNLOCK();
	UNP_LINK_RUNLOCK();

	/*
	 * Now flush all sockets, free'ing rights.  This will free the
	 * struct files associated with these sockets but leave each socket
	 * with one remaining ref.
	 */
	for (i = 0; i < total; i++) {
		struct socket *so;

		so = unref[i]->f_data;
		CURVNET_SET(so->so_vnet);
		sorflush(so);
		CURVNET_RESTORE();
	}

	/*
	 * And finally release the sockets so they can be reclaimed.
	 */
	for (i = 0; i < total; i++)
		fdrop(unref[i], NULL);
	unp_recycled += total;
	free(unref, M_TEMP);
}

static void
unp_dispose_mbuf(struct mbuf *m)
{

	if (m)
		unp_scan(m, unp_freerights);
}

/*
 * Synchronize against unp_gc, which can trip over data as we are freeing it.
 */
static void
unp_dispose(struct socket *so)
{
	struct unpcb *unp;

	unp = sotounpcb(so);
	UNP_LIST_LOCK();
	unp->unp_gcflag |= UNPGC_IGNORE_RIGHTS;
	UNP_LIST_UNLOCK();
	unp_dispose_mbuf(so->so_rcv.sb_mb);
}

static void
unp_scan(struct mbuf *m0, void (*op)(struct filedescent **, int))
{
	struct mbuf *m;
	struct cmsghdr *cm;
	void *data;
	socklen_t clen, datalen;

	while (m0 != NULL) {
		for (m = m0; m; m = m->m_next) {
			if (m->m_type != MT_CONTROL)
				continue;

			cm = mtod(m, struct cmsghdr *);
			clen = m->m_len;

			while (cm != NULL) {
				if (sizeof(*cm) > clen || cm->cmsg_len > clen)
					break;

				data = CMSG_DATA(cm);
				datalen = (caddr_t)cm + cm->cmsg_len
				    - (caddr_t)data;

				if (cm->cmsg_level == SOL_SOCKET &&
				    cm->cmsg_type == SCM_RIGHTS) {
					(*op)(data, datalen /
					    sizeof(struct filedescent *));
				}

				if (CMSG_SPACE(datalen) < clen) {
					clen -= CMSG_SPACE(datalen);
					cm = (struct cmsghdr *)
					    ((caddr_t)cm + CMSG_SPACE(datalen));
				} else {
					clen = 0;
					cm = NULL;
				}
			}
		}
		m0 = m0->m_nextpkt;
	}
}

/*
 * A helper function called by VFS before socket-type vnode reclamation.
 * For an active vnode it clears unp_vnode pointer and decrements unp_vnode
 * use count.
 */
void
vfs_unp_reclaim(struct vnode *vp)
{
	struct socket *so;
	struct unpcb *unp;
	int active;

	ASSERT_VOP_ELOCKED(vp, "vfs_unp_reclaim");
	KASSERT(vp->v_type == VSOCK,
	    ("vfs_unp_reclaim: vp->v_type != VSOCK"));

	active = 0;
	UNP_LINK_WLOCK();
	VOP_UNP_CONNECT(vp, &so);
	if (so == NULL)
		goto done;
	unp = sotounpcb(so);
	if (unp == NULL)
		goto done;
	UNP_PCB_LOCK(unp);
	if (unp->unp_vnode == vp) {
		VOP_UNP_DETACH(vp);
		unp->unp_vnode = NULL;
		active = 1;
	}
	UNP_PCB_UNLOCK(unp);
done:
	UNP_LINK_WUNLOCK();
	if (active)
		vunref(vp);
}

#ifdef DDB
static void
db_print_indent(int indent)
{
	int i;

	for (i = 0; i < indent; i++)
		db_printf(" ");
}

static void
db_print_unpflags(int unp_flags)
{
	int comma;

	comma = 0;
	if (unp_flags & UNP_HAVEPC) {
		db_printf("%sUNP_HAVEPC", comma ? ", " : "");
		comma = 1;
	}
	if (unp_flags & UNP_HAVEPCCACHED) {
		db_printf("%sUNP_HAVEPCCACHED", comma ? ", " : "");
		comma = 1;
	}
	if (unp_flags & UNP_WANTCRED) {
		db_printf("%sUNP_WANTCRED", comma ? ", " : "");
		comma = 1;
	}
	if (unp_flags & UNP_CONNWAIT) {
		db_printf("%sUNP_CONNWAIT", comma ? ", " : "");
		comma = 1;
	}
	if (unp_flags & UNP_CONNECTING) {
		db_printf("%sUNP_CONNECTING", comma ? ", " : "");
		comma = 1;
	}
	if (unp_flags & UNP_BINDING) {
		db_printf("%sUNP_BINDING", comma ? ", " : "");
		comma = 1;
	}
}

static void
db_print_xucred(int indent, struct xucred *xu)
{
	int comma, i;

	db_print_indent(indent);
	db_printf("cr_version: %u   cr_uid: %u   cr_ngroups: %d\n",
	    xu->cr_version, xu->cr_uid, xu->cr_ngroups);
	db_print_indent(indent);
	db_printf("cr_groups: ");
	comma = 0;
	for (i = 0; i < xu->cr_ngroups; i++) {
		db_printf("%s%u", comma ? ", " : "", xu->cr_groups[i]);
		comma = 1;
	}
	db_printf("\n");
}

static void
db_print_unprefs(int indent, struct unp_head *uh)
{
	struct unpcb *unp;
	int counter;

	counter = 0;
	LIST_FOREACH(unp, uh, unp_reflink) {
		if (counter % 4 == 0)
			db_print_indent(indent);
		db_printf("%p  ", unp);
		if (counter % 4 == 3)
			db_printf("\n");
		counter++;
	}
	if (counter != 0 && counter % 4 != 0)
		db_printf("\n");
}

DB_SHOW_COMMAND(unpcb, db_show_unpcb)
{
	struct unpcb *unp;

        if (!have_addr) {
                db_printf("usage: show unpcb <addr>\n");
                return;
        }
        unp = (struct unpcb *)addr;

	db_printf("unp_socket: %p   unp_vnode: %p\n", unp->unp_socket,
	    unp->unp_vnode);

	db_printf("unp_ino: %ju   unp_conn: %p\n", (uintmax_t)unp->unp_ino,
	    unp->unp_conn);

	db_printf("unp_refs:\n");
	db_print_unprefs(2, &unp->unp_refs);

	/* XXXRW: Would be nice to print the full address, if any. */
	db_printf("unp_addr: %p\n", unp->unp_addr);

	db_printf("unp_gencnt: %llu\n",
	    (unsigned long long)unp->unp_gencnt);

	db_printf("unp_flags: %x (", unp->unp_flags);
	db_print_unpflags(unp->unp_flags);
	db_printf(")\n");

	db_printf("unp_peercred:\n");
	db_print_xucred(2, &unp->unp_peercred);

	db_printf("unp_refcount: %u\n", unp->unp_refcount);
}
#endif