FreeBSD/Linux Kernel Cross Reference
sys/kern/uipc_usrreq.c

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 1982, 1986, 1989, 1991, 1993
      *      The Regents of the University of California. All Rights Reserved.
      * Copyright (c) 2004-2009 Robert N. M. Watson All Rights Reserved.
      * Copyright (c) 2018 Matthew Macy
      *
      * 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/eventhandler.h>
    #include <sys/fcntl.h>
    #include <sys/file.h>
    #include <sys/filedesc.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/malloc.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);
   
   static struct domain localdomain;
   
   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_maxdgram = 2*1024;
   static u_long   unpdg_recvspace = 16*1024;      /* support 8KB syslog msgs */
   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 | CTLFLAG_MPSAFE, 0,
       "Local domain");
   static SYSCTL_NODE(_net_local, SOCK_STREAM, stream,
       CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
       "SOCK_STREAM");
   static SYSCTL_NODE(_net_local, SOCK_DGRAM, dgram,
       CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
       "SOCK_DGRAM");
   static SYSCTL_NODE(_net_local, SOCK_SEQPACKET, seqpacket,
       CTLFLAG_RW | CTLFLAG_MPSAFE, 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_maxdgram, 0, "Maximum datagram size.");
   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:
    *
    * Several types of locks exist in the local domain socket implementation:
    * - a global linkage lock
    * - a global connection list lock
    * - the mtxpool lock
    * - per-unpcb mutexes
    *
    * The linkage lock protects the global socket lists, the generation number
    * counter and garbage collector state.
    *
    * The connection list lock protects the list of referring sockets in a datagram
    * socket PCB.  This lock is also overloaded to protect a global list of
    * sockets whose buffers contain socket references in the form of SCM_RIGHTS
    * messages.  To avoid recursion, such references are released by a dedicated
    * thread.
    *
    * The mtxpool lock protects the vnode from being modified while referenced.
    * Lock ordering rules require that it be acquired before any PCB locks.
    *
    * The unpcb lock (unp_mtx) protects the most commonly referenced fields in the
    * unpcb.  This includes the unp_conn field, which either links two connected
    * PCBs together (for connected socket types) or points at the destination
    * socket (for connectionless socket types).  The operations of creating or
    * destroying a connection therefore involve locking multiple PCBs.  To avoid
    * lock order reversals, in some cases this involves dropping a PCB lock and
    * using a reference counter to maintain liveness.
    *
    * UNIX domain sockets each have an unpcb hung off of their so_pcb pointer,
    * allocated in pr_attach() and freed in pr_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 to hold a lock on unp_conn to guarantee
    * that detach is not run clearing unp_socket.
    *
    * 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_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_LINK_WOWNED()               rw_wowned(&unp_link_rwlock)
   
   #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_REF_LIST_LOCK()             UNP_DEFERRED_LOCK();
   #define UNP_REF_LIST_UNLOCK()           UNP_DEFERRED_UNLOCK();
   
   #define UNP_PCB_LOCK_INIT(unp)          mtx_init(&(unp)->unp_mtx,       \
                                               "unp", "unp",       \
                                               MTX_DUPOK|MTX_DEF)
   #define UNP_PCB_LOCK_DESTROY(unp)       mtx_destroy(&(unp)->unp_mtx)
   #define UNP_PCB_LOCKPTR(unp)            (&(unp)->unp_mtx)
   #define UNP_PCB_LOCK(unp)               mtx_lock(&(unp)->unp_mtx)
   #define UNP_PCB_TRYLOCK(unp)            mtx_trylock(&(unp)->unp_mtx)
   #define UNP_PCB_UNLOCK(unp)             mtx_unlock(&(unp)->unp_mtx)
   #define UNP_PCB_OWNED(unp)              mtx_owned(&(unp)->unp_mtx)
   #define UNP_PCB_LOCK_ASSERT(unp)        mtx_assert(&(unp)->unp_mtx, MA_OWNED)
   #define UNP_PCB_UNLOCK_ASSERT(unp)      mtx_assert(&(unp)->unp_mtx, MA_NOTOWNED)
   
   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 *, bool);
   typedef enum { PRU_CONNECT, PRU_CONNECT2 } conn2_how;
   static void     unp_connect2(struct socket *so, struct socket *so2, conn2_how);
   static void     unp_disconnect(struct unpcb *unp, struct unpcb *unp2);
   static void     unp_dispose(struct socket *so);
   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 int      unp_internalize(struct mbuf **, struct thread *,
                       struct mbuf **, u_int *, u_int *);
   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 *,
                       int, struct mbuf **, u_int *, u_int *);
   static void     unp_process_defers(void * __unused, int);
   
   static void
   unp_pcb_hold(struct unpcb *unp)
   {
           u_int old __unused;
   
           old = refcount_acquire(&unp->unp_refcount);
           KASSERT(old > 0, ("%s: unpcb %p has no references", __func__, unp));
   }
   
   static __result_use_check bool
   unp_pcb_rele(struct unpcb *unp)
   {
           bool ret;
   
           UNP_PCB_LOCK_ASSERT(unp);
   
           if ((ret = refcount_release(&unp->unp_refcount))) {
                   UNP_PCB_UNLOCK(unp);
                   UNP_PCB_LOCK_DESTROY(unp);
                   uma_zfree(unp_zone, unp);
           }
           return (ret);
   }
   
   static void
   unp_pcb_rele_notlast(struct unpcb *unp)
   {
           bool ret __unused;
   
           ret = refcount_release(&unp->unp_refcount);
           KASSERT(!ret, ("%s: unpcb %p has no references", __func__, unp));
   }
   
   static void
   unp_pcb_lock_pair(struct unpcb *unp, struct unpcb *unp2)
   {
           UNP_PCB_UNLOCK_ASSERT(unp);
           UNP_PCB_UNLOCK_ASSERT(unp2);
   
           if (unp == unp2) {
                   UNP_PCB_LOCK(unp);
           } else if ((uintptr_t)unp2 > (uintptr_t)unp) {
                   UNP_PCB_LOCK(unp);
                   UNP_PCB_LOCK(unp2);
           } else {
                   UNP_PCB_LOCK(unp2);
                   UNP_PCB_LOCK(unp);
           }
   }
   
   static void
   unp_pcb_unlock_pair(struct unpcb *unp, struct unpcb *unp2)
   {
           UNP_PCB_UNLOCK(unp);
           if (unp != unp2)
                   UNP_PCB_UNLOCK(unp2);
   }
   
   /*
    * Try to lock the connected peer of an already locked socket.  In some cases
    * this requires that we unlock the current socket.  The pairbusy counter is
    * used to block concurrent connection attempts while the lock is dropped.  The
    * caller must be careful to revalidate PCB state.
    */
   static struct unpcb *
   unp_pcb_lock_peer(struct unpcb *unp)
   {
           struct unpcb *unp2;
   
           UNP_PCB_LOCK_ASSERT(unp);
           unp2 = unp->unp_conn;
           if (unp2 == NULL)
                   return (NULL);
           if (__predict_false(unp == unp2))
                   return (unp);
   
           UNP_PCB_UNLOCK_ASSERT(unp2);
   
           if (__predict_true(UNP_PCB_TRYLOCK(unp2)))
                   return (unp2);
           if ((uintptr_t)unp2 > (uintptr_t)unp) {
                   UNP_PCB_LOCK(unp2);
                   return (unp2);
           }
           unp->unp_pairbusy++;
           unp_pcb_hold(unp2);
           UNP_PCB_UNLOCK(unp);
   
           UNP_PCB_LOCK(unp2);
           UNP_PCB_LOCK(unp);
           KASSERT(unp->unp_conn == unp2 || unp->unp_conn == NULL,
               ("%s: socket %p was reconnected", __func__, unp));
           if (--unp->unp_pairbusy == 0 && (unp->unp_flags & UNP_WAITING) != 0) {
                   unp->unp_flags &= ~UNP_WAITING;
                   wakeup(unp);
           }
           if (unp_pcb_rele(unp2)) {
                   /* unp2 is unlocked. */
                   return (NULL);
           }
           if (unp->unp_conn == NULL) {
                   UNP_PCB_UNLOCK(unp2);
                   return (NULL);
           }
           return (unp2);
   }
   
   static void
   uipc_abort(struct socket *so)
   {
           struct unpcb *unp, *unp2;
   
           unp = sotounpcb(so);
           KASSERT(unp != NULL, ("uipc_abort: unp == NULL"));
           UNP_PCB_UNLOCK_ASSERT(unp);
   
           UNP_PCB_LOCK(unp);
           unp2 = unp->unp_conn;
           if (unp2 != NULL) {
                   unp_pcb_hold(unp2);
                   UNP_PCB_UNLOCK(unp);
                   unp_drop(unp2);
           } else
                   UNP_PCB_UNLOCK(unp);
   }
   
   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_PCB_LOCK(unp);
           unp2 = unp_pcb_lock_peer(unp);
           if (unp2 != NULL && unp2->unp_addr != NULL)
                   sa = (struct sockaddr *)unp2->unp_addr;
           else
                   sa = &sun_noname;
           bcopy(sa, *nam, sa->sa_len);
           if (unp2 != NULL)
                   unp_pcb_unlock_pair(unp, unp2);
           else
                   UNP_PCB_UNLOCK(unp);
           return (0);
   }
   
   static int
   uipc_attach(struct socket *so, int proto, struct thread *td)
   {
           u_long sendspace, recvspace;
           struct unpcb *unp;
           int error;
           bool locked;
   
           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:
                           STAILQ_INIT(&so->so_rcv.uxdg_mb);
                           STAILQ_INIT(&so->so_snd.uxdg_mb);
                           TAILQ_INIT(&so->so_rcv.uxdg_conns);
                           /*
                            * Since send buffer is either bypassed or is a part
                            * of one-to-many receive buffer, we assign both space
                            * limits to unpdg_recvspace.
                            */
                           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;
           refcount_init(&unp->unp_refcount, 1);
   
           if ((locked = UNP_LINK_WOWNED()) == false)
                   UNP_LINK_WLOCK();
   
           unp->unp_gencnt = ++unp_gencnt;
           unp->unp_ino = ++unp_ino;
           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");
           }
   
           if (locked == false)
                   UNP_LINK_WUNLOCK();
   
           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 | NOCACHE,
               UIO_SYSSPACE, buf, fd, cap_rights_init_one(&rights, CAP_BINDAT));
   /* 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_PNBUF(&nd);
                   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 | V_PCATCH);
                   if (error)
                           goto error;
                   goto restart;
           }
           VATTR_NULL(&vattr);
           vattr.va_type = VSOCK;
           vattr.va_mode = (ACCESSPERMS & ~td->td_proc->p_pd->pd_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_PNBUF(&nd);
           if (error) {
                   VOP_VPUT_PAIR(nd.ni_dvp, NULL, true);
                   vn_finished_write(mp);
                   if (error == ERELOOKUP)
                           goto restart;
                   goto error;
           }
           vp = nd.ni_vp;
           ASSERT_VOP_ELOCKED(vp, "uipc_bind");
           soun = (struct sockaddr_un *)sodupsockaddr(nam, M_WAITOK);
   
           UNP_PCB_LOCK(unp);
           VOP_UNP_BIND(vp, unp);
           unp->unp_vnode = vp;
           unp->unp_addr = soun;
           unp->unp_flags &= ~UNP_BINDING;
           UNP_PCB_UNLOCK(unp);
           vref(vp);
           VOP_VPUT_PAIR(nd.ni_dvp, &vp, true);
           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"));
           error = unp_connect(so, nam, td);
           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"));
           error = unp_connectat(fd, so, nam, td, false);
           return (error);
   }
   
   static void
   uipc_close(struct socket *so)
   {
           struct unpcb *unp, *unp2;
           struct vnode *vp = NULL;
           struct mtx *vplock;
   
           unp = sotounpcb(so);
           KASSERT(unp != NULL, ("uipc_close: unp == NULL"));
   
           vplock = NULL;
           if ((vp = unp->unp_vnode) != NULL) {
                   vplock = mtx_pool_find(mtxpool_sleep, vp);
                   mtx_lock(vplock);
           }
           UNP_PCB_LOCK(unp);
           if (vp && unp->unp_vnode == NULL) {
                   mtx_unlock(vplock);
                   vp = NULL;
           }
           if (vp != NULL) {
                   VOP_UNP_DETACH(vp);
                   unp->unp_vnode = NULL;
           }
           if ((unp2 = unp_pcb_lock_peer(unp)) != NULL)
                   unp_disconnect(unp, unp2);
           else
                   UNP_PCB_UNLOCK(unp);
           if (vp) {
                   mtx_unlock(vplock);
                   vrele(vp);
           }
   }
   
   static int
   uipc_connect2(struct socket *so1, struct socket *so2)
   {
           struct unpcb *unp, *unp2;
   
           if (so1->so_type != so2->so_type)
                   return (EPROTOTYPE);
   
           unp = so1->so_pcb;
           KASSERT(unp != NULL, ("uipc_connect2: unp == NULL"));
           unp2 = so2->so_pcb;
           KASSERT(unp2 != NULL, ("uipc_connect2: unp2 == NULL"));
           unp_pcb_lock_pair(unp, unp2);
           unp_connect2(so1, so2, PRU_CONNECT2);
           unp_pcb_unlock_pair(unp, unp2);
   
           return (0);
   }
   
   static void
   uipc_detach(struct socket *so)
   {
           struct unpcb *unp, *unp2;
           struct mtx *vplock;
           struct vnode *vp;
           int local_unp_rights;
   
           unp = sotounpcb(so);
           KASSERT(unp != NULL, ("uipc_detach: unp == NULL"));
   
           vp = NULL;
           vplock = NULL;
   
           UNP_LINK_WLOCK();
           LIST_REMOVE(unp, unp_link);
           if (unp->unp_gcflag & UNPGC_DEAD)
                   LIST_REMOVE(unp, unp_dead);
           unp->unp_gencnt = ++unp_gencnt;
           --unp_count;
           UNP_LINK_WUNLOCK();
   
           UNP_PCB_UNLOCK_ASSERT(unp);
    restart:
           if ((vp = unp->unp_vnode) != NULL) {
                   vplock = mtx_pool_find(mtxpool_sleep, vp);
                   mtx_lock(vplock);
           }
           UNP_PCB_LOCK(unp);
           if (unp->unp_vnode != vp && unp->unp_vnode != NULL) {
                   if (vplock)
                           mtx_unlock(vplock);
                   UNP_PCB_UNLOCK(unp);
                   goto restart;
           }
           if ((vp = unp->unp_vnode) != NULL) {
                   VOP_UNP_DETACH(vp);
                   unp->unp_vnode = NULL;
           }
           if ((unp2 = unp_pcb_lock_peer(unp)) != NULL)
                   unp_disconnect(unp, unp2);
           else
                   UNP_PCB_UNLOCK(unp);
   
           UNP_REF_LIST_LOCK();
           while (!LIST_EMPTY(&unp->unp_refs)) {
                   struct unpcb *ref = LIST_FIRST(&unp->unp_refs);
   
                   unp_pcb_hold(ref);
                   UNP_REF_LIST_UNLOCK();
   
                   MPASS(ref != unp);
                   UNP_PCB_UNLOCK_ASSERT(ref);
                   unp_drop(ref);
                   UNP_REF_LIST_LOCK();
           }
           UNP_REF_LIST_UNLOCK();
   
           UNP_PCB_LOCK(unp);
           local_unp_rights = unp_rights;
           unp->unp_socket->so_pcb = NULL;
           unp->unp_socket = NULL;
           free(unp->unp_addr, M_SONAME);
           unp->unp_addr = NULL;
           if (!unp_pcb_rele(unp))
                   UNP_PCB_UNLOCK(unp);
           if (vp) {
                   mtx_unlock(vplock);
                   vrele(vp);
           }
           if (local_unp_rights)
                   taskqueue_enqueue_timeout(taskqueue_thread, &unp_gc_task, -1);
   
           switch (so->so_type) {
           case SOCK_DGRAM:
                   /*
                    * Everything should have been unlinked/freed by unp_dispose()
                    * and/or unp_disconnect().
                    */
                   MPASS(so->so_rcv.uxdg_peeked == NULL);
                   MPASS(STAILQ_EMPTY(&so->so_rcv.uxdg_mb));
                   MPASS(TAILQ_EMPTY(&so->so_rcv.uxdg_conns));
                   MPASS(STAILQ_EMPTY(&so->so_snd.uxdg_mb));
           }
   }
   
   static int
   uipc_disconnect(struct socket *so)
   {
           struct unpcb *unp, *unp2;
   
           unp = sotounpcb(so);
           KASSERT(unp != NULL, ("uipc_disconnect: unp == NULL"));
   
           UNP_PCB_LOCK(unp);
           if ((unp2 = unp_pcb_lock_peer(unp)) != NULL)
                   unp_disconnect(unp, unp2);
           else
                   UNP_PCB_UNLOCK(unp);
           return (0);
   }
   
   static int
   uipc_listen(struct socket *so, int backlog, struct thread *td)
   {
           struct unpcb *unp;
           int error;
   
           MPASS(so->so_type != SOCK_DGRAM);
   
           /*
            * Synchronize with concurrent connection attempts.
            */
           error = 0;
           unp = sotounpcb(so);
           UNP_PCB_LOCK(unp);
           if (unp->unp_conn != NULL || (unp->unp_flags & UNP_CONNECTING) != 0)
                   error = EINVAL;
           else if (unp->unp_vnode == NULL)
                   error = EDESTADDRREQ;
           if (error != 0) {
                   UNP_PCB_UNLOCK(unp);
                   return (error);
           }
   
           SOCK_LOCK(so);
           error = solisten_proto_check(so);
           if (error == 0) {
                   cru2xt(td, &unp->unp_peercred);
                   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;
   
           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));
   
           error = 0;
           if (flags & PRUS_OOB) {
                   error = EOPNOTSUPP;
                   goto release;
           }
           if (control != NULL &&
               (error = unp_internalize(&control, td, NULL, NULL, NULL)))
                   goto release;
   
           unp2 = NULL;
           if ((so->so_state & SS_ISCONNECTED) == 0) {
                   if (nam != NULL) {
                           if ((error = unp_connect(so, nam, td)) != 0)
                                   goto out;
                   } else {
                           error = ENOTCONN;
                           goto out;
                   }
           }
   
           UNP_PCB_LOCK(unp);
           if ((unp2 = unp_pcb_lock_peer(unp)) == NULL) {
                   UNP_PCB_UNLOCK(unp);
                   error = ENOTCONN;
                   goto out;
           } else if (so->so_snd.sb_state & SBS_CANTSENDMORE) {
                  unp_pcb_unlock_pair(unp, unp2);
                  error = EPIPE;
                  goto out;
          }
          UNP_PCB_UNLOCK(unp);
          if ((so2 = unp2->unp_socket) == NULL) {
                  UNP_PCB_UNLOCK(unp2);
                  error = ENOTCONN;
                  goto out;
          }
          SOCKBUF_LOCK(&so2->so_rcv);
          if (unp2->unp_flags & UNP_WANTCRED_MASK) {
                  /*
                   * Credentials are passed only once on SOCK_STREAM and
                   * SOCK_SEQPACKET (LOCAL_CREDS => WANTCRED_ONESHOT), or
                   * forever (LOCAL_CREDS_PERSISTENT => WANTCRED_ALWAYS).
                   */
                  control = unp_addsockcred(td, control, unp2->unp_flags, NULL,
                      NULL, NULL);
                  unp2->unp_flags &= ~UNP_WANTCRED_ONESHOT;
          }
  
          /*
           * Send to paired receive port and wake up readers.  Don't
           * check for space available in the receive buffer if we're
           * attaching ancillary data; Unix domain sockets only check
           * for space in the sending sockbuf, and that check is
           * performed one level up the stack.  At that level we cannot
           * precisely account for the amount of buffer space used
           * (e.g., because control messages are not yet internalized).
           */
          switch (so->so_type) {
          case SOCK_STREAM:
                  if (control != NULL) {
                          sbappendcontrol_locked(&so2->so_rcv, m,
                              control, flags);
                          control = NULL;
                  } else
                          sbappend_locked(&so2->so_rcv, m, flags);
                  break;
  
          case SOCK_SEQPACKET:
                  if (sbappendaddr_nospacecheck_locked(&so2->so_rcv,
                      &sun_noname, 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;
  out:
          /*
           * PRUS_EOF is equivalent to pr_send followed by pr_shutdown.
           */
          if (flags & PRUS_EOF) {
                  UNP_PCB_LOCK(unp);
                  socantsendmore(so);
                  unp_shutdown(unp);
                  UNP_PCB_UNLOCK(unp);
          }
          if (control != NULL && error != 0)
                  unp_scan(control, unp_freerights);
  
  release:
          if (control != NULL)
                  m_freem(control);
          /*
           * In case of PRUS_NOTREADY, uipc_ready() is responsible
           * for freeing memory.
           */   
          if (m != NULL && (flags & PRUS_NOTREADY) == 0)
                  m_freem(m);
          return (error);
  }
  
  /* PF_UNIX/SOCK_DGRAM version of sbspace() */
  static inline bool
  uipc_dgram_sbspace(struct sockbuf *sb, u_int cc, u_int mbcnt)
  {
          u_int bleft, mleft;
  
          /*
           * Negative space may happen if send(2) is followed by
           * setsockopt(SO_SNDBUF/SO_RCVBUF) that shrinks maximum.
           */
          if (__predict_false(sb->sb_hiwat < sb->uxdg_cc ||
              sb->sb_mbmax < sb->uxdg_mbcnt))
                  return (false);
  
          if (__predict_false(sb->sb_state & SBS_CANTRCVMORE))
                  return (false);
  
          bleft = sb->sb_hiwat - sb->uxdg_cc;
          mleft = sb->sb_mbmax - sb->uxdg_mbcnt;
  
          return (bleft >= cc && mleft >= mbcnt);
  }
  
  /*
   * PF_UNIX/SOCK_DGRAM send
   *
   * Allocate a record consisting of 3 mbufs in the sequence of
   * from -> control -> data and append it to the socket buffer.
   *
   * The first mbuf carries sender's name and is a pkthdr that stores
   * overall length of datagram, its memory consumption and control length.
   */
  #define ctllen  PH_loc.thirtytwo[1]
  _Static_assert(offsetof(struct pkthdr, memlen) + sizeof(u_int) <=
      offsetof(struct pkthdr, ctllen), "unix/dgram can not store ctllen");
  static int
  uipc_sosend_dgram(struct socket *so, struct sockaddr *addr, struct uio *uio,
      struct mbuf *m, struct mbuf *c, int flags, struct thread *td)
  {
          struct unpcb *unp, *unp2;
          const struct sockaddr *from;
          struct socket *so2;
          struct sockbuf *sb;
          struct mbuf *f, *clast;
          u_int cc, ctl, mbcnt;
          u_int dcc __diagused, dctl __diagused, dmbcnt __diagused;
          int error;
  
          MPASS((uio != NULL && m == NULL) || (m != NULL && uio == NULL));
  
          error = 0;
          f = NULL;
          ctl = 0;
  
          if (__predict_false(flags & MSG_OOB)) {
                  error = EOPNOTSUPP;
                  goto out;
          }
          if (m == NULL) {
                  if (__predict_false(uio->uio_resid > unpdg_maxdgram)) {
                          error = EMSGSIZE;
                          goto out;
                  }
                  m = m_uiotombuf(uio, M_WAITOK, 0, max_hdr, M_PKTHDR);
                  if (__predict_false(m == NULL)) {
                          error = EFAULT;
                          goto out;
                  }
                  f = m_gethdr(M_WAITOK, MT_SONAME);
                  cc = m->m_pkthdr.len;
                  mbcnt = MSIZE + m->m_pkthdr.memlen;
                  if (c != NULL &&
                      (error = unp_internalize(&c, td, &clast, &ctl, &mbcnt)))
                          goto out;
          } else {
                  /* pr_sosend() with mbuf usually is a kernel thread. */
  
                  M_ASSERTPKTHDR(m);
                  if (__predict_false(c != NULL))
                          panic("%s: control from a kernel thread", __func__);
  
                  if (__predict_false(m->m_pkthdr.len > unpdg_maxdgram)) {
                          error = EMSGSIZE;
                          goto out;
                  }
                  if ((f = m_gethdr(M_NOWAIT, MT_SONAME)) == NULL) {
                          error = ENOBUFS;
                          goto out;
                  }
                  /* Condition the foreign mbuf to our standards. */
                  m_clrprotoflags(m);
                  m_tag_delete_chain(m, NULL);
                  m->m_pkthdr.rcvif = NULL;
                  m->m_pkthdr.flowid = 0;
                  m->m_pkthdr.csum_flags = 0;
                  m->m_pkthdr.fibnum = 0;
                  m->m_pkthdr.rsstype = 0;
  
                  cc = m->m_pkthdr.len;
                  mbcnt = MSIZE;
                  for (struct mbuf *mb = m; mb != NULL; mb = mb->m_next) {
                          mbcnt += MSIZE;
                          if (mb->m_flags & M_EXT)
                                  mbcnt += mb->m_ext.ext_size;
                  }
          }
  
          unp = sotounpcb(so);
          MPASS(unp);
  
          /*
           * XXXGL: would be cool to fully remove so_snd out of the equation
           * and avoid this lock, which is not only extraneous, but also being
           * released, thus still leaving possibility for a race.  We can easily
           * handle SBS_CANTSENDMORE/SS_ISCONNECTED complement in unpcb, but it
           * is more difficult to invent something to handle so_error.
           */
          error = SOCK_IO_SEND_LOCK(so, SBLOCKWAIT(flags));
          if (error)
                  goto out2;
          SOCK_SENDBUF_LOCK(so);
          if (so->so_snd.sb_state & SBS_CANTSENDMORE) {
                  SOCK_SENDBUF_UNLOCK(so);
                  error = EPIPE;
                  goto out3;
          }
          if (so->so_error != 0) {
                  error = so->so_error;
                  so->so_error = 0;
                  SOCK_SENDBUF_UNLOCK(so);
                  goto out3;
          }
          if (((so->so_state & SS_ISCONNECTED) == 0) && addr == NULL) {
                  SOCK_SENDBUF_UNLOCK(so);
                  error = EDESTADDRREQ;
                  goto out3;
          }
          SOCK_SENDBUF_UNLOCK(so);
  
          if (addr != NULL) {
                  if ((error = unp_connectat(AT_FDCWD, so, addr, td, true)))
                          goto out3;
                  UNP_PCB_LOCK_ASSERT(unp);
                  unp2 = unp->unp_conn;
                  UNP_PCB_LOCK_ASSERT(unp2);
          } else {
                  UNP_PCB_LOCK(unp);
                  unp2 = unp_pcb_lock_peer(unp);
                  if (unp2 == NULL) {
                          UNP_PCB_UNLOCK(unp);
                          error = ENOTCONN;
                          goto out3;
                  }
          }
  
          if (unp2->unp_flags & UNP_WANTCRED_MASK)
                  c = unp_addsockcred(td, c, unp2->unp_flags, &clast, &ctl,
                      &mbcnt);
          if (unp->unp_addr != NULL)
                  from = (struct sockaddr *)unp->unp_addr;
          else
                  from = &sun_noname;
          f->m_len = from->sa_len;
          MPASS(from->sa_len <= MLEN);
          bcopy(from, mtod(f, void *), from->sa_len);
          ctl += f->m_len;
  
          /*
           * Concatenate mbufs: from -> control -> data.
           * Save overall cc and mbcnt in "from" mbuf.
           */
          if (c != NULL) {
  #ifdef INVARIANTS
                  struct mbuf *mc;
  
                  for (mc = c; mc->m_next != NULL; mc = mc->m_next);
                  MPASS(mc == clast);
  #endif
                  f->m_next = c;
                  clast->m_next = m;
                  c = NULL;
          } else
                  f->m_next = m;
          m = NULL;
  #ifdef INVARIANTS
          dcc = dctl = dmbcnt = 0;
          for (struct mbuf *mb = f; mb != NULL; mb = mb->m_next) {
                  if (mb->m_type == MT_DATA)
                          dcc += mb->m_len;
                  else
                          dctl += mb->m_len;
                  dmbcnt += MSIZE;
                  if (mb->m_flags & M_EXT)
                          dmbcnt += mb->m_ext.ext_size;
          }
          MPASS(dcc == cc);
          MPASS(dctl == ctl);
          MPASS(dmbcnt == mbcnt);
  #endif
          f->m_pkthdr.len = cc + ctl;
          f->m_pkthdr.memlen = mbcnt;
          f->m_pkthdr.ctllen = ctl;
  
          /*
           * Destination socket buffer selection.
           *
           * Unconnected sends, when !(so->so_state & SS_ISCONNECTED) and the
           * destination address is supplied, create a temporary connection for
           * the run time of the function (see call to unp_connectat() above and
           * to unp_disconnect() below).  We distinguish them by condition of
           * (addr != NULL).  We intentionally avoid adding 'bool connected' for
           * that condition, since, again, through the run time of this code we
           * are always connected.  For such "unconnected" sends, the destination
           * buffer would be the receive buffer of destination socket so2.
           *
           * For connected sends, data lands on the send buffer of the sender's
           * socket "so".  Then, if we just added the very first datagram
           * on this send buffer, we need to add the send buffer on to the
           * receiving socket's buffer list.  We put ourselves on top of the
           * list.  Such logic gives infrequent senders priority over frequent
           * senders.
           *
           * Note on byte count management. As long as event methods kevent(2),
           * select(2) are not protocol specific (yet), we need to maintain
           * meaningful values on the receive buffer.  So, the receive buffer
           * would accumulate counters from all connected buffers potentially
           * having sb_ccc > sb_hiwat or sb_mbcnt > sb_mbmax.
           */
          so2 = unp2->unp_socket;
          sb = (addr == NULL) ? &so->so_snd : &so2->so_rcv;
          SOCK_RECVBUF_LOCK(so2);
          if (uipc_dgram_sbspace(sb, cc + ctl, mbcnt)) {
                  if (addr == NULL && STAILQ_EMPTY(&sb->uxdg_mb))
                          TAILQ_INSERT_HEAD(&so2->so_rcv.uxdg_conns, &so->so_snd,
                              uxdg_clist);
                  STAILQ_INSERT_TAIL(&sb->uxdg_mb, f, m_stailqpkt);
                  sb->uxdg_cc += cc + ctl;
                  sb->uxdg_ctl += ctl;
                  sb->uxdg_mbcnt += mbcnt;
                  so2->so_rcv.sb_acc += cc + ctl;
                  so2->so_rcv.sb_ccc += cc + ctl;
                  so2->so_rcv.sb_ctl += ctl;
                  so2->so_rcv.sb_mbcnt += mbcnt;
                  sorwakeup_locked(so2);
                  f = NULL;
          } else {
                  soroverflow_locked(so2);
                  error = (so->so_state & SS_NBIO) ? EAGAIN : ENOBUFS;
                  if (f->m_next->m_type == MT_CONTROL)
                          unp_scan(f->m_next, unp_freerights);
          }
  
          if (addr != NULL)
                  unp_disconnect(unp, unp2);
          else
                  unp_pcb_unlock_pair(unp, unp2);
  
          td->td_ru.ru_msgsnd++;
  
  out3:
          SOCK_IO_SEND_UNLOCK(so);
  out2:
          if (c)
                  unp_scan(c, unp_freerights);
  out:
          if (f)
                  m_freem(f);
          if (c)
                  m_freem(c);
          if (m)
                  m_freem(m);
  
          return (error);
  }
  
  /*
   * PF_UNIX/SOCK_DGRAM receive with MSG_PEEK.
   * The mbuf has already been unlinked from the uxdg_mb of socket buffer
   * and needs to be linked onto uxdg_peeked of receive socket buffer.
   */
  static int
  uipc_peek_dgram(struct socket *so, struct mbuf *m, struct sockaddr **psa,
      struct uio *uio, struct mbuf **controlp, int *flagsp)
  {
          ssize_t len = 0;
          int error;
  
          so->so_rcv.uxdg_peeked = m;
          so->so_rcv.uxdg_cc += m->m_pkthdr.len;
          so->so_rcv.uxdg_ctl += m->m_pkthdr.ctllen;
          so->so_rcv.uxdg_mbcnt += m->m_pkthdr.memlen;
          SOCK_RECVBUF_UNLOCK(so);
  
          KASSERT(m->m_type == MT_SONAME, ("m->m_type == %d", m->m_type));
          if (psa != NULL)
                  *psa = sodupsockaddr(mtod(m, struct sockaddr *), M_WAITOK);
  
          m = m->m_next;
          KASSERT(m, ("%s: no data or control after soname", __func__));
  
          /*
           * With MSG_PEEK the control isn't executed, just copied.
           */
          while (m != NULL && m->m_type == MT_CONTROL) {
                  if (controlp != NULL) {
                          *controlp = m_copym(m, 0, m->m_len, M_WAITOK);
                          controlp = &(*controlp)->m_next;
                  }
                  m = m->m_next;
          }
          KASSERT(m == NULL || m->m_type == MT_DATA,
              ("%s: not MT_DATA mbuf %p", __func__, m));
          while (m != NULL && uio->uio_resid > 0) {
                  len = uio->uio_resid;
                  if (len > m->m_len)
                          len = m->m_len;
                  error = uiomove(mtod(m, char *), (int)len, uio);
                  if (error) {
                          SOCK_IO_RECV_UNLOCK(so);
                          return (error);
                  }
                  if (len == m->m_len)
                          m = m->m_next;
          }
          SOCK_IO_RECV_UNLOCK(so);
  
          if (flagsp != NULL) {
                  if (m != NULL) {
                          if (*flagsp & MSG_TRUNC) {
                                  /* Report real length of the packet */
                                  uio->uio_resid -= m_length(m, NULL) - len;
                          }
                          *flagsp |= MSG_TRUNC;
                  } else
                          *flagsp &= ~MSG_TRUNC;
          }
  
          return (0);
  }
  
  /*
   * PF_UNIX/SOCK_DGRAM receive
   */
  static int
  uipc_soreceive_dgram(struct socket *so, struct sockaddr **psa, struct uio *uio,
      struct mbuf **mp0, struct mbuf **controlp, int *flagsp)
  {
          struct sockbuf *sb = NULL;
          struct mbuf *m;
          int flags, error;
          ssize_t len = 0;
          bool nonblock;
  
          MPASS(mp0 == NULL);
  
          if (psa != NULL)
                  *psa = NULL;
          if (controlp != NULL)
                  *controlp = NULL;
  
          flags = flagsp != NULL ? *flagsp : 0;
          nonblock = (so->so_state & SS_NBIO) ||
              (flags & (MSG_DONTWAIT | MSG_NBIO));
  
          error = SOCK_IO_RECV_LOCK(so, SBLOCKWAIT(flags));
          if (__predict_false(error))
                  return (error);
  
          /*
           * Loop blocking while waiting for a datagram.  Prioritize connected
           * peers over unconnected sends.  Set sb to selected socket buffer
           * containing an mbuf on exit from the wait loop.  A datagram that
           * had already been peeked at has top priority.
           */
          SOCK_RECVBUF_LOCK(so);
          while ((m = so->so_rcv.uxdg_peeked) == NULL &&
              (sb = TAILQ_FIRST(&so->so_rcv.uxdg_conns)) == NULL &&
              (m = STAILQ_FIRST(&so->so_rcv.uxdg_mb)) == NULL) {
                  if (so->so_error) {
                          error = so->so_error;
                          so->so_error = 0;
                          SOCK_RECVBUF_UNLOCK(so);
                          SOCK_IO_RECV_UNLOCK(so);
                          return (error);
                  }
                  if (so->so_rcv.sb_state & SBS_CANTRCVMORE ||
                      uio->uio_resid == 0) {
                          SOCK_RECVBUF_UNLOCK(so);
                          SOCK_IO_RECV_UNLOCK(so);
                          return (0);
                  }
                  if (nonblock) {
                          SOCK_RECVBUF_UNLOCK(so);
                          SOCK_IO_RECV_UNLOCK(so);
                          return (EWOULDBLOCK);
                  }
                  error = sbwait(so, SO_RCV);
                  if (error) {
                          SOCK_RECVBUF_UNLOCK(so);
                          SOCK_IO_RECV_UNLOCK(so);
                          return (error);
                  }
          }
  
          if (sb == NULL)
                  sb = &so->so_rcv;
          else if (m == NULL)
                  m = STAILQ_FIRST(&sb->uxdg_mb);
          else
                  MPASS(m == so->so_rcv.uxdg_peeked);
  
          MPASS(sb->uxdg_cc > 0);
          M_ASSERTPKTHDR(m);
          KASSERT(m->m_type == MT_SONAME, ("m->m_type == %d", m->m_type));
  
          if (uio->uio_td)
                  uio->uio_td->td_ru.ru_msgrcv++;
  
          if (__predict_true(m != so->so_rcv.uxdg_peeked)) {
                  STAILQ_REMOVE_HEAD(&sb->uxdg_mb, m_stailqpkt);
                  if (STAILQ_EMPTY(&sb->uxdg_mb) && sb != &so->so_rcv)
                          TAILQ_REMOVE(&so->so_rcv.uxdg_conns, sb, uxdg_clist);
          } else
                  so->so_rcv.uxdg_peeked = NULL;
  
          sb->uxdg_cc -= m->m_pkthdr.len;
          sb->uxdg_ctl -= m->m_pkthdr.ctllen;
          sb->uxdg_mbcnt -= m->m_pkthdr.memlen;
  
          if (__predict_false(flags & MSG_PEEK))
                  return (uipc_peek_dgram(so, m, psa, uio, controlp, flagsp));
  
          so->so_rcv.sb_acc -= m->m_pkthdr.len;
          so->so_rcv.sb_ccc -= m->m_pkthdr.len;
          so->so_rcv.sb_ctl -= m->m_pkthdr.ctllen;
          so->so_rcv.sb_mbcnt -= m->m_pkthdr.memlen;
          SOCK_RECVBUF_UNLOCK(so);
  
          if (psa != NULL)
                  *psa = sodupsockaddr(mtod(m, struct sockaddr *), M_WAITOK);
          m = m_free(m);
          KASSERT(m, ("%s: no data or control after soname", __func__));
  
          /*
           * Packet to copyout() is now in 'm' and it is disconnected from the
           * queue.
           *
           * Process one or more MT_CONTROL mbufs present before any data mbufs
           * in the first mbuf chain on the socket buffer.  We call into the
           * unp_externalize() to perform externalization (or freeing if
           * controlp == NULL). In some cases there can be only MT_CONTROL mbufs
           * without MT_DATA mbufs.
           */
          while (m != NULL && m->m_type == MT_CONTROL) {
                  struct mbuf *cm;
  
                  /* XXXGL: unp_externalize() is also dom_externalize() KBI and
                   * it frees whole chain, so we must disconnect the mbuf.
                   */
                  cm = m; m = m->m_next; cm->m_next = NULL;
                  error = unp_externalize(cm, controlp, flags);
                  if (error != 0) {
                          SOCK_IO_RECV_UNLOCK(so);
                          unp_scan(m, unp_freerights);
                          m_freem(m);
                          return (error);
                  }
                  if (controlp != NULL) {
                          while (*controlp != NULL)
                                  controlp = &(*controlp)->m_next;
                  }
          }
          KASSERT(m == NULL || m->m_type == MT_DATA,
              ("%s: not MT_DATA mbuf %p", __func__, m));
          while (m != NULL && uio->uio_resid > 0) {
                  len = uio->uio_resid;
                  if (len > m->m_len)
                          len = m->m_len;
                  error = uiomove(mtod(m, char *), (int)len, uio);
                  if (error) {
                          SOCK_IO_RECV_UNLOCK(so);
                          m_freem(m);
                          return (error);
                  }
                  if (len == m->m_len)
                          m = m_free(m);
                  else {
                          m->m_data += len;
                          m->m_len -= len;
                  }
          }
          SOCK_IO_RECV_UNLOCK(so);
  
          if (m != NULL) {
                  if (flagsp != NULL) {
                          if (flags & MSG_TRUNC) {
                                  /* Report real length of the packet */
                                  uio->uio_resid -= m_length(m, NULL);
                          }
                          *flagsp |= MSG_TRUNC;
                  }
                  m_freem(m);
          } else if (flagsp != NULL)
                  *flagsp &= ~MSG_TRUNC;
  
          return (0);
  }
  
  static bool
  uipc_ready_scan(struct socket *so, struct mbuf *m, int count, int *errorp)
  {
          struct mbuf *mb, *n;
          struct sockbuf *sb;
  
          SOCK_LOCK(so);
          if (SOLISTENING(so)) {
                  SOCK_UNLOCK(so);
                  return (false);
          }
          mb = NULL;
          sb = &so->so_rcv;
          SOCKBUF_LOCK(sb);
          if (sb->sb_fnrdy != NULL) {
                  for (mb = sb->sb_mb, n = mb->m_nextpkt; mb != NULL;) {
                          if (mb == m) {
                                  *errorp = sbready(sb, m, count);
                                  break;
                          }
                          mb = mb->m_next;
                          if (mb == NULL) {
                                  mb = n;
                                  if (mb != NULL)
                                          n = mb->m_nextpkt;
                          }
                  }
          }
          SOCKBUF_UNLOCK(sb);
          SOCK_UNLOCK(so);
          return (mb != NULL);
  }
  
  static int
  uipc_ready(struct socket *so, struct mbuf *m, int count)
  {
          struct unpcb *unp, *unp2;
          struct socket *so2;
          int error, i;
  
          unp = sotounpcb(so);
  
          KASSERT(so->so_type == SOCK_STREAM,
              ("%s: unexpected socket type for %p", __func__, so));
  
          UNP_PCB_LOCK(unp);
          if ((unp2 = unp_pcb_lock_peer(unp)) != NULL) {
                  UNP_PCB_UNLOCK(unp);
                  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);
                  return (error);
          }
          UNP_PCB_UNLOCK(unp);
  
          /*
           * The receiving socket has been disconnected, but may still be valid.
           * In this case, the now-ready mbufs are still present in its socket
           * buffer, so perform an exhaustive search before giving up and freeing
           * the mbufs.
           */
          UNP_LINK_RLOCK();
          LIST_FOREACH(unp, &unp_shead, unp_link) {
                  if (uipc_ready_scan(unp->unp_socket, m, count, &error))
                          break;
          }
          UNP_LINK_RUNLOCK();
  
          if (unp == NULL) {
                  for (i = 0; i < count; i++)
                          m = m_free(m);
                  error = ECONNRESET;
          }
          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;
          sb->st_dev = NODEV;
          sb->st_ino = unp->unp_ino;
          return (0);
  }
  
  static int
  uipc_shutdown(struct socket *so)
  {
          struct unpcb *unp;
  
          unp = sotounpcb(so);
          KASSERT(unp != NULL, ("uipc_shutdown: unp == NULL"));
  
          UNP_PCB_LOCK(unp);
          socantsendmore(so);
          unp_shutdown(unp);
          UNP_PCB_UNLOCK(unp);
          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 int
  uipc_ctloutput(struct socket *so, struct sockopt *sopt)
  {
          struct unpcb *unp;
          struct xucred xu;
          int error, optval;
  
          if (sopt->sopt_level != SOL_LOCAL)
                  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_ONESHOT ? 1 : 0;
                          error = sooptcopyout(sopt, &optval, sizeof(optval));
                          break;
  
                  case LOCAL_CREDS_PERSISTENT:
                          /* Unlocked read. */
                          optval = unp->unp_flags & UNP_WANTCRED_ALWAYS ? 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_CREDS_PERSISTENT:
                  case LOCAL_CONNWAIT:
                          error = sooptcopyin(sopt, &optval, sizeof(optval),
                                              sizeof(optval));
                          if (error)
                                  break;
  
  #define OPTSET(bit, exclusive) do {                                     \
          UNP_PCB_LOCK(unp);                                              \
          if (optval) {                                                   \
                  if ((unp->unp_flags & (exclusive)) != 0) {              \
                          UNP_PCB_UNLOCK(unp);                            \
                          error = EINVAL;                                 \
                          break;                                          \
                  }                                                       \
                  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_ONESHOT, UNP_WANTCRED_ALWAYS);
                                  break;
  
                          case LOCAL_CREDS_PERSISTENT:
                                  OPTSET(UNP_WANTCRED_ALWAYS, UNP_WANTCRED_ONESHOT);
                                  break;
  
                          case LOCAL_CONNWAIT:
                                  OPTSET(UNP_CONNWAIT, 0);
                                  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, false));
  }
  
  static int
  unp_connectat(int fd, struct socket *so, struct sockaddr *nam,
      struct thread *td, bool return_locked)
  {
          struct mtx *vplock;
          struct sockaddr_un *soun;
          struct vnode *vp;
          struct socket *so2;
          struct unpcb *unp, *unp2, *unp3;
          struct nameidata nd;
          char buf[SOCK_MAXADDRLEN];
          struct sockaddr *sa;
          cap_rights_t rights;
          int error, len;
          bool connreq;
  
          if (nam->sa_family != AF_UNIX)
                  return (EAFNOSUPPORT);
          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);
          soun = (struct sockaddr_un *)nam;
          bcopy(soun->sun_path, buf, len);
          buf[len] = 0;
  
          error = 0;
          unp = sotounpcb(so);
          UNP_PCB_LOCK(unp);
          for (;;) {
                  /*
                   * Wait for connection state to stabilize.  If a connection
                   * already exists, give up.  For datagram sockets, which permit
                   * multiple consecutive connect(2) calls, upper layers are
                   * responsible for disconnecting in advance of a subsequent
                   * connect(2), but this is not synchronized with PCB connection
                   * state.
                   *
                   * Also make sure that no threads are currently attempting to
                   * lock the peer socket, to ensure that unp_conn cannot
                   * transition between two valid sockets while locks are dropped.
                   */
                  if (SOLISTENING(so))
                          error = EOPNOTSUPP;
                  else if (unp->unp_conn != NULL)
                          error = EISCONN;
                  else if ((unp->unp_flags & UNP_CONNECTING) != 0) {
                          error = EALREADY;
                  }
                  if (error != 0) {
                          UNP_PCB_UNLOCK(unp);
                          return (error);
                  }
                  if (unp->unp_pairbusy > 0) {
                          unp->unp_flags |= UNP_WAITING;
                          mtx_sleep(unp, UNP_PCB_LOCKPTR(unp), 0, "unpeer", 0);
                          continue;
                  }
                  break;
          }
          unp->unp_flags |= UNP_CONNECTING;
          UNP_PCB_UNLOCK(unp);
  
          connreq = (so->so_proto->pr_flags & PR_CONNREQUIRED) != 0;
          if (connreq)
                  sa = malloc(sizeof(struct sockaddr_un), M_SONAME, M_WAITOK);
          else
                  sa = NULL;
          NDINIT_ATRIGHTS(&nd, LOOKUP, FOLLOW | LOCKSHARED | LOCKLEAF,
              UIO_SYSSPACE, buf, fd, cap_rights_init_one(&rights, CAP_CONNECTAT));
          error = namei(&nd);
          if (error)
                  vp = NULL;
          else
                  vp = nd.ni_vp;
          ASSERT_VOP_LOCKED(vp, "unp_connect");
          if (error)
                  goto bad;
          NDFREE_PNBUF(&nd);
  
          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"));
  
          vplock = mtx_pool_find(mtxpool_sleep, vp);
          mtx_lock(vplock);
          VOP_UNP_CONNECT(vp, &unp2);
          if (unp2 == NULL) {
                  error = ECONNREFUSED;
                  goto bad2;
          }
          so2 = unp2->unp_socket;
          if (so->so_type != so2->so_type) {
                  error = EPROTOTYPE;
                  goto bad2;
          }
          if (connreq) {
                  if (SOLISTENING(so2)) {
                          CURVNET_SET(so2->so_vnet);
                          so2 = sonewconn(so2, 0);
                          CURVNET_RESTORE();
                  } else
                          so2 = NULL;
                  if (so2 == NULL) {
                          error = ECONNREFUSED;
                          goto bad2;
                  }
                  unp3 = sotounpcb(so2);
                  unp_pcb_lock_pair(unp2, 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;
                  }
  
                  unp_copy_peercred(td, unp3, unp, unp2);
  
                  UNP_PCB_UNLOCK(unp2);
                  unp2 = unp3;
  
                  /*
                   * It is safe to block on the PCB lock here since unp2 is
                   * nascent and cannot be connected to any other sockets.
                   */
                  UNP_PCB_LOCK(unp);
  #ifdef MAC
                  mac_socketpeer_set_from_socket(so, so2);
                  mac_socketpeer_set_from_socket(so2, so);
  #endif
          } else {
                  unp_pcb_lock_pair(unp, unp2);
          }
          KASSERT(unp2 != NULL && so2 != NULL && unp2->unp_socket == so2 &&
              sotounpcb(so2) == unp2,
              ("%s: unp2 %p so2 %p", __func__, unp2, so2));
          unp_connect2(so, so2, PRU_CONNECT);
          KASSERT((unp->unp_flags & UNP_CONNECTING) != 0,
              ("%s: unp %p has UNP_CONNECTING clear", __func__, unp));
          unp->unp_flags &= ~UNP_CONNECTING;
          if (!return_locked)
                  unp_pcb_unlock_pair(unp, unp2);
  bad2:
          mtx_unlock(vplock);
  bad:
          if (vp != NULL) {
                  /*
                   * If we are returning locked (called via uipc_sosend_dgram()),
                   * we need to be sure that vput() won't sleep.  This is
                   * guaranteed by VOP_UNP_CONNECT() call above and unp2 lock.
                   * SOCK_STREAM/SEQPACKET can't request return_locked (yet).
                   */
                  MPASS(!(return_locked && connreq));
                  vput(vp);
          }
          free(sa, M_SONAME);
          if (__predict_false(error)) {
                  UNP_PCB_LOCK(unp);
                  KASSERT((unp->unp_flags & UNP_CONNECTING) != 0,
                      ("%s: unp %p has UNP_CONNECTING clear", __func__, unp));
                  unp->unp_flags &= ~UNP_CONNECTING;
                  UNP_PCB_UNLOCK(unp);
          }
          return (error);
  }
  
  /*
   * Set socket peer credentials at connection time.
   *
   * The client's PCB credentials are copied from its process structure.  The
   * server's PCB credentials are copied from the socket on which it called
   * listen(2).  uipc_listen cached that process's credentials at the time.
   */
  void
  unp_copy_peercred(struct thread *td, struct unpcb *client_unp,
      struct unpcb *server_unp, struct unpcb *listen_unp)
  {
          cru2xt(td, &client_unp->unp_peercred);
          client_unp->unp_flags |= UNP_HAVEPC;
  
          memcpy(&server_unp->unp_peercred, &listen_unp->unp_peercred,
              sizeof(server_unp->unp_peercred));
          server_unp->unp_flags |= UNP_HAVEPC;
          client_unp->unp_flags |= (listen_unp->unp_flags & UNP_WANTCRED_MASK);
  }
  
  static void
  unp_connect2(struct socket *so, struct socket *so2, conn2_how req)
  {
          struct unpcb *unp;
          struct unpcb *unp2;
  
          MPASS(so2->so_type == so->so_type);
          unp = sotounpcb(so);
          KASSERT(unp != NULL, ("unp_connect2: unp == NULL"));
          unp2 = sotounpcb(so2);
          KASSERT(unp2 != NULL, ("unp_connect2: unp2 == NULL"));
  
          UNP_PCB_LOCK_ASSERT(unp);
          UNP_PCB_LOCK_ASSERT(unp2);
          KASSERT(unp->unp_conn == NULL,
              ("%s: socket %p is already connected", __func__, unp));
  
          unp->unp_conn = unp2;
          unp_pcb_hold(unp2);
          unp_pcb_hold(unp);
          switch (so->so_type) {
          case SOCK_DGRAM:
                  UNP_REF_LIST_LOCK();
                  LIST_INSERT_HEAD(&unp2->unp_refs, unp, unp_reflink);
                  UNP_REF_LIST_UNLOCK();
                  soisconnected(so);
                  break;
  
          case SOCK_STREAM:
          case SOCK_SEQPACKET:
                  KASSERT(unp2->unp_conn == NULL,
                      ("%s: socket %p is already connected", __func__, unp2));
                  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");
          }
  }
  
  static void
  unp_disconnect(struct unpcb *unp, struct unpcb *unp2)
  {
          struct socket *so, *so2;
          struct mbuf *m = NULL;
  #ifdef INVARIANTS
          struct unpcb *unptmp;
  #endif
  
          UNP_PCB_LOCK_ASSERT(unp);
          UNP_PCB_LOCK_ASSERT(unp2);
          KASSERT(unp->unp_conn == unp2,
              ("%s: unpcb %p is not connected to %p", __func__, unp, unp2));
  
          unp->unp_conn = NULL;
          so = unp->unp_socket;
          so2 = unp2->unp_socket;
          switch (unp->unp_socket->so_type) {
          case SOCK_DGRAM:
                  /*
                   * Remove our send socket buffer from the peer's receive buffer.
                   * Move the data to the receive buffer only if it is empty.
                   * This is a protection against a scenario where a peer
                   * connects, floods and disconnects, effectively blocking
                   * sendto() from unconnected sockets.
                   */
                  SOCK_RECVBUF_LOCK(so2);
                  if (!STAILQ_EMPTY(&so->so_snd.uxdg_mb)) {
                          TAILQ_REMOVE(&so2->so_rcv.uxdg_conns, &so->so_snd,
                              uxdg_clist);
                          if (__predict_true((so2->so_rcv.sb_state &
                              SBS_CANTRCVMORE) == 0) &&
                              STAILQ_EMPTY(&so2->so_rcv.uxdg_mb)) {
                                  STAILQ_CONCAT(&so2->so_rcv.uxdg_mb,
                                      &so->so_snd.uxdg_mb);
                                  so2->so_rcv.uxdg_cc += so->so_snd.uxdg_cc;
                                  so2->so_rcv.uxdg_ctl += so->so_snd.uxdg_ctl;
                                  so2->so_rcv.uxdg_mbcnt += so->so_snd.uxdg_mbcnt;
                          } else {
                                  m = STAILQ_FIRST(&so->so_snd.uxdg_mb);
                                  STAILQ_INIT(&so->so_snd.uxdg_mb);
                                  so2->so_rcv.sb_acc -= so->so_snd.uxdg_cc;
                                  so2->so_rcv.sb_ccc -= so->so_snd.uxdg_cc;
                                  so2->so_rcv.sb_ctl -= so->so_snd.uxdg_ctl;
                                  so2->so_rcv.sb_mbcnt -= so->so_snd.uxdg_mbcnt;
                          }
                          /* Note: so may reconnect. */
                          so->so_snd.uxdg_cc = 0;
                          so->so_snd.uxdg_ctl = 0;
                          so->so_snd.uxdg_mbcnt = 0;
                  }
                  SOCK_RECVBUF_UNLOCK(so2);
                  UNP_REF_LIST_LOCK();
  #ifdef INVARIANTS
                  LIST_FOREACH(unptmp, &unp2->unp_refs, unp_reflink) {
                          if (unptmp == unp)
                                  break;
                  }
                  KASSERT(unptmp != NULL,
                      ("%s: %p not found in reflist of %p", __func__, unp, unp2));
  #endif
                  LIST_REMOVE(unp, unp_reflink);
                  UNP_REF_LIST_UNLOCK();
                  if (so) {
                          SOCK_LOCK(so);
                          so->so_state &= ~SS_ISCONNECTED;
                          SOCK_UNLOCK(so);
                  }
                  break;
  
          case SOCK_STREAM:
          case SOCK_SEQPACKET:
                  if (so)
                          soisdisconnected(so);
                  MPASS(unp2->unp_conn == unp);
                  unp2->unp_conn = NULL;
                  if (so2)
                          soisdisconnected(so2);
                  break;
          }
  
          if (unp == unp2) {
                  unp_pcb_rele_notlast(unp);
                  if (!unp_pcb_rele(unp))
                          UNP_PCB_UNLOCK(unp);
          } else {
                  if (!unp_pcb_rele(unp))
                          UNP_PCB_UNLOCK(unp);
                  if (!unp_pcb_rele(unp2))
                          UNP_PCB_UNLOCK(unp2);
          }
  
          if (m != NULL) {
                  unp_scan(m, unp_freerights);
                  m_freem(m);
          }
  }
  
  /*
   * 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)
  {
          struct unpcb *unp, **unp_list;
          unp_gen_t gencnt;
          struct xunpgen *xug;
          struct unp_head *head;
          struct xunpcb *xu;
          u_int i;
          int error, n;
  
          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 | M_ZERO);
          UNP_LINK_RLOCK();
          gencnt = unp_gencnt;
          n = unp_count;
          UNP_LINK_RUNLOCK();
  
          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_LINK_RLOCK();
          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_pcb_hold(unp);
                  }
                  UNP_PCB_UNLOCK(unp);
          }
          UNP_LINK_RUNLOCK();
          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);
                  if (unp_pcb_rele(unp))
                          continue;
  
                  if (unp->unp_gencnt <= gencnt) {
                          xu->xu_len = sizeof *xu;
                          xu->xu_unpp = (uintptr_t)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);
                          else
                                  bzero(&xu->xu_addr, sizeof(xu->xu_addr));
                          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);
                          else
                                  bzero(&xu->xu_caddr, sizeof(xu->xu_caddr));
                          xu->unp_vnode = (uintptr_t)unp->unp_vnode;
                          xu->unp_conn = (uintptr_t)unp->unp_conn;
                          xu->xu_firstref = (uintptr_t)LIST_FIRST(&unp->unp_refs);
                          xu->xu_nextref = (uintptr_t)LIST_NEXT(unp, unp_reflink);
                          xu->unp_gencnt = unp->unp_gencnt;
                          sotoxsocket(unp->unp_socket, &xu->xu_socket);
                          UNP_PCB_UNLOCK(unp);
                          error = SYSCTL_OUT(req, xu, sizeof *xu);
                  } else {
                          UNP_PCB_UNLOCK(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 | CTLFLAG_MPSAFE,
      (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 | CTLFLAG_MPSAFE,
      (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 | CTLFLAG_MPSAFE,
      (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_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;
          struct unpcb *unp2;
  
          /*
           * Regardless of whether the socket's peer dropped the connection
           * with this socket by aborting or disconnecting, POSIX requires
           * that ECONNRESET is returned.
           */
  
          UNP_PCB_LOCK(unp);
          so = unp->unp_socket;
          if (so)
                  so->so_error = ECONNRESET;
          if ((unp2 = unp_pcb_lock_peer(unp)) != NULL) {
                  /* Last reference dropped in unp_disconnect(). */
                  unp_pcb_rele_notlast(unp);
                  unp_disconnect(unp, unp2);
          } else if (!unp_pcb_rele(unp)) {
                  UNP_PCB_UNLOCK(unp);
          }
  }
  
  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) {
                  MPASS(clen >= sizeof(*cm) && clen >= cm->cmsg_len);
  
                  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, M_WAITOK);
  
                          fdp = (int *)
                              CMSG_DATA(mtod(*controlp, struct cmsghdr *));
                          if ((error = fdallocn(td, 0, fdp, newfds))) {
                                  FILEDESC_XUNLOCK(fdesc);
                                  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 ? O_CLOEXEC : 0,
                                      &fdep[i]->fde_caps);
                                  unp_externalize_fp(fdep[i]->fde_file);
                          }
  
                          /*
                           * The new type indicates that the mbuf data refers to
                           * kernel resources that may need to be released before
                           * the mbuf is freed.
                           */
                          m_chtype(*controlp, MT_EXTCONTROL);
                          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, M_WAITOK);
                          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);
  }
  
  #ifdef INVARIANTS
  static void
  unp_zdtor(void *mem, int size __unused, void *arg __unused)
  {
          struct unpcb *unp;
  
          unp = mem;
  
          KASSERT(LIST_EMPTY(&unp->unp_refs),
              ("%s: unpcb %p has lingering refs", __func__, unp));
          KASSERT(unp->unp_socket == NULL,
              ("%s: unpcb %p has socket backpointer", __func__, unp));
          KASSERT(unp->unp_vnode == NULL,
              ("%s: unpcb %p has vnode references", __func__, unp));
          KASSERT(unp->unp_conn == NULL,
              ("%s: unpcb %p is still connected", __func__, unp));
          KASSERT(unp->unp_addr == NULL,
              ("%s: unpcb %p has leaked addr", __func__, unp));
  }
  #endif
  
  static void
  unp_init(void *arg __unused)
  {
          uma_dtor dtor;
  
  #ifdef INVARIANTS
          dtor = unp_zdtor;
  #else
          dtor = NULL;
  #endif
          unp_zone = uma_zcreate("unpcb", sizeof(struct unpcb), NULL, dtor,
              NULL, NULL, UMA_ALIGN_CACHE, 0);
          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_DEFERRED_LOCK_INIT();
  }
  SYSINIT(unp_init, SI_SUB_PROTO_DOMAIN, SI_ORDER_SECOND, unp_init, NULL);
  
  static void
  unp_internalize_cleanup_rights(struct mbuf *control)
  {
          struct cmsghdr *cp;
          struct mbuf *m;
          void *data;
          socklen_t datalen;
  
          for (m = control; m != NULL; m = m->m_next) {
                  cp = mtod(m, struct cmsghdr *);
                  if (cp->cmsg_level != SOL_SOCKET ||
                      cp->cmsg_type != SCM_RIGHTS)
                          continue;
                  data = CMSG_DATA(cp);
                  datalen = (caddr_t)cp + cp->cmsg_len - (caddr_t)data;
                  unp_freerights(data, datalen / sizeof(struct filedesc *));
          }
  }
  
  static int
  unp_internalize(struct mbuf **controlp, struct thread *td,
      struct mbuf **clast, u_int *space, u_int *mbcnt)
  {
          struct mbuf *control, **initial_controlp;
          struct proc *p;
          struct filedesc *fdesc;
          struct bintime *bt;
          struct cmsghdr *cm;
          struct cmsgcred *cmcred;
          struct filedescent *fde, **fdep, *fdev;
          struct file *fp;
          struct timeval *tv;
          struct timespec *ts;
          void *data;
          socklen_t clen, datalen;
          int i, j, error, *fdp, oldfds;
          u_int newlen;
  
          MPASS((*controlp)->m_next == NULL); /* COMPAT_OLDSOCK may violate */
          UNP_LINK_UNLOCK_ASSERT();
  
          p = td->td_proc;
          fdesc = p->p_fd;
          error = 0;
          control = *controlp;
          *controlp = NULL;
          initial_controlp = controlp;
          for (clen = control->m_len, cm = mtod(control, struct cmsghdr *),
              data = CMSG_DATA(cm);
  
              clen >= sizeof(*cm) && cm->cmsg_level == SOL_SOCKET &&
              clen >= cm->cmsg_len && cm->cmsg_len >= sizeof(*cm) &&
              (char *)cm + cm->cmsg_len >= (char *)data;
  
              clen -= min(CMSG_SPACE(datalen), clen),
              cm = (struct cmsghdr *) ((char *)cm + CMSG_SPACE(datalen)),
              data = CMSG_DATA(cm)) {
                  datalen = (char *)cm + cm->cmsg_len - (char *)data;
                  switch (cm->cmsg_type) {
                  case SCM_CREDS:
                          *controlp = sbcreatecontrol(NULL, sizeof(*cmcred),
                              SCM_CREDS, SOL_SOCKET, M_WAITOK);
                          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)
                                  continue;
                          /* On some machines sizeof pointer is bigger than
                           * sizeof int, so we need to check if data fits into
                           * single mbuf.  We could allocate several mbufs, and
                           * unp_externalize() should even properly handle that.
                           * But it is not worth to complicate the code for an
                           * insane scenario of passing over 200 file descriptors
                           * at once.
                           */
                          newlen = oldfds * sizeof(fdep[0]);
                          if (CMSG_SPACE(newlen) > MCLBYTES) {
                                  error = EMSGSIZE;
                                  goto out;
                          }
                          /*
                           * 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_noref(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.
                           */
                          *controlp = sbcreatecontrol(NULL, newlen,
                              SCM_RIGHTS, SOL_SOCKET, M_WAITOK);
                          fdp = data;
                          for (i = 0; i < oldfds; i++, fdp++) {
                                  if (!fhold(fdesc->fd_ofiles[*fdp].fde_file)) {
                                          fdp = data;
                                          for (j = 0; j < i; j++, fdp++) {
                                                  fdrop(fdesc->fd_ofiles[*fdp].
                                                      fde_file, td);
                                          }
                                          FILEDESC_SUNLOCK(fdesc);
                                          error = EBADF;
                                          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, M_WAITOK);
                          tv = (struct timeval *)
                              CMSG_DATA(mtod(*controlp, struct cmsghdr *));
                          microtime(tv);
                          break;
  
                  case SCM_BINTIME:
                          *controlp = sbcreatecontrol(NULL, sizeof(*bt),
                              SCM_BINTIME, SOL_SOCKET, M_WAITOK);
                          bt = (struct bintime *)
                              CMSG_DATA(mtod(*controlp, struct cmsghdr *));
                          bintime(bt);
                          break;
  
                  case SCM_REALTIME:
                          *controlp = sbcreatecontrol(NULL, sizeof(*ts),
                              SCM_REALTIME, SOL_SOCKET, M_WAITOK);
                          ts = (struct timespec *)
                              CMSG_DATA(mtod(*controlp, struct cmsghdr *));
                          nanotime(ts);
                          break;
  
                  case SCM_MONOTONIC:
                          *controlp = sbcreatecontrol(NULL, sizeof(*ts),
                              SCM_MONOTONIC, SOL_SOCKET, M_WAITOK);
                          ts = (struct timespec *)
                              CMSG_DATA(mtod(*controlp, struct cmsghdr *));
                          nanouptime(ts);
                          break;
  
                  default:
                          error = EINVAL;
                          goto out;
                  }
  
                  if (space != NULL) {
                          *space += (*controlp)->m_len;
                          *mbcnt += MSIZE;
                          if ((*controlp)->m_flags & M_EXT)
                                  *mbcnt += (*controlp)->m_ext.ext_size;
                          *clast = *controlp;
                  }
                  controlp = &(*controlp)->m_next;
          }
          if (clen > 0)
                  error = EINVAL;
  
  out:
          if (error != 0 && initial_controlp != NULL)
                  unp_internalize_cleanup_rights(*initial_controlp);
          m_freem(control);
          return (error);
  }
  
  static struct mbuf *
  unp_addsockcred(struct thread *td, struct mbuf *control, int mode,
      struct mbuf **clast, u_int *space, u_int *mbcnt)
  {
          struct mbuf *m, *n, *n_prev;
          const struct cmsghdr *cm;
          int ngroups, i, cmsgtype;
          size_t ctrlsz;
  
          ngroups = MIN(td->td_ucred->cr_ngroups, CMGROUP_MAX);
          if (mode & UNP_WANTCRED_ALWAYS) {
                  ctrlsz = SOCKCRED2SIZE(ngroups);
                  cmsgtype = SCM_CREDS2;
          } else {
                  ctrlsz = SOCKCREDSIZE(ngroups);
                  cmsgtype = SCM_CREDS;
          }
  
          m = sbcreatecontrol(NULL, ctrlsz, cmsgtype, SOL_SOCKET, M_NOWAIT);
          if (m == NULL)
                  return (control);
          MPASS((m->m_flags & M_EXT) == 0 && m->m_next == NULL);
  
          if (mode & UNP_WANTCRED_ALWAYS) {
                  struct sockcred2 *sc;
  
                  sc = (void *)CMSG_DATA(mtod(m, struct cmsghdr *));
                  sc->sc_version = 0;
                  sc->sc_pid = td->td_proc->p_pid;
                  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];
          } else {
                  struct sockcred *sc;
  
                  sc = (void *)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 && cmsgtype == SCM_CREDS)
                  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;
                                  if (space != NULL) {
                                          MPASS(*space >= n->m_len);
                                          *space -= n->m_len;
                                          MPASS(*mbcnt >= MSIZE);
                                          *mbcnt -= MSIZE;
                                          if (n->m_flags & M_EXT) {
                                                  MPASS(*mbcnt >=
                                                      n->m_ext.ext_size);
                                                  *mbcnt -= n->m_ext.ext_size;
                                          }
                                          MPASS(clast);
                                          if (*clast == n) {
                                                  MPASS(n->m_next == NULL);
                                                  if (n_prev == NULL)
                                                          *clast = m;
                                                  else
                                                          *clast = n_prev;
                                          }
                                  }
                                  n = m_free(n);
                          } else {
                                  n_prev = n;
                                  n = n->m_next;
                          }
                  }
  
          /* Prepend it to the head. */
          m->m_next = control;
          if (space != NULL) {
                  *space += m->m_len;
                  *mbcnt += MSIZE;
                  if (control == NULL)
                          *clast = m;
          }
          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
                  closef_nothread(fp);
  }
  
  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_nothread(dr->ud_fp);
                          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++;
          }
          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 void
  unp_remove_dead_ref(struct filedescent **fdep, int fdcount)
  {
          struct unpcb *unp;
          struct file *fp;
          int i;
  
          /*
           * This function can only be called from the gc task.
           */
          KASSERT(taskqueue_member(taskqueue_thread, curthread) != 0,
              ("%s: not on gc callout", __func__));
          UNP_LINK_LOCK_ASSERT();
  
          for (i = 0; i < fdcount; i++) {
                  fp = fdep[i]->fde_file;
                  if ((unp = fptounp(fp)) == NULL)
                          continue;
                  if ((unp->unp_gcflag & UNPGC_DEAD) == 0)
                          continue;
                  unp->unp_gcrefs--;
          }
  }
  
  static void
  unp_restore_undead_ref(struct filedescent **fdep, int fdcount)
  {
          struct unpcb *unp;
          struct file *fp;
          int i;
  
          /*
           * This function can only be called from the gc task.
           */
          KASSERT(taskqueue_member(taskqueue_thread, curthread) != 0,
              ("%s: not on gc callout", __func__));
          UNP_LINK_LOCK_ASSERT();
  
          for (i = 0; i < fdcount; i++) {
                  fp = fdep[i]->fde_file;
                  if ((unp = fptounp(fp)) == NULL)
                          continue;
                  if ((unp->unp_gcflag & UNPGC_DEAD) == 0)
                          continue;
                  unp->unp_gcrefs++;
                  unp_marked++;
          }
  }
  
  static void
  unp_scan_socket(struct socket *so, void (*op)(struct filedescent **, int))
  {
          struct sockbuf *sb;
  
          SOCK_LOCK_ASSERT(so);
  
          if (sotounpcb(so)->unp_gcflag & UNPGC_IGNORE_RIGHTS)
                  return;
  
          SOCK_RECVBUF_LOCK(so);
          switch (so->so_type) {
          case SOCK_DGRAM:
                  unp_scan(STAILQ_FIRST(&so->so_rcv.uxdg_mb), op);
                  unp_scan(so->so_rcv.uxdg_peeked, op);
                  TAILQ_FOREACH(sb, &so->so_rcv.uxdg_conns, uxdg_clist)
                          unp_scan(STAILQ_FIRST(&sb->uxdg_mb), op);
                  break;
          case SOCK_STREAM:
          case SOCK_SEQPACKET:
                  unp_scan(so->so_rcv.sb_mb, op);
                  break;
          }
          SOCK_RECVBUF_UNLOCK(so);
  }
  
  static void
  unp_gc_scan(struct unpcb *unp, void (*op)(struct filedescent **, int))
  {
          struct socket *so, *soa;
  
          so = unp->unp_socket;
          SOCK_LOCK(so);
          if (SOLISTENING(so)) {
                  /*
                   * Mark all sockets in our accept queue.
                   */
                  TAILQ_FOREACH(soa, &so->sol_comp, so_list)
                          unp_scan_socket(soa, op);
          } else {
                  /*
                   * Mark all sockets we reference with RIGHTS.
                   */
                  unp_scan_socket(so, op);
          }
          SOCK_UNLOCK(so);
  }
  
  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.");
  
  SYSCTL_UINT(_net_local, OID_AUTO, sockcount, CTLFLAG_RD, &unp_count, 0, 
      "Number of active local sockets.");
  
  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 unp_head unp_deadhead;   /* List of potentially-dead sockets. */
          struct file *f, **unref;
          struct unpcb *unp, *unptmp;
          int i, total, unp_unreachable;
  
          LIST_INIT(&unp_deadhead);
          unp_taskcount++;
          UNP_LINK_RLOCK();
          /*
           * First determine which sockets may be in cycles.
           */
          unp_unreachable = 0;
  
          for (head = heads; *head != NULL; head++)
                  LIST_FOREACH(unp, *head, unp_link) {
                          KASSERT((unp->unp_gcflag & ~UNPGC_IGNORE_RIGHTS) == 0,
                              ("%s: unp %p has unexpected gc flags 0x%x",
                              __func__, unp, (unsigned int)unp->unp_gcflag));
  
                          f = unp->unp_file;
  
                          /*
                           * Check for an unreachable 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 (f != NULL && unp->unp_msgcount != 0 &&
                              refcount_load(&f->f_count) == unp->unp_msgcount) {
                                  LIST_INSERT_HEAD(&unp_deadhead, unp, unp_dead);
                                  unp->unp_gcflag |= UNPGC_DEAD;
                                  unp->unp_gcrefs = unp->unp_msgcount;
                                  unp_unreachable++;
                          }
                  }
  
          /*
           * Scan all sockets previously marked as potentially being in a cycle
           * and remove the references each socket holds on any UNPGC_DEAD
           * sockets in its queue.  After this step, all remaining references on
           * sockets marked UNPGC_DEAD should not be part of any cycle.
           */
          LIST_FOREACH(unp, &unp_deadhead, unp_dead)
                  unp_gc_scan(unp, unp_remove_dead_ref);
  
          /*
           * If a socket still has a non-negative refcount, it cannot be in a
           * cycle.  In this case increment refcount of all children iteratively.
           * Stop the scan once we do a complete loop without discovering
           * a new reachable socket.
           */
          do {
                  unp_marked = 0;
                  LIST_FOREACH_SAFE(unp, &unp_deadhead, unp_dead, unptmp)
                          if (unp->unp_gcrefs > 0) {
                                  unp->unp_gcflag &= ~UNPGC_DEAD;
                                  LIST_REMOVE(unp, unp_dead);
                                  KASSERT(unp_unreachable > 0,
                                      ("%s: unp_unreachable underflow.",
                                      __func__));
                                  unp_unreachable--;
                                  unp_gc_scan(unp, unp_restore_undead_ref);
                          }
          } while (unp_marked);
  
          UNP_LINK_RUNLOCK();
  
          if (unp_unreachable == 0)
                  return;
  
          /*
           * Allocate space for a local array of dead unpcbs.
           * TODO: can this path be simplified by instead using the local
           * dead list at unp_deadhead, after taking out references
           * on the file object and/or unpcb and dropping the link lock?
           */
          unref = malloc(unp_unreachable * sizeof(struct file *),
              M_TEMP, M_WAITOK);
  
          /*
           * Iterate looking for sockets which have been specifically marked
           * as unreachable and store them locally.
           */
          UNP_LINK_RLOCK();
          total = 0;
          LIST_FOREACH(unp, &unp_deadhead, unp_dead) {
                  KASSERT((unp->unp_gcflag & UNPGC_DEAD) != 0,
                      ("%s: unp %p not marked UNPGC_DEAD", __func__, unp));
                  unp->unp_gcflag &= ~UNPGC_DEAD;
                  f = unp->unp_file;
                  if (unp->unp_msgcount == 0 || f == NULL ||
                      refcount_load(&f->f_count) != unp->unp_msgcount ||
                      !fhold(f))
                          continue;
                  unref[total++] = f;
                  KASSERT(total <= unp_unreachable,
                      ("%s: incorrect unreachable count.", __func__));
          }
          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);
  }
  
  /*
   * Synchronize against unp_gc, which can trip over data as we are freeing it.
   */
  static void
  unp_dispose(struct socket *so)
  {
          struct sockbuf *sb;
          struct unpcb *unp;
          struct mbuf *m;
  
          MPASS(!SOLISTENING(so));
  
          unp = sotounpcb(so);
          UNP_LINK_WLOCK();
          unp->unp_gcflag |= UNPGC_IGNORE_RIGHTS;
          UNP_LINK_WUNLOCK();
  
          /*
           * Grab our special mbufs before calling sbrelease().
           */
          SOCK_RECVBUF_LOCK(so);
          switch (so->so_type) {
          case SOCK_DGRAM:
                  while ((sb = TAILQ_FIRST(&so->so_rcv.uxdg_conns)) != NULL) {
                          STAILQ_CONCAT(&so->so_rcv.uxdg_mb, &sb->uxdg_mb);
                          TAILQ_REMOVE(&so->so_rcv.uxdg_conns, sb, uxdg_clist);
                          /* Note: socket of sb may reconnect. */
                          sb->uxdg_cc = sb->uxdg_ctl = sb->uxdg_mbcnt = 0;
                  }
                  sb = &so->so_rcv;
                  if (sb->uxdg_peeked != NULL) {
                          STAILQ_INSERT_HEAD(&sb->uxdg_mb, sb->uxdg_peeked,
                              m_stailqpkt);
                          sb->uxdg_peeked = NULL;
                  }
                  m = STAILQ_FIRST(&sb->uxdg_mb);
                  STAILQ_INIT(&sb->uxdg_mb);
                  /* XXX: our shortened sbrelease() */
                  (void)chgsbsize(so->so_cred->cr_uidinfo, &sb->sb_hiwat, 0,
                      RLIM_INFINITY);
                  /*
                   * XXXGL Mark sb with SBS_CANTRCVMORE.  This is needed to
                   * prevent uipc_sosend_dgram() or unp_disconnect() adding more
                   * data to the socket.
                   * We are now in dom_dispose and it could be a call from
                   * soshutdown() or from the final sofree().  The sofree() case
                   * is simple as it guarantees that no more sends will happen,
                   * however we can race with unp_disconnect() from our peer.
                   * The shutdown(2) case is more exotic.  It would call into
                   * dom_dispose() only if socket is SS_ISCONNECTED.  This is
                   * possible if we did connect(2) on this socket and we also
                   * had it bound with bind(2) and receive connections from other
                   * sockets.  Because soshutdown() violates POSIX (see comment
                   * there) we will end up here shutting down our receive side.
                   * Of course this will have affect not only on the peer we
                   * connect(2)ed to, but also on all of the peers who had
                   * connect(2)ed to us.  Their sends would end up with ENOBUFS.
                   */
                  sb->sb_state |= SBS_CANTRCVMORE;
                  break;
          case SOCK_STREAM:
          case SOCK_SEQPACKET:
                  sb = &so->so_rcv;
                  m = sbcut_locked(sb, sb->sb_ccc);
                  KASSERT(sb->sb_ccc == 0 && sb->sb_mb == 0 && sb->sb_mbcnt == 0,
                      ("%s: ccc %u mb %p mbcnt %u", __func__,
                      sb->sb_ccc, (void *)sb->sb_mb, sb->sb_mbcnt));
                  sbrelease_locked(so, SO_RCV);
                  break;
          }
          SOCK_RECVBUF_UNLOCK(so);
          if (SOCK_IO_RECV_OWNED(so))
                  SOCK_IO_RECV_UNLOCK(so);
  
          if (m != NULL) {
                  unp_scan(m, unp_freerights);
                  m_freem(m);
          }
  }
  
  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;
          }
  }
  
  /*
   * Definitions of protocols supported in the LOCAL domain.
   */
  static struct protosw streamproto = {
          .pr_type =              SOCK_STREAM,
          .pr_flags =             PR_CONNREQUIRED|PR_WANTRCVD|PR_RIGHTS|
                                      PR_CAPATTACH,
          .pr_ctloutput =         &uipc_ctloutput,
          .pr_abort =             uipc_abort,
          .pr_accept =            uipc_accept,
          .pr_attach =            uipc_attach,
          .pr_bind =              uipc_bind,
          .pr_bindat =            uipc_bindat,
          .pr_connect =           uipc_connect,
          .pr_connectat =         uipc_connectat,
          .pr_connect2 =          uipc_connect2,
          .pr_detach =            uipc_detach,
          .pr_disconnect =        uipc_disconnect,
          .pr_listen =            uipc_listen,
          .pr_peeraddr =          uipc_peeraddr,
          .pr_rcvd =              uipc_rcvd,
          .pr_send =              uipc_send,
          .pr_ready =             uipc_ready,
          .pr_sense =             uipc_sense,
          .pr_shutdown =          uipc_shutdown,
          .pr_sockaddr =          uipc_sockaddr,
          .pr_soreceive =         soreceive_generic,
          .pr_close =             uipc_close,
  };
  
  static struct protosw dgramproto = {
          .pr_type =              SOCK_DGRAM,
          .pr_flags =             PR_ATOMIC | PR_ADDR |PR_RIGHTS | PR_CAPATTACH |
                                      PR_SOCKBUF,
          .pr_ctloutput =         &uipc_ctloutput,
          .pr_abort =             uipc_abort,
          .pr_accept =            uipc_accept,
          .pr_attach =            uipc_attach,
          .pr_bind =              uipc_bind,
          .pr_bindat =            uipc_bindat,
          .pr_connect =           uipc_connect,
          .pr_connectat =         uipc_connectat,
          .pr_connect2 =          uipc_connect2,
          .pr_detach =            uipc_detach,
          .pr_disconnect =        uipc_disconnect,
          .pr_peeraddr =          uipc_peeraddr,
          .pr_sosend =            uipc_sosend_dgram,
          .pr_sense =             uipc_sense,
          .pr_shutdown =          uipc_shutdown,
          .pr_sockaddr =          uipc_sockaddr,
          .pr_soreceive =         uipc_soreceive_dgram,
          .pr_close =             uipc_close,
  };
  
  static struct protosw seqpacketproto = {
          .pr_type =              SOCK_SEQPACKET,
          /*
           * 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_CAPATTACH,
          .pr_ctloutput =         &uipc_ctloutput,
          .pr_abort =             uipc_abort,
          .pr_accept =            uipc_accept,
          .pr_attach =            uipc_attach,
          .pr_bind =              uipc_bind,
          .pr_bindat =            uipc_bindat,
          .pr_connect =           uipc_connect,
          .pr_connectat =         uipc_connectat,
          .pr_connect2 =          uipc_connect2,
          .pr_detach =            uipc_detach,
          .pr_disconnect =        uipc_disconnect,
          .pr_listen =            uipc_listen,
          .pr_peeraddr =          uipc_peeraddr,
          .pr_rcvd =              uipc_rcvd,
          .pr_send =              uipc_send,
          .pr_sense =             uipc_sense,
          .pr_shutdown =          uipc_shutdown,
          .pr_sockaddr =          uipc_sockaddr,
          .pr_soreceive =         soreceive_generic,      /* XXX: or...? */
          .pr_close =             uipc_close,
  };
  
  static struct domain localdomain = {
          .dom_family =           AF_LOCAL,
          .dom_name =             "local",
          .dom_externalize =      unp_externalize,
          .dom_dispose =          unp_dispose,
          .dom_nprotosw =         3,
          .dom_protosw =          {
                  &streamproto,
                  &dgramproto,
                  &seqpacketproto,
          }
  };
  DOMAIN_SET(local);
  
  /*
   * 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 unpcb *unp;
          int active;
          struct mtx *vplock;
  
          ASSERT_VOP_ELOCKED(vp, "vfs_unp_reclaim");
          KASSERT(vp->v_type == VSOCK,
              ("vfs_unp_reclaim: vp->v_type != VSOCK"));
  
          active = 0;
          vplock = mtx_pool_find(mtxpool_sleep, vp);
          mtx_lock(vplock);
          VOP_UNP_CONNECT(vp, &unp);
          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:
          mtx_unlock(vplock);
          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_WANTCRED_ALWAYS) {
                  db_printf("%sUNP_WANTCRED_ALWAYS", comma ? ", " : "");
                  comma = 1;
          }
          if (unp_flags & UNP_WANTCRED_ONESHOT) {
                  db_printf("%sUNP_WANTCRED_ONESHOT", 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_pid: %d   cr_ngroups: %d\n",
              xu->cr_version, xu->cr_uid, xu->cr_pid, 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