accept: Save foreign address earlier, if protocol supports it

[dragonfly.git] / sys / kern / uipc_socket2.c

/*
 * Copyright (c) 2005 Jeffrey M. Hsu.  All rights reserved.
 * Copyright (c) 1982, 1986, 1988, 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. 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.
 *
 *      @(#)uipc_socket2.c      8.1 (Berkeley) 6/10/93
 * $FreeBSD: src/sys/kern/uipc_socket2.c,v 1.55.2.17 2002/08/31 19:04:55 dwmalone Exp $
 * $DragonFly: src/sys/kern/uipc_socket2.c,v 1.33 2008/09/02 16:17:52 dillon Exp $
 */

#include "opt_param.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/domain.h>
#include <sys/file.h>   /* for maxfiles */
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/resourcevar.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/socketops.h>
#include <sys/signalvar.h>
#include <sys/sysctl.h>
#include <sys/event.h>

#include <sys/thread2.h>
#include <sys/msgport2.h>
#include <sys/socketvar2.h>

int     maxsockets;

/*
 * Primitive routines for operating on sockets and socket buffers
 */

u_long  sb_max = SB_MAX;
u_long  sb_max_adj =
    SB_MAX * MCLBYTES / (MSIZE + MCLBYTES); /* adjusted sb_max */

static  u_long sb_efficiency = 8;       /* parameter for sbreserve() */

/************************************************************************
 * signalsockbuf procedures                                             *
 ************************************************************************/

/*
 * Wait for data to arrive at/drain from a socket buffer.
 *
 * NOTE: Caller must generally hold the ssb_lock (client side lock) since
 *       WAIT/WAKEUP only works for one client at a time.
 *
 * NOTE: Caller always retries whatever operation it was waiting on.
 */
int
ssb_wait(struct signalsockbuf *ssb)
{
        uint32_t flags;
        int pflags;
        int error;

        pflags = (ssb->ssb_flags & SSB_NOINTR) ? 0 : PCATCH;

        for (;;) {
                flags = ssb->ssb_flags;
                cpu_ccfence();

                /*
                 * WAKEUP and WAIT interlock eachother.  We can catch the
                 * race by checking to see if WAKEUP has already been set,
                 * and only setting WAIT if WAKEUP is clear.
                 */
                if (flags & SSB_WAKEUP) {
                        if (atomic_cmpset_int(&ssb->ssb_flags, flags,
                                              flags & ~SSB_WAKEUP)) {
                                error = 0;
                                break;
                        }
                        continue;
                }

                /*
                 * Only set WAIT if WAKEUP is clear.
                 */
                tsleep_interlock(&ssb->ssb_cc, pflags);
                if (atomic_cmpset_int(&ssb->ssb_flags, flags,
                                      flags | SSB_WAIT)) {
                        error = tsleep(&ssb->ssb_cc, pflags | PINTERLOCKED,
                                       "sbwait", ssb->ssb_timeo);
                        break;
                }
        }
        return (error);
}

/*
 * Lock a sockbuf already known to be locked;
 * return any error returned from sleep (EINTR).
 */
int
_ssb_lock(struct signalsockbuf *ssb)
{
        uint32_t flags;
        int pflags;
        int error;

        pflags = (ssb->ssb_flags & SSB_NOINTR) ? 0 : PCATCH;

        for (;;) {
                flags = ssb->ssb_flags;
                cpu_ccfence();
                if (flags & SSB_LOCK) {
                        tsleep_interlock(&ssb->ssb_flags, pflags);
                        if (atomic_cmpset_int(&ssb->ssb_flags, flags,
                                              flags | SSB_WANT)) {
                                error = tsleep(&ssb->ssb_flags,
                                               pflags | PINTERLOCKED,
                                               "sblock", 0);
                                if (error)
                                        break;
                        }
                } else {
                        if (atomic_cmpset_int(&ssb->ssb_flags, flags,
                                              flags | SSB_LOCK)) {
                                lwkt_gettoken(&ssb->ssb_token);
                                error = 0;
                                break;
                        }
                }
        }
        return (error);
}

/*
 * This does the same for sockbufs.  Note that the xsockbuf structure,
 * since it is always embedded in a socket, does not include a self
 * pointer nor a length.  We make this entry point public in case
 * some other mechanism needs it.
 */
void
ssbtoxsockbuf(struct signalsockbuf *ssb, struct xsockbuf *xsb)
{
        xsb->sb_cc = ssb->ssb_cc;
        xsb->sb_hiwat = ssb->ssb_hiwat;
        xsb->sb_mbcnt = ssb->ssb_mbcnt;
        xsb->sb_mbmax = ssb->ssb_mbmax;
        xsb->sb_lowat = ssb->ssb_lowat;
        xsb->sb_flags = ssb->ssb_flags;
        xsb->sb_timeo = ssb->ssb_timeo;
}


/************************************************************************
 * Procedures which manipulate socket state flags, wakeups, etc.        *
 ************************************************************************
 *
 * Normal sequence from the active (originating) side is that
 * soisconnecting() is called during processing of connect() call, resulting
 * in an eventual call to soisconnected() if/when the connection is
 * established.  When the connection is torn down soisdisconnecting() is
 * called during processing of disconnect() call, and soisdisconnected() is
 * called when the connection to the peer is totally severed.
 *
 * The semantics of these routines are such that connectionless protocols
 * can call soisconnected() and soisdisconnected() only, bypassing the
 * in-progress calls when setting up a ``connection'' takes no time.
 *
 * From the passive side, a socket is created with two queues of sockets:
 * so_incomp for connections in progress and so_comp for connections
 * already made and awaiting user acceptance.  As a protocol is preparing
 * incoming connections, it creates a socket structure queued on so_incomp
 * by calling sonewconn().  When the connection is established,
 * soisconnected() is called, and transfers the socket structure to so_comp,
 * making it available to accept().
 *
 * If a socket is closed with sockets on either so_incomp or so_comp, these
 * sockets are dropped.
 *
 * If higher level protocols are implemented in the kernel, the wakeups
 * done here will sometimes cause software-interrupt process scheduling.
 */

void
soisconnecting(struct socket *so)
{
        soclrstate(so, SS_ISCONNECTED | SS_ISDISCONNECTING);
        sosetstate(so, SS_ISCONNECTING);
}

void
soisconnected(struct socket *so)
{
        struct socket *head;

        while ((head = so->so_head) != NULL) {
                lwkt_getpooltoken(head);
                if (so->so_head == head)
                        break;
                lwkt_relpooltoken(head);
        }

        soclrstate(so, SS_ISCONNECTING | SS_ISDISCONNECTING | SS_ISCONFIRMING);
        sosetstate(so, SS_ISCONNECTED);
        if (head && (so->so_state & SS_INCOMP)) {
                if ((so->so_options & SO_ACCEPTFILTER) != 0) {
                        so->so_upcall = head->so_accf->so_accept_filter->accf_callback;
                        so->so_upcallarg = head->so_accf->so_accept_filter_arg;
                        atomic_set_int(&so->so_rcv.ssb_flags, SSB_UPCALL);
                        so->so_options &= ~SO_ACCEPTFILTER;
                        so->so_upcall(so, so->so_upcallarg, 0);
                        lwkt_relpooltoken(head);
                        return;
                }

                /*
                 * Listen socket are not per-cpu.
                 */
                TAILQ_REMOVE(&head->so_incomp, so, so_list);
                head->so_incqlen--;
                TAILQ_INSERT_TAIL(&head->so_comp, so, so_list);
                head->so_qlen++;
                sosetstate(so, SS_COMP);
                soclrstate(so, SS_INCOMP);

                /*
                 * XXX head may be on a different protocol thread.
                 *     sorwakeup()->sowakeup() is hacked atm.
                 */
                sorwakeup(head);
                wakeup_one(&head->so_timeo);
        } else {
                wakeup(&so->so_timeo);
                sorwakeup(so);
                sowwakeup(so);
        }
        if (head)
                lwkt_relpooltoken(head);
}

void
soisdisconnecting(struct socket *so)
{
        soclrstate(so, SS_ISCONNECTING);
        sosetstate(so, SS_ISDISCONNECTING | SS_CANTRCVMORE | SS_CANTSENDMORE);
        wakeup((caddr_t)&so->so_timeo);
        sowwakeup(so);
        sorwakeup(so);
}

void
soisdisconnected(struct socket *so)
{
        soclrstate(so, SS_ISCONNECTING | SS_ISCONNECTED | SS_ISDISCONNECTING);
        sosetstate(so, SS_CANTRCVMORE | SS_CANTSENDMORE | SS_ISDISCONNECTED);
        wakeup((caddr_t)&so->so_timeo);
        sbdrop(&so->so_snd.sb, so->so_snd.ssb_cc);
        sowwakeup(so);
        sorwakeup(so);
}

void
soisreconnecting(struct socket *so)
{
        soclrstate(so, SS_ISDISCONNECTING | SS_ISDISCONNECTED |
                       SS_CANTRCVMORE | SS_CANTSENDMORE);
        sosetstate(so, SS_ISCONNECTING);
}

void
soisreconnected(struct socket *so)
{
        soclrstate(so, SS_ISDISCONNECTED | SS_CANTRCVMORE | SS_CANTSENDMORE);
        soisconnected(so);
}

/*
 * Set or change the message port a socket receives commands on.
 *
 * XXX
 */
void
sosetport(struct socket *so, lwkt_port_t port)
{
        so->so_port = port;
}

/*
 * When an attempt at a new connection is noted on a socket
 * which accepts connections, sonewconn is called.  If the
 * connection is possible (subject to space constraints, etc.)
 * then we allocate a new structure, propoerly linked into the
 * data structure of the original socket, and return this.
 * Connstatus may be 0, or SO_ISCONFIRMING, or SO_ISCONNECTED.
 *
 * The new socket is returned with one ref and so_pcb assigned.
 * The reference is implied by so_pcb.
 */
struct socket *
sonewconn_faddr(struct socket *head, int connstatus,
    const struct sockaddr *faddr)
{
        struct socket *so;
        struct socket *sp;
        struct pru_attach_info ai;

        if (head->so_qlen > 3 * head->so_qlimit / 2)
                return (NULL);
        so = soalloc(1);
        if (so == NULL)
                return (NULL);

        /*
         * Set the port prior to attaching the inpcb to the current
         * cpu's protocol thread (which should be the current thread
         * but might not be in all cases).  This serializes any pcb ops
         * which occur to our cpu allowing us to complete the attachment
         * without racing anything.
         */
        sosetport(so, cpu_portfn(mycpu->gd_cpuid));
        if ((head->so_options & SO_ACCEPTFILTER) != 0)
                connstatus = 0;
        so->so_head = head;
        so->so_type = head->so_type;
        so->so_options = head->so_options &~ SO_ACCEPTCONN;
        so->so_linger = head->so_linger;

        /*
         * NOTE: Clearing NOFDREF implies referencing the so with
         *       soreference().
         */
        so->so_state = head->so_state | SS_NOFDREF | SS_ASSERTINPROG;
        so->so_proto = head->so_proto;
        so->so_cred = crhold(head->so_cred);
        ai.sb_rlimit = NULL;
        ai.p_ucred = NULL;
        ai.fd_rdir = NULL;              /* jail code cruft XXX JH */

        /*
         * Reserve space and call pru_attach.  We can direct-call the
         * function since we're already in the protocol thread.
         */
        if (soreserve(so, head->so_snd.ssb_hiwat,
                      head->so_rcv.ssb_hiwat, NULL) ||
            so_pru_attach_direct(so, 0, &ai)) {
                so->so_head = NULL;
                soclrstate(so, SS_ASSERTINPROG);
                sofree(so);             /* remove implied pcb ref */
                return (NULL);
        }
        KKASSERT(so->so_refs == 2);     /* attach + our base ref */
        sofree(so);
        KKASSERT(so->so_port != NULL);
        so->so_rcv.ssb_lowat = head->so_rcv.ssb_lowat;
        so->so_snd.ssb_lowat = head->so_snd.ssb_lowat;
        so->so_rcv.ssb_timeo = head->so_rcv.ssb_timeo;
        so->so_snd.ssb_timeo = head->so_snd.ssb_timeo;

        if (head->so_rcv.ssb_flags & SSB_AUTOLOWAT)
                so->so_rcv.ssb_flags |= SSB_AUTOLOWAT;
        else
                so->so_rcv.ssb_flags &= ~SSB_AUTOLOWAT;

        if (head->so_snd.ssb_flags & SSB_AUTOLOWAT)
                so->so_snd.ssb_flags |= SSB_AUTOLOWAT;
        else
                so->so_snd.ssb_flags &= ~SSB_AUTOLOWAT;

        if (head->so_rcv.ssb_flags & SSB_AUTOSIZE)
                so->so_rcv.ssb_flags |= SSB_AUTOSIZE;
        else
                so->so_rcv.ssb_flags &= ~SSB_AUTOSIZE;

        if (head->so_snd.ssb_flags & SSB_AUTOSIZE)
                so->so_snd.ssb_flags |= SSB_AUTOSIZE;
        else
                so->so_snd.ssb_flags &= ~SSB_AUTOSIZE;

        /*
         * Save the faddr, if the information is provided and
         * the protocol can perform the saving opertation.
         */
        if (faddr != NULL && so->so_proto->pr_usrreqs->pru_savefaddr != NULL)
                so->so_proto->pr_usrreqs->pru_savefaddr(so, faddr);

        lwkt_getpooltoken(head);
        if (connstatus) {
                TAILQ_INSERT_TAIL(&head->so_comp, so, so_list);
                sosetstate(so, SS_COMP);
                head->so_qlen++;
        } else {
                if (head->so_incqlen > head->so_qlimit) {
                        sp = TAILQ_FIRST(&head->so_incomp);
                        TAILQ_REMOVE(&head->so_incomp, sp, so_list);
                        head->so_incqlen--;
                        soclrstate(sp, SS_INCOMP);
                        sp->so_head = NULL;
                        soaborta(sp);
                }
                TAILQ_INSERT_TAIL(&head->so_incomp, so, so_list);
                sosetstate(so, SS_INCOMP);
                head->so_incqlen++;
        }
        lwkt_relpooltoken(head);
        if (connstatus) {
                /*
                 * XXX head may be on a different protocol thread.
                 *     sorwakeup()->sowakeup() is hacked atm.
                 */
                sorwakeup(head);
                wakeup((caddr_t)&head->so_timeo);
                sosetstate(so, connstatus);
        }
        soclrstate(so, SS_ASSERTINPROG);
        return (so);
}

struct socket *
sonewconn(struct socket *head, int connstatus)
{
        return sonewconn_faddr(head, connstatus, NULL);
}

/*
 * Socantsendmore indicates that no more data will be sent on the
 * socket; it would normally be applied to a socket when the user
 * informs the system that no more data is to be sent, by the protocol
 * code (in case PRU_SHUTDOWN).  Socantrcvmore indicates that no more data
 * will be received, and will normally be applied to the socket by a
 * protocol when it detects that the peer will send no more data.
 * Data queued for reading in the socket may yet be read.
 */
void
socantsendmore(struct socket *so)
{
        sosetstate(so, SS_CANTSENDMORE);
        sowwakeup(so);
}

void
socantrcvmore(struct socket *so)
{
        sosetstate(so, SS_CANTRCVMORE);
        sorwakeup(so);
}

/*
 * Wakeup processes waiting on a socket buffer.  Do asynchronous notification
 * via SIGIO if the socket has the SS_ASYNC flag set.
 *
 * For users waiting on send/recv try to avoid unnecessary context switch
 * thrashing.  Particularly for senders of large buffers (needs to be
 * extended to sel and aio? XXX)
 *
 * WARNING!  Can be called on a foreign socket from the wrong protocol
 *           thread.  aka is called on the 'head' listen socket when
 *           a new connection comes in.
 */
void
sowakeup(struct socket *so, struct signalsockbuf *ssb)
{
        struct kqinfo *kqinfo = &ssb->ssb_kq;
        uint32_t flags;

        /*
         * Check conditions, set the WAKEUP flag, and clear and signal if
         * the WAIT flag is found to be set.  This interlocks against the
         * client side.
         */
        for (;;) {
                flags = ssb->ssb_flags;
                cpu_ccfence();

                if ((ssb == &so->so_snd && ssb_space(ssb) >= ssb->ssb_lowat) ||
                    (ssb == &so->so_rcv && ssb->ssb_cc >= ssb->ssb_lowat) ||
                    (ssb == &so->so_snd && (so->so_state & SS_CANTSENDMORE)) ||
                    (ssb == &so->so_rcv && (so->so_state & SS_CANTRCVMORE))
                ) {
                        if (atomic_cmpset_int(&ssb->ssb_flags, flags,
                                          (flags | SSB_WAKEUP) & ~SSB_WAIT)) {
                                if (flags & SSB_WAIT)
                                        wakeup(&ssb->ssb_cc);
                                break;
                        }
                } else {
                        break;
                }
        }

        /*
         * Misc other events
         */
        if ((so->so_state & SS_ASYNC) && so->so_sigio != NULL)
                pgsigio(so->so_sigio, SIGIO, 0);
        if (ssb->ssb_flags & SSB_UPCALL)
                (*so->so_upcall)(so, so->so_upcallarg, MB_DONTWAIT);
        KNOTE(&kqinfo->ki_note, 0);

        /*
         * This is a bit of a hack.  Multiple threads can wind up scanning
         * ki_mlist concurrently due to the fact that this function can be
         * called on a foreign socket, so we can't afford to block here.
         *
         * We need the pool token for (so) (likely the listne socket if
         * SSB_MEVENT is set) because the predicate function may have
         * to access the accept queue.
         */
        if (ssb->ssb_flags & SSB_MEVENT) {
                struct netmsg_so_notify *msg, *nmsg;

                lwkt_getpooltoken(so);
                TAILQ_FOREACH_MUTABLE(msg, &kqinfo->ki_mlist, nm_list, nmsg) {
                        if (msg->nm_predicate(msg)) {
                                TAILQ_REMOVE(&kqinfo->ki_mlist, msg, nm_list);
                                lwkt_replymsg(&msg->base.lmsg,
                                              msg->base.lmsg.ms_error);
                        }
                }
                if (TAILQ_EMPTY(&ssb->ssb_kq.ki_mlist))
                        atomic_clear_int(&ssb->ssb_flags, SSB_MEVENT);
                lwkt_relpooltoken(so);
        }
}

/*
 * Socket buffer (struct signalsockbuf) utility routines.
 *
 * Each socket contains two socket buffers: one for sending data and
 * one for receiving data.  Each buffer contains a queue of mbufs,
 * information about the number of mbufs and amount of data in the
 * queue, and other fields allowing kevent()/select()/poll() statements
 * and notification on data availability to be implemented.
 *
 * Data stored in a socket buffer is maintained as a list of records.
 * Each record is a list of mbufs chained together with the m_next
 * field.  Records are chained together with the m_nextpkt field. The upper
 * level routine soreceive() expects the following conventions to be
 * observed when placing information in the receive buffer:
 *
 * 1. If the protocol requires each message be preceded by the sender's
 *    name, then a record containing that name must be present before
 *    any associated data (mbuf's must be of type MT_SONAME).
 * 2. If the protocol supports the exchange of ``access rights'' (really
 *    just additional data associated with the message), and there are
 *    ``rights'' to be received, then a record containing this data
 *    should be present (mbuf's must be of type MT_RIGHTS).
 * 3. If a name or rights record exists, then it must be followed by
 *    a data record, perhaps of zero length.
 *
 * Before using a new socket structure it is first necessary to reserve
 * buffer space to the socket, by calling sbreserve().  This should commit
 * some of the available buffer space in the system buffer pool for the
 * socket (currently, it does nothing but enforce limits).  The space
 * should be released by calling ssb_release() when the socket is destroyed.
 */
int
soreserve(struct socket *so, u_long sndcc, u_long rcvcc, struct rlimit *rl)
{
        if (so->so_snd.ssb_lowat == 0)
                atomic_set_int(&so->so_snd.ssb_flags, SSB_AUTOLOWAT);
        if (ssb_reserve(&so->so_snd, sndcc, so, rl) == 0)
                goto bad;
        if (ssb_reserve(&so->so_rcv, rcvcc, so, rl) == 0)
                goto bad2;
        if (so->so_rcv.ssb_lowat == 0)
                so->so_rcv.ssb_lowat = 1;
        if (so->so_snd.ssb_lowat == 0)
                so->so_snd.ssb_lowat = MCLBYTES;
        if (so->so_snd.ssb_lowat > so->so_snd.ssb_hiwat)
                so->so_snd.ssb_lowat = so->so_snd.ssb_hiwat;
        return (0);
bad2:
        ssb_release(&so->so_snd, so);
bad:
        return (ENOBUFS);
}

static int
sysctl_handle_sb_max(SYSCTL_HANDLER_ARGS)
{
        int error = 0;
        u_long old_sb_max = sb_max;

        error = SYSCTL_OUT(req, arg1, sizeof(int));
        if (error || !req->newptr)
                return (error);
        error = SYSCTL_IN(req, arg1, sizeof(int));
        if (error)
                return (error);
        if (sb_max < MSIZE + MCLBYTES) {
                sb_max = old_sb_max;
                return (EINVAL);
        }
        sb_max_adj = (u_quad_t)sb_max * MCLBYTES / (MSIZE + MCLBYTES);
        return (0);
}
        
/*
 * Allot mbufs to a signalsockbuf.
 *
 * Attempt to scale mbmax so that mbcnt doesn't become limiting
 * if buffering efficiency is near the normal case.
 *
 * sb_max only applies to user-sockets (where rl != NULL).  It does
 * not apply to kernel sockets or kernel-controlled sockets.  Note
 * that NFS overrides the sockbuf limits created when nfsd creates
 * a socket.
 */
int
ssb_reserve(struct signalsockbuf *ssb, u_long cc, struct socket *so,
            struct rlimit *rl)
{
        /*
         * rl will only be NULL when we're in an interrupt (eg, in tcp_input)
         * or when called from netgraph (ie, ngd_attach)
         */
        if (rl && cc > sb_max_adj)
                cc = sb_max_adj;
        if (!chgsbsize(so->so_cred->cr_uidinfo, &ssb->ssb_hiwat, cc,
                       rl ? rl->rlim_cur : RLIM_INFINITY)) {
                return (0);
        }
        if (rl)
                ssb->ssb_mbmax = min(cc * sb_efficiency, sb_max);
        else
                ssb->ssb_mbmax = cc * sb_efficiency;

        /*
         * AUTOLOWAT is set on send buffers and prevents large writes
         * from generating a huge number of context switches.
         */
        if (ssb->ssb_flags & SSB_AUTOLOWAT) {
                ssb->ssb_lowat = ssb->ssb_hiwat / 2;
                if (ssb->ssb_lowat < MCLBYTES)
                        ssb->ssb_lowat = MCLBYTES;
        }
        if (ssb->ssb_lowat > ssb->ssb_hiwat)
                ssb->ssb_lowat = ssb->ssb_hiwat;
        return (1);
}

/*
 * Free mbufs held by a socket, and reserved mbuf space.
 */
void
ssb_release(struct signalsockbuf *ssb, struct socket *so)
{
        sbflush(&ssb->sb);
        (void)chgsbsize(so->so_cred->cr_uidinfo, &ssb->ssb_hiwat, 0,
            RLIM_INFINITY);
        ssb->ssb_mbmax = 0;
}

/*
 * Some routines that return EOPNOTSUPP for entry points that are not
 * supported by a protocol.  Fill in as needed.
 */
void
pr_generic_notsupp(netmsg_t msg)
{
        lwkt_replymsg(&msg->lmsg, EOPNOTSUPP);
}

int
pru_sosend_notsupp(struct socket *so, struct sockaddr *addr, struct uio *uio,
           struct mbuf *top, struct mbuf *control, int flags,
           struct thread *td)
{
        if (top)
                m_freem(top);
        if (control)
                m_freem(control);
        return (EOPNOTSUPP);
}

int
pru_soreceive_notsupp(struct socket *so, struct sockaddr **paddr,
                      struct uio *uio, struct sockbuf *sio,
                      struct mbuf **controlp, int *flagsp)
{
        return (EOPNOTSUPP);
}

/*
 * This isn't really a ``null'' operation, but it's the default one
 * and doesn't do anything destructive.
 */
void
pru_sense_null(netmsg_t msg)
{
        msg->sense.nm_stat->st_blksize = msg->base.nm_so->so_snd.ssb_hiwat;
        lwkt_replymsg(&msg->lmsg, 0);
}

/*
 * Make a copy of a sockaddr in a malloced buffer of type M_SONAME.  Callers
 * of this routine assume that it always succeeds, so we have to use a 
 * blockable allocation even though we might be called from a critical thread.
 */
struct sockaddr *
dup_sockaddr(const struct sockaddr *sa)
{
        struct sockaddr *sa2;

        sa2 = kmalloc(sa->sa_len, M_SONAME, M_INTWAIT);
        bcopy(sa, sa2, sa->sa_len);
        return (sa2);
}

/*
 * Create an external-format (``xsocket'') structure using the information
 * in the kernel-format socket structure pointed to by so.  This is done
 * to reduce the spew of irrelevant information over this interface,
 * to isolate user code from changes in the kernel structure, and
 * potentially to provide information-hiding if we decide that
 * some of this information should be hidden from users.
 */
void
sotoxsocket(struct socket *so, struct xsocket *xso)
{
        xso->xso_len = sizeof *xso;
        xso->xso_so = so;
        xso->so_type = so->so_type;
        xso->so_options = so->so_options;
        xso->so_linger = so->so_linger;
        xso->so_state = so->so_state;
        xso->so_pcb = so->so_pcb;
        xso->xso_protocol = so->so_proto->pr_protocol;
        xso->xso_family = so->so_proto->pr_domain->dom_family;
        xso->so_qlen = so->so_qlen;
        xso->so_incqlen = so->so_incqlen;
        xso->so_qlimit = so->so_qlimit;
        xso->so_timeo = so->so_timeo;
        xso->so_error = so->so_error;
        xso->so_pgid = so->so_sigio ? so->so_sigio->sio_pgid : 0;
        xso->so_oobmark = so->so_oobmark;
        ssbtoxsockbuf(&so->so_snd, &xso->so_snd);
        ssbtoxsockbuf(&so->so_rcv, &xso->so_rcv);
        xso->so_uid = so->so_cred->cr_uid;
}

/*
 * Here is the definition of some of the basic objects in the kern.ipc
 * branch of the MIB.
 */
SYSCTL_NODE(_kern, KERN_IPC, ipc, CTLFLAG_RW, 0, "IPC");

/*
 * This takes the place of kern.maxsockbuf, which moved to kern.ipc.
 *
 * NOTE! sb_max only applies to user-created socket buffers.
 */
static int dummy;
SYSCTL_INT(_kern, KERN_DUMMY, dummy, CTLFLAG_RW, &dummy, 0, "");
SYSCTL_OID(_kern_ipc, KIPC_MAXSOCKBUF, maxsockbuf, CTLTYPE_INT|CTLFLAG_RW, 
    &sb_max, 0, sysctl_handle_sb_max, "I", "Maximum socket buffer size");
SYSCTL_INT(_kern_ipc, OID_AUTO, maxsockets, CTLFLAG_RD, 
    &maxsockets, 0, "Maximum number of sockets available");
SYSCTL_INT(_kern_ipc, KIPC_SOCKBUF_WASTE, sockbuf_waste_factor, CTLFLAG_RW,
    &sb_efficiency, 0,
    "Socket buffer limit scaler");

/*
 * Initialize maxsockets 
 */
static void
init_maxsockets(void *ignored)
{
    TUNABLE_INT_FETCH("kern.ipc.maxsockets", &maxsockets);
    maxsockets = imax(maxsockets, imax(maxfiles, nmbclusters));
}
SYSINIT(param, SI_BOOT1_TUNABLES, SI_ORDER_ANY,
        init_maxsockets, NULL);