uipc_sockbuf.c

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/*-
 * 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.
 * 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
 */

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

#include "opt_param.h"

#include <sys/param.h>
#include <sys/aio.h> /* for aio_swake proto */
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mbuf.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/protosw.h>
#include <sys/resourcevar.h>
#include <sys/signalvar.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/sx.h>
#include <sys/sysctl.h>

/*
 * Function pointer set by the AIO routines so that the socket buffer code
 * can call back into the AIO module if it is loaded.
 */
void    (*aio_swake)(struct socket *, struct sockbuf *);

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

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

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

static void     sbdrop_internal(struct sockbuf *sb, int len);
static void     sbflush_internal(struct sockbuf *sb);

/*
 * 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_locked(struct socket *so)
{

        SOCKBUF_LOCK_ASSERT(&so->so_snd);

        so->so_snd.sb_state |= SBS_CANTSENDMORE;
        sowwakeup_locked(so);
        mtx_assert(SOCKBUF_MTX(&so->so_snd), MA_NOTOWNED);
}

void
socantsendmore(struct socket *so)
{

        SOCKBUF_LOCK(&so->so_snd);
        socantsendmore_locked(so);
        mtx_assert(SOCKBUF_MTX(&so->so_snd), MA_NOTOWNED);
}

void
socantrcvmore_locked(struct socket *so)
{

        SOCKBUF_LOCK_ASSERT(&so->so_rcv);

        so->so_rcv.sb_state |= SBS_CANTRCVMORE;
        sorwakeup_locked(so);
        mtx_assert(SOCKBUF_MTX(&so->so_rcv), MA_NOTOWNED);
}

void
socantrcvmore(struct socket *so)
{

        SOCKBUF_LOCK(&so->so_rcv);
        socantrcvmore_locked(so);
        mtx_assert(SOCKBUF_MTX(&so->so_rcv), MA_NOTOWNED);
}

/*
 * Wait for data to arrive at/drain from a socket buffer.
 */
int
sbwait(struct sockbuf *sb)
{

        SOCKBUF_LOCK_ASSERT(sb);

        sb->sb_flags |= SB_WAIT;
        return (msleep(&sb->sb_cc, &sb->sb_mtx,
            (sb->sb_flags & SB_NOINTR) ? PSOCK : PSOCK | PCATCH, "sbwait",
            sb->sb_timeo));
}

int
sblock(struct sockbuf *sb, int flags)
{

        KASSERT((flags & SBL_VALID) == flags,
            ("sblock: flags invalid (0x%x)", flags));

        if (flags & SBL_WAIT) {
                if ((sb->sb_flags & SB_NOINTR) ||
                    (flags & SBL_NOINTR)) {
                        sx_xlock(&sb->sb_sx);
                        return (0);
                }
                return (sx_xlock_sig(&sb->sb_sx));
        } else {
                if (sx_try_xlock(&sb->sb_sx) == 0)
                        return (EWOULDBLOCK);
                return (0);
        }
}

void
sbunlock(struct sockbuf *sb)
{

        sx_xunlock(&sb->sb_sx);
}

/*
 * Wakeup processes waiting on a socket buffer.  Do asynchronous notification
 * via SIGIO if the socket has the SS_ASYNC flag set.
 *
 * Called with the socket buffer lock held; will release the lock by the end
 * of the function.  This allows the caller to acquire the socket buffer lock
 * while testing for the need for various sorts of wakeup and hold it through
 * to the point where it's no longer required.  We currently hold the lock
 * through calls out to other subsystems (with the exception of kqueue), and
 * then release it to avoid lock order issues.  It's not clear that's
 * correct.
 */
void
sowakeup(struct socket *so, struct sockbuf *sb)
{
        int ret;

        SOCKBUF_LOCK_ASSERT(sb);

        selwakeuppri(&sb->sb_sel, PSOCK);
        if (!SEL_WAITING(&sb->sb_sel))
                sb->sb_flags &= ~SB_SEL;
        if (sb->sb_flags & SB_WAIT) {
                sb->sb_flags &= ~SB_WAIT;
                wakeup(&sb->sb_cc);
        }
        KNOTE_LOCKED(&sb->sb_sel.si_note, 0);
        if (sb->sb_upcall != NULL) {
                ret = sb->sb_upcall(so, sb->sb_upcallarg, M_DONTWAIT);
                if (ret == SU_ISCONNECTED) {
                        KASSERT(sb == &so->so_rcv,
                            ("SO_SND upcall returned SU_ISCONNECTED"));
                        soupcall_clear(so, SO_RCV);
                }
        } else
                ret = SU_OK;
        if (sb->sb_flags & SB_AIO)
                aio_swake(so, sb);
        SOCKBUF_UNLOCK(sb);
        if (ret == SU_ISCONNECTED)
                soisconnected(so);
        if ((so->so_state & SS_ASYNC) && so->so_sigio != NULL)
                pgsigio(&so->so_sigio, SIGIO, 0);
        mtx_assert(SOCKBUF_MTX(sb), MA_NOTOWNED);
}

/*
 * Socket buffer (struct sockbuf) 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 select() 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 sbrelease() when the socket is destroyed.
 */
int
soreserve(struct socket *so, u_long sndcc, u_long rcvcc)
{
        struct thread *td = curthread;

        SOCKBUF_LOCK(&so->so_snd);
        SOCKBUF_LOCK(&so->so_rcv);
        if (sbreserve_locked(&so->so_snd, sndcc, so, td) == 0)
                goto bad;
        if (sbreserve_locked(&so->so_rcv, rcvcc, so, td) == 0)
                goto bad2;
        if (so->so_rcv.sb_lowat == 0)
                so->so_rcv.sb_lowat = 1;
        if (so->so_snd.sb_lowat == 0)
                so->so_snd.sb_lowat = MCLBYTES;
        if (so->so_snd.sb_lowat > so->so_snd.sb_hiwat)
                so->so_snd.sb_lowat = so->so_snd.sb_hiwat;
        SOCKBUF_UNLOCK(&so->so_rcv);
        SOCKBUF_UNLOCK(&so->so_snd);
        return (0);
bad2:
        sbrelease_locked(&so->so_snd, so);
bad:
        SOCKBUF_UNLOCK(&so->so_rcv);
        SOCKBUF_UNLOCK(&so->so_snd);
        return (ENOBUFS);
}

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

        error = sysctl_handle_long(oidp, &tmp_sb_max, arg2, req);
        if (error || !req->newptr)
                return (error);
        if (tmp_sb_max < MSIZE + MCLBYTES)
                return (EINVAL);
        sb_max = tmp_sb_max;
        sb_max_adj = (u_quad_t)sb_max * MCLBYTES / (MSIZE + MCLBYTES);
        return (0);
}
        
/*
 * Allot mbufs to a sockbuf.  Attempt to scale mbmax so that mbcnt doesn't
 * become limiting if buffering efficiency is near the normal case.
 */
int
sbreserve_locked(struct sockbuf *sb, u_long cc, struct socket *so,
    struct thread *td)
{
        rlim_t sbsize_limit;

        SOCKBUF_LOCK_ASSERT(sb);

        /*
         * When a thread is passed, we take into account the thread's socket
         * buffer size limit.  The caller will generally pass curthread, but
         * in the TCP input path, NULL will be passed to indicate that no
         * appropriate thread resource limits are available.  In that case,
         * we don't apply a process limit.
         */
        if (cc > sb_max_adj)
                return (0);
        if (td != NULL) {
                PROC_LOCK(td->td_proc);
                sbsize_limit = lim_cur(td->td_proc, RLIMIT_SBSIZE);
                PROC_UNLOCK(td->td_proc);
        } else
                sbsize_limit = RLIM_INFINITY;
        if (!chgsbsize(so->so_cred->cr_uidinfo, &sb->sb_hiwat, cc,
            sbsize_limit))
                return (0);
        sb->sb_mbmax = min(cc * sb_efficiency, sb_max);
        if (sb->sb_lowat > sb->sb_hiwat)
                sb->sb_lowat = sb->sb_hiwat;
        return (1);
}

int
sbreserve(struct sockbuf *sb, u_long cc, struct socket *so, 
    struct thread *td)
{
        int error;

        SOCKBUF_LOCK(sb);
        error = sbreserve_locked(sb, cc, so, td);
        SOCKBUF_UNLOCK(sb);
        return (error);
}

/*
 * Free mbufs held by a socket, and reserved mbuf space.
 */
void
sbrelease_internal(struct sockbuf *sb, struct socket *so)
{

        sbflush_internal(sb);
        (void)chgsbsize(so->so_cred->cr_uidinfo, &sb->sb_hiwat, 0,
            RLIM_INFINITY);
        sb->sb_mbmax = 0;
}

void
sbrelease_locked(struct sockbuf *sb, struct socket *so)
{

        SOCKBUF_LOCK_ASSERT(sb);

        sbrelease_internal(sb, so);
}

void
sbrelease(struct sockbuf *sb, struct socket *so)
{

        SOCKBUF_LOCK(sb);
        sbrelease_locked(sb, so);
        SOCKBUF_UNLOCK(sb);
}

void
sbdestroy(struct sockbuf *sb, struct socket *so)
{

        sbrelease_internal(sb, so);
}

/*
 * Routines to add and remove data from an mbuf queue.
 *
 * The routines sbappend() or sbappendrecord() are normally called to append
 * new mbufs to a socket buffer, after checking that adequate space is
 * available, comparing the function sbspace() with the amount of data to be
 * added.  sbappendrecord() differs from sbappend() in that data supplied is
 * treated as the beginning of a new record.  To place a sender's address,
 * optional access rights, and data in a socket receive buffer,
 * sbappendaddr() should be used.  To place access rights and data in a
 * socket receive buffer, sbappendrights() should be used.  In either case,
 * the new data begins a new record.  Note that unlike sbappend() and
 * sbappendrecord(), these routines check for the caller that there will be
 * enough space to store the data.  Each fails if there is not enough space,
 * or if it cannot find mbufs to store additional information in.
 *
 * Reliable protocols may use the socket send buffer to hold data awaiting
 * acknowledgement.  Data is normally copied from a socket send buffer in a
 * protocol with m_copy for output to a peer, and then removing the data from
 * the socket buffer with sbdrop() or sbdroprecord() when the data is
 * acknowledged by the peer.
 */
#ifdef SOCKBUF_DEBUG
void
sblastrecordchk(struct sockbuf *sb, const char *file, int line)
{
        struct mbuf *m = sb->sb_mb;

        SOCKBUF_LOCK_ASSERT(sb);

        while (m && m->m_nextpkt)
                m = m->m_nextpkt;

        if (m != sb->sb_lastrecord) {
                printf("%s: sb_mb %p sb_lastrecord %p last %p\n",
                        __func__, sb->sb_mb, sb->sb_lastrecord, m);
                printf("packet chain:\n");
                for (m = sb->sb_mb; m != NULL; m = m->m_nextpkt)
                        printf("\t%p\n", m);
                panic("%s from %s:%u", __func__, file, line);
        }
}

void
sblastmbufchk(struct sockbuf *sb, const char *file, int line)
{
        struct mbuf *m = sb->sb_mb;
        struct mbuf *n;

        SOCKBUF_LOCK_ASSERT(sb);

        while (m && m->m_nextpkt)
                m = m->m_nextpkt;

        while (m && m->m_next)
                m = m->m_next;

        if (m != sb->sb_mbtail) {
                printf("%s: sb_mb %p sb_mbtail %p last %p\n",
                        __func__, sb->sb_mb, sb->sb_mbtail, m);
                printf("packet tree:\n");
                for (m = sb->sb_mb; m != NULL; m = m->m_nextpkt) {
                        printf("\t");
                        for (n = m; n != NULL; n = n->m_next)
                                printf("%p ", n);
                        printf("\n");
                }
                panic("%s from %s:%u", __func__, file, line);
        }
}
#endif /* SOCKBUF_DEBUG */

#define SBLINKRECORD(sb, m0) do {                                       \
        SOCKBUF_LOCK_ASSERT(sb);                                        \
        if ((sb)->sb_lastrecord != NULL)                                \
                (sb)->sb_lastrecord->m_nextpkt = (m0);                  \
        else                                                            \
                (sb)->sb_mb = (m0);                                     \
        (sb)->sb_lastrecord = (m0);                                     \
} while (/*CONSTCOND*/0)

/*
 * Append mbuf chain m to the last record in the socket buffer sb.  The
 * additional space associated the mbuf chain is recorded in sb.  Empty mbufs
 * are discarded and mbufs are compacted where possible.
 */
void
sbappend_locked(struct sockbuf *sb, struct mbuf *m)
{
        struct mbuf *n;

        SOCKBUF_LOCK_ASSERT(sb);

        if (m == 0)
                return;

        SBLASTRECORDCHK(sb);
        n = sb->sb_mb;
        if (n) {
                while (n->m_nextpkt)
                        n = n->m_nextpkt;
                do {
                        if (n->m_flags & M_EOR) {
                                sbappendrecord_locked(sb, m); /* XXXXXX!!!! */
                                return;
                        }
                } while (n->m_next && (n = n->m_next));
        } else {
                /*
                 * XXX Would like to simply use sb_mbtail here, but
                 * XXX I need to verify that I won't miss an EOR that
                 * XXX way.
                 */
                if ((n = sb->sb_lastrecord) != NULL) {
                        do {
                                if (n->m_flags & M_EOR) {
                                        sbappendrecord_locked(sb, m); /* XXXXXX!!!! */
                                        return;
                                }
                        } while (n->m_next && (n = n->m_next));
                } else {
                        /*
                         * If this is the first record in the socket buffer,
                         * it's also the last record.
                         */
                        sb->sb_lastrecord = m;
                }
        }
        sbcompress(sb, m, n);
        SBLASTRECORDCHK(sb);
}

/*
 * Append mbuf chain m to the last record in the socket buffer sb.  The
 * additional space associated the mbuf chain is recorded in sb.  Empty mbufs
 * are discarded and mbufs are compacted where possible.
 */
void
sbappend(struct sockbuf *sb, struct mbuf *m)
{

        SOCKBUF_LOCK(sb);
        sbappend_locked(sb, m);
        SOCKBUF_UNLOCK(sb);
}

/*
 * This version of sbappend() should only be used when the caller absolutely
 * knows that there will never be more than one record in the socket buffer,
 * that is, a stream protocol (such as TCP).
 */
void
sbappendstream_locked(struct sockbuf *sb, struct mbuf *m)
{
        SOCKBUF_LOCK_ASSERT(sb);

        KASSERT(m->m_nextpkt == NULL,("sbappendstream 0"));
        KASSERT(sb->sb_mb == sb->sb_lastrecord,("sbappendstream 1"));

        SBLASTMBUFCHK(sb);

        sbcompress(sb, m, sb->sb_mbtail);

        sb->sb_lastrecord = sb->sb_mb;
        SBLASTRECORDCHK(sb);
}

/*
 * This version of sbappend() should only be used when the caller absolutely
 * knows that there will never be more than one record in the socket buffer,
 * that is, a stream protocol (such as TCP).
 */
void
sbappendstream(struct sockbuf *sb, struct mbuf *m)
{

        SOCKBUF_LOCK(sb);
        sbappendstream_locked(sb, m);
        SOCKBUF_UNLOCK(sb);
}

#ifdef SOCKBUF_DEBUG
void
sbcheck(struct sockbuf *sb)
{
        struct mbuf *m;
        struct mbuf *n = 0;
        u_long len = 0, mbcnt = 0;

        SOCKBUF_LOCK_ASSERT(sb);

        for (m = sb->sb_mb; m; m = n) {
            n = m->m_nextpkt;
            for (; m; m = m->m_next) {
                len += m->m_len;
                mbcnt += MSIZE;
                if (m->m_flags & M_EXT) /*XXX*/ /* pretty sure this is bogus */
                        mbcnt += m->m_ext.ext_size;
            }
        }
        if (len != sb->sb_cc || mbcnt != sb->sb_mbcnt) {
                printf("cc %ld != %u || mbcnt %ld != %u\n", len, sb->sb_cc,
                    mbcnt, sb->sb_mbcnt);
                panic("sbcheck");
        }
}
#endif

/*
 * As above, except the mbuf chain begins a new record.
 */
void
sbappendrecord_locked(struct sockbuf *sb, struct mbuf *m0)
{
        struct mbuf *m;

        SOCKBUF_LOCK_ASSERT(sb);

        if (m0 == 0)
                return;
        /*
         * Put the first mbuf on the queue.  Note this permits zero length
         * records.
         */
        sballoc(sb, m0);
        SBLASTRECORDCHK(sb);
        SBLINKRECORD(sb, m0);
        sb->sb_mbtail = m0;
        m = m0->m_next;
        m0->m_next = 0;
        if (m && (m0->m_flags & M_EOR)) {
                m0->m_flags &= ~M_EOR;
                m->m_flags |= M_EOR;
        }
        /* always call sbcompress() so it can do SBLASTMBUFCHK() */
        sbcompress(sb, m, m0);
}

/*
 * As above, except the mbuf chain begins a new record.
 */
void
sbappendrecord(struct sockbuf *sb, struct mbuf *m0)
{

        SOCKBUF_LOCK(sb);
        sbappendrecord_locked(sb, m0);
        SOCKBUF_UNLOCK(sb);
}

/* Helper routine that appends data, control, and address to a sockbuf. */
static int
sbappendaddr_locked_internal(struct sockbuf *sb, const struct sockaddr *asa,
    struct mbuf *m0, struct mbuf *control, struct mbuf *ctrl_last)
{
        struct mbuf *m, *n, *nlast;
#if MSIZE <= 256
        if (asa->sa_len > MLEN)
                return (0);
#endif
        MGET(m, M_DONTWAIT, MT_SONAME);
        if (m == 0)
                return (0);
        m->m_len = asa->sa_len;
        bcopy(asa, mtod(m, caddr_t), asa->sa_len);
        if (ctrl_last)
                ctrl_last->m_next = m0; /* concatenate data to control */
        else
                control = m0;
        m->m_next = control;
        for (n = m; n->m_next != NULL; n = n->m_next)
                sballoc(sb, n);
        sballoc(sb, n);
        nlast = n;
        SBLINKRECORD(sb, m);

        sb->sb_mbtail = nlast;
        SBLASTMBUFCHK(sb);

        SBLASTRECORDCHK(sb);
        return (1);
}

/*
 * Append address and data, and optionally, control (ancillary) data to the
 * receive queue of a socket.  If present, m0 must include a packet header
 * with total length.  Returns 0 if no space in sockbuf or insufficient
 * mbufs.
 */
int
sbappendaddr_locked(struct sockbuf *sb, const struct sockaddr *asa,
    struct mbuf *m0, struct mbuf *control)
{
        struct mbuf *ctrl_last;
        int space = asa->sa_len;

        SOCKBUF_LOCK_ASSERT(sb);

        if (m0 && (m0->m_flags & M_PKTHDR) == 0)
                panic("sbappendaddr_locked");
        if (m0)
                space += m0->m_pkthdr.len;
        space += m_length(control, &ctrl_last);

        if (space > sbspace(sb))
                return (0);
        return (sbappendaddr_locked_internal(sb, asa, m0, control, ctrl_last));
}

/*
 * Append address and data, and optionally, control (ancillary) data to the
 * receive queue of a socket.  If present, m0 must include a packet header
 * with total length.  Returns 0 if insufficient mbufs.  Does not validate space
 * on the receiving sockbuf.
 */
int
sbappendaddr_nospacecheck_locked(struct sockbuf *sb, const struct sockaddr *asa,
    struct mbuf *m0, struct mbuf *control)
{
        struct mbuf *ctrl_last;

        SOCKBUF_LOCK_ASSERT(sb);

        ctrl_last = (control == NULL) ? NULL : m_last(control);
        return (sbappendaddr_locked_internal(sb, asa, m0, control, ctrl_last));
}

/*
 * Append address and data, and optionally, control (ancillary) data to the
 * receive queue of a socket.  If present, m0 must include a packet header
 * with total length.  Returns 0 if no space in sockbuf or insufficient
 * mbufs.
 */
int
sbappendaddr(struct sockbuf *sb, const struct sockaddr *asa,
    struct mbuf *m0, struct mbuf *control)
{
        int retval;

        SOCKBUF_LOCK(sb);
        retval = sbappendaddr_locked(sb, asa, m0, control);
        SOCKBUF_UNLOCK(sb);
        return (retval);
}

int
sbappendcontrol_locked(struct sockbuf *sb, struct mbuf *m0,
    struct mbuf *control)
{
        struct mbuf *m, *n, *mlast;
        int space;

        SOCKBUF_LOCK_ASSERT(sb);

        if (control == 0)
                panic("sbappendcontrol_locked");
        space = m_length(control, &n) + m_length(m0, NULL);

        if (space > sbspace(sb))
                return (0);
        n->m_next = m0;                 /* concatenate data to control */

        SBLASTRECORDCHK(sb);

        for (m = control; m->m_next; m = m->m_next)
                sballoc(sb, m);
        sballoc(sb, m);
        mlast = m;
        SBLINKRECORD(sb, control);

        sb->sb_mbtail = mlast;
        SBLASTMBUFCHK(sb);

        SBLASTRECORDCHK(sb);
        return (1);
}

int
sbappendcontrol(struct sockbuf *sb, struct mbuf *m0, struct mbuf *control)
{
        int retval;

        SOCKBUF_LOCK(sb);
        retval = sbappendcontrol_locked(sb, m0, control);
        SOCKBUF_UNLOCK(sb);
        return (retval);
}

/*
 * Append the data in mbuf chain (m) into the socket buffer sb following mbuf
 * (n).  If (n) is NULL, the buffer is presumed empty.
 *
 * When the data is compressed, mbufs in the chain may be handled in one of
 * three ways:
 *
 * (1) The mbuf may simply be dropped, if it contributes nothing (no data, no
 *     record boundary, and no change in data type).
 *
 * (2) The mbuf may be coalesced -- i.e., data in the mbuf may be copied into
 *     an mbuf already in the socket buffer.  This can occur if an
 *     appropriate mbuf exists, there is room, and no merging of data types
 *     will occur.
 *
 * (3) The mbuf may be appended to the end of the existing mbuf chain.
 *
 * If any of the new mbufs is marked as M_EOR, mark the last mbuf appended as
 * end-of-record.
 */
void
sbcompress(struct sockbuf *sb, struct mbuf *m, struct mbuf *n)
{
        int eor = 0;
        struct mbuf *o;

        SOCKBUF_LOCK_ASSERT(sb);

        while (m) {
                eor |= m->m_flags & M_EOR;
                if (m->m_len == 0 &&
                    (eor == 0 ||
                     (((o = m->m_next) || (o = n)) &&
                      o->m_type == m->m_type))) {
                        if (sb->sb_lastrecord == m)
                                sb->sb_lastrecord = m->m_next;
                        m = m_free(m);
                        continue;
                }
                if (n && (n->m_flags & M_EOR) == 0 &&
                    M_WRITABLE(n) &&
                    ((sb->sb_flags & SB_NOCOALESCE) == 0) &&
                    m->m_len <= MCLBYTES / 4 && /* XXX: Don't copy too much */
                    m->m_len <= M_TRAILINGSPACE(n) &&
                    n->m_type == m->m_type) {
                        bcopy(mtod(m, caddr_t), mtod(n, caddr_t) + n->m_len,
                            (unsigned)m->m_len);
                        n->m_len += m->m_len;
                        sb->sb_cc += m->m_len;
                        if (m->m_type != MT_DATA && m->m_type != MT_OOBDATA)
                                /* XXX: Probably don't need.*/
                                sb->sb_ctl += m->m_len;
                        m = m_free(m);
                        continue;
                }
                if (n)
                        n->m_next = m;
                else
                        sb->sb_mb = m;
                sb->sb_mbtail = m;
                sballoc(sb, m);
                n = m;
                m->m_flags &= ~M_EOR;
                m = m->m_next;
                n->m_next = 0;
        }
        if (eor) {
                KASSERT(n != NULL, ("sbcompress: eor && n == NULL"));
                n->m_flags |= eor;
        }
        SBLASTMBUFCHK(sb);
}

/*
 * Free all mbufs in a sockbuf.  Check that all resources are reclaimed.
 */
static void
sbflush_internal(struct sockbuf *sb)
{

        while (sb->sb_mbcnt) {
                /*
                 * Don't call sbdrop(sb, 0) if the leading mbuf is non-empty:
                 * we would loop forever. Panic instead.
                 */
                if (!sb->sb_cc && (sb->sb_mb == NULL || sb->sb_mb->m_len))
                        break;
                sbdrop_internal(sb, (int)sb->sb_cc);
        }
        if (sb->sb_cc || sb->sb_mb || sb->sb_mbcnt)
                panic("sbflush_internal: cc %u || mb %p || mbcnt %u",
                    sb->sb_cc, (void *)sb->sb_mb, sb->sb_mbcnt);
}

void
sbflush_locked(struct sockbuf *sb)
{

        SOCKBUF_LOCK_ASSERT(sb);
        sbflush_internal(sb);
}

void
sbflush(struct sockbuf *sb)
{

        SOCKBUF_LOCK(sb);
        sbflush_locked(sb);
        SOCKBUF_UNLOCK(sb);
}

/*
 * Drop data from (the front of) a sockbuf.
 */
static void
sbdrop_internal(struct sockbuf *sb, int len)
{
        struct mbuf *m;
        struct mbuf *next;

        next = (m = sb->sb_mb) ? m->m_nextpkt : 0;
        while (len > 0) {
                if (m == 0) {
                        if (next == 0)
                                panic("sbdrop");
                        m = next;
                        next = m->m_nextpkt;
                        continue;
                }
                if (m->m_len > len) {
                        m->m_len -= len;
                        m->m_data += len;
                        sb->sb_cc -= len;
                        if (sb->sb_sndptroff != 0)
                                sb->sb_sndptroff -= len;
                        if (m->m_type != MT_DATA && m->m_type != MT_OOBDATA)
                                sb->sb_ctl -= len;
                        break;
                }
                len -= m->m_len;
                sbfree(sb, m);
                m = m_free(m);
        }
        while (m && m->m_len == 0) {
                sbfree(sb, m);
                m = m_free(m);
        }
        if (m) {
                sb->sb_mb = m;
                m->m_nextpkt = next;
        } else
                sb->sb_mb = next;
        /*
         * First part is an inline SB_EMPTY_FIXUP().  Second part makes sure
         * sb_lastrecord is up-to-date if we dropped part of the last record.
         */
        m = sb->sb_mb;
        if (m == NULL) {
                sb->sb_mbtail = NULL;
                sb->sb_lastrecord = NULL;
        } else if (m->m_nextpkt == NULL) {
                sb->sb_lastrecord = m;
        }
}

/*
 * Drop data from (the front of) a sockbuf.
 */
void
sbdrop_locked(struct sockbuf *sb, int len)
{

        SOCKBUF_LOCK_ASSERT(sb);

        sbdrop_internal(sb, len);
}

void
sbdrop(struct sockbuf *sb, int len)
{

        SOCKBUF_LOCK(sb);
        sbdrop_locked(sb, len);
        SOCKBUF_UNLOCK(sb);
}

/*
 * Maintain a pointer and offset pair into the socket buffer mbuf chain to
 * avoid traversal of the entire socket buffer for larger offsets.
 */
struct mbuf *
sbsndptr(struct sockbuf *sb, u_int off, u_int len, u_int *moff)
{
        struct mbuf *m, *ret;

        KASSERT(sb->sb_mb != NULL, ("%s: sb_mb is NULL", __func__));
        KASSERT(off + len <= sb->sb_cc, ("%s: beyond sb", __func__));
        KASSERT(sb->sb_sndptroff <= sb->sb_cc, ("%s: sndptroff broken", __func__));

        /*
         * Is off below stored offset? Happens on retransmits.
         * Just return, we can't help here.
         */
        if (sb->sb_sndptroff > off) {
                *moff = off;
                return (sb->sb_mb);
        }

        /* Return closest mbuf in chain for current offset. */
        *moff = off - sb->sb_sndptroff;
        m = ret = sb->sb_sndptr ? sb->sb_sndptr : sb->sb_mb;
        if (*moff == m->m_len) {
                *moff = 0;
                sb->sb_sndptroff += m->m_len;
                m = ret = m->m_next;
                KASSERT(ret->m_len > 0,
                    ("mbuf %p in sockbuf %p chain has no valid data", ret, sb));
        }

        /* Advance by len to be as close as possible for the next transmit. */
        for (off = off - sb->sb_sndptroff + len - 1;
             off > 0 && m != NULL && off >= m->m_len;
             m = m->m_next) {
                sb->sb_sndptroff += m->m_len;
                off -= m->m_len;
        }
        if (off > 0 && m == NULL)
                panic("%s: sockbuf %p and mbuf %p clashing", __func__, sb, ret);
        sb->sb_sndptr = m;

        return (ret);
}

/*
 * Return the first mbuf and the mbuf data offset for the provided
 * send offset without changing the "sb_sndptroff" field.
 */
struct mbuf *
sbsndmbuf(struct sockbuf *sb, u_int off, u_int *moff)
{
        struct mbuf *m;

        KASSERT(sb->sb_mb != NULL, ("%s: sb_mb is NULL", __func__));

        /*
         * If the "off" is below the stored offset, which happens on
         * retransmits, just use "sb_mb":
         */
        if (sb->sb_sndptr == NULL || sb->sb_sndptroff > off) {
                m = sb->sb_mb;
        } else {
                m = sb->sb_sndptr;
                off -= sb->sb_sndptroff;
        }
        while (off > 0 && m != NULL) {
                if (off < m->m_len)
                        break;
                off -= m->m_len;
                m = m->m_next;
        }
        *moff = off;
        return (m);
}

/*
 * Drop a record off the front of a sockbuf and move the next record to the
 * front.
 */
void
sbdroprecord_locked(struct sockbuf *sb)
{
        struct mbuf *m;

        SOCKBUF_LOCK_ASSERT(sb);

        m = sb->sb_mb;
        if (m) {
                sb->sb_mb = m->m_nextpkt;
                do {
                        sbfree(sb, m);
                        m = m_free(m);
                } while (m);
        }
        SB_EMPTY_FIXUP(sb);
}

/*
 * Drop a record off the front of a sockbuf and move the next record to the
 * front.
 */
void
sbdroprecord(struct sockbuf *sb)
{

        SOCKBUF_LOCK(sb);
        sbdroprecord_locked(sb);
        SOCKBUF_UNLOCK(sb);
}

/*
 * Create a "control" mbuf containing the specified data with the specified
 * type for presentation on a socket buffer.
 */
struct mbuf *
sbcreatecontrol(caddr_t p, int size, int type, int level)
{
        struct cmsghdr *cp;
        struct mbuf *m;

        if (CMSG_SPACE((u_int)size) > MCLBYTES)
                return ((struct mbuf *) NULL);
        if (CMSG_SPACE((u_int)size) > MLEN)
                m = m_getcl(M_DONTWAIT, MT_CONTROL, 0);
        else
                m = m_get(M_DONTWAIT, MT_CONTROL);
        if (m == NULL)
                return ((struct mbuf *) NULL);
        cp = mtod(m, struct cmsghdr *);
        m->m_len = 0;
        KASSERT(CMSG_SPACE((u_int)size) <= M_TRAILINGSPACE(m),
            ("sbcreatecontrol: short mbuf"));
        /*
         * Don't leave the padding between the msg header and the
         * cmsg data and the padding after the cmsg data un-initialized.
         */
        bzero(cp, CMSG_SPACE((u_int)size));
        if (p != NULL)
                (void)memcpy(CMSG_DATA(cp), p, size);
        m->m_len = CMSG_SPACE(size);
        cp->cmsg_len = CMSG_LEN(size);
        cp->cmsg_level = level;
        cp->cmsg_type = type;
        return (m);
}

/*
 * This does the same for socket buffers that sotoxsocket does for sockets:
 * generate an user-format data structure describing the socket buffer.  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
sbtoxsockbuf(struct sockbuf *sb, struct xsockbuf *xsb)
{

        xsb->sb_cc = sb->sb_cc;
        xsb->sb_hiwat = sb->sb_hiwat;
        xsb->sb_mbcnt = sb->sb_mbcnt;
        xsb->sb_mcnt = sb->sb_mcnt;     
        xsb->sb_ccnt = sb->sb_ccnt;
        xsb->sb_mbmax = sb->sb_mbmax;
        xsb->sb_lowat = sb->sb_lowat;
        xsb->sb_flags = sb->sb_flags;
        xsb->sb_timeo = sb->sb_timeo;
}

/* This takes the place of kern.maxsockbuf, which moved to kern.ipc. */
static int dummy;
SYSCTL_INT(_kern, KERN_DUMMY, dummy, CTLFLAG_RW, &dummy, 0, "");
SYSCTL_OID(_kern_ipc, KIPC_MAXSOCKBUF, maxsockbuf, CTLTYPE_ULONG|CTLFLAG_RW,
    &sb_max, 0, sysctl_handle_sb_max, "LU", "Maximum socket buffer size");
SYSCTL_ULONG(_kern_ipc, KIPC_SOCKBUF_WASTE, sockbuf_waste_factor, CTLFLAG_RW,
    &sb_efficiency, 0, "");