/*      $OpenBSD: nfs_syscalls.c,v 1.130 2025/03/27 23:30:54 tedu Exp $ */
/*      $NetBSD: nfs_syscalls.c,v 1.19 1996/02/18 11:53:52 fvdl Exp $   */

/*
 * Copyright (c) 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Rick Macklem at The University of Guelph.
 *
 * 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.
 *
 *      @(#)nfs_syscalls.c      8.5 (Berkeley) 3/30/95
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/file.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/pool.h>
#include <sys/malloc.h>
#include <sys/buf.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/domain.h>
#include <sys/protosw.h>
#include <sys/filedesc.h>
#include <sys/signalvar.h>
#include <sys/kthread.h>
#include <sys/queue.h>

#include <sys/syscallargs.h>

#include <netinet/in.h>
#include <netinet/tcp.h>
#include <nfs/nfsproto.h>
#include <nfs/nfs.h>
#include <nfs/nfsrvcache.h>
#include <nfs/nfsnode.h>
#include <nfs/nfs_var.h>

/* Global defs. */
extern int nfs_numasync;
extern struct nfsstats nfsstats;
struct nfssvc_sock *nfs_udpsock;
int nfsd_waiting = 0;

#ifdef NFSSERVER
struct pool nfsrv_descript_pl;

int nfsrv_getslp(struct nfsd *nfsd);

static int nfs_numnfsd = 0;
static int (*const nfsrv3_procs[NFS_NPROCS])(struct nfsrv_descript *,
    struct nfssvc_sock *, struct proc *, struct mbuf **) = {
        nfsrv_null,
        nfsrv_getattr,
        nfsrv_setattr,
        nfsrv_lookup,
        nfsrv3_access,
        nfsrv_readlink,
        nfsrv_read,
        nfsrv_write,
        nfsrv_create,
        nfsrv_mkdir,
        nfsrv_symlink,
        nfsrv_mknod,
        nfsrv_remove,
        nfsrv_rmdir,
        nfsrv_rename,
        nfsrv_link,
        nfsrv_readdir,
        nfsrv_readdirplus,
        nfsrv_statfs,
        nfsrv_fsinfo,
        nfsrv_pathconf,
        nfsrv_commit,
        nfsrv_noop
};
#endif

TAILQ_HEAD(, nfssvc_sock) nfssvc_sockhead;
struct nfsdhead nfsd_head;

int nfssvc_sockhead_flag;
#define SLP_INIT        0x01    /* NFS data undergoing initialization */
#define SLP_WANTINIT    0x02    /* thread waiting on NFS initialization */
int nfsd_head_flag;

#ifdef NFSCLIENT
struct proc *nfs_asyncdaemon[NFS_MAXASYNCDAEMON];
int nfs_niothreads = -1;
#endif

int nfssvc_addsock(struct file *, struct mbuf *);
int nfssvc_nfsd(struct nfsd *);
void nfsrv_slpderef(struct nfssvc_sock *);
void nfsrv_zapsock(struct nfssvc_sock *);
void nfssvc_iod(void *);

/*
 * NFS server pseudo system call for the nfsd's
 * Based on the flag value it either:
 * - adds a socket to the selection list
 * - remains in the kernel as an nfsd
 */
int
sys_nfssvc(struct proc *p, void *v, register_t *retval)
{
        int error = 0;
#ifdef NFSSERVER
        struct sys_nfssvc_args /* {
                syscallarg(int) flag;
                syscallarg(caddr_t) argp;
        } */ *uap = v;
        int flags = SCARG(uap, flag);
        struct file *fp;
        struct mbuf *nam;
        struct nfsd_args nfsdarg;
        struct nfsd_srvargs nfsd_srvargs, *nsd = &nfsd_srvargs;
        struct nfsd *nfsd;
#endif

        /* Must be super user */
        error = suser(p);
        if (error)
                return (error);

#ifndef NFSSERVER
        error = ENOSYS;
#else

        while (nfssvc_sockhead_flag & SLP_INIT) {
                nfssvc_sockhead_flag |= SLP_WANTINIT;
                tsleep_nsec(&nfssvc_sockhead, PSOCK, "nfsd init", INFSLP);
        }

        switch (flags) {
        case NFSSVC_ADDSOCK:
                error = copyin(SCARG(uap, argp), &nfsdarg, sizeof(nfsdarg));
                if (error)
                        return (error);

                error = getsock(p, nfsdarg.sock, &fp);
                if (error)
                        return (error);

                /*
                 * Get the client address for connected sockets.
                 */
                if (nfsdarg.name == NULL || nfsdarg.namelen == 0)
                        nam = NULL;
                else {
                        error = sockargs(&nam, nfsdarg.name, nfsdarg.namelen,
                                MT_SONAME);
                        if (error) {
                                FRELE(fp, p);
                                return (error);
                        }
                }
                error = nfssvc_addsock(fp, nam);
                FRELE(fp, p);
                break;
        case NFSSVC_NFSD:
                error = copyin(SCARG(uap, argp), nsd, sizeof(*nsd));
                if (error)
                        return (error);

                nfsd = malloc(sizeof(*nfsd), M_NFSD, M_WAITOK|M_ZERO);
                nfsd->nfsd_procp = p;
                nfsd->nfsd_slp = NULL;

                error = nfssvc_nfsd(nfsd);
                break;
        default:
                error = EINVAL;
                break;
        }

        if (error == EINTR || error == ERESTART)
                error = 0;
#endif  /* !NFSSERVER */

        return (error);
}

#ifdef NFSSERVER
/*
 * Adds a socket to the list for servicing by nfsds.
 */
int
nfssvc_addsock(struct file *fp, struct mbuf *mynam)
{
        struct mbuf *m;
        int siz;
        struct nfssvc_sock *slp;
        struct socket *so;
        struct nfssvc_sock *tslp;
        int error;

        so = (struct socket *)fp->f_data;
        tslp = NULL;
        /*
         * Add it to the list, as required.
         */
        if (so->so_proto->pr_protocol == IPPROTO_UDP) {
                tslp = nfs_udpsock;
                if (tslp->ns_flag & SLP_VALID) {
                        m_freem(mynam);
                        return (EPERM);
                }
        }
        /*
         * Allow only IPv4 UDP and TCP sockets.
         */
        if ((so->so_type != SOCK_STREAM && so->so_type != SOCK_DGRAM) || 
            so->so_proto->pr_domain->dom_family != AF_INET) {
                m_freem(mynam);
                return (EINVAL);
        }

        if (so->so_type == SOCK_STREAM)
                siz = NFS_MAXPACKET + sizeof (u_long);
        else
                siz = NFS_MAXPACKET;
        solock_shared(so);
        error = soreserve(so, siz, siz); 
        sounlock_shared(so);
        if (error) {
                m_freem(mynam);
                return (error);
        }

        /*
         * Set protocol specific options { for now TCP only } and
         * reserve some space. For datagram sockets, this can get called
         * repeatedly for the same socket, but that isn't harmful.
         */
        if (so->so_type == SOCK_STREAM) {
                MGET(m, M_WAIT, MT_SOOPTS);
                *mtod(m, int32_t *) = 1;
                m->m_len = sizeof(int32_t);
                sosetopt(so, SOL_SOCKET, SO_KEEPALIVE, m);
                m_freem(m);
        }
        if (so->so_proto->pr_domain->dom_family == AF_INET &&
            so->so_proto->pr_protocol == IPPROTO_TCP) {
                MGET(m, M_WAIT, MT_SOOPTS);
                *mtod(m, int32_t *) = 1;
                m->m_len = sizeof(int32_t);
                sosetopt(so, IPPROTO_TCP, TCP_NODELAY, m);
                m_freem(m);
        }
        solock_shared(so);
        mtx_enter(&so->so_rcv.sb_mtx);
        so->so_rcv.sb_flags &= ~SB_NOINTR;
        so->so_rcv.sb_timeo_nsecs = INFSLP;
        mtx_leave(&so->so_rcv.sb_mtx);
        mtx_enter(&so->so_snd.sb_mtx);
        so->so_snd.sb_flags &= ~SB_NOINTR;
        so->so_snd.sb_timeo_nsecs = INFSLP;
        mtx_leave(&so->so_snd.sb_mtx);
        sounlock_shared(so);
        if (tslp)
                slp = tslp;
        else {
                slp = malloc(sizeof(*slp), M_NFSSVC, M_WAITOK|M_ZERO);
                TAILQ_INSERT_TAIL(&nfssvc_sockhead, slp, ns_chain);
        }
        slp->ns_so = so;
        slp->ns_nam = mynam;
        FREF(fp);
        slp->ns_fp = fp;
        so->so_upcallarg = (caddr_t)slp;
        so->so_upcall = nfsrv_rcv;
        slp->ns_flag = (SLP_VALID | SLP_NEEDQ);
        nfsrv_wakenfsd(slp);
        return (0);
}

static inline int
nfssvc_checknam(struct mbuf *nam)
{
        struct sockaddr_in *sin;

        if (nam == NULL ||
            in_nam2sin(nam, &sin) != 0 ||
            ntohs(sin->sin_port) >= IPPORT_RESERVED) {
                return -1;
        }
        return 0;
}

/*
 * Called by nfssvc() for nfsds. Just loops around servicing rpc requests
 * until it is killed by a signal.
 */
int
nfssvc_nfsd(struct nfsd *nfsd)
{
        struct mbuf *m;
        int siz;
        struct nfssvc_sock *slp;
        struct socket *so;
        int *solockp;
        struct nfsrv_descript *nd = NULL;
        struct mbuf *mreq;
        int error = 0, cacherep, sotype;

        cacherep = RC_DOIT;

        TAILQ_INSERT_TAIL(&nfsd_head, nfsd, nfsd_chain);
        nfs_numnfsd++;

        /* Loop getting rpc requests until SIGKILL. */
loop:
        if (!ISSET(nfsd->nfsd_flag, NFSD_REQINPROG)) {

                /* attach an nfssvc_sock to nfsd */
                error = nfsrv_getslp(nfsd);
                if (error)
                        goto done;

                slp = nfsd->nfsd_slp;

                if (ISSET(slp->ns_flag, SLP_VALID)) {
                        if ((slp->ns_flag & (SLP_DISCONN | SLP_NEEDQ)) ==
                            SLP_NEEDQ) {
                                CLR(slp->ns_flag, SLP_NEEDQ);
                                nfs_sndlock(&slp->ns_solock, NULL);
                                nfsrv_rcv(slp->ns_so, (caddr_t)slp, M_WAIT);
                                nfs_sndunlock(&slp->ns_solock);
                        }
                        if (ISSET(slp->ns_flag, SLP_DISCONN))
                                nfsrv_zapsock(slp);

                        error = nfsrv_dorec(slp, nfsd, &nd);
                        SET(nfsd->nfsd_flag, NFSD_REQINPROG);
                }
        } else {
                error = 0;
                slp = nfsd->nfsd_slp;
        }

        if (error || !ISSET(slp->ns_flag, SLP_VALID)) {
                if (nd != NULL) {
                        pool_put(&nfsrv_descript_pl, nd);
                        nd = NULL;
                }
                nfsd->nfsd_slp = NULL;
                CLR(nfsd->nfsd_flag, NFSD_REQINPROG);
                nfsrv_slpderef(slp);
                goto loop;
        }

        so = slp->ns_so;
        sotype = so->so_type;
        if (ISSET(so->so_proto->pr_flags, PR_CONNREQUIRED))
                solockp = &slp->ns_solock;
        else
                solockp = NULL;

        if (nd) {
                if (nd->nd_nam2)
                        nd->nd_nam = nd->nd_nam2;
                else
                        nd->nd_nam = slp->ns_nam;
        }

        cacherep = nfsrv_getcache(nd, slp, &mreq);
        switch (cacherep) {
        case RC_DOIT:
                /*
                 * Unless this is a null request (server ping), make
                 * sure that the client is using a reserved source port.
                 */
                if (nd->nd_procnum != 0 && nfssvc_checknam(nd->nd_nam) == -1) {
                        /* drop it */
                        m_freem(nd->nd_mrep);
                        m_freem(nd->nd_nam2);
                        break;
                }
                error = (*(nfsrv3_procs[nd->nd_procnum]))(nd, slp, nfsd->nfsd_procp, &mreq);
                if (mreq == NULL) {
                        if (nd != NULL) {
                                m_freem(nd->nd_nam2);
                                m_freem(nd->nd_mrep);
                        }
                        break;
                }
                if (error) {
                        nfsstats.srv_errs++;
                        nfsrv_updatecache(nd, 0, mreq);
                        m_freem(nd->nd_nam2);
                        break;
                }
                nfsstats.srvrpccnt[nd->nd_procnum]++;
                nfsrv_updatecache(nd, 1, mreq);
                nd->nd_mrep = NULL;

                /* FALLTHROUGH */
        case RC_REPLY:
                m = mreq;
                siz = 0;
                while (m) {
                        siz += m->m_len;
                        m = m->m_next;
                }

                if (siz <= 0 || siz > NFS_MAXPACKET)
                        panic("bad nfs svc reply, siz = %i", siz);

                m = mreq;
                m->m_pkthdr.len = siz;
                m->m_pkthdr.ph_ifidx = 0;

                /* For stream protocols, prepend a Sun RPC Record Mark. */
                if (sotype == SOCK_STREAM) {
                        M_PREPEND(m, NFSX_UNSIGNED, M_WAIT);
                        *mtod(m, u_int32_t *) = htonl(0x80000000 | siz);
                }

                if (solockp)
                        nfs_sndlock(solockp, NULL);

                if (ISSET(slp->ns_flag, SLP_VALID))
                    error = nfs_send(so, nd->nd_nam2, m, NULL);
                else {
                    error = EPIPE;
                    m_freem(m);
                }
                m_freem(nd->nd_nam2);
                m_freem(nd->nd_mrep);
                if (error == EPIPE)
                        nfsrv_zapsock(slp);
                if (solockp)
                        nfs_sndunlock(solockp);
                if (error == EINTR || error == ERESTART) {
                        pool_put(&nfsrv_descript_pl, nd);
                        nfsrv_slpderef(slp);
                        goto done;
                }
                break;
        case RC_DROPIT:
                m_freem(nd->nd_mrep);
                m_freem(nd->nd_nam2);
                break;
        }

        if (nd) {
                pool_put(&nfsrv_descript_pl, nd);
                nd = NULL;
        }

        if (nfsrv_dorec(slp, nfsd, &nd)) {
                nfsd->nfsd_flag &= ~NFSD_REQINPROG;
                nfsd->nfsd_slp = NULL;
                nfsrv_slpderef(slp);
        }
        goto loop;

done:
        TAILQ_REMOVE(&nfsd_head, nfsd, nfsd_chain);
        free(nfsd, M_NFSD, sizeof(*nfsd));
        if (--nfs_numnfsd == 0)
                nfsrv_init(1);  /* Reinitialize everything */
        return (error);
}

/*
 * Shut down a socket associated with an nfssvc_sock structure.
 * Should be called with the send lock set, if required.
 * The trick here is to increment the sref at the start, so that the nfsds
 * will stop using it and clear ns_flag at the end so that it will not be
 * reassigned during cleanup.
 */
void
nfsrv_zapsock(struct nfssvc_sock *slp)
{
        struct socket *so;
        struct file *fp;
        struct mbuf *m, *n;

        slp->ns_flag &= ~SLP_ALLFLAGS;
        fp = slp->ns_fp;
        if (fp) {
                FREF(fp);
                slp->ns_fp = NULL;
                so = slp->ns_so;
                so->so_upcall = NULL;
                soshutdown(so, SHUT_RDWR);
                closef(fp, NULL);
                if (slp->ns_nam)
                        m = m_free(slp->ns_nam);
                m_freem(slp->ns_raw);
                m = slp->ns_rec;
                while (m) {
                        n = m->m_nextpkt;
                        m_freem(m);
                        m = n;
                }
        }
}

/*
 * Dereference a server socket structure. If it has no more references and
 * is no longer valid, you can throw it away.
 */
void
nfsrv_slpderef(struct nfssvc_sock *slp)
{
        if (--(slp->ns_sref) == 0 && (slp->ns_flag & SLP_VALID) == 0) {
                TAILQ_REMOVE(&nfssvc_sockhead, slp, ns_chain);
                free(slp, M_NFSSVC, sizeof(*slp));
        }
}

/*
 * Initialize the data structures for the server.
 * Handshake with any new nfsds starting up to avoid any chance of
 * corruption.
 */
void
nfsrv_init(int terminating)
{
        struct nfssvc_sock *slp, *nslp;

        if (nfssvc_sockhead_flag & SLP_INIT)
                panic("nfsd init");
        nfssvc_sockhead_flag |= SLP_INIT;
        if (terminating) {
                for (slp = TAILQ_FIRST(&nfssvc_sockhead); slp != NULL;
                    slp = nslp) {
                        nslp = TAILQ_NEXT(slp, ns_chain);
                        if (slp->ns_flag & SLP_VALID)
                                nfsrv_zapsock(slp);
                        TAILQ_REMOVE(&nfssvc_sockhead, slp, ns_chain);
                        free(slp, M_NFSSVC, sizeof(*slp));
                }
                nfsrv_cleancache();     /* And clear out server cache */
        }

        TAILQ_INIT(&nfssvc_sockhead);
        nfssvc_sockhead_flag &= ~SLP_INIT;
        if (nfssvc_sockhead_flag & SLP_WANTINIT) {
                nfssvc_sockhead_flag &= ~SLP_WANTINIT;
                wakeup((caddr_t)&nfssvc_sockhead);
        }

        TAILQ_INIT(&nfsd_head);
        nfsd_head_flag &= ~NFSD_CHECKSLP;

        nfs_udpsock =  malloc(sizeof(*nfs_udpsock), M_NFSSVC,
            M_WAITOK|M_ZERO);
        TAILQ_INSERT_HEAD(&nfssvc_sockhead, nfs_udpsock, ns_chain);

        if (!terminating) {
                pool_init(&nfsrv_descript_pl, sizeof(struct nfsrv_descript),
                    0, IPL_NONE, PR_WAITOK, "ndscpl", NULL);
        }
}
#endif /* NFSSERVER */

#ifdef NFSCLIENT
/*
 * Asynchronous I/O threads for client nfs.
 * They do read-ahead and write-behind operations on the block I/O cache.
 * Never returns unless it fails or gets killed.
 */
void
nfssvc_iod(void *arg)
{
        struct proc *p = curproc;
        struct buf *bp, *nbp;
        int i, myiod;
        struct vnode *vp;
        int error = 0, s, bufcount;

        bufcount = MIN(256, bcstats.kvaslots / 8);
        bufcount = MIN(bufcount, bcstats.numbufs / 8);

        /* Assign my position or return error if too many already running. */
        myiod = -1;
        for (i = 0; i < NFS_MAXASYNCDAEMON; i++) {
                if (nfs_asyncdaemon[i] == NULL) {
                        myiod = i;
                        break;
                }
        }
        if (myiod == -1)
                kthread_exit(EBUSY);

        nfs_asyncdaemon[myiod] = p;
        nfs_numasync++;

        /* Upper limit on how many bufs we'll queue up for this iod. */
        if (nfs_bufqmax > bcstats.kvaslots / 4) {
                nfs_bufqmax = bcstats.kvaslots / 4;
                bufcount = 0;
        } 
        if (nfs_bufqmax > bcstats.numbufs / 4) {
                nfs_bufqmax = bcstats.numbufs / 4;
                bufcount = 0;
        }

        nfs_bufqmax += bufcount;
        wakeup(&nfs_bufqlen); /* wake up anyone waiting for room to enqueue IO */

        /* Just loop around doin our stuff until SIGKILL. */
        for (;;) {
            while (TAILQ_FIRST(&nfs_bufq) == NULL && error == 0) {
                    error = tsleep_nsec(&nfs_bufq,
                        PWAIT | PCATCH, "nfsidl", INFSLP);
            }
            while ((bp = TAILQ_FIRST(&nfs_bufq)) != NULL) {
                /* Take one off the front of the list */
                TAILQ_REMOVE(&nfs_bufq, bp, b_freelist);
                nfs_bufqlen--;
                wakeup_one(&nfs_bufqlen);
                if (bp->b_flags & B_READ)
                    (void) nfs_doio(bp, NULL);
                else do {
                    /*
                     * Look for a delayed write for the same vnode, so I can do 
                     * it now. We must grab it before calling nfs_doio() to
                     * avoid any risk of the vnode getting vclean()'d while
                     * we are doing the write rpc.
                     */
                    vp = bp->b_vp;
                    s = splbio();
                    LIST_FOREACH(nbp, &vp->v_dirtyblkhd, b_vnbufs) {
                        if ((nbp->b_flags &
                            (B_BUSY|B_DELWRI|B_NEEDCOMMIT|B_NOCACHE))!=B_DELWRI)
                            continue;
                        nbp->b_flags |= B_ASYNC;
                        bufcache_take(nbp);
                        buf_acquire(nbp);
                        break;
                    }
                    /*
                     * For the delayed write, do the first part of nfs_bwrite()
                     * up to, but not including nfs_strategy().
                     */
                    if (nbp) {
                        nbp->b_flags &= ~(B_READ|B_DONE|B_ERROR);
                        buf_undirty(nbp);
                        nbp->b_vp->v_numoutput++;
                    }
                    splx(s);

                    (void) nfs_doio(bp, NULL);
                } while ((bp = nbp) != NULL);
            }
            if (error) {
                nfs_asyncdaemon[myiod] = NULL;
                nfs_numasync--;
                nfs_bufqmax -= bufcount;
                kthread_exit(error);
            }
        }
}

void
nfs_getset_niothreads(int set)
{
        int i, have, start;
        
        for (have = 0, i = 0; i < NFS_MAXASYNCDAEMON; i++)
                if (nfs_asyncdaemon[i] != NULL)
                        have++;

        if (set) {
                /* clamp to sane range */
                nfs_niothreads = max(0, min(nfs_niothreads, NFS_MAXASYNCDAEMON));

                start = nfs_niothreads - have;

                while (start > 0) {
                        kthread_create(nfssvc_iod, NULL, NULL, "nfsio");
                        start--;
                }

                for (i = 0; (start < 0) && (i < NFS_MAXASYNCDAEMON); i++)
                        if (nfs_asyncdaemon[i] != NULL) {
                                psignal(nfs_asyncdaemon[i], SIGKILL);
                                start++;
                        }
        } else {
                if (nfs_niothreads >= 0)
                        nfs_niothreads = have;
        }
}
#endif /* NFSCLIENT */

#ifdef NFSSERVER
/*
 * Find an nfssrv_sock for nfsd, sleeping if needed.
 */
int
nfsrv_getslp(struct nfsd *nfsd)
{
        struct nfssvc_sock *slp;
        int error;

again:
        while (nfsd->nfsd_slp == NULL &&
            (nfsd_head_flag & NFSD_CHECKSLP) == 0) {
                nfsd->nfsd_flag |= NFSD_WAITING;
                nfsd_waiting++;
                error = tsleep_nsec(nfsd, PSOCK | PCATCH, "nfsd", INFSLP);
                nfsd_waiting--;
                if (error)
                        return (error);
        }

        if (nfsd->nfsd_slp == NULL &&
            (nfsd_head_flag & NFSD_CHECKSLP) != 0) {
                TAILQ_FOREACH(slp, &nfssvc_sockhead, ns_chain) {
                        if ((slp->ns_flag & (SLP_VALID | SLP_DOREC)) ==
                            (SLP_VALID | SLP_DOREC)) {
                                slp->ns_flag &= ~SLP_DOREC;
                                slp->ns_sref++;
                                nfsd->nfsd_slp = slp;
                                break;
                        }
                }
                if (slp == NULL)
                        nfsd_head_flag &= ~NFSD_CHECKSLP;
        }

        if (nfsd->nfsd_slp == NULL)
                goto again;

        return (0);
}
#endif /* NFSSERVER */