bridge.4: Add missing .Bl/.El

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

/*-
 * Copyright (c) 1982, 1986, 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * 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.
 *
 *      @(#)kern_resource.c     8.5 (Berkeley) 1/21/94
 * $FreeBSD: src/sys/kern/kern_resource.c,v 1.55.2.5 2001/11/03 01:41:08 ps Exp $
 * $DragonFly: src/sys/kern/kern_resource.c,v 1.35 2008/05/27 05:25:34 dillon Exp $
 */

#include "opt_compat.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysproto.h>
#include <sys/file.h>
#include <sys/kern_syscall.h>
#include <sys/kernel.h>
#include <sys/resourcevar.h>
#include <sys/malloc.h>
#include <sys/proc.h>
#include <sys/priv.h>
#include <sys/time.h>
#include <sys/lockf.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <sys/lock.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>

#include <sys/thread2.h>
#include <sys/spinlock2.h>

static int donice (struct proc *chgp, int n);
static int doionice (struct proc *chgp, int n);

static MALLOC_DEFINE(M_UIDINFO, "uidinfo", "uidinfo structures");
#define UIHASH(uid)     (&uihashtbl[(uid) & uihash])
static struct spinlock uihash_lock;
static LIST_HEAD(uihashhead, uidinfo) *uihashtbl;
static u_long uihash;           /* size of hash table - 1 */

static struct uidinfo   *uicreate (uid_t uid);
static struct uidinfo   *uilookup (uid_t uid);

/*
 * Resource controls and accounting.
 */

struct getpriority_info {
        int low;
        int who;
};

static int getpriority_callback(struct proc *p, void *data);

/*
 * MPALMOSTSAFE
 */
int
sys_getpriority(struct getpriority_args *uap)
{
        struct getpriority_info info;
        struct proc *curp = curproc;
        struct proc *p;
        int low = PRIO_MAX + 1;
        int error;

        switch (uap->which) {
        case PRIO_PROCESS:
                if (uap->who == 0) {
                        p = curp;
                        PHOLD(p);
                } else {
                        p = pfind(uap->who);
                }
                if (p) {
                        if (PRISON_CHECK(curp->p_ucred, p->p_ucred)) {
                                low = p->p_nice;
                        }
                        PRELE(p);
                }
                break;

        case PRIO_PGRP: 
        {
                struct pgrp *pg;

                if (uap->who == 0) {
                        pg = curp->p_pgrp;
                        pgref(pg);
                } else if ((pg = pgfind(uap->who)) == NULL) {
                        break;
                } /* else ref held from pgfind */

                LIST_FOREACH(p, &pg->pg_members, p_pglist) {
                        if (PRISON_CHECK(curp->p_ucred, p->p_ucred) &&
                            p->p_nice < low) {
                                low = p->p_nice;
                        }
                }
                pgrel(pg);
                break;
        }
        case PRIO_USER:
                if (uap->who == 0)
                        uap->who = curp->p_ucred->cr_uid;
                info.low = low;
                info.who = uap->who;
                allproc_scan(getpriority_callback, &info);
                low = info.low;
                break;

        default:
                error = EINVAL;
                goto done;
        }
        if (low == PRIO_MAX + 1) {
                error = ESRCH;
                goto done;
        }
        uap->sysmsg_result = low;
        error = 0;
done:
        return (error);
}

/*
 * Figure out the current lowest nice priority for processes owned
 * by the specified user.
 */
static
int
getpriority_callback(struct proc *p, void *data)
{
        struct getpriority_info *info = data;

        if (PRISON_CHECK(curproc->p_ucred, p->p_ucred) &&
            p->p_ucred->cr_uid == info->who &&
            p->p_nice < info->low) {
                info->low = p->p_nice;
        }
        return(0);
}

struct setpriority_info {
        int prio;
        int who;
        int error;
        int found;
};

static int setpriority_callback(struct proc *p, void *data);

/*
 * MPALMOSTSAFE
 */
int
sys_setpriority(struct setpriority_args *uap)
{
        struct setpriority_info info;
        struct proc *curp = curproc;
        struct proc *p;
        int found = 0, error = 0;

        lwkt_gettoken(&proc_token);

        switch (uap->which) {
        case PRIO_PROCESS:
                if (uap->who == 0) {
                        p = curp;
                        PHOLD(p);
                } else {
                        p = pfind(uap->who);
                }
                if (p) {
                        if (PRISON_CHECK(curp->p_ucred, p->p_ucred)) {
                                error = donice(p, uap->prio);
                                found++;
                        }
                        PRELE(p);
                }
                break;

        case PRIO_PGRP: 
        {
                struct pgrp *pg;

                if (uap->who == 0) {
                        pg = curp->p_pgrp;
                        pgref(pg);
                } else if ((pg = pgfind(uap->who)) == NULL) {
                        break;
                } /* else ref held from pgfind */

                LIST_FOREACH(p, &pg->pg_members, p_pglist) {
                        if (PRISON_CHECK(curp->p_ucred, p->p_ucred)) {
                                error = donice(p, uap->prio);
                                found++;
                        }
                }
                pgrel(pg);
                break;
        }
        case PRIO_USER:
                if (uap->who == 0)
                        uap->who = curp->p_ucred->cr_uid;
                info.prio = uap->prio;
                info.who = uap->who;
                info.error = 0;
                info.found = 0;
                allproc_scan(setpriority_callback, &info);
                error = info.error;
                found = info.found;
                break;

        default:
                error = EINVAL;
                found = 1;
                break;
        }

        lwkt_reltoken(&proc_token);

        if (found == 0)
                error = ESRCH;
        return (error);
}

static
int
setpriority_callback(struct proc *p, void *data)
{
        struct setpriority_info *info = data;
        int error;

        if (p->p_ucred->cr_uid == info->who &&
            PRISON_CHECK(curproc->p_ucred, p->p_ucred)) {
                error = donice(p, info->prio);
                if (error)
                        info->error = error;
                ++info->found;
        }
        return(0);
}

static int
donice(struct proc *chgp, int n)
{
        struct proc *curp = curproc;
        struct ucred *cr = curp->p_ucred;
        struct lwp *lp;

        if (cr->cr_uid && cr->cr_ruid &&
            cr->cr_uid != chgp->p_ucred->cr_uid &&
            cr->cr_ruid != chgp->p_ucred->cr_uid)
                return (EPERM);
        if (n > PRIO_MAX)
                n = PRIO_MAX;
        if (n < PRIO_MIN)
                n = PRIO_MIN;
        if (n < chgp->p_nice && priv_check_cred(cr, PRIV_SCHED_SETPRIORITY, 0))
                return (EACCES);
        chgp->p_nice = n;
        FOREACH_LWP_IN_PROC(lp, chgp)
                chgp->p_usched->resetpriority(lp);
        return (0);
}


struct ioprio_get_info {
        int high;
        int who;
};

static int ioprio_get_callback(struct proc *p, void *data);

/*
 * MPALMOSTSAFE
 */
int
sys_ioprio_get(struct ioprio_get_args *uap)
{
        struct ioprio_get_info info;
        struct proc *curp = curproc;
        struct proc *p;
        int high = IOPRIO_MIN-2;
        int error;

        lwkt_gettoken(&proc_token);

        switch (uap->which) {
        case PRIO_PROCESS:
                if (uap->who == 0) {
                        p = curp;
                        PHOLD(p);
                } else {
                        p = pfind(uap->who);
                }
                if (p) {
                        if (PRISON_CHECK(curp->p_ucred, p->p_ucred))
                                high = p->p_ionice;
                        PRELE(p);
                }
                break;

        case PRIO_PGRP:
        {
                struct pgrp *pg;

                if (uap->who == 0) {
                        pg = curp->p_pgrp;
                        pgref(pg);
                } else if ((pg = pgfind(uap->who)) == NULL) {
                        break;
                } /* else ref held from pgfind */

                LIST_FOREACH(p, &pg->pg_members, p_pglist) {
                        if (PRISON_CHECK(curp->p_ucred, p->p_ucred) &&
                            p->p_nice > high)
                                high = p->p_ionice;
                }
                pgrel(pg);
                break;
        }
        case PRIO_USER:
                if (uap->who == 0)
                        uap->who = curp->p_ucred->cr_uid;
                info.high = high;
                info.who = uap->who;
                allproc_scan(ioprio_get_callback, &info);
                high = info.high;
                break;

        default:
                error = EINVAL;
                goto done;
        }
        if (high == IOPRIO_MIN-2) {
                error = ESRCH;
                goto done;
        }
        uap->sysmsg_result = high;
        error = 0;
done:
        lwkt_reltoken(&proc_token);

        return (error);
}

/*
 * Figure out the current lowest nice priority for processes owned
 * by the specified user.
 */
static
int
ioprio_get_callback(struct proc *p, void *data)
{
        struct ioprio_get_info *info = data;

        if (PRISON_CHECK(curproc->p_ucred, p->p_ucred) &&
            p->p_ucred->cr_uid == info->who &&
            p->p_ionice > info->high) {
                info->high = p->p_ionice;
        }
        return(0);
}


struct ioprio_set_info {
        int prio;
        int who;
        int error;
        int found;
};

static int ioprio_set_callback(struct proc *p, void *data);

/*
 * MPALMOSTSAFE
 */
int
sys_ioprio_set(struct ioprio_set_args *uap)
{
        struct ioprio_set_info info;
        struct proc *curp = curproc;
        struct proc *p;
        int found = 0, error = 0;

        lwkt_gettoken(&proc_token);

        switch (uap->which) {
        case PRIO_PROCESS:
                if (uap->who == 0) {
                        p = curp;
                        PHOLD(p);
                } else {
                        p = pfind(uap->who);
                }
                if (p) {
                        if (PRISON_CHECK(curp->p_ucred, p->p_ucred)) {
                                error = doionice(p, uap->prio);
                                found++;
                        }
                        PRELE(p);
                }
                break;

        case PRIO_PGRP:
        {
                struct pgrp *pg;

                if (uap->who == 0) {
                        pg = curp->p_pgrp;
                        pgref(pg);
                } else if ((pg = pgfind(uap->who)) == NULL) {
                        break;
                } /* else ref held from pgfind */

                LIST_FOREACH(p, &pg->pg_members, p_pglist) {
                        if (PRISON_CHECK(curp->p_ucred, p->p_ucred)) {
                                error = doionice(p, uap->prio);
                                found++;
                        }
                }
                pgrel(pg);
                break;
        }
        case PRIO_USER:
                if (uap->who == 0)
                        uap->who = curp->p_ucred->cr_uid;
                info.prio = uap->prio;
                info.who = uap->who;
                info.error = 0;
                info.found = 0;
                allproc_scan(ioprio_set_callback, &info);
                error = info.error;
                found = info.found;
                break;

        default:
                error = EINVAL;
                found = 1;
                break;
        }

        lwkt_reltoken(&proc_token);

        if (found == 0)
                error = ESRCH;
        return (error);
}

static
int
ioprio_set_callback(struct proc *p, void *data)
{
        struct ioprio_set_info *info = data;
        int error;

        if (p->p_ucred->cr_uid == info->who &&
            PRISON_CHECK(curproc->p_ucred, p->p_ucred)) {
                error = doionice(p, info->prio);
                if (error)
                        info->error = error;
                ++info->found;
        }
        return(0);
}

int
doionice(struct proc *chgp, int n)
{
        struct proc *curp = curproc;
        struct ucred *cr = curp->p_ucred;

        if (cr->cr_uid && cr->cr_ruid &&
            cr->cr_uid != chgp->p_ucred->cr_uid &&
            cr->cr_ruid != chgp->p_ucred->cr_uid)
                return (EPERM);
        if (n > IOPRIO_MAX)
                n = IOPRIO_MAX;
        if (n < IOPRIO_MIN)
                n = IOPRIO_MIN;
        if (n < chgp->p_ionice && priv_check_cred(cr, PRIV_SCHED_SETPRIORITY, 0))
                return (EACCES);
        chgp->p_ionice = n;

        return (0);

}

/*
 * MPALMOSTSAFE
 */
int
sys_lwp_rtprio(struct lwp_rtprio_args *uap)
{
        struct proc *p;
        struct lwp *lp;
        struct rtprio rtp;
        struct ucred *cr = curthread->td_ucred;
        int error;

        error = copyin(uap->rtp, &rtp, sizeof(struct rtprio));
        if (error)
                return error;
        if (uap->pid < 0)
                return EINVAL;

        lwkt_gettoken(&proc_token);

        if (uap->pid == 0) {
                p = curproc;
                PHOLD(p);
        } else {
                p = pfind(uap->pid);
        }

        if (p == NULL) {
                error = ESRCH;
                goto done;
        }

        if (uap->tid < -1) {
                error = EINVAL;
                goto done;
        }
        if (uap->tid == -1) {
                /*
                 * sadly, tid can be 0 so we can't use 0 here
                 * like sys_rtprio()
                 */
                lp = curthread->td_lwp;
        } else {
                lp = lwp_rb_tree_RB_LOOKUP(&p->p_lwp_tree, uap->tid);
                if (lp == NULL) {
                        error = ESRCH;
                        goto done;
                }
        }

        switch (uap->function) {
        case RTP_LOOKUP:
                error = copyout(&lp->lwp_rtprio, uap->rtp,
                                sizeof(struct rtprio));
                break;
        case RTP_SET:
                if (cr->cr_uid && cr->cr_ruid &&
                    cr->cr_uid != p->p_ucred->cr_uid &&
                    cr->cr_ruid != p->p_ucred->cr_uid) {
                        error = EPERM;
                        break;
                }
                /* disallow setting rtprio in most cases if not superuser */
                if (priv_check_cred(cr, PRIV_SCHED_RTPRIO, 0)) {
                        /* can't set someone else's */
                        if (uap->pid) { /* XXX */
                                error = EPERM;
                                break;
                        }
                        /* can't set realtime priority */
/*
 * Realtime priority has to be restricted for reasons which should be
 * obvious. However, for idle priority, there is a potential for
 * system deadlock if an idleprio process gains a lock on a resource
 * that other processes need (and the idleprio process can't run
 * due to a CPU-bound normal process). Fix me! XXX
 */
                        if (RTP_PRIO_IS_REALTIME(rtp.type)) {
                                error = EPERM;
                                break;
                        }
                }
                switch (rtp.type) {
#ifdef RTP_PRIO_FIFO
                case RTP_PRIO_FIFO:
#endif
                case RTP_PRIO_REALTIME:
                case RTP_PRIO_NORMAL:
                case RTP_PRIO_IDLE:
                        if (rtp.prio > RTP_PRIO_MAX) {
                                error = EINVAL;
                        } else {
                                lp->lwp_rtprio = rtp;
                                error = 0;
                        }
                        break;
                default:
                        error = EINVAL;
                        break;
                }
                break;
        default:
                error = EINVAL;
                break;
        }

done:
        if (p)
                PRELE(p);
        lwkt_reltoken(&proc_token);

        return (error);
}

/*
 * Set realtime priority
 *
 * MPALMOSTSAFE
 */
int
sys_rtprio(struct rtprio_args *uap)
{
        struct proc *p;
        struct lwp *lp;
        struct ucred *cr = curthread->td_ucred;
        struct rtprio rtp;
        int error;

        error = copyin(uap->rtp, &rtp, sizeof(struct rtprio));
        if (error)
                return (error);

        lwkt_gettoken(&proc_token);

        if (uap->pid == 0) {
                p = curproc;
                PHOLD(p);
        } else {
                p = pfind(uap->pid);
        }

        if (p == NULL) {
                error = ESRCH;
                goto done;
        }

        /* XXX lwp */
        lp = FIRST_LWP_IN_PROC(p);
        switch (uap->function) {
        case RTP_LOOKUP:
                error = copyout(&lp->lwp_rtprio, uap->rtp,
                                sizeof(struct rtprio));
                break;
        case RTP_SET:
                if (cr->cr_uid && cr->cr_ruid &&
                    cr->cr_uid != p->p_ucred->cr_uid &&
                    cr->cr_ruid != p->p_ucred->cr_uid) {
                        error = EPERM;
                        break;
                }
                /* disallow setting rtprio in most cases if not superuser */
                if (priv_check_cred(cr, PRIV_SCHED_RTPRIO, 0)) {
                        /* can't set someone else's */
                        if (uap->pid) {
                                error = EPERM;
                                break;
                        }
                        /* can't set realtime priority */
/*
 * Realtime priority has to be restricted for reasons which should be
 * obvious. However, for idle priority, there is a potential for
 * system deadlock if an idleprio process gains a lock on a resource
 * that other processes need (and the idleprio process can't run
 * due to a CPU-bound normal process). Fix me! XXX
 */
                        if (RTP_PRIO_IS_REALTIME(rtp.type)) {
                                error = EPERM;
                                break;
                        }
                }
                switch (rtp.type) {
#ifdef RTP_PRIO_FIFO
                case RTP_PRIO_FIFO:
#endif
                case RTP_PRIO_REALTIME:
                case RTP_PRIO_NORMAL:
                case RTP_PRIO_IDLE:
                        if (rtp.prio > RTP_PRIO_MAX) {
                                error = EINVAL;
                                break;
                        }
                        lp->lwp_rtprio = rtp;
                        error = 0;
                        break;
                default:
                        error = EINVAL;
                        break;
                }
                break;
        default:
                error = EINVAL;
                break;
        }
done:
        if (p)
                PRELE(p);
        lwkt_reltoken(&proc_token);

        return (error);
}

/*
 * MPSAFE
 */
int
sys_setrlimit(struct __setrlimit_args *uap)
{
        struct rlimit alim;
        int error;

        error = copyin(uap->rlp, &alim, sizeof(alim));
        if (error)
                return (error);

        error = kern_setrlimit(uap->which, &alim);

        return (error);
}

/*
 * MPSAFE
 */
int
sys_getrlimit(struct __getrlimit_args *uap)
{
        struct rlimit lim;
        int error;

        error = kern_getrlimit(uap->which, &lim);

        if (error == 0)
                error = copyout(&lim, uap->rlp, sizeof(*uap->rlp));
        return error;
}

/*
 * Transform the running time and tick information in lwp lp's thread into user,
 * system, and interrupt time usage.
 *
 * Since we are limited to statclock tick granularity this is a statisical
 * calculation which will be correct over the long haul, but should not be
 * expected to measure fine grained deltas.
 *
 * It is possible to catch a lwp in the midst of being created, so
 * check whether lwp_thread is NULL or not.
 */
void
calcru(struct lwp *lp, struct timeval *up, struct timeval *sp)
{
        struct thread *td;

        /*
         * Calculate at the statclock level.  YYY if the thread is owned by
         * another cpu we need to forward the request to the other cpu, or
         * have a token to interlock the information in order to avoid racing
         * thread destruction.
         */
        if ((td = lp->lwp_thread) != NULL) {
                crit_enter();
                up->tv_sec = td->td_uticks / 1000000;
                up->tv_usec = td->td_uticks % 1000000;
                sp->tv_sec = td->td_sticks / 1000000;
                sp->tv_usec = td->td_sticks % 1000000;
                crit_exit();
        }
}

/*
 * Aggregate resource statistics of all lwps of a process.
 *
 * proc.p_ru keeps track of all statistics directly related to a proc.  This
 * consists of RSS usage and nswap information and aggregate numbers for all
 * former lwps of this proc.
 *
 * proc.p_cru is the sum of all stats of reaped children.
 *
 * lwp.lwp_ru contains the stats directly related to one specific lwp, meaning
 * packet, scheduler switch or page fault counts, etc.  This information gets
 * added to lwp.lwp_proc.p_ru when the lwp exits.
 */
void
calcru_proc(struct proc *p, struct rusage *ru)
{
        struct timeval upt, spt;
        long *rip1, *rip2;
        struct lwp *lp;

        *ru = p->p_ru;

        FOREACH_LWP_IN_PROC(lp, p) {
                calcru(lp, &upt, &spt);
                timevaladd(&ru->ru_utime, &upt);
                timevaladd(&ru->ru_stime, &spt);
                for (rip1 = &ru->ru_first, rip2 = &lp->lwp_ru.ru_first;
                     rip1 <= &ru->ru_last;
                     rip1++, rip2++)
                        *rip1 += *rip2;
        }
}


/*
 * MPALMOSTSAFE
 */
int
sys_getrusage(struct getrusage_args *uap)
{
        struct rusage ru;
        struct rusage *rup;
        int error;

        lwkt_gettoken(&proc_token);

        switch (uap->who) {
        case RUSAGE_SELF:
                rup = &ru;
                calcru_proc(curproc, rup);
                error = 0;
                break;
        case RUSAGE_CHILDREN:
                rup = &curproc->p_cru;
                error = 0;
                break;
        default:
                error = EINVAL;
                break;
        }
        if (error == 0)
                error = copyout(rup, uap->rusage, sizeof(struct rusage));
        lwkt_reltoken(&proc_token);
        return (error);
}

void
ruadd(struct rusage *ru, struct rusage *ru2)
{
        long *ip, *ip2;
        int i;

        timevaladd(&ru->ru_utime, &ru2->ru_utime);
        timevaladd(&ru->ru_stime, &ru2->ru_stime);
        if (ru->ru_maxrss < ru2->ru_maxrss)
                ru->ru_maxrss = ru2->ru_maxrss;
        ip = &ru->ru_first; ip2 = &ru2->ru_first;
        for (i = &ru->ru_last - &ru->ru_first; i >= 0; i--)
                *ip++ += *ip2++;
}

/*
 * Find the uidinfo structure for a uid.  This structure is used to
 * track the total resource consumption (process count, socket buffer
 * size, etc.) for the uid and impose limits.
 */
void
uihashinit(void)
{
        spin_init(&uihash_lock);
        uihashtbl = hashinit(maxproc / 16, M_UIDINFO, &uihash);
}

/*
 * NOTE: Must be called with uihash_lock held
 *
 * MPSAFE
 */
static struct uidinfo *
uilookup(uid_t uid)
{
        struct  uihashhead *uipp;
        struct  uidinfo *uip;

        uipp = UIHASH(uid);
        LIST_FOREACH(uip, uipp, ui_hash) {
                if (uip->ui_uid == uid)
                        break;
        }
        return (uip);
}

/*
 * Helper function to creat ea uid that could not be found.
 * This function will properly deal with races.
 *
 * MPSAFE
 */
static struct uidinfo *
uicreate(uid_t uid)
{
        struct  uidinfo *uip, *tmp;

        /*
         * Allocate space and check for a race
         */
        uip = kmalloc(sizeof(*uip), M_UIDINFO, M_WAITOK|M_ZERO);

        /*
         * Initialize structure and enter it into the hash table
         */
        spin_init(&uip->ui_lock);
        uip->ui_uid = uid;
        uip->ui_ref = 1;        /* we're returning a ref */
        varsymset_init(&uip->ui_varsymset, NULL);

        /*
         * Somebody may have already created the uidinfo for this
         * uid. If so, return that instead.
         */
        spin_lock(&uihash_lock);
        tmp = uilookup(uid);
        if (tmp != NULL) {
                uihold(tmp);
                spin_unlock(&uihash_lock);

                spin_uninit(&uip->ui_lock);
                varsymset_clean(&uip->ui_varsymset);
                FREE(uip, M_UIDINFO);
                uip = tmp;
        } else {
                LIST_INSERT_HEAD(UIHASH(uid), uip, ui_hash);
                spin_unlock(&uihash_lock);
        }
        return (uip);
}

/*
 *
 *
 * MPSAFE
 */
struct uidinfo *
uifind(uid_t uid)
{
        struct  uidinfo *uip;

        spin_lock(&uihash_lock);
        uip = uilookup(uid);
        if (uip == NULL) {
                spin_unlock(&uihash_lock);
                uip = uicreate(uid);
        } else {
                uihold(uip);
                spin_unlock(&uihash_lock);
        }
        return (uip);
}

/*
 * Helper funtion to remove a uidinfo whos reference count is
 * transitioning from 1->0.  The reference count is 1 on call.
 *
 * Zero is returned on success, otherwise non-zero and the
 * uiphas not been removed.
 *
 * MPSAFE
 */
static __inline int
uifree(struct uidinfo *uip)
{
        /*
         * If we are still the only holder after acquiring the uihash_lock
         * we can safely unlink the uip and destroy it.  Otherwise we lost
         * a race and must fail.
         */
        spin_lock(&uihash_lock);
        if (uip->ui_ref != 1) {
                spin_unlock(&uihash_lock);
                return(-1);
        }
        LIST_REMOVE(uip, ui_hash);
        spin_unlock(&uihash_lock);

        /*
         * The uip is now orphaned and we can destroy it at our
         * leisure.
         */
        if (uip->ui_sbsize != 0)
                kprintf("freeing uidinfo: uid = %d, sbsize = %jd\n",
                    uip->ui_uid, (intmax_t)uip->ui_sbsize);
        if (uip->ui_proccnt != 0)
                kprintf("freeing uidinfo: uid = %d, proccnt = %ld\n",
                    uip->ui_uid, uip->ui_proccnt);
        
        varsymset_clean(&uip->ui_varsymset);
        lockuninit(&uip->ui_varsymset.vx_lock);
        spin_uninit(&uip->ui_lock);
        FREE(uip, M_UIDINFO);
        return(0);
}

/*
 * MPSAFE
 */
void
uihold(struct uidinfo *uip)
{
        atomic_add_int(&uip->ui_ref, 1);
        KKASSERT(uip->ui_ref >= 0);
}

/*
 * NOTE: It is important for us to not drop the ref count to 0
 *       because this can cause a 2->0/2->0 race with another
 *       concurrent dropper.  Losing the race in that situation
 *       can cause uip to become stale for one of the other
 *       threads.
 *
 * MPSAFE
 */
void
uidrop(struct uidinfo *uip)
{
        int ref;

        KKASSERT(uip->ui_ref > 0);

        for (;;) {
                ref = uip->ui_ref;
                cpu_ccfence();
                if (ref == 1) {
                        if (uifree(uip) == 0)
                                break;
                } else if (atomic_cmpset_int(&uip->ui_ref, ref, ref - 1)) {
                        break;
                }
                /* else retry */
        }
}

void
uireplace(struct uidinfo **puip, struct uidinfo *nuip)
{
        uidrop(*puip);
        *puip = nuip;
}

/*
 * Change the count associated with number of processes
 * a given user is using.  When 'max' is 0, don't enforce a limit
 */
int
chgproccnt(struct uidinfo *uip, int diff, int max)
{
        int ret;
        spin_lock(&uip->ui_lock);
        /* don't allow them to exceed max, but allow subtraction */
        if (diff > 0 && uip->ui_proccnt + diff > max && max != 0) {
                ret = 0;
        } else {
                uip->ui_proccnt += diff;
                if (uip->ui_proccnt < 0)
                        kprintf("negative proccnt for uid = %d\n", uip->ui_uid);
                ret = 1;
        }
        spin_unlock(&uip->ui_lock);
        return ret;
}

/*
 * Change the total socket buffer size a user has used.
 */
int
chgsbsize(struct uidinfo *uip, u_long *hiwat, u_long to, rlim_t max)
{
        rlim_t new;

        spin_lock(&uip->ui_lock);
        new = uip->ui_sbsize + to - *hiwat;
        KKASSERT(new >= 0);

        /*
         * If we are trying to increase the socket buffer size
         * Scale down the hi water mark when we exceed the user's
         * allowed socket buffer space.
         *
         * We can't scale down too much or we will blow up atomic packet
         * operations.
         */
        if (to > *hiwat && to > MCLBYTES && new > max) {
                to = to * max / new;
                if (to < MCLBYTES)
                        to = MCLBYTES;
        }
        uip->ui_sbsize = new;
        *hiwat = to;
        spin_unlock(&uip->ui_lock);
        return (1);
}