/* $FreeBSD: src/sys/kern/sysv_sem.c,v 1.69 2004/03/17 09:37:13 cperciva Exp $ */

/*
 * Implementation of SVID semaphores
 *
 * Author:  Daniel Boulet
 *
 * This software is provided ``AS IS'' without any warranties of any kind.
 */

#include "opt_sysvipc.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysmsg.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/sem.h>
#include <sys/sysent.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/jail.h>
#include <sys/thread.h>

static MALLOC_DEFINE(M_SEM, "sem", "SVID compatible semaphores");

static void seminit (void *);

static struct sem_undo *semu_alloc (struct proc *p);
static int semundo_adjust (struct proc *p, int semid, int semnum, int adjval);
static void semundo_clear (int semid, int semnum);

static struct lwkt_token semu_token = LWKT_TOKEN_INITIALIZER(semu_token);
static int      semtot = 0;
static struct semid_pool *sema; /* semaphore id pool */
static TAILQ_HEAD(, sem_undo) semu_list = TAILQ_HEAD_INITIALIZER(semu_list);
static struct lock sema_lk;

struct sem {
        u_short semval;         /* semaphore value */
        pid_t   sempid;         /* pid of last operation */
        u_short semncnt;        /* # awaiting semval > cval */
        u_short semzcnt;        /* # awaiting semval = 0 */
};

/*
 * Undo structure (one per process)
 */
struct sem_undo {
        TAILQ_ENTRY(sem_undo) un_entry; /* linked list for semundo_clear() */
        struct  proc *un_proc;          /* owner of this structure */
        int     un_refs;                /* prevent unlink/kfree */
        short   un_cnt;                 /* # of active entries */
        short   un_unused;
        struct undo {
                short   un_adjval;      /* adjust on exit values */
                short   un_num;         /* semaphore # */
                int     un_id;          /* semid */
        } un_ent[1];                    /* undo entries */
};

/*
 * Configuration parameters
 */
#ifndef SEMMNI
#define SEMMNI  1024            /* # of semaphore identifiers */
#endif
#ifndef SEMMNS
#define SEMMNS  32767           /* # of semaphores in system */
#endif
#ifndef SEMUME
#define SEMUME  25              /* max # of undo entries per process */
#endif
#ifndef SEMMNU
#define SEMMNU  1024            /* # of undo structures in system */
                                /* NO LONGER USED */
#endif

/* shouldn't need tuning */
#ifndef SEMMAP
#define SEMMAP  128             /* # of entries in semaphore map */
#endif
#ifndef SEMMSL
#define SEMMSL  SEMMNS          /* max # of semaphores per id */
#endif
#ifndef SEMOPM
#define SEMOPM  100             /* max # of operations per semop call */
#endif

#define SEMVMX  32767           /* semaphore maximum value */
#define SEMAEM  16384           /* adjust on exit max value */

/*
 * Due to the way semaphore memory is allocated, we have to ensure that
 * SEMUSZ is properly aligned.
 */

#define SEM_ALIGN(bytes) roundup2(bytes, sizeof(long))

/* actual size of an undo structure */
#define SEMUSZ(nent)    SEM_ALIGN(offsetof(struct sem_undo, un_ent[nent]))

/*
 * semaphore info struct
 */
struct seminfo seminfo = {
                SEMMAP,         /* # of entries in semaphore map */
                SEMMNI,         /* # of semaphore identifiers */
                SEMMNS,         /* # of semaphores in system */
                SEMMNU,         /* # of undo structures in system */
                SEMMSL,         /* max # of semaphores per id */
                SEMOPM,         /* max # of operations per semop call */
                SEMUME,         /* max # of undo entries per process */
                SEMUSZ(SEMUME), /* size in bytes of undo structure */
                SEMVMX,         /* semaphore maximum value */
                SEMAEM          /* adjust on exit max value */
};

TUNABLE_INT("kern.ipc.semmap", &seminfo.semmap);
TUNABLE_INT("kern.ipc.semmni", &seminfo.semmni);
TUNABLE_INT("kern.ipc.semmns", &seminfo.semmns);
TUNABLE_INT("kern.ipc.semmnu", &seminfo.semmnu);
TUNABLE_INT("kern.ipc.semmsl", &seminfo.semmsl);
TUNABLE_INT("kern.ipc.semopm", &seminfo.semopm);
TUNABLE_INT("kern.ipc.semume", &seminfo.semume);
TUNABLE_INT("kern.ipc.semusz", &seminfo.semusz);
TUNABLE_INT("kern.ipc.semvmx", &seminfo.semvmx);
TUNABLE_INT("kern.ipc.semaem", &seminfo.semaem);

SYSCTL_INT(_kern_ipc, OID_AUTO, semmap, CTLFLAG_RW, &seminfo.semmap, 0,
    "Number of entries in semaphore map");
SYSCTL_INT(_kern_ipc, OID_AUTO, semmni, CTLFLAG_RD, &seminfo.semmni, 0,
    "Number of semaphore identifiers");
SYSCTL_INT(_kern_ipc, OID_AUTO, semmns, CTLFLAG_RD, &seminfo.semmns, 0,
    "Total number of semaphores");
SYSCTL_INT(_kern_ipc, OID_AUTO, semmnu, CTLFLAG_RD, &seminfo.semmnu, 0,
    "Total number of undo structures");
SYSCTL_INT(_kern_ipc, OID_AUTO, semmsl, CTLFLAG_RW, &seminfo.semmsl, 0,
    "Max number of semaphores per id");
SYSCTL_INT(_kern_ipc, OID_AUTO, semopm, CTLFLAG_RD, &seminfo.semopm, 0,
    "Max number of operations per semop call");
SYSCTL_INT(_kern_ipc, OID_AUTO, semume, CTLFLAG_RD, &seminfo.semume, 0,
    "Max number of undo entries per process");
SYSCTL_INT(_kern_ipc, OID_AUTO, semusz, CTLFLAG_RD, &seminfo.semusz, 0,
    "Size in bytes of undo structure");
SYSCTL_INT(_kern_ipc, OID_AUTO, semvmx, CTLFLAG_RW, &seminfo.semvmx, 0,
    "Semaphore maximum value");
SYSCTL_INT(_kern_ipc, OID_AUTO, semaem, CTLFLAG_RW, &seminfo.semaem, 0,
    "Adjust on exit max value");

#if 0
RO seminfo.semmap       /* SEMMAP unused */
RO seminfo.semmni
RO seminfo.semmns
RO seminfo.semmnu       /* undo entries per system */
RW seminfo.semmsl
RO seminfo.semopm       /* SEMOPM unused */
RO seminfo.semume
RO seminfo.semusz       /* param - derived from SEMUME for per-proc sizeof */
RO seminfo.semvmx       /* SEMVMX unused - user param */
RO seminfo.semaem       /* SEMAEM unused - user param */
#endif

static void
seminit(void *dummy)
{
        int i;

        sema = kmalloc(sizeof(struct semid_pool) * seminfo.semmni,
                      M_SEM, M_WAITOK | M_ZERO);

        lockinit(&sema_lk, "semglb", 0, 0);
        for (i = 0; i < seminfo.semmni; i++) {
                struct semid_pool *semaptr = &sema[i];

                lockinit(&semaptr->lk, "semary", 0, 0);
                semaptr->ds.sem_base = NULL;
                semaptr->ds.sem_perm.mode = 0;
        }
}
SYSINIT(sysv_sem, SI_SUB_SYSV_SEM, SI_ORDER_FIRST, seminit, NULL);

/*
 * Allocate a new sem_undo structure for a process
 * (returns ptr to structure or NULL if no more room)
 */
static struct sem_undo *
semu_alloc(struct proc *p)
{
        struct sem_undo *semu;

        /*
         * Allocate the semu structure and associate it with the process,
         * as necessary.
         */
        while ((semu = p->p_sem_undo) == NULL) {
                semu = kmalloc(SEMUSZ(seminfo.semume), M_SEM,
                               M_WAITOK | M_ZERO);
                lwkt_gettoken(&semu_token);
                lwkt_gettoken(&p->p_token);
                if (p->p_sem_undo == NULL) {
                        p->p_sem_undo = semu;
                        p->p_flags |= P_SYSVSEM;
                        semu->un_proc = p;
                        TAILQ_INSERT_TAIL(&semu_list, semu, un_entry);
                } else {
                        kfree(semu, M_SEM);
                }
                lwkt_reltoken(&p->p_token);
                lwkt_reltoken(&semu_token);
        }
        return(semu);
}

/*
 * Adjust a particular entry for a particular proc
 */
static int
semundo_adjust(struct proc *p, int semid, int semnum, int adjval)
{
        struct sem_undo *suptr;
        struct undo *sunptr;
        int i;
        int error = 0;

        /*
         * Look for and remember the sem_undo if the caller doesn't
         * provide it.
         */
        suptr = semu_alloc(p);
        lwkt_gettoken(&p->p_token);

        /*
         * Look for the requested entry and adjust it (delete if adjval becomes
         * 0).
         */
        sunptr = &suptr->un_ent[0];
        for (i = 0; i < suptr->un_cnt; i++, sunptr++) {
                if (sunptr->un_id != semid || sunptr->un_num != semnum)
                        continue;
                if (adjval == 0)
                        sunptr->un_adjval = 0;
                else
                        sunptr->un_adjval += adjval;
                if (sunptr->un_adjval == 0) {
                        suptr->un_cnt--;
                        if (i < suptr->un_cnt)
                                suptr->un_ent[i] = suptr->un_ent[suptr->un_cnt];
                }
                goto done;
        }

        /* Didn't find the right entry - create it */
        if (adjval == 0)
                goto done;
        if (suptr->un_cnt != seminfo.semume) {
                sunptr = &suptr->un_ent[suptr->un_cnt];
                suptr->un_cnt++;
                sunptr->un_adjval = adjval;
                sunptr->un_id = semid;
                sunptr->un_num = semnum;
        } else {
                error = EINVAL;
        }
done:
        lwkt_reltoken(&p->p_token);

        return (error);
}

/*
 * This is rather expensive
 */
static void
semundo_clear(int semid, int semnum)
{
        struct proc *p;
        struct sem_undo *suptr;
        struct sem_undo *sunext;
        struct undo *sunptr;
        int i;

        lwkt_gettoken(&semu_token);
        sunext = TAILQ_FIRST(&semu_list);
        while ((suptr = sunext) != NULL) {
                if ((p = suptr->un_proc) == NULL) {
                        sunext = TAILQ_NEXT(suptr, un_entry);
                        continue;
                }
                ++suptr->un_refs;
                PHOLD(p);
                lwkt_gettoken(&p->p_token);

                /*
                 * Check for semexit() race
                 */
                if (p->p_sem_undo != suptr)
                        goto skip;

                sunptr = &suptr->un_ent[0];
                i = 0;

                while (i < suptr->un_cnt) {
                        if (sunptr->un_id == semid) {
                                if (semnum == -1 || sunptr->un_num == semnum) {
                                        suptr->un_cnt--;
                                        if (i < suptr->un_cnt) {
                                                suptr->un_ent[i] =
                                                  suptr->un_ent[suptr->un_cnt];
                                                /*
                                                 * do not increment i
                                                 * or sunptr after copydown.
                                                 */
                                                continue;
                                        }
                                }
                                if (semnum != -1)
                                        break;
                        }
                        ++i;
                        ++sunptr;
                }

skip:
                lwkt_reltoken(&p->p_token);
                PRELE(p);

                /*
                 * Handle deletion and semexit races
                 */
                sunext = TAILQ_NEXT(suptr, un_entry);
                if (--suptr->un_refs == 0 && suptr->un_proc == NULL) {
                        KKASSERT(suptr->un_cnt == 0);
                        TAILQ_REMOVE(&semu_list, suptr, un_entry);
                        kfree(suptr, M_SEM);
                }
        }
        lwkt_reltoken(&semu_token);
}

/*
 * Note that the user-mode half of this passes a union, not a pointer
 *
 * MPALMOSTSAFE
 */
int
sys___semctl(struct sysmsg *sysmsg, const struct __semctl_args *uap)
{
        struct thread *td = curthread;
        struct prison *pr = td->td_proc->p_ucred->cr_prison;
        int semid = uap->semid;
        int semnum = uap->semnum;
        int cmd = uap->cmd;
        union semun *arg = uap->arg;
        union semun real_arg;
        struct ucred *cred = td->td_ucred;
        int i, rval, eval;
        struct semid_ds sbuf;
        struct semid_pool *semaptr;
        struct sem *semptr;

#ifdef SEM_DEBUG
        kprintf("call to semctl(%d, %d, %d, 0x%x)\n", semid, semnum, cmd, arg);
#endif

        if (pr && !PRISON_CAP_ISSET(pr->pr_caps, PRISON_CAP_SYS_SYSVIPC))
                return (ENOSYS);

        semid = IPCID_TO_IX(semid);
        if (semid < 0 || semid >= seminfo.semmni) {
                return(EINVAL);
        }
        semaptr = &sema[semid];
        lockmgr(&semaptr->lk, LK_EXCLUSIVE);

        if ((semaptr->ds.sem_perm.mode & SEM_ALLOC) == 0 ||
            semaptr->ds.sem_perm.seq != IPCID_TO_SEQ(uap->semid)) {
                lockmgr(&semaptr->lk, LK_RELEASE);
                return(EINVAL);
        }

        eval = 0;
        rval = 0;

        switch (cmd) {
        case IPC_RMID:
                eval = ipcperm(td->td_proc, &semaptr->ds.sem_perm, IPC_M);
                if (eval != 0)
                        break;
                semaptr->ds.sem_perm.cuid = cred->cr_uid;
                semaptr->ds.sem_perm.uid = cred->cr_uid;

                /*
                 * NOTE: Nobody will be waiting on the semaphores since
                 *       we have an exclusive lock on semaptr->lk).
                 */
                lockmgr(&sema_lk, LK_EXCLUSIVE);
                semtot -= semaptr->ds.sem_nsems;
                kfree(semaptr->ds.sem_base, M_SEM);
                semaptr->ds.sem_base = NULL;
                semaptr->ds.sem_perm.mode = 0;  /* clears SEM_ALLOC */
                lockmgr(&sema_lk, LK_RELEASE);

                semundo_clear(semid, -1);
                break;

        case IPC_SET:
                eval = ipcperm(td->td_proc, &semaptr->ds.sem_perm, IPC_M);
                if (eval)
                        break;
                if ((eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0)
                        break;
                if ((eval = copyin(real_arg.buf, (caddr_t)&sbuf,
                                   sizeof(sbuf))) != 0) {
                        break;
                }
                semaptr->ds.sem_perm.uid = sbuf.sem_perm.uid;
                semaptr->ds.sem_perm.gid = sbuf.sem_perm.gid;
                semaptr->ds.sem_perm.mode =
                        (semaptr->ds.sem_perm.mode & ~0777) |
                        (sbuf.sem_perm.mode & 0777);
                semaptr->ds.sem_ctime = time_second;
                break;

        case IPC_STAT:
                eval = ipcperm(td->td_proc, &semaptr->ds.sem_perm, IPC_R);
                if (eval)
                        break;
                if ((eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0)
                        break;
                eval = copyout(&semaptr->ds, real_arg.buf,
                               sizeof(struct semid_ds));
                break;
        case SEM_STAT:
                /*
                 * For this command we assume semid is an array index
                 * rather than an IPC id.  However, the conversion is
                 * just a mask so just validate that the passed-in semid
                 * matches the masked semid.
                 */
                if (uap->semid != semid) {
                        eval = EINVAL;
                        break;
                }
                eval = ipcperm(td->td_proc, &semaptr->ds.sem_perm, IPC_R);
                if (eval)
                        break;
                if ((eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0)
                        break;
                eval = copyout(&semaptr->ds, real_arg.buf,
                               sizeof(struct semid_ds));
                rval = IXSEQ_TO_IPCID(semid, semaptr->ds.sem_perm);
                break;

        case GETNCNT:
                eval = ipcperm(td->td_proc, &semaptr->ds.sem_perm, IPC_R);
                if (eval)
                        break;
                if (semnum < 0 || semnum >= semaptr->ds.sem_nsems) {
                        eval = EINVAL;
                        break;
                }
                rval = semaptr->ds.sem_base[semnum].semncnt;
                break;

        case GETPID:
                eval = ipcperm(td->td_proc, &semaptr->ds.sem_perm, IPC_R);
                if (eval)
                        break;
                if (semnum < 0 || semnum >= semaptr->ds.sem_nsems) {
                        eval = EINVAL;
                        break;
                }
                rval = semaptr->ds.sem_base[semnum].sempid;
                break;

        case GETVAL:
                eval = ipcperm(td->td_proc, &semaptr->ds.sem_perm, IPC_R);
                if (eval)
                        break;
                if (semnum < 0 || semnum >= semaptr->ds.sem_nsems) {
                        eval = EINVAL;
                        break;
                }
                rval = semaptr->ds.sem_base[semnum].semval;
                break;

        case GETALL:
                eval = ipcperm(td->td_proc, &semaptr->ds.sem_perm, IPC_R);
                if (eval)
                        break;
                if ((eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0)
                        break;
                for (i = 0; i < semaptr->ds.sem_nsems; i++) {
                        eval = copyout(&semaptr->ds.sem_base[i].semval,
                                       &real_arg.array[i],
                                       sizeof(real_arg.array[0]));
                        if (eval)
                                break;
                }
                break;

        case GETZCNT:
                eval = ipcperm(td->td_proc, &semaptr->ds.sem_perm, IPC_R);
                if (eval)
                        break;
                if (semnum < 0 || semnum >= semaptr->ds.sem_nsems) {
                        eval = EINVAL;
                        break;
                }
                rval = semaptr->ds.sem_base[semnum].semzcnt;
                break;

        case SETVAL:
                eval = ipcperm(td->td_proc, &semaptr->ds.sem_perm, IPC_W);
                if (eval)
                        break;
                if (semnum < 0 || semnum >= semaptr->ds.sem_nsems) {
                        eval = EINVAL;
                        break;
                }
                if ((eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0)
                        break;

                /*
                 * Because we hold semaptr->lk exclusively we can safely
                 * modify any semptr content without acquiring its token.
                 */
                semptr = &semaptr->ds.sem_base[semnum];
                semptr->semval = real_arg.val;
                semundo_clear(semid, semnum);
                if (semptr->semzcnt || semptr->semncnt)
                        wakeup(semptr);
                break;

        case SETALL:
                eval = ipcperm(td->td_proc, &semaptr->ds.sem_perm, IPC_W);
                if (eval)
                        break;
                if ((eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0)
                        break;
                /*
                 * Because we hold semaptr->lk exclusively we can safely
                 * modify any semptr content without acquiring its token.
                 */
                for (i = 0; i < semaptr->ds.sem_nsems; i++) {
                        semptr = &semaptr->ds.sem_base[i];
                        eval = copyin(&real_arg.array[i],
                                      (caddr_t)&semptr->semval,
                                      sizeof(real_arg.array[0]));
                        if (semptr->semzcnt || semptr->semncnt)
                                wakeup(semptr);
                        if (eval != 0)
                                break;
                }
                semundo_clear(semid, -1);
                break;

        default:
                eval = EINVAL;
                break;
        }
        lockmgr(&semaptr->lk, LK_RELEASE);

        if (eval == 0)
                sysmsg->sysmsg_result = rval;
        return(eval);
}

/*
 * MPALMOSTSAFE
 */
int
sys_semget(struct sysmsg *sysmsg, const struct semget_args *uap)
{
        struct thread *td = curthread;
        struct prison *pr = td->td_proc->p_ucred->cr_prison;
        int semid, eval;
        int key = uap->key;
        int nsems = uap->nsems;
        int semflg = uap->semflg;
        struct ucred *cred = td->td_ucred;

#ifdef SEM_DEBUG
        kprintf("semget(0x%x, %d, 0%o)\n", key, nsems, semflg);
#endif

        if (pr && !PRISON_CAP_ISSET(pr->pr_caps, PRISON_CAP_SYS_SYSVIPC))
                return (ENOSYS);

        eval = 0;

        if (key != IPC_PRIVATE) {
                for (semid = 0; semid < seminfo.semmni; semid++) {
                        if ((sema[semid].ds.sem_perm.mode & SEM_ALLOC) == 0 ||
                            sema[semid].ds.sem_perm.key != key) {
                                continue;
                        }
                        lockmgr(&sema[semid].lk, LK_EXCLUSIVE);
                        if ((sema[semid].ds.sem_perm.mode & SEM_ALLOC) == 0 ||
                            sema[semid].ds.sem_perm.key != key) {
                                lockmgr(&sema[semid].lk, LK_RELEASE);
                                continue;
                        }
                        break;
                }
                if (semid < seminfo.semmni) {
                        /* sema[semid].lk still locked from above */
#ifdef SEM_DEBUG
                        kprintf("found public key\n");
#endif
                        if ((eval = ipcperm(td->td_proc,
                                            &sema[semid].ds.sem_perm,
                                            semflg & 0700))) {
                                lockmgr(&sema[semid].lk, LK_RELEASE);
                                goto done;
                        }
                        if (nsems > 0 && sema[semid].ds.sem_nsems < nsems) {
#ifdef SEM_DEBUG
                                kprintf("too small\n");
#endif
                                eval = EINVAL;
                                lockmgr(&sema[semid].lk, LK_RELEASE);
                                goto done;
                        }
                        if ((semflg & IPC_CREAT) && (semflg & IPC_EXCL)) {
#ifdef SEM_DEBUG
                                kprintf("not exclusive\n");
#endif
                                eval = EEXIST;
                                lockmgr(&sema[semid].lk, LK_RELEASE);
                                goto done;
                        }

                        /*
                         * Return this one.
                         */
                        lockmgr(&sema[semid].lk, LK_RELEASE);
                        goto done;
                }
        }

#ifdef SEM_DEBUG
        kprintf("need to allocate the semid_ds\n");
#endif
        if (key == IPC_PRIVATE || (semflg & IPC_CREAT)) {
                if (nsems <= 0 || nsems > seminfo.semmsl) {
#ifdef SEM_DEBUG
                        kprintf("nsems out of range (0<%d<=%d)\n",
                                nsems, seminfo.semmsl);
#endif
                        eval = EINVAL;
                        goto done;
                }

                /*
                 * SEM_ALLOC flag cannot be set unless sema_lk is locked.
                 * semtot field also protected by sema_lk.
                 */
                lockmgr(&sema_lk, LK_EXCLUSIVE);
                if (nsems > seminfo.semmns - semtot) {
#ifdef SEM_DEBUG
                        kprintf("not enough semaphores left "
                                "(need %d, got %d)\n",
                                nsems, seminfo.semmns - semtot);
#endif
                        eval = ENOSPC;
                        lockmgr(&sema_lk, LK_RELEASE);
                        goto done;
                }
                for (semid = 0; semid < seminfo.semmni; semid++) {
                        if ((sema[semid].ds.sem_perm.mode & SEM_ALLOC) == 0)
                                break;
                }
                if (semid == seminfo.semmni) {
#ifdef SEM_DEBUG
                        kprintf("no more semid_ds's available\n");
#endif
                        eval = ENOSPC;
                        lockmgr(&sema_lk, LK_RELEASE);
                        goto done;
                }
#ifdef SEM_DEBUG
                kprintf("semid %d is available\n", semid);
#endif
                lockmgr(&sema[semid].lk, LK_EXCLUSIVE);
                sema[semid].ds.sem_perm.key = key;
                sema[semid].ds.sem_perm.cuid = cred->cr_uid;
                sema[semid].ds.sem_perm.uid = cred->cr_uid;
                sema[semid].ds.sem_perm.cgid = cred->cr_gid;
                sema[semid].ds.sem_perm.gid = cred->cr_gid;
                sema[semid].ds.sem_perm.mode = (semflg & 0777) | SEM_ALLOC;
                sema[semid].ds.sem_perm.seq =
                    (sema[semid].ds.sem_perm.seq + 1) & 0x7fff;
                sema[semid].ds.sem_nsems = nsems;
                sema[semid].ds.sem_otime = 0;
                sema[semid].ds.sem_ctime = time_second;
                sema[semid].ds.sem_base = kmalloc(sizeof(struct sem) * nsems,
                                               M_SEM, M_WAITOK|M_ZERO);
                semtot += nsems;
                ++sema[semid].gen;
                lockmgr(&sema[semid].lk, LK_RELEASE);
                lockmgr(&sema_lk, LK_RELEASE);
#ifdef SEM_DEBUG
                kprintf("sembase = 0x%x, next = 0x%x\n",
                        sema[semid].ds.sem_base, &sem[semtot]);
#endif
                /* eval == 0 */
        } else {
#ifdef SEM_DEBUG
                kprintf("didn't find it and wasn't asked to create it\n");
#endif
                eval = ENOENT;
        }

done:
        if (eval == 0) {
                sysmsg->sysmsg_result =
                        IXSEQ_TO_IPCID(semid, sema[semid].ds.sem_perm);
        }
        return(eval);
}

/*
 * MPSAFE
 */
int
sys_semop(struct sysmsg *sysmsg, const struct semop_args *uap)
{
        struct thread *td = curthread;
        struct prison *pr = td->td_proc->p_ucred->cr_prison;
        int semid = uap->semid;
        u_int nsops = uap->nsops;
        struct sembuf sops[MAX_SOPS];
        struct semid_pool *semaptr;
        struct sembuf *sopptr;
        struct sem *semptr;
        struct sem *xsemptr;
        int i, j, eval;
        int do_undos;

#ifdef SEM_DEBUG
        kprintf("call to semop(%d, 0x%x, %u)\n", semid, sops, nsops);
#endif
        if (pr && !PRISON_CAP_ISSET(pr->pr_caps, PRISON_CAP_SYS_SYSVIPC))
                return (ENOSYS);

        semid = IPCID_TO_IX(semid);     /* Convert back to zero origin */

        if (semid < 0 || semid >= seminfo.semmni) {
                eval = EINVAL;
                goto done2;
        }

        wakeup_start_delayed();
        semaptr = &sema[semid];
        lockmgr(&semaptr->lk, LK_SHARED);

        if ((semaptr->ds.sem_perm.mode & SEM_ALLOC) == 0) {
                eval = EINVAL;
                goto done;
        }
        if (semaptr->ds.sem_perm.seq != IPCID_TO_SEQ(uap->semid)) {
                eval = EINVAL;
                goto done;
        }

        if ((eval = ipcperm(td->td_proc, &semaptr->ds.sem_perm, IPC_W))) {
#ifdef SEM_DEBUG
                kprintf("eval = %d from ipaccess\n", eval);
#endif
                goto done;
        }

        if (nsops > MAX_SOPS) {
#ifdef SEM_DEBUG
                kprintf("too many sops (max=%d, nsops=%u)\n", MAX_SOPS, nsops);
#endif
                eval = E2BIG;
                goto done;
        }

        if ((eval = copyin(uap->sops, &sops, nsops * sizeof(sops[0]))) != 0) {
#ifdef SEM_DEBUG
                kprintf("eval = %d from copyin(%08x, %08x, %u)\n", eval,
                    uap->sops, &sops, nsops * sizeof(sops[0]));
#endif
                goto done;
        }

        /*
         * Loop trying to satisfy the vector of requests.
         * If we reach a point where we must wait, any requests already
         * performed are rolled back and we go to sleep until some other
         * process wakes us up.  At this point, we start all over again.
         *
         * This ensures that from the perspective of other tasks, a set
         * of requests is atomic (never partially satisfied).
         */
        do_undos = 0;

        for (;;) {
                long gen;

                semptr = NULL;

                for (i = 0; i < nsops; i++) {
                        sopptr = &sops[i];

                        if (sopptr->sem_num >= semaptr->ds.sem_nsems) {
                                eval = EFBIG;
                                goto done;
                        }

                        semptr = &semaptr->ds.sem_base[sopptr->sem_num];
                        lwkt_getpooltoken(semptr);

#ifdef SEM_DEBUG
                        kprintf("semop:  semaptr=%x, sem_base=%x, semptr=%x, "
                                "sem[%d]=%d : op=%d, flag=%s\n",
                            semaptr, semaptr->ds.sem_base, semptr,
                            sopptr->sem_num, semptr->semval, sopptr->sem_op,
                            (sopptr->sem_flg & IPC_NOWAIT) ? "nowait" : "wait");
#endif

                        if (sopptr->sem_op < 0) {
                                if (semptr->semval + sopptr->sem_op < 0) {
#ifdef SEM_DEBUG
                                        kprintf("semop:  can't do it now\n");
#endif
                                        break;
                                } else {
                                        semptr->semval += sopptr->sem_op;
                                        if (semptr->semval == 0 &&
                                            semptr->semzcnt > 0) {
                                                wakeup(semptr);
                                        }
                                }
                                if (sopptr->sem_flg & SEM_UNDO)
                                        do_undos = 1;
                        } else if (sopptr->sem_op == 0) {
                                if (semptr->semval > 0) {
#ifdef SEM_DEBUG
                                        kprintf("semop:  not zero now\n");
#endif
                                        break;
                                }
                        } else {
                                semptr->semval += sopptr->sem_op;
                                if (sopptr->sem_flg & SEM_UNDO)
                                        do_undos = 1;
                                if (semptr->semncnt > 0)
                                        wakeup(semptr);
                        }
                        lwkt_relpooltoken(semptr);
                }

                /*
                 * Did we get through the entire vector?
                 */
                if (i >= nsops)
                        goto donex;

                /*
                 * No, protect the semaphore request which also flags that
                 * a wakeup is needed, then release semptr since we know
                 * another process is likely going to need to access it
                 * soon.
                 */
                if (sopptr->sem_op == 0)
                        semptr->semzcnt++;
                else
                        semptr->semncnt++;
                tsleep_interlock(semptr, PCATCH);
                lwkt_relpooltoken(semptr);

                /*
                 * Rollback the semaphores we had acquired.
                 */
#ifdef SEM_DEBUG
                kprintf("semop:  rollback 0 through %d\n", i-1);
#endif
                for (j = 0; j < i; j++) {
                        xsemptr = &semaptr->ds.sem_base[sops[j].sem_num];
                        lwkt_getpooltoken(xsemptr);
                        xsemptr->semval -= sops[j].sem_op;
                        if (xsemptr->semval == 0 && xsemptr->semzcnt > 0)
                                wakeup(xsemptr);
                        if (xsemptr->semval <= 0 && xsemptr->semncnt > 0)
                                wakeup(xsemptr);
                        lwkt_relpooltoken(xsemptr);
                }

                /*
                 * If the request that we couldn't satisfy has the
                 * NOWAIT flag set then return with EAGAIN.
                 */
                if (sopptr->sem_flg & IPC_NOWAIT) {
                        eval = EAGAIN;
                        goto done;
                }

                /*
                 * Release semaptr->lk while sleeping, allowing other
                 * semops (like SETVAL, SETALL, etc), which require an
                 * exclusive lock and might wake us up.
                 *
                 * Reload and recheck the validity of semaptr on return.
                 * Note that semptr itself might have changed too, but
                 * we've already interlocked for semptr and that is what
                 * will be woken up if it wakes up the tsleep on a MP
                 * race.
                 *
                 * gen protects against destroy/re-create races where the
                 * creds match.
                 */
#ifdef SEM_DEBUG
                kprintf("semop:  good night!\n");
#endif
                gen = semaptr->gen;
                lockmgr(&semaptr->lk, LK_RELEASE);
                eval = tsleep(semptr, PCATCH | PINTERLOCKED, "semwait", hz);
                lockmgr(&semaptr->lk, LK_SHARED);
#ifdef SEM_DEBUG
                kprintf("semop:  good morning (eval=%d)!\n", eval);
#endif

                /* return code is checked below, after sem[nz]cnt-- */

                /*
                 * Make sure that the semaphore still exists
                 */
                if (semaptr->gen != gen ||
                    (semaptr->ds.sem_perm.mode & SEM_ALLOC) == 0 ||
                    semaptr->ds.sem_perm.seq != IPCID_TO_SEQ(uap->semid)) {
                        eval = EIDRM;
                        goto done;
                }

                /*
                 * The semaphore is still alive.  Readjust the count of
                 * waiting processes.
                 */
                semptr = &semaptr->ds.sem_base[sopptr->sem_num];
                lwkt_getpooltoken(semptr);
                if (sopptr->sem_op == 0)
                        semptr->semzcnt--;
                else
                        semptr->semncnt--;
                lwkt_relpooltoken(semptr);

                /*
                 * Is it really morning, or was our sleep interrupted?
                 * (Delayed check of tsleep() return code because we
                 * need to decrement sem[nz]cnt either way.)
                 */
                if (eval) {
                        eval = EINTR;
                        goto done;
                }
#ifdef SEM_DEBUG
                kprintf("semop:  good morning!\n");
#endif
                /* RETRY LOOP */
        }

donex:
        /*
         * Process any SEM_UNDO requests.
         */
        if (do_undos) {
                for (i = 0; i < nsops; i++) {
                        /*
                         * We only need to deal with SEM_UNDO's for non-zero
                         * op's.
                         */
                        int adjval;

                        if ((sops[i].sem_flg & SEM_UNDO) == 0)
                                continue;
                        adjval = sops[i].sem_op;
                        if (adjval == 0)
                                continue;
                        eval = semundo_adjust(td->td_proc, semid,
                                              sops[i].sem_num, -adjval);
                        if (eval == 0)
                                continue;

                        /*
                         * Oh-Oh!  We ran out of either sem_undo's or undo's.
                         * Rollback the adjustments to this point and then
                         * rollback the semaphore ups and down so we can return
                         * with an error with all structures restored.  We
                         * rollback the undo's in the exact reverse order that
                         * we applied them.  This guarantees that we won't run
                         * out of space as we roll things back out.
                         */
                        for (j = i - 1; j >= 0; j--) {
                                if ((sops[j].sem_flg & SEM_UNDO) == 0)
                                        continue;
                                adjval = sops[j].sem_op;
                                if (adjval == 0)
                                        continue;
                                if (semundo_adjust(td->td_proc, semid,
                                               sops[j].sem_num, adjval) != 0)
                                        panic("semop - can't undo undos");
                        }

                        for (j = 0; j < nsops; j++) {
                                xsemptr = &semaptr->ds.sem_base[
                                                        sops[j].sem_num];
                                lwkt_getpooltoken(xsemptr);
                                xsemptr->semval -= sops[j].sem_op;
                                if (xsemptr->semval == 0 &&
                                    xsemptr->semzcnt > 0)
                                        wakeup(xsemptr);
                                if (xsemptr->semval <= 0 &&
                                    xsemptr->semncnt > 0)
                                        wakeup(xsemptr);
                                lwkt_relpooltoken(xsemptr);
                        }

#ifdef SEM_DEBUG
                        kprintf("eval = %d from semundo_adjust\n", eval);
#endif
                        goto done;
                } /* loop through the sops */
        } /* if (do_undos) */

        /* We're definitely done - set the sempid's */
        for (i = 0; i < nsops; i++) {
                sopptr = &sops[i];
                semptr = &semaptr->ds.sem_base[sopptr->sem_num];
                lwkt_getpooltoken(semptr);
                semptr->sempid = td->td_proc->p_pid;
                lwkt_relpooltoken(semptr);
        }

        /* Do a wakeup if any semaphore was up'd. */
#ifdef SEM_DEBUG
        kprintf("semop:  done\n");
#endif
        sysmsg->sysmsg_result = 0;
        eval = 0;
done:
        lockmgr(&semaptr->lk, LK_RELEASE);
        wakeup_end_delayed();
done2:
        return(eval);
}

/*
 * Go through the undo structures for this process and apply the adjustments to
 * semaphores.
 *
 * (p->p_token is held by the caller)
 */
void
semexit(struct proc *p)
{
        struct sem_undo *suptr;
        struct sem *semptr;

        /*
         * We're getting a global token, don't do it if we couldn't
         * possibly have any semaphores.
         */
        if ((p->p_flags & P_SYSVSEM) == 0)
                return;
        suptr = p->p_sem_undo;
        KKASSERT(suptr != NULL);

        /*
         * Disconnect suptr from the process and increment un_refs to
         * prevent anyone else from being able to destroy the structure.
         * Do not remove it from the linked list until after we are through
         * scanning it as other semaphore calls might still effect it.
         */
        lwkt_gettoken(&semu_token);
#if 0
        /*
         * do not disconnect proc yet, doing so prevents RMID
         * from cleaning up the structure atomically with SEM_ALLOC
         */
        p->p_sem_undo = NULL;
        p->p_flags &= ~P_SYSVSEM;
        suptr->un_proc = NULL;
#endif
        ++suptr->un_refs;
        lwkt_reltoken(&semu_token);

        while (suptr->un_cnt) {
                struct semid_pool *semaptr;
                int semid;
                int semnum;
                int adjval;
                int ix;

                /*
                 * These values are stable because we hold p->p_token.
                 * However, they can get ripped out from under us when
                 * we block or obtain other tokens so we have to re-check.
                 */
                ix = suptr->un_cnt - 1;
                semid = suptr->un_ent[ix].un_id;
                semnum = suptr->un_ent[ix].un_num;
                adjval = suptr->un_ent[ix].un_adjval;

                semaptr = &sema[semid];

                /*
                 * Recheck after locking, then execute the undo
                 * operation.  semptr remains valid due to the
                 * semaptr->lk.
                 */
                lockmgr(&semaptr->lk, LK_EXCLUSIVE);
                semptr = &semaptr->ds.sem_base[semnum];
                lwkt_getpooltoken(semptr);

                if (ix == suptr->un_cnt - 1 &&
                    semid == suptr->un_ent[ix].un_id &&
                    semnum == suptr->un_ent[ix].un_num &&
                    adjval == suptr->un_ent[ix].un_adjval) {
                        /*
                         * Only do assertions when we aren't in a SMP race.
                         */
                        if ((semaptr->ds.sem_perm.mode & SEM_ALLOC) == 0)
                                panic("semexit - semid not allocated");
                        if (semnum >= semaptr->ds.sem_nsems)
                                panic("semexit - semnum out of range");
                        --suptr->un_cnt;

                        if (adjval < 0) {
                                if (semptr->semval < -adjval)
                                        semptr->semval = 0;
                                else
                                        semptr->semval += adjval;
                        } else {
                                semptr->semval += adjval;
                        }
                        wakeup(semptr);
                }
                lwkt_relpooltoken(semptr);
                lockmgr(&semaptr->lk, LK_RELEASE);
        }

        /*
         * Final cleanup, remove from the list, remove the process association,
         * then deallocate on last ref.
         */
        lwkt_gettoken(&semu_token);

        p->p_sem_undo = NULL;
        p->p_flags &= ~P_SYSVSEM;
        suptr->un_proc = NULL;

        if (--suptr->un_refs == 0) {
                TAILQ_REMOVE(&semu_list, suptr, un_entry);
                KKASSERT(suptr->un_cnt == 0);
                kfree(suptr, M_SEM);
        }
        lwkt_reltoken(&semu_token);
}