sys/kern/sysv_sem.c

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

#ifdef SYSVSEM

#include "param.h"
#include "systm.h"
#include "kernel.h"
#include "proc.h"
#include "sem.h"
#include "malloc.h"

static int      semctl(), semget(), semop(), semconfig();
int     (*semcalls[])() = { semctl, semget, semop, semconfig };
int     semtot = 0;

static struct proc *semlock_holder = NULL;

void
seminit()
{
    register int i;
    vm_offset_t whocares1, whocares2;

    if ( sema == NULL ) {
        panic("sema is NULL");
    }
    for ( i = 0; i < seminfo.semmni; i += 1 ) {
        sema[i].sem_base = 0;
        sema[i].sem_perm.mode = 0;
    }
    if ( semu == NULL ) {
        panic("semu is NULL");
    }
    for ( i = 0; i < seminfo.semmnu; i += 1 ) {
        register struct sem_undo *suptr = SEMU(i);
        suptr->un_proc = NULL;
    }
    semu_list = NULL;
}

TEXT_SET(pseudo_set, seminit);

/*
 * Entry point for all SEM calls
 */

struct semsys_args {
        u_int   which;
};

int
semsys(p, uap, retval)
        struct proc *p;
        struct semsys_args *uap;
        int *retval;
{
        while ( semlock_holder != NULL && semlock_holder != p ) {
            /* printf("semaphore facility locked - sleeping ...\n"); */
            tsleep( (caddr_t)&semlock_holder, (PZERO - 4), "semsys", 0 );
        }

        if (uap->which >= sizeof(semcalls)/sizeof(semcalls[0]))
                return (EINVAL);
        return ((*semcalls[uap->which])(p, &uap[1], retval));
}

/*
 * Lock or unlock the entire semaphore facility.
 *
 * This will probably eventually evolve into a general purpose semaphore
 * facility status enquiry mechanism (I don't like the "read /dev/kmem"
 * approach currently taken by ipcs and the amount of info that we want
 * to be able to extract for ipcs is probably beyond what the capability
 * of the getkerninfo facility.
 *
 * At the time that the current version of semconfig was written, ipcs is
 * the only user of the semconfig facility.  It uses it to ensure that the
 * semaphore facility data structures remain static while it fishes around
 * in /dev/kmem.
 */

struct semconfig_args {
        semconfig_ctl_t flag;
};

static int
semconfig(p, uap, retval)
        struct proc *p;
        struct semconfig_args *uap;
        int *retval;
{
    int eval = 0;

    switch ( uap->flag ) {
    case SEM_CONFIG_FREEZE:
        semlock_holder = p;
        break;
    case SEM_CONFIG_THAW:
        semlock_holder = NULL;
        wakeup( (caddr_t)&semlock_holder );
        break;
    default:
        printf("semconfig:  unknown flag parameter value (%d) - ignored\n",uap->flag);
        eval = EINVAL;
        break;
    }

    *retval = 0;
    return(eval);
}

/*
 * Allocate a new sem_undo structure for a process
 * (returns ptr to structure or NULL if no more room)
 */

struct sem_undo *
semu_alloc(struct proc *p)
{
    register int i;
    register struct sem_undo *suptr;
    register struct sem_undo **supptr;
    int attempt;

    /*
     * Try twice to allocate something.
     * (we'll purge any empty structures after the first pass so
     * two passes are always enough)
     */

    for ( attempt = 0; attempt < 2; attempt += 1 ) {

        /*
         * Look for a free structure.
         * Fill it in and return it if we find one.
         */

        for ( i = 0; i < seminfo.semmnu; i += 1 ) {
            suptr = SEMU(i);
            if ( suptr->un_proc == NULL ) {
                suptr->un_next = semu_list;
                semu_list = suptr;
                suptr->un_cnt = 0;
                suptr->un_proc = p;
                return(suptr);
            }
        }

        /*
         * We didn't find a free one, if this is the first attempt
         * then try to free some structures.
         */

        if ( attempt == 0 ) {

            /* All the structures are in use - try to free some */

            int did_something = 0;

            supptr = &semu_list;
            while ( (suptr = *supptr) != NULL ) {
                if ( suptr->un_cnt == 0 )  {
                    suptr->un_proc = NULL;
                    *supptr = suptr->un_next;
                    did_something = 1;
                } else {
                    supptr = &(suptr->un_next);
                }
            }

            /* If we didn't free anything then just give-up */

            if ( !did_something ) {
                return(NULL);
            }

        } else {

            /*
             * The second pass failed even though we freed
             * something after the first pass!
             * This is IMPOSSIBLE!
             */

            panic("semu_alloc - second attempt failed");

        }

    }

    /* NOTREACHED */
    while (1);
}

/*
 * Adjust a particular entry for a particular proc
 */

int
semundo_adjust(register struct proc *p,struct sem_undo **supptr,int semid,int semnum,int adjval)
{
    register struct sem_undo *suptr;
    register struct undo *sunptr;
    int i;

    /* Look for and remember the sem_undo if the caller doesn't provide it */

    suptr = *supptr;
    if ( suptr == NULL ) {
        /* printf("adjust:  need to find suptr\n"); */
        for ( suptr = semu_list; suptr != NULL; suptr = suptr->un_next ) {
            if ( suptr->un_proc == p ) {
                /* printf("adjust:  found suptr @%08x\n",suptr); */
                *supptr = suptr;
                break;
            }
        }
        if ( suptr == NULL ) {
            if ( adjval == 0 ) {
                return(0);      /* Don't create it if it doesn't exist */
            }
            suptr = semu_alloc(p);
            if ( suptr == NULL ) {
                return(ENOSPC);
            }
            /* printf("adjust:  allocated suptr @%08x\n",suptr); */
            *supptr = suptr;
        }
    }

    /* 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 += 1, sunptr += 1 ) {

        if ( sunptr->un_id == semid && sunptr->un_num == semnum ) {

            /* Found the right entry - adjust it */

            if ( adjval == 0 ) {
                sunptr->un_adjval = 0;
            } else {
                /* printf("adjust:  %08x %d:%d(%d) += %d\n",suptr->un_proc,semid,semnum,sunptr->un_adjval,adjval); */
                sunptr->un_adjval += adjval;
            }
            if ( sunptr->un_adjval == 0 ) {
                /* printf("adjust:  %08x deleting entry %d:%d\n",suptr->un_proc,semid,semnum); */
                suptr->un_cnt -= 1;
                if ( i < suptr->un_cnt ) {
                    suptr->un_ent[i] = suptr->un_ent[suptr->un_cnt];
                }
            }
            return(0);

        }
    }

    /* Didn't find the right entry - create it */

    if ( adjval == 0 ) {
        return(0);
    }
    if ( suptr->un_cnt == SEMUME ) {
        return(EINVAL);
    } else {
        /* printf("adjust:  %08x allocating entry %d as %d:%d(%d)\n",suptr->un_proc,suptr->un_cnt,semid,semnum,adjval); */
        sunptr = &(suptr->un_ent[suptr->un_cnt]);
        suptr->un_cnt += 1;
        sunptr->un_adjval = adjval;
        sunptr->un_id = semid; sunptr->un_num = semnum;
    }
    return(0);
}


void
semundo_clear(int semid,int semnum)
{
    register struct sem_undo *suptr;

    for ( suptr = semu_list; suptr != NULL; suptr = suptr->un_next ) {

        register struct undo *sunptr = &(suptr->un_ent[0]);
        register int i = 0;

        while ( i < suptr->un_cnt ) {
            int advance = 1;

            if ( sunptr->un_id == semid ) {
                if ( semnum == -1 || sunptr->un_num == semnum ) {
                    /* printf("clear:  %08x %d:%d(%d)\n",suptr->un_proc,semid,sunptr->un_num,sunptr->un_adjval); */
                    suptr->un_cnt -= 1;
                    if ( i < suptr->un_cnt ) {
                        suptr->un_ent[i] = suptr->un_ent[suptr->un_cnt];
                        advance = 0;
                    }
                }
                if ( semnum != -1 ) {
                    break;
                }
            }

            if ( advance ) {
                i += 1;
                sunptr += 1;
            }

        }

    }

}

struct semctl_args {
        int     semid;
        int     semnum;
        int     cmd;
        union   semun *arg;
};

static int
semctl(p, uap, retval)
        struct proc *p;
        register struct semctl_args *uap;
        int *retval;
{
    int semid = uap->semid;
    int semnum = uap->semnum;
    int cmd = uap->cmd;
    union semun *arg = uap->arg;
    union semun real_arg;
    struct ucred *cred = p->p_ucred;
    int i, rval, eval;
    struct semid_ds sbuf;
    register struct semid_ds *semaptr;

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

    semid = IPCID_TO_IX(semid);

    if ( semid < 0 || semid >= seminfo.semmsl ) {
        /* printf("semid out of range (0<=%d<%d)\n",semid,seminfo.semmsl); */
        return(EINVAL);
    }

    semaptr = &sema[semid];

    if ( semaptr->sem_perm.seq != IPCID_TO_SEQ(uap->semid) ) {
        /* printf("invalid sequence number\n"); */
        return(EINVAL);
    }

    if ( (semaptr->sem_perm.mode & SEM_ALLOC) == 0 ) {
        /* printf("no such semaphore id\n"); */
        return(EINVAL);
    }

    eval = 0;
    rval = 0;

    switch (cmd) {

    case IPC_RMID:
        if ( cred->cr_uid != 0
        && semaptr->sem_perm.cuid != cred->cr_uid
        && semaptr->sem_perm.uid != cred->cr_uid ) {
            return(EPERM);
        }
        semaptr->sem_perm.cuid = cred->cr_uid;
        semaptr->sem_perm.uid = cred->cr_uid;
        semtot -= semaptr->sem_nsems;
        for ( i = semaptr->sem_base - sem; i < semtot; i += 1 ) {
            /* printf("0x%x = 0x%x; ",&sem[i],&sem[i + semaptr->sem_nsems]); */
            sem[i] = sem[i + semaptr->sem_nsems];
        }
        /* printf("\n"); */
        for ( i = 0; i < seminfo.semmni; i += 1 ) {
            if ( (sema[i].sem_perm.mode & SEM_ALLOC)
            && sema[i].sem_base > semaptr->sem_base ) {
                /* printf("sema[%d].sem_base was 0x%x",i,sema[i].sem_base); */
                sema[i].sem_base -= semaptr->sem_nsems;
                /* printf(", now 0x%x\n",sema[i].sem_base); */
            }
        }
        semaptr->sem_perm.mode = 0;

        /* Delete any undo entries for this semid */

        semundo_clear(semid,-1);

        /* Make sure that anybody who is waiting notices the deletion */

        wakeup( (caddr_t)semaptr );

        break;

    case IPC_SET:
        /* printf("IPC_SET\n"); */
        if ( cred->cr_uid != 0
        && semaptr->sem_perm.cuid != cred->cr_uid
        && semaptr->sem_perm.uid != cred->cr_uid ) {
            return(EPERM);
        }
        if ( (eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0 ) {
            return(eval);
        }
        if ( (eval = copyin(real_arg.buf, (caddr_t)&sbuf, sizeof(sbuf)) ) != 0 ) {
            return(eval);
        }
        semaptr->sem_perm.uid = sbuf.sem_perm.uid;
        semaptr->sem_perm.gid = sbuf.sem_perm.gid;
        semaptr->sem_perm.mode = (semaptr->sem_perm.mode & ~0777)
        | (sbuf.sem_perm.mode & 0777);
        semaptr->sem_ctime = time.tv_sec;
        break;

    case IPC_STAT:
        /* printf("IPC_STAT\n"); */
        if ( (eval = ipcaccess(&semaptr->sem_perm, IPC_R, cred)) ) {
            return(eval);
        }
        rval = 0;
        if ( (eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0 ) {
            return(eval);
        }
        eval = copyout((caddr_t)semaptr, real_arg.buf, sizeof(struct semid_ds)) ;
        break;

    case GETNCNT:
        /* printf("GETNCNT(%d)\n",semnum); */
        if ( (eval = ipcaccess(&semaptr->sem_perm, IPC_R, cred)) ) {
            return(eval);
        }
        if ( semnum < 0 || semnum >= semaptr->sem_nsems ) return(EINVAL);
        rval = semaptr->sem_base[semnum].semncnt;
        break;

    case GETPID:
        /* printf("GETPID(%d)\n",semnum); */
        if ( (eval = ipcaccess(&semaptr->sem_perm, IPC_R, cred)) ) {
            return(eval);
        }
        if ( semnum < 0 || semnum >= semaptr->sem_nsems ) return(EINVAL);
        rval = semaptr->sem_base[semnum].sempid;
        break;

    case GETVAL:
        /* printf("GETVAL(%d)\n",semnum); */
        if ( (eval = ipcaccess(&semaptr->sem_perm, IPC_R, cred)) ) {
            return(eval);
        }
        if ( semnum < 0 || semnum >= semaptr->sem_nsems ) return(EINVAL);
        rval = semaptr->sem_base[semnum].semval;
        break;

    case GETALL:
        /* printf("GETALL\n"); */
        if ( (eval = ipcaccess(&semaptr->sem_perm, IPC_R, cred)) ) {
            return(eval);
        }
        rval = 0;
        if ( (eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0 ) {
            /* printf("initial copyin failed (addr=0x%x)\n",arg); */
            return(eval);
        }
        /* printf("%d semaphores\n",semaptr->sem_nsems); */
        for ( i = 0; i < semaptr->sem_nsems; i += 1 ) {
            /* printf("copyout to 0x%x\n",&real_arg.array[i]); */
            eval =
                copyout((caddr_t)&semaptr->sem_base[i].semval,
                &real_arg.array[i],
                sizeof(real_arg.array[0]));
            if ( eval != 0 ) {
                /* printf("copyout to 0x%x failed\n",&real_arg.array[i]); */
                break;
            }
        }
        break;

    case GETZCNT:
        if ( (eval = ipcaccess(&semaptr->sem_perm, IPC_R, cred)) ) {
            return(eval);
        }
        /* printf("GETZCNT(%d)\n",semnum); */
        if ( semnum < 0 || semnum >= semaptr->sem_nsems ) return(EINVAL);
        rval = semaptr->sem_base[semnum].semzcnt;
        break;

    case SETVAL:
#ifdef SEM_DEBUG
        printf("SETVAL(%d)\n",semnum);
#endif
        if ( (eval = ipcaccess(&semaptr->sem_perm, IPC_W, cred)) ) {
            return(eval);
        }
        if ( semnum < 0 || semnum >= semaptr->sem_nsems ) return(EINVAL);
        rval = 0;
        if ( (eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0 ) {
            return(eval);
        }
#ifdef SEM_DEBUG
        printf("semaptr=%x, sem_base=%x, semptr=%x, oldval=%d, ",
        semaptr,semaptr->sem_base,&semaptr->sem_base[semnum],semaptr->sem_base[semnum].semval);
#endif
        semaptr->sem_base[semnum].semval = real_arg.val;
#ifdef SEM_DEBUG
        printf(" newval=%d\n", semaptr->sem_base[semnum].semval);
#endif
        semundo_clear(semid,semnum);
        wakeup( (caddr_t)semaptr );     /* somebody else might care */
        break;

    case SETALL:
        /* printf("SETALL\n"); */
        if ( (eval = ipcaccess(&semaptr->sem_perm, IPC_W, cred)) ) {
            return(eval);
        }
        rval = 0;
        if ( (eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0 ) {
            return(eval);
        }
        for ( i = 0; i < semaptr->sem_nsems; i += 1 ) {
            eval =
                copyin(&real_arg.array[i],
                (caddr_t)&semaptr->sem_base[i].semval,
                sizeof(real_arg.array[0]));
            if ( eval != 0 ) {
                break;
            }
        }
        semundo_clear(semid,-1);
        wakeup( (caddr_t)semaptr );     /* somebody else might care */
        break;
    default:
        /* printf("invalid command %d\n",cmd); */
        return(EINVAL);
    }

    if ( eval == 0 ) {
        *retval = rval;
    }
    return(eval);
}

struct semget_args {
        key_t   key;
        int     nsems;
        int     semflg;
};

static int
semget(p, uap, retval)
        struct proc *p;
        register struct semget_args *uap;
        int *retval;
{
    int semid, eval;
    int key = uap->key;
    int nsems = uap->nsems;
    int semflg = uap->semflg;
    struct ucred *cred = p->p_ucred;

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

    if ( key == IPC_PRIVATE ) {
#ifdef SEM_DEBUG
        printf("private key\n");
#endif
        semid = seminfo.semmni;
    } else {
        for ( semid = 0; semid < seminfo.semmni; semid += 1 ) {
            if ( (sema[semid].sem_perm.mode & SEM_ALLOC)
            && sema[semid].sem_perm.key == key ) {
                break;
            }
        }
        if ( semid < seminfo.semmni ) {
#ifdef SEM_DEBUG
            printf("found public key\n");
#endif
            if ( (eval = ipcaccess(&sema[semid].sem_perm, semflg & 0700, cred)) ) {
                return(eval);
            }
            if ( nsems > 0 && sema[semid].sem_nsems < nsems ) {
#ifdef SEM_DEBUG
                printf("too small\n");
#endif
                return(EINVAL);
            }
            if ( (semflg & IPC_CREAT) && (semflg & IPC_EXCL) ) {
#ifdef SEM_DEBUG
                printf("not exclusive\n");
#endif
                return(EEXIST);
            }
        } else {
#ifdef SEM_DEBUG
            printf("didn't find public key\n");
#endif
        }
    }

    if ( semid == seminfo.semmni ) {
#ifdef SEM_DEBUG
        printf("need to allocate the semid_ds\n");
#endif
        if ( key == IPC_PRIVATE || (semflg & IPC_CREAT) ) {
            if ( nsems <= 0 || nsems > seminfo.semmsl ) {
#ifdef SEM_DEBUG
                printf("nsems out of range (0<%d<=%d)\n",nsems,seminfo.semmsl);
#endif
                return(EINVAL);
            }
            if ( nsems > seminfo.semmns - semtot ) {
#ifdef SEM_DEBUG
                printf("not enough semaphores left (need %d, got %d)\n",
                nsems,seminfo.semmns - semtot);
#endif
                return(ENOSPC);
            }
            for ( semid = 0; semid < seminfo.semmni; semid += 1 ) {
                if ( (sema[semid].sem_perm.mode & SEM_ALLOC) == 0 ) {
                    break;
                }
            }
            if ( semid == seminfo.semmni ) {
#ifdef SEM_DEBUG
                printf("no more semid_ds's available\n");
#endif
                return(ENOSPC);
            }
#ifdef SEM_DEBUG
            printf("semid %d is available\n",semid);
#endif
            sema[semid].sem_perm.key = key;
            sema[semid].sem_perm.cuid = cred->cr_uid;
            sema[semid].sem_perm.uid = cred->cr_uid;
            sema[semid].sem_perm.cgid = cred->cr_gid;
            sema[semid].sem_perm.gid = cred->cr_gid;
            sema[semid].sem_perm.mode = (semflg & 0777) | SEM_ALLOC;
            sema[semid].sem_perm.seq = (sema[semid].sem_perm.seq + 1) & 0x7fff; /* avoid semid overflows */
            sema[semid].sem_nsems = nsems;
            sema[semid].sem_otime = 0;
            sema[semid].sem_ctime = time.tv_sec;
            sema[semid].sem_base = &sem[semtot];
            semtot += nsems;
            bzero(sema[semid].sem_base,sizeof(sema[semid].sem_base[0])*nsems);
#ifdef SEM_DEBUG
            printf("sembase = 0x%x, next = 0x%x\n",sema[semid].sem_base,&sem[semtot]);
#endif
        } else {
#ifdef SEM_DEBUG
            printf("didn't find it and wasn't asked to create it\n");
#endif
            return(ENOENT);
        }
    }

    *retval = IXSEQ_TO_IPCID(semid,sema[semid].sem_perm);       /* Convert to one origin */
    return(0);
}

struct semop_args {
        int     semid;
        struct  sembuf *sops;
        int     nsops;
};

static int
semop(p, uap, retval)
        struct proc *p;
        register struct semop_args *uap;
        int *retval;
{
    int semid = uap->semid;
    int nsops = uap->nsops;
    struct sembuf sops[MAX_SOPS];
    register struct semid_ds *semaptr;
    register struct sembuf *sopptr;
    register struct sem *semptr;
    struct sem_undo *suptr = NULL;
    struct ucred *cred = p->p_ucred;
    int i, j, eval;
    int all_ok, do_wakeup, do_undos;

#ifdef SEM_DEBUG
    printf("call to semop(%d,0x%x,%d)\n",semid,sops,nsops);
#endif

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

    if ( semid < 0 || semid >= seminfo.semmsl ) {
        /* printf("semid out of range (0<=%d<%d)\n",semid,seminfo.semmsl); */
        return(EINVAL);
    }

    semaptr = &sema[semid];
    if ( (semaptr->sem_perm.mode & SEM_ALLOC) == 0 ) {
        /* printf("no such semaphore id\n"); */
        return(EINVAL);
    }

    if ( semaptr->sem_perm.seq != IPCID_TO_SEQ(uap->semid) ) {
        /* printf("invalid sequence number\n"); */
        return(EINVAL);
    }

    if ( (eval = ipcaccess(&semaptr->sem_perm, IPC_W, cred)) ) {
#ifdef SEM_DEBUG
        printf("eval = %d from ipaccess\n",eval);
#endif
        return(eval);
    }

    if ( nsops > MAX_SOPS ) {
#ifdef SEM_DEBUG
        printf("too many sops (max=%d, nsops=%d)\n",MAX_SOPS,nsops);
#endif
        return(E2BIG);
    }

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

    /*
     * 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;

    while (1) {

        do_wakeup = 0;

        for ( i = 0; i < nsops; i += 1 ) {

            sopptr = &sops[i];

            if ( sopptr->sem_num >= semaptr->sem_nsems ) {
                return(EFBIG);
            }

            semptr = &semaptr->sem_base[sopptr->sem_num];

#ifdef SEM_DEBUG
            printf("semop:  semaptr=%x, sem_base=%x, semptr=%x, sem[%d]=%d : op=%d, flag=%s\n",
            semaptr,semaptr->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
                    printf("semop:  can't do it now\n");
#endif
                    break;
                } else {
                    semptr->semval += sopptr->sem_op;
                    if ( semptr->semval == 0 && semptr->semzcnt > 0 ) {
                        do_wakeup = 1;
                    }
                }
                if ( sopptr->sem_flg & SEM_UNDO ) {
                    do_undos = 1;
                }

            } else if ( sopptr->sem_op == 0 ) {

                if ( semptr->semval > 0 ) {
#ifdef SEM_DEBUG
                    printf("semop:  not zero now\n");
#endif
                    break;
                }

            } else {

                if ( semptr->semncnt > 0 ) {
                    do_wakeup = 1;
                }
                semptr->semval += sopptr->sem_op;
                if ( sopptr->sem_flg & SEM_UNDO ) {
                    do_undos = 1;
                }

            }
        }

        /*
         * Did we get through the entire vector?
         */

        if ( i < nsops ) {

            /*
             * No ... rollback anything that we've already done
             */

#ifdef SEM_DEBUG
            printf("semop:  rollback 0 through %d\n",i-1);
#endif
            for ( j = 0; j < i; j += 1 ) {
                semaptr->sem_base[sops[j].sem_num].semval -= sops[j].sem_op;
            }

            /*
             * If the request that we couldn't satisfy has the NOWAIT
             * flag set then return with EAGAIN.
             */

            if ( sopptr->sem_flg & IPC_NOWAIT ) {
                return(EAGAIN);
            }

            if ( sopptr->sem_op == 0 ) {
                semptr->semzcnt += 1;
            } else {
                semptr->semncnt += 1;
            }

#ifdef SEM_DEBUG
            printf("semop:  good night!\n");
#endif
            eval = tsleep( (caddr_t)semaptr, (PZERO - 4) | PCATCH, "sem wait", 0 );
#ifdef SEM_DEBUG
            printf("semop:  good morning (eval=%d)!\n",eval);
#endif

            suptr = NULL;       /* The sem_undo may have been reallocated */

            if ( eval != 0 ) {
                /* printf("semop:  interrupted system call\n"); */
                return( EINTR );
            }
#ifdef SEM_DEBUG
            printf("semop:  good morning!\n");
#endif

            /*
             * Make sure that the semaphore still exists
             */

            if ( (semaptr->sem_perm.mode & SEM_ALLOC) == 0
            || semaptr->sem_perm.seq != IPCID_TO_SEQ(uap->semid) ) {

                /* printf("semaphore id deleted\n"); */
                /* The man page says to return EIDRM. */
                /* Unfortunately, BSD doesn't define that code! */
#ifdef EIDRM
                return(EIDRM);
#else
                return(EINVAL);
#endif
            }

            /*
             * The semaphore is still alive.  Readjust the count of
             * waiting processes.
             */

            if ( sopptr->sem_op == 0 ) {
                semptr->semzcnt -= 1;
            } else {
                semptr->semncnt -= 1;
            }


        } else {

            /*
             * Yes ... we're done.
             * Process any SEM_UNDO requests.
             */

            if ( do_undos ) {

                for ( i = 0; i < nsops; i += 1 ) {

                    /* We only need to deal with SEM_UNDO's for non-zero op's */
                    int adjval;

                    if ( (sops[i].sem_flg & SEM_UNDO) != 0 && (adjval = sops[i].sem_op) != 0 ) {

                        eval = semundo_adjust(p,&suptr,semid,sops[i].sem_num,-adjval);
                        if ( eval != 0 ) {

                            /*
                             * 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 -= 1 ) {

                                if ( (sops[i].sem_flg & SEM_UNDO) != 0 && (adjval = sops[i].sem_op) != 0 ) {

                                    if ( semundo_adjust(p,&suptr,semid,sops[j].sem_num,adjval) != 0 ) {

                                        /* This is impossible!  */
                                        panic("semop - can't undo undos");

                                    }
                                }

                            } /* loop backwards through sops */

                            for ( j = 0; j < nsops; j += 1 ) {
                                semaptr->sem_base[sops[j].sem_num].semval -= sops[j].sem_op;
                            }

#ifdef SEM_DEBUG
                            printf("eval = %d from semundo_adjust\n",eval);
#endif
                            return( eval );

                        } /* semundo_adjust failed */

                    } /* if ( SEM_UNDO && adjval != 0 ) */

                } /* loop through the sops */

            } /* if ( do_undos ) */

            /* We're definitely done - set the sempid's */

            for ( i = 0; i < nsops; i += 1 ) {

                sopptr = &sops[i];
                semptr = &semaptr->sem_base[sopptr->sem_num];
                semptr->sempid = p->p_pid;

            }

            /* Do a wakeup if any semaphore was up'd. */

            if ( do_wakeup ) {
#ifdef SEM_DEBUG
                printf("semop:  doing wakeup\n");
#ifdef SEM_WAKEUP
                sem_wakeup( (caddr_t)semaptr );
#else
                wakeup( (caddr_t)semaptr );
#endif
                printf("semop:  back from wakeup\n");
#else
                wakeup( (caddr_t)semaptr );
#endif
            }
#ifdef SEM_DEBUG
            printf("semop:  done\n");
#endif
            *retval = 0;
            return(0);

        }

    }

    panic("semop: how did we get here???");
}

/*
 * Go through the undo structures for this process and apply the
 * adjustments to semaphores.
 */

void
semexit(p)
    struct proc *p;
{
    register struct sem_undo *suptr;
    register struct sem_undo **supptr;
    int did_something;

    /*
     * If somebody else is holding the global semaphore facility lock
     * then sleep until it is released.
     */

    while ( semlock_holder != NULL && semlock_holder != p ) {
#ifdef SEM_DEBUG
        printf("semaphore facility locked - sleeping ...\n");
#endif
        tsleep( (caddr_t)&semlock_holder, (PZERO - 4), "semexit", 0 );
    }

    did_something = 0;

    /*
     * Go through the chain of undo vectors looking for one
     * associated with this process.
     */

    for ( supptr = &semu_list;
    (suptr = *supptr) != NULL;
    supptr = &(suptr->un_next)
    ) {

        if ( suptr->un_proc == p ) {

#ifdef SEM_DEBUG
            printf("proc @%08x has undo structure with %d entries\n",p,suptr->un_cnt);
#endif

            /*
             * If there are any active undo elements then process them.
             */

            if ( suptr->un_cnt > 0 ) {

                int ix;

                for ( ix = 0; ix < suptr->un_cnt; ix += 1 ) {

                    int semid = suptr->un_ent[ix].un_id;
                    int semnum = suptr->un_ent[ix].un_num;
                    int adjval = suptr->un_ent[ix].un_adjval;
                    struct semid_ds *semaptr;

                    semaptr = &sema[semid];
                    if ( (semaptr->sem_perm.mode & SEM_ALLOC) == 0 ) {
                        panic("semexit - semid not allocated");
                    }
                    if ( semnum >= semaptr->sem_nsems ) {
                        panic("semexit - semnum out of range");
                    }

#ifdef SEM_DEBUG
                    printf("semexit:  %08x id=%d num=%d(adj=%d) ; sem=%d\n",suptr->un_proc,
                    suptr->un_ent[ix].un_id,suptr->un_ent[ix].un_num,suptr->un_ent[ix].un_adjval,
                    semaptr->sem_base[semnum].semval);
#endif

                    if ( adjval < 0 ) {
                        if ( semaptr->sem_base[semnum].semval < -adjval ) {
                            semaptr->sem_base[semnum].semval = 0;
                        } else {
                            semaptr->sem_base[semnum].semval += adjval;
                        }
                    } else {
                        semaptr->sem_base[semnum].semval += adjval;
                    }

                    /* printf("semval now %d\n",semaptr->sem_base[semnum].semval); */

#ifdef SEM_WAKEUP
                    sem_wakeup((caddr_t)semaptr);       /* A little sloppy (we should KNOW if anybody is waiting). */
#else
                    wakeup((caddr_t)semaptr);           /* A little sloppy (we should KNOW if anybody is waiting). */
#endif
#ifdef SEM_DEBUG
                    printf("semexit:  back from wakeup\n");
#endif

                }

            }

            /*
             * Deallocate the undo vector.
             */

#ifdef SEM_DEBUG
            printf("removing vector\n");
#endif
            suptr->un_proc = NULL;
            *supptr = suptr->un_next;

            /* Done. */

            break;


        }

    }

    /*
     * If the exiting process is holding the global semaphore facility
     * lock then release it.
     */

    if ( semlock_holder == p ) {
        semlock_holder = NULL;
        wakeup( (caddr_t)&semlock_holder );
    }
}
#endif