xnu-1228.12.14.tar.gz

[apple/xnu.git] / bsd / kern / sysv_msg.c

/*
 * Copyright (c) 2000-2007 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * Implementation of SVID messages
 *
 * Author:  Daniel Boulet
 *
 * Copyright 1993 Daniel Boulet and RTMX Inc.
 *
 * This system call was implemented by Daniel Boulet under contract from RTMX.
 *
 * Redistribution and use in source forms, with and without modification,
 * are permitted provided that this entire comment appears intact.
 *
 * Redistribution in binary form may occur without any restrictions.
 * Obviously, it would be nice if you gave credit where credit is due
 * but requiring it would be too onerous.
 *
 * This software is provided ``AS IS'' without any warranties of any kind.
 */
/*
 * NOTICE: This file was modified by SPARTA, Inc. in 2005 to introduce
 * support for mandatory and extensible security protections.  This notice
 * is included in support of clause 2.2 (b) of the Apple Public License,
 * Version 2.0.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/proc_internal.h>
#include <sys/kauth.h>
#include <sys/msg.h>
#include <sys/malloc.h>
#include <mach/mach_types.h>

#include <bsm/audit_kernel.h>

#include <sys/filedesc.h>
#include <sys/file_internal.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
#include <sys/ipcs.h>

#if SYSV_MSG

static int msginit(void *);

#define MSG_DEBUG
#undef MSG_DEBUG_OK

/* Uncomment this line to see MAC debugging output. */
/* #define      MAC_DEBUG */
#if CONFIG_MACF_DEBUG
#define MPRINTF(a)      printf(a)
#else
#define MPRINTF(a)
#endif
static void msg_freehdr(struct msg *msghdr);

typedef int     sy_call_t(struct proc *, void *, int *);

/* XXX casting to (sy_call_t *) is bogus, as usual. */
static sy_call_t *msgcalls[] = {
        (sy_call_t *)msgctl, (sy_call_t *)msgget,
        (sy_call_t *)msgsnd, (sy_call_t *)msgrcv
};

static int              nfree_msgmaps;  /* # of free map entries */
static short            free_msgmaps;   /* free map entries list head */
static struct msg       *free_msghdrs;  /* list of free msg headers */
char                    *msgpool;       /* MSGMAX byte long msg buffer pool */
struct msgmap           *msgmaps;       /* MSGSEG msgmap structures */
struct msg              *msghdrs;       /* MSGTQL msg headers */
struct msqid_kernel     *msqids;        /* MSGMNI msqid_kernel structs (wrapping user_msqid_ds structs) */

static lck_grp_t       *sysv_msg_subsys_lck_grp;
static lck_grp_attr_t  *sysv_msg_subsys_lck_grp_attr;
static lck_attr_t      *sysv_msg_subsys_lck_attr;
static lck_mtx_t        sysv_msg_subsys_mutex;

#define SYSV_MSG_SUBSYS_LOCK() lck_mtx_lock(&sysv_msg_subsys_mutex)
#define SYSV_MSG_SUBSYS_UNLOCK() lck_mtx_unlock(&sysv_msg_subsys_mutex)

void sysv_msg_lock_init(void);


#ifdef __APPLE_API_PRIVATE
        int     msgmax,         /* max chars in a message */
                msgmni,         /* max message queue identifiers */
                msgmnb,         /* max chars in a queue */
                msgtql,         /* max messages in system */
                msgssz,         /* size of a message segment (see notes above) */
                msgseg;         /* number of message segments */
struct msginfo msginfo = {
                MSGMAX,         /* = (MSGSSZ*MSGSEG) : max chars in a message */
                MSGMNI,         /* = 40 : max message queue identifiers */
                MSGMNB,         /* = 2048 : max chars in a queue */
                MSGTQL,         /* = 40 : max messages in system */
                MSGSSZ,         /* = 8 : size of a message segment (2^N long) */
                MSGSEG          /* = 2048 : number of message segments */
};
#endif /* __APPLE_API_PRIVATE */

/* Initialize the mutex governing access to the SysV msg subsystem */
__private_extern__ void
sysv_msg_lock_init( void )
{
        sysv_msg_subsys_lck_grp_attr = lck_grp_attr_alloc_init();

        sysv_msg_subsys_lck_grp = lck_grp_alloc_init("sysv_msg_subsys_lock", sysv_msg_subsys_lck_grp_attr);

        sysv_msg_subsys_lck_attr = lck_attr_alloc_init();
        lck_mtx_init(&sysv_msg_subsys_mutex, sysv_msg_subsys_lck_grp, sysv_msg_subsys_lck_attr);
}

static __inline__ user_time_t
sysv_msgtime(void)
{
        struct timeval  tv;
        microtime(&tv);
        return (tv.tv_sec);
}

/*
 * NOTE: Source and target may *NOT* overlap! (target is smaller)
 */
static void
msqid_ds_64to32(struct user_msqid_ds *in, struct msqid_ds *out)
{
        out->msg_perm   = in->msg_perm;
        out->msg_qnum   = in->msg_qnum;
        out->msg_cbytes = in->msg_cbytes;       /* for ipcs */
        out->msg_qbytes = in->msg_qbytes;
        out->msg_lspid  = in->msg_lspid;
        out->msg_lrpid  = in->msg_lrpid;
        out->msg_stime  = in->msg_stime;        /* XXX loss of range */
        out->msg_rtime  = in->msg_rtime;        /* XXX loss of range */
        out->msg_ctime  = in->msg_ctime;        /* XXX loss of range */
}

/*
 * NOTE: Source and target may are permitted to overlap! (source is smaller);
 * this works because we copy fields in order from the end of the struct to
 * the beginning.
 */
static void
msqid_ds_32to64(struct msqid_ds *in, struct user_msqid_ds *out)
{
        out->msg_ctime  = in->msg_ctime;
        out->msg_rtime  = in->msg_rtime;
        out->msg_stime  = in->msg_stime;
        out->msg_lrpid  = in->msg_lrpid;
        out->msg_lspid  = in->msg_lspid;
        out->msg_qbytes = in->msg_qbytes;
        out->msg_cbytes = in->msg_cbytes;       /* for ipcs */
        out->msg_qnum   = in->msg_qnum;
        out->msg_perm   = in->msg_perm;
}

/* This routine assumes the system is locked prior to calling this routine */
static int
msginit(__unused void *dummy)
{
        static int initted = 0;
        register int i;

        /* Lazy initialization on first system call; we don't have SYSINIT(). */
        if (initted)
                return (initted);

        /*
         * msginfo.msgssz should be a power of two for efficiency reasons.
         * It is also pretty silly if msginfo.msgssz is less than 8
         * or greater than about 256 so ...
         */
        i = 8;
        while (i < 1024 && i != msginfo.msgssz)
                i <<= 1;
        if (i != msginfo.msgssz) {
                printf("msginfo.msgssz=%d (0x%x) not a small power of 2; resetting to %d\n", msginfo.msgssz, msginfo.msgssz, MSGSSZ);
                msginfo.msgssz = MSGSSZ;
        }

        if (msginfo.msgseg > 32767) {
                printf("msginfo.msgseg=%d (> 32767); resetting to %d\n", msginfo.msgseg, MSGSEG);
                msginfo.msgseg = MSGSEG;
        }


        /*
         * Allocate memory for message pool, maps, headers, and queue IDs;
         * if this fails, fail safely and leave it uninitialized (related
         * system calls will fail).
         */
        msgpool = (char *)_MALLOC(msginfo.msgmax, M_SHM, M_WAITOK);
        if (msgpool == NULL) {
                printf("msginit: can't allocate msgpool");
                goto bad;
        }
        MALLOC(msgmaps, struct msgmap *,
                        sizeof(struct msgmap) * msginfo.msgseg, 
                        M_SHM, M_WAITOK);
        if (msgmaps == NULL) {
                printf("msginit: can't allocate msgmaps");
                goto bad;
        }

        MALLOC(msghdrs, struct msg *,
                        sizeof(struct msg) * msginfo.msgtql, 
                        M_SHM, M_WAITOK);
        if (msghdrs == NULL) {
                printf("msginit: can't allocate msghdrs");
                goto bad;
        }

        MALLOC(msqids, struct msqid_kernel *,
                        sizeof(struct user_msqid_ds) * msginfo.msgmni, 
                        M_SHM, M_WAITOK);
        if (msqids == NULL) {
                printf("msginit: can't allocate msqids");
                goto bad;
        }


        /* init msgmaps */
        for (i = 0; i < msginfo.msgseg; i++) {
                if (i > 0)
                        msgmaps[i-1].next = i;
                msgmaps[i].next = -1;   /* implies entry is available */
        }
        free_msgmaps = 0;
        nfree_msgmaps = msginfo.msgseg;


        /* init msghdrs */
        for (i = 0; i < msginfo.msgtql; i++) {
                msghdrs[i].msg_type = 0;
                if (i > 0)
                        msghdrs[i-1].msg_next = &msghdrs[i];
                msghdrs[i].msg_next = NULL;
#if CONFIG_MACF
                mac_sysvmsg_label_init(&msghdrs[i]);
#endif
        }
        free_msghdrs = &msghdrs[0];

        /* init msqids */
        for (i = 0; i < msginfo.msgmni; i++) {
                msqids[i].u.msg_qbytes = 0;     /* implies entry is available */
                msqids[i].u.msg_perm._seq = 0;  /* reset to a known value */
                msqids[i].u.msg_perm.mode = 0;
#if CONFIG_MACF
                mac_sysvmsq_label_init(&msqids[i]);
#endif
        }

        initted = 1;
bad:
        if (!initted) {
                if (msgpool != NULL)
                        _FREE(msgpool, M_SHM);
                if (msgmaps != NULL)
                        FREE(msgmaps, M_SHM);
                if (msghdrs != NULL)
                        FREE(msghdrs, M_SHM);
                if (msqids != NULL)
                        FREE(msqids, M_SHM);
        }
        return (initted);
}

/*
 * Entry point for all MSG calls
 */
        /* XXX actually varargs. */
int
msgsys(struct proc *p, struct msgsys_args *uap, register_t *retval)
{
        if (uap->which >= sizeof(msgcalls)/sizeof(msgcalls[0]))
                return (EINVAL);
        return ((*msgcalls[uap->which])(p, &uap->a2, retval));
}

static void
msg_freehdr(struct msg *msghdr)
{
        while (msghdr->msg_ts > 0) {
                short next;
                if (msghdr->msg_spot < 0 || msghdr->msg_spot >= msginfo.msgseg)
                        panic("msghdr->msg_spot out of range");
                next = msgmaps[msghdr->msg_spot].next;
                msgmaps[msghdr->msg_spot].next = free_msgmaps;
                free_msgmaps = msghdr->msg_spot;
                nfree_msgmaps++;
                msghdr->msg_spot = next;
                if (msghdr->msg_ts >= msginfo.msgssz)
                        msghdr->msg_ts -= msginfo.msgssz;
                else
                        msghdr->msg_ts = 0;
        }
        if (msghdr->msg_spot != -1)
                panic("msghdr->msg_spot != -1");
        msghdr->msg_next = free_msghdrs;
        free_msghdrs = msghdr;
#if CONFIG_MACF
        mac_sysvmsg_label_recycle(msghdr);
#endif
        /*
         * Notify waiters that there are free message headers and segments
         * now available.
         */
        wakeup((caddr_t)&free_msghdrs);
}

int
msgctl(struct proc *p, struct msgctl_args *uap, register_t *retval)
{
        int msqid = uap->msqid;
        int cmd = uap->cmd;
        kauth_cred_t cred = kauth_cred_get();
        int rval, eval;
        struct user_msqid_ds msqbuf;
        struct msqid_kernel *msqptr;
        struct user_msqid_ds umsds;

        SYSV_MSG_SUBSYS_LOCK();

        if (!msginit(0)) {
                eval =  ENOMEM;
                goto msgctlout;
        }

#ifdef MSG_DEBUG_OK
        printf("call to msgctl(%d, %d, 0x%qx)\n", msqid, cmd, uap->buf);
#endif

        AUDIT_ARG(svipc_cmd, cmd);
        AUDIT_ARG(svipc_id, msqid);
        msqid = IPCID_TO_IX(msqid);

        if (msqid < 0 || msqid >= msginfo.msgmni) {
#ifdef MSG_DEBUG_OK
                printf("msqid (%d) out of range (0<=msqid<%d)\n", msqid,
                    msginfo.msgmni);
#endif
                eval = EINVAL;
                goto msgctlout;
        }

        msqptr = &msqids[msqid];

        if (msqptr->u.msg_qbytes == 0) {
#ifdef MSG_DEBUG_OK
                printf("no such msqid\n");
#endif
                eval = EINVAL;
                goto msgctlout;
        }
        if (msqptr->u.msg_perm._seq != IPCID_TO_SEQ(uap->msqid)) {
#ifdef MSG_DEBUG_OK
                printf("wrong sequence number\n");
#endif
                eval = EINVAL;
                goto msgctlout;
        }
#if CONFIG_MACF
        eval = mac_sysvmsq_check_msqctl(kauth_cred_get(), msqptr, cmd);
        if (eval) 
                goto msgctlout;
#endif

        eval = 0;
        rval = 0;

        switch (cmd) {

        case IPC_RMID:
        {
                struct msg *msghdr;
                if ((eval = ipcperm(cred, &msqptr->u.msg_perm, IPC_M)))
                        goto msgctlout;
#if CONFIG_MACF
                /*
                 * Check that the thread has MAC access permissions to
                 * individual msghdrs.  Note: We need to do this in a
                 * separate loop because the actual loop alters the
                 * msq/msghdr info as it progresses, and there is no going
                 * back if half the way through we discover that the
                 * thread cannot free a certain msghdr.  The msq will get
                 * into an inconsistent state.
                 */
                for (msghdr = msqptr->u.msg_first; msghdr != NULL;
                    msghdr = msghdr->msg_next) {
                        eval = mac_sysvmsq_check_msgrmid(kauth_cred_get(), msghdr);
                        if (eval) 
                                goto msgctlout;
                }
#endif
                /* Free the message headers */
                msghdr = msqptr->u.msg_first;
                while (msghdr != NULL) {
                        struct msg *msghdr_tmp;

                        /* Free the segments of each message */
                        msqptr->u.msg_cbytes -= msghdr->msg_ts;
                        msqptr->u.msg_qnum--;
                        msghdr_tmp = msghdr;
                        msghdr = msghdr->msg_next;
                        msg_freehdr(msghdr_tmp);
                }

                if (msqptr->u.msg_cbytes != 0)
                        panic("msg_cbytes is messed up");
                if (msqptr->u.msg_qnum != 0)
                        panic("msg_qnum is messed up");

                msqptr->u.msg_qbytes = 0;       /* Mark it as free */
#if CONFIG_MACF
                mac_sysvmsq_label_recycle(msqptr);
#endif

                wakeup((caddr_t)msqptr);
        }

                break;

        case IPC_SET:
                if ((eval = ipcperm(cred, &msqptr->u.msg_perm, IPC_M)))
                        goto msgctlout;

                SYSV_MSG_SUBSYS_UNLOCK();

                if (IS_64BIT_PROCESS(p)) {
                        eval = copyin(uap->buf, &msqbuf, sizeof(struct user_msqid_ds));
                } else {
                        eval = copyin(uap->buf, &msqbuf, sizeof(struct msqid_ds));
                        /* convert in place; ugly, but safe */
                        msqid_ds_32to64((struct msqid_ds *)&msqbuf, &msqbuf);
                }
                if (eval)
                        return(eval);

                SYSV_MSG_SUBSYS_LOCK();

                if (msqbuf.msg_qbytes > msqptr->u.msg_qbytes) {
                        eval = suser(cred, &p->p_acflag);
                        if (eval)
                                goto msgctlout;
                }


                /* compare (msglen_t) value against restrict (int) value */
                if (msqbuf.msg_qbytes > (msglen_t)msginfo.msgmnb) {
#ifdef MSG_DEBUG_OK
                        printf("can't increase msg_qbytes beyond %d (truncating)\n",
                            msginfo.msgmnb);
#endif
                        msqbuf.msg_qbytes = msginfo.msgmnb;     /* silently restrict qbytes to system limit */
                }
                if (msqbuf.msg_qbytes == 0) {
#ifdef MSG_DEBUG_OK
                        printf("can't reduce msg_qbytes to 0\n");
#endif
                        eval = EINVAL;
                        goto msgctlout;
                }
                msqptr->u.msg_perm.uid = msqbuf.msg_perm.uid;   /* change the owner */
                msqptr->u.msg_perm.gid = msqbuf.msg_perm.gid;   /* change the owner */
                msqptr->u.msg_perm.mode = (msqptr->u.msg_perm.mode & ~0777) |
                    (msqbuf.msg_perm.mode & 0777);
                msqptr->u.msg_qbytes = msqbuf.msg_qbytes;
                msqptr->u.msg_ctime = sysv_msgtime();
                break;

        case IPC_STAT:
                if ((eval = ipcperm(cred, &msqptr->u.msg_perm, IPC_R))) {
#ifdef MSG_DEBUG_OK
                        printf("requester doesn't have read access\n");
#endif
                        goto msgctlout;
                }

                bcopy(msqptr, &umsds, sizeof(struct user_msqid_ds));

                SYSV_MSG_SUBSYS_UNLOCK();
                if (IS_64BIT_PROCESS(p)) {
                        eval = copyout(&umsds, uap->buf, sizeof(struct user_msqid_ds));
                } else {
                        struct msqid_ds msqid_ds32;
                        msqid_ds_64to32(&umsds, &msqid_ds32);
                        eval = copyout(&msqid_ds32, uap->buf, sizeof(struct msqid_ds));
                }
                SYSV_MSG_SUBSYS_LOCK();
                break;

        default:
#ifdef MSG_DEBUG_OK
                printf("invalid command %d\n", cmd);
#endif
                eval = EINVAL;
                goto msgctlout;
        }

        if (eval == 0)
                *retval = rval;
msgctlout:
        SYSV_MSG_SUBSYS_UNLOCK();
        return(eval);
}

int
msgget(__unused struct proc *p, struct msgget_args *uap, register_t *retval)
{
        int msqid, eval;
        int key = uap->key;
        int msgflg = uap->msgflg;
        kauth_cred_t cred = kauth_cred_get();
        struct msqid_kernel *msqptr = NULL;

        SYSV_MSG_SUBSYS_LOCK();

        if (!msginit(0)) {
                eval =  ENOMEM;
                goto msggetout;
        }

#ifdef MSG_DEBUG_OK
        printf("msgget(0x%x, 0%o)\n", key, msgflg);
#endif

        if (key != IPC_PRIVATE) {
                for (msqid = 0; msqid < msginfo.msgmni; msqid++) {
                        msqptr = &msqids[msqid];
                        if (msqptr->u.msg_qbytes != 0 &&
                            msqptr->u.msg_perm._key == key)
                                break;
                }
                if (msqid < msginfo.msgmni) {
#ifdef MSG_DEBUG_OK
                        printf("found public key\n");
#endif
                        if ((msgflg & IPC_CREAT) && (msgflg & IPC_EXCL)) {
#ifdef MSG_DEBUG_OK
                                printf("not exclusive\n");
#endif
                                eval = EEXIST;
                                goto msggetout;
                        }
                        if ((eval = ipcperm(cred, &msqptr->u.msg_perm, msgflg & 0700 ))) {
#ifdef MSG_DEBUG_OK
                                printf("requester doesn't have 0%o access\n",
                                    msgflg & 0700);
#endif
                                goto msggetout;
                        }
#if CONFIG_MACF
                        eval = mac_sysvmsq_check_msqget(cred, msqptr);
                        if (eval) 
                                goto msggetout;
#endif
                        goto found;
                }
        }

#ifdef MSG_DEBUG_OK
        printf("need to allocate the user_msqid_ds\n");
#endif
        if (key == IPC_PRIVATE || (msgflg & IPC_CREAT)) {
                for (msqid = 0; msqid < msginfo.msgmni; msqid++) {
                        /*
                         * Look for an unallocated and unlocked user_msqid_ds.
                         * user_msqid_ds's can be locked by msgsnd or msgrcv
                         * while they are copying the message in/out.  We
                         * can't re-use the entry until they release it.
                         */
                        msqptr = &msqids[msqid];
                        if (msqptr->u.msg_qbytes == 0 &&
                            (msqptr->u.msg_perm.mode & MSG_LOCKED) == 0)
                                break;
                }
                if (msqid == msginfo.msgmni) {
#ifdef MSG_DEBUG_OK
                        printf("no more user_msqid_ds's available\n");
#endif
                        eval = ENOSPC;
                        goto msggetout;
                }
#ifdef MSG_DEBUG_OK
                printf("msqid %d is available\n", msqid);
#endif
                msqptr->u.msg_perm._key = key;
                msqptr->u.msg_perm.cuid = kauth_cred_getuid(cred);
                msqptr->u.msg_perm.uid = kauth_cred_getuid(cred);
                msqptr->u.msg_perm.cgid = cred->cr_gid;
                msqptr->u.msg_perm.gid = cred->cr_gid;
                msqptr->u.msg_perm.mode = (msgflg & 0777);
                /* Make sure that the returned msqid is unique */
                msqptr->u.msg_perm._seq++;
                msqptr->u.msg_first = NULL;
                msqptr->u.msg_last = NULL;
                msqptr->u.msg_cbytes = 0;
                msqptr->u.msg_qnum = 0;
                msqptr->u.msg_qbytes = msginfo.msgmnb;
                msqptr->u.msg_lspid = 0;
                msqptr->u.msg_lrpid = 0;
                msqptr->u.msg_stime = 0;
                msqptr->u.msg_rtime = 0;
                msqptr->u.msg_ctime = sysv_msgtime();
#if CONFIG_MACF
                mac_sysvmsq_label_associate(cred, msqptr);
#endif
        } else {
#ifdef MSG_DEBUG_OK
                printf("didn't find it and wasn't asked to create it\n");
#endif
                eval = ENOENT;
                goto msggetout;
        }

found:
        /* Construct the unique msqid */
        *retval = IXSEQ_TO_IPCID(msqid, msqptr->u.msg_perm);
        AUDIT_ARG(svipc_id, *retval);
        eval = 0;
msggetout:
        SYSV_MSG_SUBSYS_UNLOCK();
        return(eval);
}


int
msgsnd(struct proc *p, struct msgsnd_args *uap, register_t *retval)
{
        __pthread_testcancel(1);
        return(msgsnd_nocancel(p, (struct msgsnd_nocancel_args *)uap, retval));
}

int
msgsnd_nocancel(struct proc *p, struct msgsnd_nocancel_args *uap, register_t *retval)
{
        int msqid = uap->msqid;
        user_addr_t user_msgp = uap->msgp;
        size_t msgsz = (size_t)uap->msgsz;      /* limit to 4G */
        int msgflg = uap->msgflg;
        int segs_needed, eval;
        struct msqid_kernel *msqptr;
        struct msg *msghdr;
        short next;
        user_long_t msgtype;


        SYSV_MSG_SUBSYS_LOCK();

        if (!msginit(0)) {
                eval =  ENOMEM;
                goto msgsndout;
        }

#ifdef MSG_DEBUG_OK
        printf("call to msgsnd(%d, 0x%qx, %d, %d)\n", msqid, user_msgp, msgsz,
            msgflg);
#endif

        AUDIT_ARG(svipc_id, msqid);
        msqid = IPCID_TO_IX(msqid);

        if (msqid < 0 || msqid >= msginfo.msgmni) {
#ifdef MSG_DEBUG_OK
                printf("msqid (%d) out of range (0<=msqid<%d)\n", msqid,
                    msginfo.msgmni);
#endif
                eval = EINVAL;
                goto msgsndout;
        }

        msqptr = &msqids[msqid];
        if (msqptr->u.msg_qbytes == 0) {
#ifdef MSG_DEBUG_OK
                printf("no such message queue id\n");
#endif
                eval = EINVAL;
                goto msgsndout;
        }
        if (msqptr->u.msg_perm._seq != IPCID_TO_SEQ(uap->msqid)) {
#ifdef MSG_DEBUG_OK
                printf("wrong sequence number\n");
#endif
                eval = EINVAL;
                goto msgsndout;
        }

        if ((eval = ipcperm(kauth_cred_get(), &msqptr->u.msg_perm, IPC_W))) {
#ifdef MSG_DEBUG_OK
                printf("requester doesn't have write access\n");
#endif
                goto msgsndout;
        }

#if CONFIG_MACF
        eval = mac_sysvmsq_check_msqsnd(kauth_cred_get(), msqptr);
        if (eval) 
                goto msgsndout;
#endif
        segs_needed = (msgsz + msginfo.msgssz - 1) / msginfo.msgssz;
#ifdef MSG_DEBUG_OK
        printf("msgsz=%d, msgssz=%d, segs_needed=%d\n", msgsz, msginfo.msgssz,
            segs_needed);
#endif

        /*
         * If we suffer resource starvation, we will sleep in this loop and
         * wait for more resources to become available.  This is a loop to
         * ensure reacquisition of the mutex following any sleep, since there
         * are multiple resources under contention.
         */
        for (;;) {
                void *blocking_resource = NULL;

                /*
                 * Check that we have not had the maximum message size change
                 * out from under us and render our message invalid while we
                 * slept waiting for some resource.
                 */
                if (msgsz > msqptr->u.msg_qbytes) {
#ifdef MSG_DEBUG_OK
                        printf("msgsz > msqptr->msg_qbytes\n");
#endif
                        eval = EINVAL;
                        goto msgsndout;
                }

                /*
                 * If the user_msqid_ds is already locked, we need to sleep on
                 * the queue until it's unlocked.
                 */
                if (msqptr->u.msg_perm.mode & MSG_LOCKED) {
#ifdef MSG_DEBUG_OK
                        printf("msqid is locked\n");
#endif
                        blocking_resource = msqptr;
                }

                /*
                 * If our message plus the messages already in the queue would
                 * cause us to exceed the maximum number of bytes wer are
                 * permitted to queue, then block on the queue until it drains.
                 */
                if (msgsz + msqptr->u.msg_cbytes > msqptr->u.msg_qbytes) {
#ifdef MSG_DEBUG_OK
                        printf("msgsz + msg_cbytes > msg_qbytes\n");
#endif
                        blocking_resource = msqptr;
                }

                /*
                 * Both message maps and message headers are protected by
                 * sleeping on the address of the pointer to the list of free
                 * message headers, since they are allocated and freed in
                 * tandem.
                 */
                if (segs_needed > nfree_msgmaps) {
#ifdef MSG_DEBUG_OK
                        printf("segs_needed > nfree_msgmaps\n");
#endif
                        blocking_resource = &free_msghdrs;
                }
                if (free_msghdrs == NULL) {
#ifdef MSG_DEBUG_OK
                        printf("no more msghdrs\n");
#endif
                        blocking_resource = &free_msghdrs;
                }

                if (blocking_resource != NULL) {
                        int we_own_it;

                        if ((msgflg & IPC_NOWAIT) != 0) {
#ifdef MSG_DEBUG_OK
                                printf("need more resources but caller doesn't want to wait\n");
#endif
                                eval = EAGAIN;
                                goto msgsndout;
                        }

                        if ((msqptr->u.msg_perm.mode & MSG_LOCKED) != 0) {
#ifdef MSG_DEBUG_OK
                                printf("we don't own the user_msqid_ds\n");
#endif
                                we_own_it = 0;
                        } else {
                                /* Force later arrivals to wait for our
                                   request */
#ifdef MSG_DEBUG_OK
                                printf("we own the user_msqid_ds\n");
#endif
                                msqptr->u.msg_perm.mode |= MSG_LOCKED;
                                we_own_it = 1;
                        }
#ifdef MSG_DEBUG_OK
                        printf("goodnight\n");
#endif
                        eval = msleep(blocking_resource, &sysv_msg_subsys_mutex, (PZERO - 4) | PCATCH,
                            "msgwait", 0);
#ifdef MSG_DEBUG_OK
                        printf("good morning, eval=%d\n", eval);
#endif
                        if (we_own_it)
                                msqptr->u.msg_perm.mode &= ~MSG_LOCKED;
                        if (eval != 0) {
#ifdef MSG_DEBUG_OK
                                printf("msgsnd:  interrupted system call\n");
#endif
                                eval = EINTR;
                                goto msgsndout;
                        }

                        /*
                         * Make sure that the msq queue still exists
                         */

                        if (msqptr->u.msg_qbytes == 0) {
#ifdef MSG_DEBUG_OK
                                printf("msqid deleted\n");
#endif
                                eval = EIDRM;
                                goto msgsndout;
                        
                        }

                } else {
#ifdef MSG_DEBUG_OK
                        printf("got all the resources that we need\n");
#endif
                        break;
                }
        }

        /*
         * We have the resources that we need.
         * Make sure!
         */

        if (msqptr->u.msg_perm.mode & MSG_LOCKED)
                panic("msg_perm.mode & MSG_LOCKED");
        if (segs_needed > nfree_msgmaps)
                panic("segs_needed > nfree_msgmaps");
        if (msgsz + msqptr->u.msg_cbytes > msqptr->u.msg_qbytes)
                panic("msgsz + msg_cbytes > msg_qbytes");
        if (free_msghdrs == NULL)
                panic("no more msghdrs");

        /*
         * Re-lock the user_msqid_ds in case we page-fault when copying in
         * the message
         */
        if ((msqptr->u.msg_perm.mode & MSG_LOCKED) != 0)
                panic("user_msqid_ds is already locked");
        msqptr->u.msg_perm.mode |= MSG_LOCKED;

        /*
         * Allocate a message header
         */
        msghdr = free_msghdrs;
        free_msghdrs = msghdr->msg_next;
        msghdr->msg_spot = -1;
        msghdr->msg_ts = msgsz;

#if CONFIG_MACF
        mac_sysvmsg_label_associate(kauth_cred_get(), msqptr, msghdr);
#endif
        /*
         * Allocate space for the message
         */

        while (segs_needed > 0) {
                if (nfree_msgmaps <= 0)
                        panic("not enough msgmaps");
                if (free_msgmaps == -1)
                        panic("nil free_msgmaps");
                next = free_msgmaps;
                if (next <= -1)
                        panic("next too low #1");
                if (next >= msginfo.msgseg)
                        panic("next out of range #1");
#ifdef MSG_DEBUG_OK
                printf("allocating segment %d to message\n", next);
#endif
                free_msgmaps = msgmaps[next].next;
                nfree_msgmaps--;
                msgmaps[next].next = msghdr->msg_spot;
                msghdr->msg_spot = next;
                segs_needed--;
        }

        /*
         * Copy in the message type.  For a 64 bit process, this is 64 bits,
         * but we only ever use the low 32 bits, so the cast is OK.
         */
        if (IS_64BIT_PROCESS(p)) {
                SYSV_MSG_SUBSYS_UNLOCK();
                eval = copyin(user_msgp, &msgtype, sizeof(msgtype));
                SYSV_MSG_SUBSYS_LOCK();
                msghdr->msg_type = CAST_DOWN(long,msgtype);
                user_msgp = user_msgp + sizeof(msgtype);        /* ptr math */
        } else {
                SYSV_MSG_SUBSYS_UNLOCK();
                eval = copyin(user_msgp, &msghdr->msg_type, sizeof(long));
                SYSV_MSG_SUBSYS_LOCK();
                user_msgp = user_msgp + sizeof(long);           /* ptr math */
        }

        if (eval != 0) {
#ifdef MSG_DEBUG_OK
                printf("error %d copying the message type\n", eval);
#endif
                msg_freehdr(msghdr);
                msqptr->u.msg_perm.mode &= ~MSG_LOCKED;
                wakeup((caddr_t)msqptr);
                goto msgsndout;
        }


        /*
         * Validate the message type
         */
        if (msghdr->msg_type < 1) {
                msg_freehdr(msghdr);
                msqptr->u.msg_perm.mode &= ~MSG_LOCKED;
                wakeup((caddr_t)msqptr);
#ifdef MSG_DEBUG_OK
                printf("mtype (%d) < 1\n", msghdr->msg_type);
#endif
                eval = EINVAL;
                goto msgsndout;
        }

        /*
         * Copy in the message body
         */
        next = msghdr->msg_spot;
        while (msgsz > 0) {
                size_t tlen;
                /* compare input (size_t) value against restrict (int) value */
                if (msgsz > (size_t)msginfo.msgssz)
                        tlen = msginfo.msgssz;
                else
                        tlen = msgsz;
                if (next <= -1)
                        panic("next too low #2");
                if (next >= msginfo.msgseg)
                        panic("next out of range #2");

                SYSV_MSG_SUBSYS_UNLOCK();
                eval = copyin(user_msgp, &msgpool[next * msginfo.msgssz], tlen);
                SYSV_MSG_SUBSYS_LOCK();

                if (eval != 0) {
#ifdef MSG_DEBUG_OK
                        printf("error %d copying in message segment\n", eval);
#endif
                        msg_freehdr(msghdr);
                        msqptr->u.msg_perm.mode &= ~MSG_LOCKED;
                        wakeup((caddr_t)msqptr);

                        goto msgsndout;
                }
                msgsz -= tlen;
                user_msgp = user_msgp + tlen;   /* ptr math */
                next = msgmaps[next].next;
        }
        if (next != -1)
                panic("didn't use all the msg segments");

        /*
         * We've got the message.  Unlock the user_msqid_ds.
         */

        msqptr->u.msg_perm.mode &= ~MSG_LOCKED;

        /*
         * Make sure that the user_msqid_ds is still allocated.
         */

        if (msqptr->u.msg_qbytes == 0) {
                msg_freehdr(msghdr);
                wakeup((caddr_t)msqptr);
                /* The SVID says to return EIDRM. */
#ifdef EIDRM
                eval = EIDRM;
#else
                /* Unfortunately, BSD doesn't define that code yet! */
                eval = EINVAL;
#endif
                goto msgsndout;
        }

#if CONFIG_MACF
        /*
         * Note: Since the task/thread allocates the msghdr and usually
         * primes it with its own MAC label, for a majority of policies, it
         * won't be necessary to check whether the msghdr has access
         * permissions to the msgq.  The mac_sysvmsq_check_msqsnd check would
         * suffice in that case.  However, this hook may be required where
         * individual policies derive a non-identical label for the msghdr
         * from the current thread label and may want to check the msghdr
         * enqueue permissions, along with read/write permissions to the
         * msgq.
         */
        eval = mac_sysvmsq_check_enqueue(kauth_cred_get(), msghdr, msqptr);
        if (eval) {
                msg_freehdr(msghdr);
                wakeup((caddr_t) msqptr);
                goto msgsndout;
        }
#endif
        /*
         * Put the message into the queue
         */

        if (msqptr->u.msg_first == NULL) {
                msqptr->u.msg_first = msghdr;
                msqptr->u.msg_last = msghdr;
        } else {
                msqptr->u.msg_last->msg_next = msghdr;
                msqptr->u.msg_last = msghdr;
        }
        msqptr->u.msg_last->msg_next = NULL;

        msqptr->u.msg_cbytes += msghdr->msg_ts;
        msqptr->u.msg_qnum++;
        msqptr->u.msg_lspid = p->p_pid;
        msqptr->u.msg_stime = sysv_msgtime();

        wakeup((caddr_t)msqptr);
        *retval = 0;
        eval = 0;

msgsndout:
        SYSV_MSG_SUBSYS_UNLOCK();
        return(eval);
}


int
msgrcv(struct proc *p, struct msgrcv_args *uap, user_ssize_t *retval)
{
        __pthread_testcancel(1);
        return(msgrcv_nocancel(p, (struct msgrcv_nocancel_args *)uap, retval));
}

int
msgrcv_nocancel(struct proc *p, struct msgrcv_nocancel_args *uap, user_ssize_t *retval)
{
        int msqid = uap->msqid;
        user_addr_t user_msgp = uap->msgp;
        size_t msgsz = (size_t)uap->msgsz;      /* limit to 4G */
        long msgtyp = (long)uap->msgtyp;        /* limit to 32 bits */
        int msgflg = uap->msgflg;
        size_t len;
        struct msqid_kernel *msqptr;
        struct msg *msghdr;
        int eval;
        short next;
        user_long_t msgtype;
        long msg_type_long;

        SYSV_MSG_SUBSYS_LOCK();

        if (!msginit(0)) {
                eval =  ENOMEM;
                goto msgrcvout;
        }

#ifdef MSG_DEBUG_OK
        printf("call to msgrcv(%d, 0x%qx, %d, %ld, %d)\n", msqid, user_msgp,
            msgsz, msgtyp, msgflg);
#endif

        AUDIT_ARG(svipc_id, msqid);
        msqid = IPCID_TO_IX(msqid);

        if (msqid < 0 || msqid >= msginfo.msgmni) {
#ifdef MSG_DEBUG_OK
                printf("msqid (%d) out of range (0<=msqid<%d)\n", msqid,
                    msginfo.msgmni);
#endif
                eval = EINVAL;
                goto msgrcvout;
        }

        msqptr = &msqids[msqid];
        if (msqptr->u.msg_qbytes == 0) {
#ifdef MSG_DEBUG_OK
                printf("no such message queue id\n");
#endif
                eval = EINVAL;
                goto msgrcvout;
        }
        if (msqptr->u.msg_perm._seq != IPCID_TO_SEQ(uap->msqid)) {
#ifdef MSG_DEBUG_OK
                printf("wrong sequence number\n");
#endif
                eval = EINVAL;
                goto msgrcvout;
        }

        if ((eval = ipcperm(kauth_cred_get(), &msqptr->u.msg_perm, IPC_R))) {
#ifdef MSG_DEBUG_OK
                printf("requester doesn't have read access\n");
#endif
                goto msgrcvout;
        }

#if CONFIG_MACF
        eval = mac_sysvmsq_check_msqrcv(kauth_cred_get(), msqptr);
        if (eval) 
                goto msgrcvout;
#endif
        msghdr = NULL;
        while (msghdr == NULL) {
                if (msgtyp == 0) {
                        msghdr = msqptr->u.msg_first;
                        if (msghdr != NULL) {
                                if (msgsz < msghdr->msg_ts &&
                                    (msgflg & MSG_NOERROR) == 0) {
#ifdef MSG_DEBUG_OK
                                        printf("first message on the queue is too big (want %d, got %d)\n",
                                            msgsz, msghdr->msg_ts);
#endif
                                        eval = E2BIG;
                                        goto msgrcvout;
                                }
#if CONFIG_MACF
                                eval = mac_sysvmsq_check_msgrcv(kauth_cred_get(),
                                    msghdr);
                                if (eval) 
                                        goto msgrcvout;
#endif
                                if (msqptr->u.msg_first == msqptr->u.msg_last) {
                                        msqptr->u.msg_first = NULL;
                                        msqptr->u.msg_last = NULL;
                                } else {
                                        msqptr->u.msg_first = msghdr->msg_next;
                                        if (msqptr->u.msg_first == NULL)
                                                panic("msg_first/last messed up #1");
                                }
                        }
                } else {
                        struct msg *previous;
                        struct msg **prev;

                        previous = NULL;
                        prev = &(msqptr->u.msg_first);
                        while ((msghdr = *prev) != NULL) {
                                /*
                                 * Is this message's type an exact match or is
                                 * this message's type less than or equal to
                                 * the absolute value of a negative msgtyp?
                                 * Note that the second half of this test can
                                 * NEVER be true if msgtyp is positive since
                                 * msg_type is always positive!
                                 */

                                if (msgtyp == msghdr->msg_type ||
                                    msghdr->msg_type <= -msgtyp) {
#ifdef MSG_DEBUG_OK
                                        printf("found message type %d, requested %d\n",
                                            msghdr->msg_type, msgtyp);
#endif
                                        if (msgsz < msghdr->msg_ts &&
                                            (msgflg & MSG_NOERROR) == 0) {
#ifdef MSG_DEBUG_OK
                                                printf("requested message on the queue is too big (want %d, got %d)\n",
                                                    msgsz, msghdr->msg_ts);
#endif
                                                eval = E2BIG;
                                                goto msgrcvout;
                                        }
#if CONFIG_MACF
                                        eval = mac_sysvmsq_check_msgrcv(
                                            kauth_cred_get(), msghdr);
                                        if (eval) 
                                                goto msgrcvout;
#endif
                                        *prev = msghdr->msg_next;
                                        if (msghdr == msqptr->u.msg_last) {
                                                if (previous == NULL) {
                                                        if (prev !=
                                                            &msqptr->u.msg_first)
                                                                panic("msg_first/last messed up #2");
                                                        msqptr->u.msg_first =
                                                            NULL;
                                                        msqptr->u.msg_last =
                                                            NULL;
                                                } else {
                                                        if (prev ==
                                                            &msqptr->u.msg_first)
                                                                panic("msg_first/last messed up #3");
                                                        msqptr->u.msg_last =
                                                            previous;
                                                }
                                        }
                                        break;
                                }
                                previous = msghdr;
                                prev = &(msghdr->msg_next);
                        }
                }

                /*
                 * We've either extracted the msghdr for the appropriate
                 * message or there isn't one.
                 * If there is one then bail out of this loop.
                 */

                if (msghdr != NULL)
                        break;

                /*
                 * Hmph!  No message found.  Does the user want to wait?
                 */

                if ((msgflg & IPC_NOWAIT) != 0) {
#ifdef MSG_DEBUG_OK
                        printf("no appropriate message found (msgtyp=%d)\n",
                            msgtyp);
#endif
                        /* The SVID says to return ENOMSG. */
#ifdef ENOMSG
                        eval = ENOMSG;
#else
                        /* Unfortunately, BSD doesn't define that code yet! */
                        eval = EAGAIN;
#endif
                        goto msgrcvout;
                }

                /*
                 * Wait for something to happen
                 */

#ifdef MSG_DEBUG_OK
                printf("msgrcv:  goodnight\n");
#endif
                eval = msleep((caddr_t)msqptr, &sysv_msg_subsys_mutex, (PZERO - 4) | PCATCH, "msgwait",
                    0);
#ifdef MSG_DEBUG_OK
                printf("msgrcv:  good morning (eval=%d)\n", eval);
#endif

                if (eval != 0) {
#ifdef MSG_DEBUG_OK
                        printf("msgsnd:  interrupted system call\n");
#endif
                        eval = EINTR;
                        goto msgrcvout;
                }

                /*
                 * Make sure that the msq queue still exists
                 */

                if (msqptr->u.msg_qbytes == 0 ||
                    msqptr->u.msg_perm._seq != IPCID_TO_SEQ(uap->msqid)) {
#ifdef MSG_DEBUG_OK
                        printf("msqid deleted\n");
#endif
                        /* The SVID says to return EIDRM. */
#ifdef EIDRM
                        eval = EIDRM;
#else
                        /* Unfortunately, BSD doesn't define that code yet! */
                        eval = EINVAL;
#endif
                        goto msgrcvout;
                }
        }

        /*
         * Return the message to the user.
         *
         * First, do the bookkeeping (before we risk being interrupted).
         */

        msqptr->u.msg_cbytes -= msghdr->msg_ts;
        msqptr->u.msg_qnum--;
        msqptr->u.msg_lrpid = p->p_pid;
        msqptr->u.msg_rtime = sysv_msgtime();

        /*
         * Make msgsz the actual amount that we'll be returning.
         * Note that this effectively truncates the message if it is too long
         * (since msgsz is never increased).
         */

#ifdef MSG_DEBUG_OK
        printf("found a message, msgsz=%d, msg_ts=%d\n", msgsz,
            msghdr->msg_ts);
#endif
        if (msgsz > msghdr->msg_ts)
                msgsz = msghdr->msg_ts;

        /*
         * Return the type to the user.
         */

        /*
         * Copy out the message type.  For a 64 bit process, this is 64 bits,
         * but we only ever use the low 32 bits, so the cast is OK.
         */
        if (IS_64BIT_PROCESS(p)) {
                msgtype = msghdr->msg_type;
                SYSV_MSG_SUBSYS_UNLOCK();
                eval = copyout(&msgtype, user_msgp, sizeof(msgtype));
                SYSV_MSG_SUBSYS_LOCK();
                user_msgp = user_msgp + sizeof(msgtype);        /* ptr math */
        } else {
                msg_type_long = msghdr->msg_type;
                SYSV_MSG_SUBSYS_UNLOCK();
                eval = copyout(&msg_type_long, user_msgp, sizeof(long));
                SYSV_MSG_SUBSYS_LOCK();
                user_msgp = user_msgp + sizeof(long);           /* ptr math */
        }

        if (eval != 0) {
#ifdef MSG_DEBUG_OK
                printf("error (%d) copying out message type\n", eval);
#endif
                msg_freehdr(msghdr);
                wakeup((caddr_t)msqptr);

                goto msgrcvout;
        }


        /*
         * Return the segments to the user
         */

        next = msghdr->msg_spot;
        for (len = 0; len < msgsz; len += msginfo.msgssz) {
                size_t tlen;

                /* compare input (size_t) value against restrict (int) value */
                if (msgsz > (size_t)msginfo.msgssz)
                        tlen = msginfo.msgssz;
                else
                        tlen = msgsz;
                if (next <= -1)
                        panic("next too low #3");
                if (next >= msginfo.msgseg)
                        panic("next out of range #3");
                SYSV_MSG_SUBSYS_UNLOCK();
                eval = copyout(&msgpool[next * msginfo.msgssz],
                    user_msgp, tlen);
                SYSV_MSG_SUBSYS_LOCK();
                if (eval != 0) {
#ifdef MSG_DEBUG_OK
                        printf("error (%d) copying out message segment\n",
                            eval);
#endif
                        msg_freehdr(msghdr);
                        wakeup((caddr_t)msqptr);
                        goto msgrcvout;
                }
                user_msgp = user_msgp + tlen;   /* ptr math */
                next = msgmaps[next].next;
        }

        /*
         * Done, return the actual number of bytes copied out.
         */

        msg_freehdr(msghdr);
        wakeup((caddr_t)msqptr);
        *retval = msgsz;
        eval = 0;
msgrcvout:
        SYSV_MSG_SUBSYS_UNLOCK();
        return(eval);
}

static int
IPCS_msg_sysctl(__unused struct sysctl_oid *oidp, __unused void *arg1,
        __unused int arg2, struct sysctl_req *req)
{
        int error;
        int cursor;
        union {
                struct IPCS_command u32;
                struct user_IPCS_command u64;
        } ipcs;
        struct msqid_ds msqid_ds32;     /* post conversion, 32 bit version */
        void *msqid_dsp;
        size_t ipcs_sz = sizeof(struct user_IPCS_command);
        size_t msqid_ds_sz = sizeof(struct user_msqid_ds);
        struct proc *p = current_proc();

        if (!IS_64BIT_PROCESS(p)) {
                ipcs_sz = sizeof(struct IPCS_command);
                msqid_ds_sz = sizeof(struct msqid_ds);
        }

        /* Copy in the command structure */
        if ((error = SYSCTL_IN(req, &ipcs, ipcs_sz)) != 0) {
                return(error);
        }

        if (!IS_64BIT_PROCESS(p))       /* convert in place */
                ipcs.u64.ipcs_data = CAST_USER_ADDR_T(ipcs.u32.ipcs_data);

        /* Let us version this interface... */
        if (ipcs.u64.ipcs_magic != IPCS_MAGIC) {
                return(EINVAL);
        }

        SYSV_MSG_SUBSYS_LOCK();

        switch(ipcs.u64.ipcs_op) {
        case IPCS_MSG_CONF:     /* Obtain global configuration data */
                if (ipcs.u64.ipcs_datalen != sizeof(struct msginfo)) {
                        error = ERANGE;
                        break;
                }
                if (ipcs.u64.ipcs_cursor != 0) {        /* fwd. compat. */
                        error = EINVAL;
                        break;
                }
                SYSV_MSG_SUBSYS_UNLOCK();
                error = copyout(&msginfo, ipcs.u64.ipcs_data, ipcs.u64.ipcs_datalen);
                SYSV_MSG_SUBSYS_LOCK();
                break;

        case IPCS_MSG_ITER:     /* Iterate over existing segments */
                /* Not done up top so we can set limits via sysctl (later) */
                if (!msginit(0)) {
                        error =  ENOMEM;
                        break;
                }

                cursor = ipcs.u64.ipcs_cursor;
                if (cursor < 0 || cursor >= msginfo.msgmni) {
                        error = ERANGE;
                        break;
                }
                if (ipcs.u64.ipcs_datalen != (int)msqid_ds_sz) {
                        error = EINVAL;
                        break;
                }
                for( ; cursor < msginfo.msgmni; cursor++) {
                        if (msqids[cursor].u.msg_qbytes != 0)   /* allocated */
                                break;
                        continue;
                }
                if (cursor == msginfo.msgmni) {
                        error = ENOENT;
                        break;
                }

                msqid_dsp = &msqids[cursor];    /* default: 64 bit */

                /*
                 * If necessary, convert the 64 bit kernel segment
                 * descriptor to a 32 bit user one.
                 */
                if (!IS_64BIT_PROCESS(p)) {
                        msqid_ds_64to32(msqid_dsp, &msqid_ds32);
                        msqid_dsp = &msqid_ds32;
                }
                SYSV_MSG_SUBSYS_UNLOCK();
                error = copyout(msqid_dsp, ipcs.u64.ipcs_data, ipcs.u64.ipcs_datalen);
                if (!error) {
                        /* update cursor */
                        ipcs.u64.ipcs_cursor = cursor + 1;

                        if (!IS_64BIT_PROCESS(p))       /* convert in place */
                                ipcs.u32.ipcs_data = CAST_DOWN(void *,ipcs.u64.ipcs_data);
                        error = SYSCTL_OUT(req, &ipcs, ipcs_sz);
                }
                SYSV_MSG_SUBSYS_LOCK();
                break;

        default:
                error = EINVAL;
                break;
        }

        SYSV_MSG_SUBSYS_UNLOCK();
        return(error);
}

SYSCTL_DECL(_kern_sysv_ipcs);
SYSCTL_PROC(_kern_sysv_ipcs, OID_AUTO, msg, CTLFLAG_RW|CTLFLAG_ANYBODY,
        0, 0, IPCS_msg_sysctl,
        "S,IPCS_msg_command",
        "ipcs msg command interface");

#endif /* SYSV_MSG */