/*
 * linux/ipc/msg.c
 * Copyright (C) 1992 Krishna Balasubramanian
 *
 * Removed all the remaining kerneld mess
 * Catch the -EFAULT stuff properly
 * Use GFP_KERNEL for messages as in 1.2
 * Fixed up the unchecked user space derefs
 * Copyright (C) 1998 Alan Cox & Andi Kleen
 *
 * /proc/sysvipc/msg support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
 *
 * mostly rewritten, threaded and wake-one semantics added
 * MSGMAX limit removed, sysctl's added
 * (c) 1999 Manfred Spraul <manfred@colorfullife.com>
 *
 * support for audit of ipc object properties and permission changes
 * Dustin Kirkland <dustin.kirkland@us.ibm.com>
 *
 * namespaces support
 * OpenVZ, SWsoft Inc.
 * Pavel Emelianov <xemul@openvz.org>
 */

#include <linux/capability.h>
#include <linux/slab.h>
#include <linux/msg.h>
#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/list.h>
#include <linux/security.h>
#include <linux/sched.h>
#include <linux/syscalls.h>
#include <linux/audit.h>
#include <linux/seq_file.h>
#include <linux/mutex.h>
#include <linux/nsproxy.h>

#include <asm/current.h>
#include <asm/uaccess.h>
#include "util.h"

/*
 * one msg_receiver structure for each sleeping receiver:
 */
struct msg_receiver {
        struct list_head        r_list;
        struct task_struct      *r_tsk;

        int                     r_mode;
        long                    r_msgtype;
        long                    r_maxsize;

        struct msg_msg          *volatile r_msg;
};

/* one msg_sender for each sleeping sender */
struct msg_sender {
        struct list_head        list;
        struct task_struct      *tsk;
};

#define SEARCH_ANY              1
#define SEARCH_EQUAL            2
#define SEARCH_NOTEQUAL         3
#define SEARCH_LESSEQUAL        4

static atomic_t msg_bytes =     ATOMIC_INIT(0);
static atomic_t msg_hdrs =      ATOMIC_INIT(0);

static struct ipc_ids init_msg_ids;

#define msg_ids(ns)     (*((ns)->ids[IPC_MSG_IDS]))

#define msg_lock(ns, id)        ((struct msg_queue*)ipc_lock(&msg_ids(ns), id))
#define msg_unlock(msq)         ipc_unlock(&(msq)->q_perm)
#define msg_rmid(ns, id)        ((struct msg_queue*)ipc_rmid(&msg_ids(ns), id))
#define msg_checkid(ns, msq, msgid)     \
        ipc_checkid(&msg_ids(ns), &msq->q_perm, msgid)
#define msg_buildid(ns, id, seq) \
        ipc_buildid(&msg_ids(ns), id, seq)

static void freeque (struct ipc_namespace *ns, struct msg_queue *msq, int id);
static int newque (struct ipc_namespace *ns, key_t key, int msgflg);
#ifdef CONFIG_PROC_FS
static int sysvipc_msg_proc_show(struct seq_file *s, void *it);
#endif

static void __ipc_init __msg_init_ns(struct ipc_namespace *ns, struct ipc_ids *ids)
{
        ns->ids[IPC_MSG_IDS] = ids;
        ns->msg_ctlmax = MSGMAX;
        ns->msg_ctlmnb = MSGMNB;
        ns->msg_ctlmni = MSGMNI;
        ipc_init_ids(ids, ns->msg_ctlmni);
}

#ifdef CONFIG_IPC_NS
int msg_init_ns(struct ipc_namespace *ns)
{
        struct ipc_ids *ids;

        ids = kmalloc(sizeof(struct ipc_ids), GFP_KERNEL);
        if (ids == NULL)
                return -ENOMEM;

        __msg_init_ns(ns, ids);
        return 0;
}

void msg_exit_ns(struct ipc_namespace *ns)
{
        int i;
        struct msg_queue *msq;

        mutex_lock(&msg_ids(ns).mutex);
        for (i = 0; i <= msg_ids(ns).max_id; i++) {
                msq = msg_lock(ns, i);
                if (msq == NULL)
                        continue;

                freeque(ns, msq, i);
        }
        mutex_unlock(&msg_ids(ns).mutex);

        ipc_fini_ids(ns->ids[IPC_MSG_IDS]);
        kfree(ns->ids[IPC_MSG_IDS]);
        ns->ids[IPC_MSG_IDS] = NULL;
}
#endif

void __init msg_init(void)
{
        __msg_init_ns(&init_ipc_ns, &init_msg_ids);
        ipc_init_proc_interface("sysvipc/msg",
                                "       key      msqid perms      cbytes       qnum lspid lrpid   uid   gid  cuid  cgid      stime      rtime      ctime\n",
                                IPC_MSG_IDS, sysvipc_msg_proc_show);
}

static int newque (struct ipc_namespace *ns, key_t key, int msgflg)
{
        struct msg_queue *msq;
        int id, retval;

        msq = ipc_rcu_alloc(sizeof(*msq));
        if (!msq)
                return -ENOMEM;

        msq->q_perm.mode = msgflg & S_IRWXUGO;
        msq->q_perm.key = key;

        msq->q_perm.security = NULL;
        retval = security_msg_queue_alloc(msq);
        if (retval) {
                ipc_rcu_putref(msq);
                return retval;
        }

        id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni);
        if (id == -1) {
                security_msg_queue_free(msq);
                ipc_rcu_putref(msq);
                return -ENOSPC;
        }

        msq->q_id = msg_buildid(ns, id, msq->q_perm.seq);
        msq->q_stime = msq->q_rtime = 0;
        msq->q_ctime = get_seconds();
        msq->q_cbytes = msq->q_qnum = 0;
        msq->q_qbytes = ns->msg_ctlmnb;
        msq->q_lspid = msq->q_lrpid = 0;
        INIT_LIST_HEAD(&msq->q_messages);
        INIT_LIST_HEAD(&msq->q_receivers);
        INIT_LIST_HEAD(&msq->q_senders);
        msg_unlock(msq);

        return msq->q_id;
}

static inline void ss_add(struct msg_queue *msq, struct msg_sender *mss)
{
        mss->tsk = current;
        current->state = TASK_INTERRUPTIBLE;
        list_add_tail(&mss->list, &msq->q_senders);
}

static inline void ss_del(struct msg_sender *mss)
{
        if (mss->list.next != NULL)
                list_del(&mss->list);
}

static void ss_wakeup(struct list_head *h, int kill)
{
        struct list_head *tmp;

        tmp = h->next;
        while (tmp != h) {
                struct msg_sender *mss;

                mss = list_entry(tmp, struct msg_sender, list);
                tmp = tmp->next;
                if (kill)
                        mss->list.next = NULL;
                wake_up_process(mss->tsk);
        }
}

static void expunge_all(struct msg_queue *msq, int res)
{
        struct list_head *tmp;

        tmp = msq->q_receivers.next;
        while (tmp != &msq->q_receivers) {
                struct msg_receiver *msr;

                msr = list_entry(tmp, struct msg_receiver, r_list);
                tmp = tmp->next;
                msr->r_msg = NULL;
                wake_up_process(msr->r_tsk);
                smp_mb();
                msr->r_msg = ERR_PTR(res);
        }
}

/*
 * freeque() wakes up waiters on the sender and receiver waiting queue,
 * removes the message queue from message queue ID
 * array, and cleans up all the messages associated with this queue.
 *
 * msg_ids.mutex and the spinlock for this message queue is hold
 * before freeque() is called. msg_ids.mutex remains locked on exit.
 */
static void freeque(struct ipc_namespace *ns, struct msg_queue *msq, int id)
{
        struct list_head *tmp;

        expunge_all(msq, -EIDRM);
        ss_wakeup(&msq->q_senders, 1);
        msq = msg_rmid(ns, id);
        msg_unlock(msq);

        tmp = msq->q_messages.next;
        while (tmp != &msq->q_messages) {
                struct msg_msg *msg = list_entry(tmp, struct msg_msg, m_list);

                tmp = tmp->next;
                atomic_dec(&msg_hdrs);
                free_msg(msg);
        }
        atomic_sub(msq->q_cbytes, &msg_bytes);
        security_msg_queue_free(msq);
        ipc_rcu_putref(msq);
}

asmlinkage long sys_msgget(key_t key, int msgflg)
{
        struct msg_queue *msq;
        int id, ret = -EPERM;
        struct ipc_namespace *ns;

        ns = current->nsproxy->ipc_ns;
        
        mutex_lock(&msg_ids(ns).mutex);
        if (key == IPC_PRIVATE) 
                ret = newque(ns, key, msgflg);
        else if ((id = ipc_findkey(&msg_ids(ns), key)) == -1) { /* key not used */
                if (!(msgflg & IPC_CREAT))
                        ret = -ENOENT;
                else
                        ret = newque(ns, key, msgflg);
        } else if (msgflg & IPC_CREAT && msgflg & IPC_EXCL) {
                ret = -EEXIST;
        } else {
                msq = msg_lock(ns, id);
                BUG_ON(msq == NULL);
                if (ipcperms(&msq->q_perm, msgflg))
                        ret = -EACCES;
                else {
                        int qid = msg_buildid(ns, id, msq->q_perm.seq);

                        ret = security_msg_queue_associate(msq, msgflg);
                        if (!ret)
                                ret = qid;
                }
                msg_unlock(msq);
        }
        mutex_unlock(&msg_ids(ns).mutex);

        return ret;
}

static inline unsigned long
copy_msqid_to_user(void __user *buf, struct msqid64_ds *in, int version)
{
        switch(version) {
        case IPC_64:
                return copy_to_user(buf, in, sizeof(*in));
        case IPC_OLD:
        {
                struct msqid_ds out;

                memset(&out, 0, sizeof(out));

                ipc64_perm_to_ipc_perm(&in->msg_perm, &out.msg_perm);

                out.msg_stime           = in->msg_stime;
                out.msg_rtime           = in->msg_rtime;
                out.msg_ctime           = in->msg_ctime;

                if (in->msg_cbytes > USHRT_MAX)
                        out.msg_cbytes  = USHRT_MAX;
                else
                        out.msg_cbytes  = in->msg_cbytes;
                out.msg_lcbytes         = in->msg_cbytes;

                if (in->msg_qnum > USHRT_MAX)
                        out.msg_qnum    = USHRT_MAX;
                else
                        out.msg_qnum    = in->msg_qnum;

                if (in->msg_qbytes > USHRT_MAX)
                        out.msg_qbytes  = USHRT_MAX;
                else
                        out.msg_qbytes  = in->msg_qbytes;
                out.msg_lqbytes         = in->msg_qbytes;

                out.msg_lspid           = in->msg_lspid;
                out.msg_lrpid           = in->msg_lrpid;

                return copy_to_user(buf, &out, sizeof(out));
        }
        default:
                return -EINVAL;
        }
}

struct msq_setbuf {
        unsigned long   qbytes;
        uid_t           uid;
        gid_t           gid;
        mode_t          mode;
};

static inline unsigned long
copy_msqid_from_user(struct msq_setbuf *out, void __user *buf, int version)
{
        switch(version) {
        case IPC_64:
        {
                struct msqid64_ds tbuf;

                if (copy_from_user(&tbuf, buf, sizeof(tbuf)))
                        return -EFAULT;

                out->qbytes             = tbuf.msg_qbytes;
                out->uid                = tbuf.msg_perm.uid;
                out->gid                = tbuf.msg_perm.gid;
                out->mode               = tbuf.msg_perm.mode;

                return 0;
        }
        case IPC_OLD:
        {
                struct msqid_ds tbuf_old;

                if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
                        return -EFAULT;

                out->uid                = tbuf_old.msg_perm.uid;
                out->gid                = tbuf_old.msg_perm.gid;
                out->mode               = tbuf_old.msg_perm.mode;

                if (tbuf_old.msg_qbytes == 0)
                        out->qbytes     = tbuf_old.msg_lqbytes;
                else
                        out->qbytes     = tbuf_old.msg_qbytes;

                return 0;
        }
        default:
                return -EINVAL;
        }
}

asmlinkage long sys_msgctl(int msqid, int cmd, struct msqid_ds __user *buf)
{
        struct kern_ipc_perm *ipcp;
        struct msq_setbuf setbuf;
        struct msg_queue *msq;
        int err, version;
        struct ipc_namespace *ns;

        if (msqid < 0 || cmd < 0)
                return -EINVAL;

        version = ipc_parse_version(&cmd);
        ns = current->nsproxy->ipc_ns;

        switch (cmd) {
        case IPC_INFO:
        case MSG_INFO:
        {
                struct msginfo msginfo;
                int max_id;

                if (!buf)
                        return -EFAULT;
                /*
                 * We must not return kernel stack data.
                 * due to padding, it's not enough
                 * to set all member fields.
                 */
                err = security_msg_queue_msgctl(NULL, cmd);
                if (err)
                        return err;

                memset(&msginfo, 0, sizeof(msginfo));
                msginfo.msgmni = ns->msg_ctlmni;
                msginfo.msgmax = ns->msg_ctlmax;
                msginfo.msgmnb = ns->msg_ctlmnb;
                msginfo.msgssz = MSGSSZ;
                msginfo.msgseg = MSGSEG;
                mutex_lock(&msg_ids(ns).mutex);
                if (cmd == MSG_INFO) {
                        msginfo.msgpool = msg_ids(ns).in_use;
                        msginfo.msgmap = atomic_read(&msg_hdrs);
                        msginfo.msgtql = atomic_read(&msg_bytes);
                } else {
                        msginfo.msgmap = MSGMAP;
                        msginfo.msgpool = MSGPOOL;
                        msginfo.msgtql = MSGTQL;
                }
                max_id = msg_ids(ns).max_id;
                mutex_unlock(&msg_ids(ns).mutex);
                if (copy_to_user(buf, &msginfo, sizeof(struct msginfo)))
                        return -EFAULT;
                return (max_id < 0) ? 0 : max_id;
        }
        case MSG_STAT:
        case IPC_STAT:
        {
                struct msqid64_ds tbuf;
                int success_return;

                if (!buf)
                        return -EFAULT;
                if (cmd == MSG_STAT && msqid >= msg_ids(ns).entries->size)
                        return -EINVAL;

                memset(&tbuf, 0, sizeof(tbuf));

                msq = msg_lock(ns, msqid);
                if (msq == NULL)
                        return -EINVAL;

                if (cmd == MSG_STAT) {
                        success_return = msg_buildid(ns, msqid, msq->q_perm.seq);
                } else {
                        err = -EIDRM;
                        if (msg_checkid(ns, msq, msqid))
                                goto out_unlock;
                        success_return = 0;
                }
                err = -EACCES;
                if (ipcperms(&msq->q_perm, S_IRUGO))
                        goto out_unlock;

                err = security_msg_queue_msgctl(msq, cmd);
                if (err)
                        goto out_unlock;

                kernel_to_ipc64_perm(&msq->q_perm, &tbuf.msg_perm);
                tbuf.msg_stime  = msq->q_stime;
                tbuf.msg_rtime  = msq->q_rtime;
                tbuf.msg_ctime  = msq->q_ctime;
                tbuf.msg_cbytes = msq->q_cbytes;
                tbuf.msg_qnum   = msq->q_qnum;
                tbuf.msg_qbytes = msq->q_qbytes;
                tbuf.msg_lspid  = msq->q_lspid;
                tbuf.msg_lrpid  = msq->q_lrpid;
                msg_unlock(msq);
                if (copy_msqid_to_user(buf, &tbuf, version))
                        return -EFAULT;
                return success_return;
        }
        case IPC_SET:
                if (!buf)
                        return -EFAULT;
                if (copy_msqid_from_user(&setbuf, buf, version))
                        return -EFAULT;
                break;
        case IPC_RMID:
                break;
        default:
                return  -EINVAL;
        }

        mutex_lock(&msg_ids(ns).mutex);
        msq = msg_lock(ns, msqid);
        err = -EINVAL;
        if (msq == NULL)
                goto out_up;

        err = -EIDRM;
        if (msg_checkid(ns, msq, msqid))
                goto out_unlock_up;
        ipcp = &msq->q_perm;

        err = audit_ipc_obj(ipcp);
        if (err)
                goto out_unlock_up;
        if (cmd==IPC_SET) {
                err = audit_ipc_set_perm(setbuf.qbytes, setbuf.uid, setbuf.gid,
                                         setbuf.mode);
                if (err)
                        goto out_unlock_up;
        }

        err = -EPERM;
        if (current->euid != ipcp->cuid &&
            current->euid != ipcp->uid && !capable(CAP_SYS_ADMIN))
                /* We _could_ check for CAP_CHOWN above, but we don't */
                goto out_unlock_up;

        err = security_msg_queue_msgctl(msq, cmd);
        if (err)
                goto out_unlock_up;

        switch (cmd) {
        case IPC_SET:
        {
                err = -EPERM;
                if (setbuf.qbytes > ns->msg_ctlmnb && !capable(CAP_SYS_RESOURCE))
                        goto out_unlock_up;

                msq->q_qbytes = setbuf.qbytes;

                ipcp->uid = setbuf.uid;
                ipcp->gid = setbuf.gid;
                ipcp->mode = (ipcp->mode & ~S_IRWXUGO) |
                             (S_IRWXUGO & setbuf.mode);
                msq->q_ctime = get_seconds();
                /* sleeping receivers might be excluded by
                 * stricter permissions.
                 */
                expunge_all(msq, -EAGAIN);
                /* sleeping senders might be able to send
                 * due to a larger queue size.
                 */
                ss_wakeup(&msq->q_senders, 0);
                msg_unlock(msq);
                break;
        }
        case IPC_RMID:
                freeque(ns, msq, msqid);
                break;
        }
        err = 0;
out_up:
        mutex_unlock(&msg_ids(ns).mutex);
        return err;
out_unlock_up:
        msg_unlock(msq);
        goto out_up;
out_unlock:
        msg_unlock(msq);
        return err;
}

static int testmsg(struct msg_msg *msg, long type, int mode)
{
        switch(mode)
        {
                case SEARCH_ANY:
                        return 1;
                case SEARCH_LESSEQUAL:
                        if (msg->m_type <=type)
                                return 1;
                        break;
                case SEARCH_EQUAL:
                        if (msg->m_type == type)
                                return 1;
                        break;
                case SEARCH_NOTEQUAL:
                        if (msg->m_type != type)
                                return 1;
                        break;
        }
        return 0;
}

static inline int pipelined_send(struct msg_queue *msq, struct msg_msg *msg)
{
        struct list_head *tmp;

        tmp = msq->q_receivers.next;
        while (tmp != &msq->q_receivers) {
                struct msg_receiver *msr;

                msr = list_entry(tmp, struct msg_receiver, r_list);
                tmp = tmp->next;
                if (testmsg(msg, msr->r_msgtype, msr->r_mode) &&
                    !security_msg_queue_msgrcv(msq, msg, msr->r_tsk,
                                               msr->r_msgtype, msr->r_mode)) {

                        list_del(&msr->r_list);
                        if (msr->r_maxsize < msg->m_ts) {
                                msr->r_msg = NULL;
                                wake_up_process(msr->r_tsk);
                                smp_mb();
                                msr->r_msg = ERR_PTR(-E2BIG);
                        } else {
                                msr->r_msg = NULL;
                                msq->q_lrpid = msr->r_tsk->pid;
                                msq->q_rtime = get_seconds();
                                wake_up_process(msr->r_tsk);
                                smp_mb();
                                msr->r_msg = msg;

                                return 1;
                        }
                }
        }
        return 0;
}

long do_msgsnd(int msqid, long mtype, void __user *mtext,
                size_t msgsz, int msgflg)
{
        struct msg_queue *msq;
        struct msg_msg *msg;
        int err;
        struct ipc_namespace *ns;

        ns = current->nsproxy->ipc_ns;

        if (msgsz > ns->msg_ctlmax || (long) msgsz < 0 || msqid < 0)
                return -EINVAL;
        if (mtype < 1)
                return -EINVAL;

        msg = load_msg(mtext, msgsz);
        if (IS_ERR(msg))
                return PTR_ERR(msg);

        msg->m_type = mtype;
        msg->m_ts = msgsz;

        msq = msg_lock(ns, msqid);
        err = -EINVAL;
        if (msq == NULL)
                goto out_free;

        err= -EIDRM;
        if (msg_checkid(ns, msq, msqid))
                goto out_unlock_free;

        for (;;) {
                struct msg_sender s;

                err = -EACCES;
                if (ipcperms(&msq->q_perm, S_IWUGO))
                        goto out_unlock_free;

                err = security_msg_queue_msgsnd(msq, msg, msgflg);
                if (err)
                        goto out_unlock_free;

                if (msgsz + msq->q_cbytes <= msq->q_qbytes &&
                                1 + msq->q_qnum <= msq->q_qbytes) {
                        break;
                }

                /* queue full, wait: */
                if (msgflg & IPC_NOWAIT) {
                        err = -EAGAIN;
                        goto out_unlock_free;
                }
                ss_add(msq, &s);
                ipc_rcu_getref(msq);
                msg_unlock(msq);
                schedule();

                ipc_lock_by_ptr(&msq->q_perm);
                ipc_rcu_putref(msq);
                if (msq->q_perm.deleted) {
                        err = -EIDRM;
                        goto out_unlock_free;
                }
                ss_del(&s);

                if (signal_pending(current)) {
                        err = -ERESTARTNOHAND;
                        goto out_unlock_free;
                }
        }

        msq->q_lspid = current->tgid;
        msq->q_stime = get_seconds();

        if (!pipelined_send(msq, msg)) {
                /* noone is waiting for this message, enqueue it */
                list_add_tail(&msg->m_list, &msq->q_messages);
                msq->q_cbytes += msgsz;
                msq->q_qnum++;
                atomic_add(msgsz, &msg_bytes);
                atomic_inc(&msg_hdrs);
        }

        err = 0;
        msg = NULL;

out_unlock_free:
        msg_unlock(msq);
out_free:
        if (msg != NULL)
                free_msg(msg);
        return err;
}

asmlinkage long
sys_msgsnd(int msqid, struct msgbuf __user *msgp, size_t msgsz, int msgflg)
{
        long mtype;

        if (get_user(mtype, &msgp->mtype))
                return -EFAULT;
        return do_msgsnd(msqid, mtype, msgp->mtext, msgsz, msgflg);
}

static inline int convert_mode(long *msgtyp, int msgflg)
{
        /*
         *  find message of correct type.
         *  msgtyp = 0 => get first.
         *  msgtyp > 0 => get first message of matching type.
         *  msgtyp < 0 => get message with least type must be < abs(msgtype).
         */
        if (*msgtyp == 0)
                return SEARCH_ANY;
        if (*msgtyp < 0) {
                *msgtyp = -*msgtyp;
                return SEARCH_LESSEQUAL;
        }
        if (msgflg & MSG_EXCEPT)
                return SEARCH_NOTEQUAL;
        return SEARCH_EQUAL;
}

long do_msgrcv(int msqid, long *pmtype, void __user *mtext,
                size_t msgsz, long msgtyp, int msgflg)
{
        struct msg_queue *msq;
        struct msg_msg *msg;
        int mode;
        struct ipc_namespace *ns;

        if (msqid < 0 || (long) msgsz < 0)
                return -EINVAL;
        mode = convert_mode(&msgtyp, msgflg);
        ns = current->nsproxy->ipc_ns;

        msq = msg_lock(ns, msqid);
        if (msq == NULL)
                return -EINVAL;

        msg = ERR_PTR(-EIDRM);
        if (msg_checkid(ns, msq, msqid))
                goto out_unlock;

        for (;;) {
                struct msg_receiver msr_d;
                struct list_head *tmp;

                msg = ERR_PTR(-EACCES);
                if (ipcperms(&msq->q_perm, S_IRUGO))
                        goto out_unlock;

                msg = ERR_PTR(-EAGAIN);
                tmp = msq->q_messages.next;
                while (tmp != &msq->q_messages) {
                        struct msg_msg *walk_msg;

                        walk_msg = list_entry(tmp, struct msg_msg, m_list);
                        if (testmsg(walk_msg, msgtyp, mode) &&
                            !security_msg_queue_msgrcv(msq, walk_msg, current,
                                                       msgtyp, mode)) {

                                msg = walk_msg;
                                if (mode == SEARCH_LESSEQUAL &&
                                                walk_msg->m_type != 1) {
                                        msg = walk_msg;
                                        msgtyp = walk_msg->m_type - 1;
                                } else {
                                        msg = walk_msg;
                                        break;
                                }
                        }
                        tmp = tmp->next;
                }
                if (!IS_ERR(msg)) {
                        /*
                         * Found a suitable message.
                         * Unlink it from the queue.
                         */
                        if ((msgsz < msg->m_ts) && !(msgflg & MSG_NOERROR)) {
                                msg = ERR_PTR(-E2BIG);
                                goto out_unlock;
                        }
                        list_del(&msg->m_list);
                        msq->q_qnum--;
                        msq->q_rtime = get_seconds();
                        msq->q_lrpid = current->tgid;
                        msq->q_cbytes -= msg->m_ts;
                        atomic_sub(msg->m_ts, &msg_bytes);
                        atomic_dec(&msg_hdrs);
                        ss_wakeup(&msq->q_senders, 0);
                        msg_unlock(msq);
                        break;
                }
                /* No message waiting. Wait for a message */
                if (msgflg & IPC_NOWAIT) {
                        msg = ERR_PTR(-ENOMSG);
                        goto out_unlock;
                }
                list_add_tail(&msr_d.r_list, &msq->q_receivers);
                msr_d.r_tsk = current;
                msr_d.r_msgtype = msgtyp;
                msr_d.r_mode = mode;
                if (msgflg & MSG_NOERROR)
                        msr_d.r_maxsize = INT_MAX;
                else
                        msr_d.r_maxsize = msgsz;
                msr_d.r_msg = ERR_PTR(-EAGAIN);
                current->state = TASK_INTERRUPTIBLE;
                msg_unlock(msq);

                schedule();

                /* Lockless receive, part 1:
                 * Disable preemption.  We don't hold a reference to the queue
                 * and getting a reference would defeat the idea of a lockless
                 * operation, thus the code relies on rcu to guarantee the
                 * existance of msq:
                 * Prior to destruction, expunge_all(-EIRDM) changes r_msg.
                 * Thus if r_msg is -EAGAIN, then the queue not yet destroyed.
                 * rcu_read_lock() prevents preemption between reading r_msg
                 * and the spin_lock() inside ipc_lock_by_ptr().
                 */
                rcu_read_lock();

                /* Lockless receive, part 2:
                 * Wait until pipelined_send or expunge_all are outside of
                 * wake_up_process(). There is a race with exit(), see
                 * ipc/mqueue.c for the details.
                 */
                msg = (struct msg_msg*)msr_d.r_msg;
                while (msg == NULL) {
                        cpu_relax();
                        msg = (struct msg_msg *)msr_d.r_msg;
                }

                /* Lockless receive, part 3:
                 * If there is a message or an error then accept it without
                 * locking.
                 */
                if (msg != ERR_PTR(-EAGAIN)) {
                        rcu_read_unlock();
                        break;
                }

                /* Lockless receive, part 3:
                 * Acquire the queue spinlock.
                 */
                ipc_lock_by_ptr(&msq->q_perm);
                rcu_read_unlock();

                /* Lockless receive, part 4:
                 * Repeat test after acquiring the spinlock.
                 */
                msg = (struct msg_msg*)msr_d.r_msg;
                if (msg != ERR_PTR(-EAGAIN))
                        goto out_unlock;

                list_del(&msr_d.r_list);
                if (signal_pending(current)) {
                        msg = ERR_PTR(-ERESTARTNOHAND);
out_unlock:
                        msg_unlock(msq);
                        break;
                }
        }
        if (IS_ERR(msg))
                return PTR_ERR(msg);

        msgsz = (msgsz > msg->m_ts) ? msg->m_ts : msgsz;
        *pmtype = msg->m_type;
        if (store_msg(mtext, msg, msgsz))
                msgsz = -EFAULT;

        free_msg(msg);

        return msgsz;
}

asmlinkage long sys_msgrcv(int msqid, struct msgbuf __user *msgp, size_t msgsz,
                           long msgtyp, int msgflg)
{
        long err, mtype;

        err =  do_msgrcv(msqid, &mtype, msgp->mtext, msgsz, msgtyp, msgflg);
        if (err < 0)
                goto out;

        if (put_user(mtype, &msgp->mtype))
                err = -EFAULT;
out:
        return err;
}

#ifdef CONFIG_PROC_FS
static int sysvipc_msg_proc_show(struct seq_file *s, void *it)
{
        struct msg_queue *msq = it;

        return seq_printf(s,
                        "%10d %10d  %4o  %10lu %10lu %5u %5u %5u %5u %5u %5u %10lu %10lu %10lu\n",
                        msq->q_perm.key,
                        msq->q_id,
                        msq->q_perm.mode,
                        msq->q_cbytes,
                        msq->q_qnum,
                        msq->q_lspid,
                        msq->q_lrpid,
                        msq->q_perm.uid,
                        msq->q_perm.gid,
                        msq->q_perm.cuid,
                        msq->q_perm.cgid,
                        msq->q_stime,
                        msq->q_rtime,
                        msq->q_ctime);
}
#endif