/*
   * 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
  ",

  				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
  ",
  			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