Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 862 insertions, 0 deletions

diff --git a/ipc/msg.c b/ipc/msg.c
new file mode 100644
index 000000000000..27e516f96cdc
--- /dev/null
+++ b/ipc/msg.c
@@ -0,0 +1,862 @@
+/*
+ * 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 <manfreds@colorfullife.com>
+ */
+
+#include <linux/config.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 <asm/current.h>
+#include <asm/uaccess.h>
+#include "util.h"
+
+/* sysctl: */
+int msg_ctlmax = MSGMAX;
+int msg_ctlmnb = MSGMNB;
+int msg_ctlmni = MSGMNI;
+
+/* 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 msg_ids;
+
+#define msg_lock(id)	((struct msg_queue*)ipc_lock(&msg_ids,id))
+#define msg_unlock(msq)	ipc_unlock(&(msq)->q_perm)
+#define msg_rmid(id)	((struct msg_queue*)ipc_rmid(&msg_ids,id))
+#define msg_checkid(msq, msgid)	\
+	ipc_checkid(&msg_ids,&msq->q_perm,msgid)
+#define msg_buildid(id, seq) \
+	ipc_buildid(&msg_ids, id, seq)
+
+static void freeque (struct msg_queue *msq, int id);
+static int newque (key_t key, int msgflg);
+#ifdef CONFIG_PROC_FS
+static int sysvipc_msg_read_proc(char *buffer, char **start, off_t offset, int length, int *eof, void *data);
+#endif
+
+void __init msg_init (void)
+{
+	ipc_init_ids(&msg_ids,msg_ctlmni);
+
+#ifdef CONFIG_PROC_FS
+	create_proc_read_entry("sysvipc/msg", 0, NULL, sysvipc_msg_read_proc, NULL);
+#endif
+}
+
+static int newque (key_t key, int msgflg)
+{
+	int id;
+	int retval;
+	struct msg_queue *msq;
+
+	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, &msq->q_perm, msg_ctlmni);
+	if(id == -1) {
+		security_msg_queue_free(msq);
+		ipc_rcu_putref(msq);
+		return -ENOSPC;
+	}
+
+	msq->q_stime = msq->q_rtime = 0;
+	msq->q_ctime = get_seconds();
+	msq->q_cbytes = msq->q_qnum = 0;
+	msq->q_qbytes = 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 msg_buildid(id,msq->q_perm.seq);
+}
+
+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.sem and the spinlock for this message queue is hold
+ * before freeque() is called. msg_ids.sem remains locked on exit.
+ */
+static void freeque (struct msg_queue *msq, int id)
+{
+	struct list_head *tmp;
+
+	expunge_all(msq,-EIDRM);
+	ss_wakeup(&msq->q_senders,1);
+	msq = msg_rmid(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)
+{
+	int id, ret = -EPERM;
+	struct msg_queue *msq;
+	
+	down(&msg_ids.sem);
+	if (key == IPC_PRIVATE) 
+		ret = newque(key, msgflg);
+	else if ((id = ipc_findkey(&msg_ids, key)) == -1) { /* key not used */
+		if (!(msgflg & IPC_CREAT))
+			ret = -ENOENT;
+		else
+			ret = newque(key, msgflg);
+	} else if (msgflg & IPC_CREAT && msgflg & IPC_EXCL) {
+		ret = -EEXIST;
+	} else {
+		msq = msg_lock(id);
+		if(msq==NULL)
+			BUG();
+		if (ipcperms(&msq->q_perm, msgflg))
+			ret = -EACCES;
+		else {
+			int qid = msg_buildid(id, msq->q_perm.seq);
+		    	ret = security_msg_queue_associate(msq, msgflg);
+			if (!ret)
+				ret = qid;
+		}
+		msg_unlock(msq);
+	}
+	up(&msg_ids.sem);
+	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)
+{
+	int err, version;
+	struct msg_queue *msq;
+	struct msq_setbuf setbuf;
+	struct kern_ipc_perm *ipcp;
+	
+	if (msqid < 0 || cmd < 0)
+		return -EINVAL;
+
+	version = ipc_parse_version(&cmd);
+
+	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 = msg_ctlmni;
+		msginfo.msgmax = msg_ctlmax;
+		msginfo.msgmnb = msg_ctlmnb;
+		msginfo.msgssz = MSGSSZ;
+		msginfo.msgseg = MSGSEG;
+		down(&msg_ids.sem);
+		if (cmd == MSG_INFO) {
+			msginfo.msgpool = msg_ids.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.max_id;
+		up(&msg_ids.sem);
+		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.entries->size)
+			return -EINVAL;
+
+		memset(&tbuf,0,sizeof(tbuf));
+
+		msq = msg_lock(msqid);
+		if (msq == NULL)
+			return -EINVAL;
+
+		if(cmd == MSG_STAT) {
+			success_return = msg_buildid(msqid, msq->q_perm.seq);
+		} else {
+			err = -EIDRM;
+			if (msg_checkid(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;
+		if ((err = audit_ipc_perms(setbuf.qbytes, setbuf.uid, setbuf.gid, setbuf.mode)))
+			return err;
+		break;
+	case IPC_RMID:
+		break;
+	default:
+		return  -EINVAL;
+	}
+
+	down(&msg_ids.sem);
+	msq = msg_lock(msqid);
+	err=-EINVAL;
+	if (msq == NULL)
+		goto out_up;
+
+	err = -EIDRM;
+	if (msg_checkid(msq,msqid))
+		goto out_unlock_up;
+	ipcp = &msq->q_perm;
+	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 > 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 (msq, msqid); 
+		break;
+	}
+	err = 0;
+out_up:
+	up(&msg_ids.sem);
+	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;
+}
+
+asmlinkage long sys_msgsnd (int msqid, struct msgbuf __user *msgp, size_t msgsz, int msgflg)
+{
+	struct msg_queue *msq;
+	struct msg_msg *msg;
+	long mtype;
+	int err;
+	
+	if (msgsz > msg_ctlmax || (long) msgsz < 0 || msqid < 0)
+		return -EINVAL;
+	if (get_user(mtype, &msgp->mtype))
+		return -EFAULT; 
+	if (mtype < 1)
+		return -EINVAL;
+
+	msg = load_msg(msgp->mtext, msgsz);
+	if(IS_ERR(msg))
+		return PTR_ERR(msg);
+
+	msg->m_type = mtype;
+	msg->m_ts = msgsz;
+
+	msq = msg_lock(msqid);
+	err=-EINVAL;
+	if(msq==NULL)
+		goto out_free;
+
+	err= -EIDRM;
+	if (msg_checkid(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;
+}
+
+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;
+}
+
+asmlinkage long sys_msgrcv (int msqid, struct msgbuf __user *msgp, size_t msgsz,
+			    long msgtyp, int msgflg)
+{
+	struct msg_queue *msq;
+	struct msg_msg *msg;
+	int mode;
+
+	if (msqid < 0 || (long) msgsz < 0)
+		return -EINVAL;
+	mode = convert_mode(&msgtyp,msgflg);
+
+	msq = msg_lock(msqid);
+	if(msq==NULL)
+		return -EINVAL;
+
+	msg = ERR_PTR(-EIDRM);
+	if (msg_checkid(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;
+	if (put_user (msg->m_type, &msgp->mtype) ||
+	    store_msg(msgp->mtext, msg, msgsz)) {
+		    msgsz = -EFAULT;
+	}
+	free_msg(msg);
+	return msgsz;
+}
+
+#ifdef CONFIG_PROC_FS
+static int sysvipc_msg_read_proc(char *buffer, char **start, off_t offset, int length, int *eof, void *data)
+{
+	off_t pos = 0;
+	off_t begin = 0;
+	int i, len = 0;
+
+	down(&msg_ids.sem);
+	len += sprintf(buffer, "       key      msqid perms      cbytes       qnum lspid lrpid   uid   gid  cuid  cgid      stime      rtime      ctime\n");
+
+	for(i = 0; i <= msg_ids.max_id; i++) {
+		struct msg_queue * msq;
+		msq = msg_lock(i);
+		if(msq != NULL) {
+			len += sprintf(buffer + len, "%10d %10d  %4o  %10lu %10lu %5u %5u %5u %5u %5u %5u %10lu %10lu %10lu\n",
+				msq->q_perm.key,
+				msg_buildid(i,msq->q_perm.seq),
+				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);
+			msg_unlock(msq);
+
+			pos += len;
+			if(pos < offset) {
+				len = 0;
+				begin = pos;
+			}
+			if(pos > offset + length)
+				goto done;
+		}
+
+	}
+	*eof = 1;
+done:
+	up(&msg_ids.sem);
+	*start = buffer + (offset - begin);
+	len -= (offset - begin);
+	if(len > length)
+		len = length;
+	if(len < 0)
+		len = 0;
+	return len;
+}
+#endif