xref: /src/sys/kern/sys_mqueue.c

/*	$NetBSD: sys_mqueue.c,v 1.7 2008/03/21 21:55:00 ad Exp $	*/

/*
 * Copyright (c) 2007, Mindaugas Rasiukevicius <rmind at NetBSD org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * Implementation of POSIX message queues.
 * Defined in the Base Definitions volume of IEEE Std 1003.1-2001.
 *
 * Locking
 *  Global list of message queues and proc::p_mqueue_cnt counter are protected
 *  by mqlist_mtx lock.  Concrete message queue and its members are protected
 *  by mqueue::mq_mtx.
 *
 * Lock order:
 * 	mqlist_mtx
 * 	  -> mqueue::mq_mtx
 *
 * TODO:
 *  - Hashing or RB-tree for the global list.
 *  - Support for select(), poll() and perhaps kqueue().
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: sys_mqueue.c,v 1.7 2008/03/21 21:55:00 ad Exp $");

#include <sys/param.h>
#include <sys/types.h>
#include <sys/condvar.h>
#include <sys/errno.h>
#include <sys/fcntl.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/kauth.h>
#include <sys/kernel.h>
#include <sys/kmem.h>
#include <sys/lwp.h>
#include <sys/mqueue.h>
#include <sys/mutex.h>
#include <sys/pool.h>
#include <sys/proc.h>
#include <sys/queue.h>
#include <sys/signal.h>
#include <sys/signalvar.h>
#include <sys/sysctl.h>
#include <sys/syscallargs.h>
#include <sys/systm.h>
#include <sys/unistd.h>
#include <sys/vnode.h>

/* System-wide limits. */
static u_int			mq_open_max = MQ_OPEN_MAX;
static u_int			mq_prio_max = MQ_PRIO_MAX;

static u_int			mq_max_msgsize = 16 * MQ_DEF_MSGSIZE;
static u_int			mq_def_maxmsg = 32;

static kmutex_t			mqlist_mtx;
static struct pool		mqmsg_poll;
static LIST_HEAD(, mqueue)	mqueue_head =
	LIST_HEAD_INITIALIZER(mqueue_head);

static int	mq_close_fop(file_t *);

static const struct fileops mqops = {
	fbadop_read, fbadop_write, fbadop_ioctl, fnullop_fcntl, fnullop_poll,
	fbadop_stat, mq_close_fop, fnullop_kqfilter
};

/*
 * Initialize POSIX message queue subsystem.
 */
void
mqueue_sysinit(void)
{

	pool_init(&mqmsg_poll, MQ_DEF_MSGSIZE, 0, 0, 0,
	    "mqmsg_poll", &pool_allocator_nointr, IPL_NONE);
	mutex_init(&mqlist_mtx, MUTEX_DEFAULT, IPL_NONE);
}

/*
 * Free the message.
 */
static void
mqueue_freemsg(struct mq_msg *msg, const size_t size)
{

	if (size > MQ_DEF_MSGSIZE)
		kmem_free(msg, size);
	else
		pool_put(&mqmsg_poll, msg);
}

/*
 * Destroy the message queue.
 */
static void
mqueue_destroy(struct mqueue *mq)
{
	struct mq_msg *msg;

	while ((msg = TAILQ_FIRST(&mq->mq_head)) != NULL) {
		TAILQ_REMOVE(&mq->mq_head, msg, msg_queue);
		mqueue_freemsg(msg, sizeof(struct mq_msg) + msg->msg_len);
	}
	cv_destroy(&mq->mq_send_cv);
	cv_destroy(&mq->mq_recv_cv);
	mutex_destroy(&mq->mq_mtx);
	kmem_free(mq, sizeof(struct mqueue));
}

/*
 * Lookup for file name in general list of message queues.
 *  => locks the message queue
 */
static void *
mqueue_lookup(char *name)
{
	struct mqueue *mq;
	KASSERT(mutex_owned(&mqlist_mtx));

	LIST_FOREACH(mq, &mqueue_head, mq_list) {
		if (strncmp(mq->mq_name, name, MQ_NAMELEN) == 0) {
			mutex_enter(&mq->mq_mtx);
			return mq;
		}
	}

	return NULL;
}

/*
 * Check access against message queue.
 */
static inline int
mqueue_access(struct lwp *l, struct mqueue *mq, mode_t acc_mode)
{

	KASSERT(mutex_owned(&mq->mq_mtx));
	return vaccess(VNON, mq->mq_mode, mq->mq_euid, mq->mq_egid,
	    acc_mode, l->l_cred);
}

/*
 * Get the mqueue from the descriptor.
 *  => locks the message queue
 *  => increments the reference on file entry
 */
static int
mqueue_get(struct lwp *l, mqd_t mqd, mode_t acc_mode, file_t **fpr)
{
	file_t *fp;
	struct mqueue *mq;

	/* Get the file and descriptor */
	fp = fd_getfile((int)mqd);
	if (fp == NULL)
		return EBADF;

	/* Increment the reference of file entry, and lock the mqueue */
	mq = fp->f_data;
	*fpr = fp;
	mutex_enter(&mq->mq_mtx);

	/* Check the access mode and permission if needed */
	if (acc_mode == VNOVAL)
		return 0;
	if ((acc_mode & fp->f_flag) == 0 || mqueue_access(l, mq, acc_mode)) {
		mutex_exit(&mq->mq_mtx);
		fd_putfile((int)mqd);
		return EPERM;
	}

	return 0;
}

/*
 * Converter from struct timespec to the ticks.
 * Used by mq_timedreceive(), mq_timedsend().
 */
static int
abstimeout2timo(const void *uaddr, int *timo)
{
	struct timespec ts;
	int error;

	error = copyin(uaddr, &ts, sizeof(struct timespec));
	if (error)
		return error;

	/*
	 * According to POSIX, validation check is needed only in case of
	 * blocking.  Thus, set the invalid value right now, and fail latter.
	 */
	error = itimespecfix(&ts);
	*timo = (error == 0) ? tstohz(&ts) : -1;

	return 0;
}

static int
mq_close_fop(file_t *fp)
{
	struct proc *p = curproc;
	struct mqueue *mq = fp->f_data;
	bool destroy;

	mutex_enter(&mqlist_mtx);
	mutex_enter(&mq->mq_mtx);

	/* Decrease the counters */
	p->p_mqueue_cnt--;
	mq->mq_refcnt--;

	/* Remove notification if registered for this process */
	if (mq->mq_notify_proc == p)
		mq->mq_notify_proc = NULL;

	/*
	 * If this is the last reference and mqueue is marked for unlink,
	 * remove and later destroy the message queue.
	 */
	if (mq->mq_refcnt == 0 && (mq->mq_attrib.mq_flags & MQ_UNLINK)) {
		LIST_REMOVE(mq, mq_list);
		destroy = true;
	} else
		destroy = false;

	mutex_exit(&mq->mq_mtx);
	mutex_exit(&mqlist_mtx);

	if (destroy)
		mqueue_destroy(mq);

	return 0;
}

/*
 * General mqueue system calls.
 */

int
sys_mq_open(struct lwp *l, const struct sys_mq_open_args *uap, register_t *retval)
{
	/* {
		syscallarg(const char *) name;
		syscallarg(int) oflag;
		syscallarg(mode_t) mode;
		syscallarg(struct mq_attr) attr;
	} */
	struct proc *p = l->l_proc;
	struct mqueue *mq, *mq_new = NULL;
	file_t *fp;
	char *name;
	int mqd, error, oflag;

	/* Check access mode flags */
	oflag = SCARG(uap, oflag);
	if ((oflag & (O_RDWR | O_RDONLY | O_WRONLY)) == 0)
		return EINVAL;

	/* Get the name from the user-space */
	name = kmem_zalloc(MQ_NAMELEN, KM_SLEEP);
	error = copyinstr(SCARG(uap, name), name, MQ_NAMELEN - 1, NULL);
	if (error) {
		kmem_free(name, MQ_NAMELEN);
		return error;
	}

	if (oflag & O_CREAT) {
		struct mq_attr attr;

		/* Check the limit */
		if (p->p_mqueue_cnt == mq_open_max) {
			kmem_free(name, MQ_NAMELEN);
			return EMFILE;
		}

		/* Check for mqueue attributes */
		if (SCARG(uap, attr)) {
			error = copyin(SCARG(uap, attr), &attr,
				sizeof(struct mq_attr));
			if (error) {
				kmem_free(name, MQ_NAMELEN);
				return error;
			}
			if (attr.mq_maxmsg <= 0 || attr.mq_msgsize <= 0 ||
			    attr.mq_msgsize > mq_max_msgsize) {
				kmem_free(name, MQ_NAMELEN);
				return EINVAL;
			}
			attr.mq_curmsgs = 0;
		} else {
			memset(&attr, 0, sizeof(struct mq_attr));
			attr.mq_maxmsg = mq_def_maxmsg;
			attr.mq_msgsize =
			    MQ_DEF_MSGSIZE - sizeof(struct mq_msg);
		}

		/*
		 * Allocate new mqueue, initialize data structures,
		 * copy the name, attributes and set the flag.
		 */
		mq_new = kmem_zalloc(sizeof(struct mqueue), KM_SLEEP);

		mutex_init(&mq_new->mq_mtx, MUTEX_DEFAULT, IPL_NONE);
		cv_init(&mq_new->mq_send_cv, "mqsendcv");
		cv_init(&mq_new->mq_recv_cv, "mqrecvcv");
		TAILQ_INIT(&mq_new->mq_head);

		strlcpy(mq_new->mq_name, name, MQ_NAMELEN);
		memcpy(&mq_new->mq_attrib, &attr, sizeof(struct mq_attr));
		mq_new->mq_attrib.mq_flags = oflag;

		/* Store mode and effective UID with GID */
		mq_new->mq_mode = SCARG(uap, mode);
		mq_new->mq_euid = kauth_cred_geteuid(l->l_cred);
		mq_new->mq_egid = kauth_cred_getegid(l->l_cred);
	}

	/* Allocate file structure and descriptor */
	error = fd_allocfile(&fp, &mqd);
	if (error) {
		if (mq_new)
			mqueue_destroy(mq_new);
		kmem_free(name, MQ_NAMELEN);
		return error;
	}
	fp->f_type = DTYPE_MQUEUE;
	fp->f_flag = (oflag & O_RDWR) ? (VREAD | VWRITE) :
	    ((oflag & O_RDONLY) ? VREAD : VWRITE);
	fp->f_ops = &mqops;

	/* Look up for mqueue with such name */
	mutex_enter(&mqlist_mtx);
	mq = mqueue_lookup(name);
	if (mq) {
		KASSERT(mutex_owned(&mq->mq_mtx));
		/* Check if mqueue is not marked as unlinking */
		if (mq->mq_attrib.mq_flags & MQ_UNLINK) {
			error = EACCES;
			goto exit;
		}
		/* Fail if O_EXCL is set, and mqueue already exists */
		if ((oflag & O_CREAT) && (oflag & O_EXCL)) {
			error = EEXIST;
			goto exit;
		}
		/* Check the permission */
		if (mqueue_access(l, mq, fp->f_flag)) {
			error = EACCES;
			goto exit;
		}
	} else {
		/* Fail if mqueue neither exists, nor we create it */
		if ((oflag & O_CREAT) == 0) {
			mutex_exit(&mqlist_mtx);
			KASSERT(mq_new == NULL);
			fd_abort(p, fp, mqd);
			kmem_free(name, MQ_NAMELEN);
			return ENOENT;
		}

		/* Check the limit */
		if (p->p_mqueue_cnt == mq_open_max) {
			error = EMFILE;
			goto exit;
		}

		/* Insert the queue to the list */
		mq = mq_new;
		mutex_enter(&mq->mq_mtx);
		LIST_INSERT_HEAD(&mqueue_head, mq, mq_list);
		mq_new = NULL;
	}

	/* Increase the counters, and make descriptor ready */
	p->p_mqueue_cnt++;
	mq->mq_refcnt++;
	fp->f_data = mq;
exit:
	mutex_exit(&mq->mq_mtx);
	mutex_exit(&mqlist_mtx);

	if (mq_new)
		mqueue_destroy(mq_new);
	if (error) {
		fd_abort(p, fp, mqd);
	} else {
		fd_affix(p, fp, mqd);
		*retval = mqd;
	}
	kmem_free(name, MQ_NAMELEN);

	return error;
}

int
sys_mq_close(struct lwp *l, const struct sys_mq_close_args *uap, register_t *retval)
{

	return sys_close(l, (const void *)uap, retval);
}

/*
 * Primary mq_receive1() function.
 */
static int
mq_receive1(struct lwp *l, mqd_t mqdes, void *msg_ptr, size_t msg_len,
    unsigned *msg_prio, int t, ssize_t *mlen)
{
	file_t *fp = NULL;
	struct mqueue *mq;
	struct mq_msg *msg = NULL;
	int error;

	/* Get the message queue */
	error = mqueue_get(l, mqdes, VREAD, &fp);
	if (error)
		return error;
	mq = fp->f_data;

	/* Check the message size limits */
	if (msg_len < mq->mq_attrib.mq_msgsize) {
		error = EMSGSIZE;
		goto error;
	}

	/* Check if queue is empty */
	while (TAILQ_EMPTY(&mq->mq_head)) {
		if (mq->mq_attrib.mq_flags & O_NONBLOCK) {
			error = EAGAIN;
			goto error;
		}
		if (t < 0) {
			error = EINVAL;
			goto error;
		}
		/*
		 * Block until someone sends the message.
		 * While doing this, notification should not be sent.
		 */
		mq->mq_attrib.mq_flags |= MQ_RECEIVE;
		error = cv_timedwait_sig(&mq->mq_send_cv, &mq->mq_mtx, t);
		mq->mq_attrib.mq_flags &= ~MQ_RECEIVE;
		if (error || (mq->mq_attrib.mq_flags & MQ_UNLINK)) {
			error = (error == EWOULDBLOCK) ? ETIMEDOUT : EINTR;
			goto error;
		}
	}

	/* Remove the message from the queue */
	msg = TAILQ_FIRST(&mq->mq_head);
	KASSERT(msg != NULL);
	TAILQ_REMOVE(&mq->mq_head, msg, msg_queue);

	/* Decrement the counter and signal waiter, if any */
	mq->mq_attrib.mq_curmsgs--;
	cv_signal(&mq->mq_recv_cv);
error:
	mutex_exit(&mq->mq_mtx);
	fd_putfile((int)mqdes);
	if (error)
		return error;

	/*
	 * Copy the data to the user-space.
	 * Note: According to POSIX, no message should be removed from the
	 * queue in case of fail - this would be violated.
	 */
	*mlen = msg->msg_len;
	error = copyout(msg->msg_ptr, msg_ptr, msg->msg_len);
	if (error == 0 && msg_prio)
		error = copyout(&msg->msg_prio, msg_prio, sizeof(unsigned));
	mqueue_freemsg(msg, sizeof(struct mq_msg) + msg->msg_len);

	return error;
}

int
sys_mq_receive(struct lwp *l, const struct sys_mq_receive_args *uap, register_t *retval)
{
	/* {
		syscallarg(mqd_t) mqdes;
		syscallarg(char *) msg_ptr;
		syscallarg(size_t) msg_len;
		syscallarg(unsigned *) msg_prio;
	} */
	int error;
	ssize_t mlen;

	error = mq_receive1(l, SCARG(uap, mqdes), SCARG(uap, msg_ptr),
	    SCARG(uap, msg_len), SCARG(uap, msg_prio), 0, &mlen);
	if (error == 0)
		*retval = mlen;

	return error;
}

int
sys_mq_timedreceive(struct lwp *l, const struct sys_mq_timedreceive_args *uap, register_t *retval)
{
	/* {
		syscallarg(mqd_t) mqdes;
		syscallarg(char *) msg_ptr;
		syscallarg(size_t) msg_len;
		syscallarg(unsigned *) msg_prio;
		syscallarg(const struct timespec *) abs_timeout;
	} */
	int error, t;
	ssize_t mlen;

	/* Get and convert time value */
	if (SCARG(uap, abs_timeout)) {
		error = abstimeout2timo(SCARG(uap, abs_timeout), &t);
		if (error)
			return error;
	} else
		t = 0;

	error = mq_receive1(l, SCARG(uap, mqdes), SCARG(uap, msg_ptr),
	    SCARG(uap, msg_len), SCARG(uap, msg_prio), t, &mlen);
	if (error == 0)
		*retval = mlen;

	return error;
}

/*
 * Primary mq_send1() function.
 */
static int
mq_send1(struct lwp *l, mqd_t mqdes, const char *msg_ptr, size_t msg_len,
    unsigned msg_prio, int t)
{
	file_t *fp = NULL;
	struct mqueue *mq;
	struct mq_msg *msg, *pos_msg;
	struct proc *notify = NULL;
	ksiginfo_t ksi;
	size_t size;
	int error;

	/* Check the priority range */
	if (msg_prio >= mq_prio_max)
		return EINVAL;

	/* Allocate a new message */
	size = sizeof(struct mq_msg) + msg_len;
	if (size > mq_max_msgsize)
		return EMSGSIZE;

	if (size > MQ_DEF_MSGSIZE)
		msg = kmem_alloc(size, KM_SLEEP);
	else
		msg = pool_get(&mqmsg_poll, PR_WAITOK);

	/* Get the data from user-space */
	error = copyin(msg_ptr, msg->msg_ptr, msg_len);
	if (error) {
		mqueue_freemsg(msg, size);
		return error;
	}
	msg->msg_len = msg_len;
	msg->msg_prio = msg_prio;

	/* Get the mqueue */
	error = mqueue_get(l, mqdes, VWRITE, &fp);
	if (error) {
		mqueue_freemsg(msg, size);
		return error;
	}
	mq = fp->f_data;

	/* Check the message size limit */
	if (msg_len <= 0 || msg_len > mq->mq_attrib.mq_msgsize) {
		error = EMSGSIZE;
		goto error;
	}

	/* Check if queue is full */
	while (mq->mq_attrib.mq_curmsgs >= mq->mq_attrib.mq_maxmsg) {
		if (mq->mq_attrib.mq_flags & O_NONBLOCK) {
			error = EAGAIN;
			goto error;
		}
		if (t < 0) {
			error = EINVAL;
			goto error;
		}
		/* Block until queue becomes available */
		error = cv_timedwait_sig(&mq->mq_recv_cv, &mq->mq_mtx, t);
		if (error || (mq->mq_attrib.mq_flags & MQ_UNLINK)) {
			error = (error == EWOULDBLOCK) ? ETIMEDOUT : error;
			goto error;
		}
	}
	KASSERT(mq->mq_attrib.mq_curmsgs < mq->mq_attrib.mq_maxmsg);

	/* Insert message into the queue, according to the priority */
	TAILQ_FOREACH(pos_msg, &mq->mq_head, msg_queue)
		if (msg->msg_prio > pos_msg->msg_prio)
			break;
	if (pos_msg == NULL)
		TAILQ_INSERT_TAIL(&mq->mq_head, msg, msg_queue);
	else
		TAILQ_INSERT_BEFORE(pos_msg, msg, msg_queue);

	/* Check for the notify */
	if (mq->mq_attrib.mq_curmsgs == 0 && mq->mq_notify_proc &&
	    (mq->mq_attrib.mq_flags & MQ_RECEIVE) == 0) {
		/* Initialize the signal */
		KSI_INIT(&ksi);
		ksi.ksi_signo = mq->mq_sig_notify.sigev_signo;
		ksi.ksi_code = SI_MESGQ;
		ksi.ksi_value = mq->mq_sig_notify.sigev_value;
		/* Unregister the process */
		notify = mq->mq_notify_proc;
		mq->mq_notify_proc = NULL;
	}

	/* Increment the counter and signal waiter, if any */
	mq->mq_attrib.mq_curmsgs++;
	cv_signal(&mq->mq_send_cv);
error:
	mutex_exit(&mq->mq_mtx);
	fd_putfile((int)mqdes);

	if (error) {
		mqueue_freemsg(msg, size);
	} else if (notify) {
		/* Send the notify, if needed */
		mutex_enter(&proclist_mutex);
		kpsignal(notify, &ksi, NULL);
		mutex_exit(&proclist_mutex);
	}

	return error;
}

int
sys_mq_send(struct lwp *l, const struct sys_mq_send_args *uap, register_t *retval)
{
	/* {
		syscallarg(mqd_t) mqdes;
		syscallarg(const char *) msg_ptr;
		syscallarg(size_t) msg_len;
		syscallarg(unsigned) msg_prio;
	} */

	return mq_send1(l, SCARG(uap, mqdes), SCARG(uap, msg_ptr),
	    SCARG(uap, msg_len), SCARG(uap, msg_prio), 0);
}

int
sys_mq_timedsend(struct lwp *l, const struct sys_mq_timedsend_args *uap, register_t *retval)
{
	/* {
		syscallarg(mqd_t) mqdes;
		syscallarg(const char *) msg_ptr;
		syscallarg(size_t) msg_len;
		syscallarg(unsigned) msg_prio;
		syscallarg(const struct timespec *) abs_timeout;
	} */
	int t;

	/* Get and convert time value */
	if (SCARG(uap, abs_timeout)) {
		int error = abstimeout2timo(SCARG(uap, abs_timeout), &t);
		if (error)
			return error;
	} else
		t = 0;

	return mq_send1(l, SCARG(uap, mqdes), SCARG(uap, msg_ptr),
	    SCARG(uap, msg_len), SCARG(uap, msg_prio), t);
}

int
sys_mq_notify(struct lwp *l, const struct sys_mq_notify_args *uap, register_t *retval)
{
	/* {
		syscallarg(mqd_t) mqdes;
		syscallarg(const struct sigevent *) notification;
	} */
	file_t *fp = NULL;
	struct mqueue *mq;
	struct sigevent sig;
	int error;

	if (SCARG(uap, notification)) {
		/* Get the signal from user-space */
		error = copyin(SCARG(uap, notification), &sig,
		    sizeof(struct sigevent));
		if (error)
			return error;
	}

	error = mqueue_get(l, SCARG(uap, mqdes), VNOVAL, &fp);
	if (error)
		return error;
	mq = fp->f_data;

	if (SCARG(uap, notification)) {
		/* Register notification: set the signal and target process */
		if (mq->mq_notify_proc == NULL) {
			memcpy(&mq->mq_sig_notify, &sig,
			    sizeof(struct sigevent));
			mq->mq_notify_proc = l->l_proc;
		} else {
			/* Fail if someone else already registered */
			error = EBUSY;
		}
	} else {
		/* Unregister the notification */
		mq->mq_notify_proc = NULL;
	}
	mutex_exit(&mq->mq_mtx);
	fd_putfile((int)SCARG(uap, mqdes));

	return error;
}

int
sys_mq_getattr(struct lwp *l, const struct sys_mq_getattr_args *uap, register_t *retval)
{
	/* {
		syscallarg(mqd_t) mqdes;
		syscallarg(struct mq_attr *) mqstat;
	} */
	file_t *fp = NULL;
	struct mqueue *mq;
	struct mq_attr attr;
	int error;

	/* Get the message queue */
	error = mqueue_get(l, SCARG(uap, mqdes), VNOVAL, &fp);
	if (error)
		return error;
	mq = fp->f_data;
	memcpy(&attr, &mq->mq_attrib, sizeof(struct mq_attr));
	mutex_exit(&mq->mq_mtx);
	fd_putfile((int)SCARG(uap, mqdes));

	return copyout(&attr, SCARG(uap, mqstat), sizeof(struct mq_attr));
}

int
sys_mq_setattr(struct lwp *l, const struct sys_mq_setattr_args *uap, register_t *retval)
{
	/* {
		syscallarg(mqd_t) mqdes;
		syscallarg(const struct mq_attr *) mqstat;
		syscallarg(struct mq_attr *) omqstat;
	} */
	file_t *fp = NULL;
	struct mqueue *mq;
	struct mq_attr attr;
	int error, nonblock;

	error = copyin(SCARG(uap, mqstat), &attr, sizeof(struct mq_attr));
	if (error)
		return error;
	nonblock = (attr.mq_flags & O_NONBLOCK);

	/* Get the message queue */
	error = mqueue_get(l, SCARG(uap, mqdes), VNOVAL, &fp);
	if (error)
		return error;
	mq = fp->f_data;

	/* Copy the old attributes, if needed */
	if (SCARG(uap, omqstat))
		memcpy(&attr, &mq->mq_attrib, sizeof(struct mq_attr));

	/* Ignore everything, except O_NONBLOCK */
	if (nonblock)
		mq->mq_attrib.mq_flags |= O_NONBLOCK;
	else
		mq->mq_attrib.mq_flags &= ~O_NONBLOCK;

	mutex_exit(&mq->mq_mtx);
	fd_putfile((int)SCARG(uap, mqdes));

	/*
	 * Copy the data to the user-space.
	 * Note: According to POSIX, the new attributes should not be set in
	 * case of fail - this would be violated.
	 */
	if (SCARG(uap, omqstat))
		error = copyout(&attr, SCARG(uap, omqstat),
		    sizeof(struct mq_attr));

	return error;
}

int
sys_mq_unlink(struct lwp *l, const struct sys_mq_unlink_args *uap, register_t *retval)
{
	/* {
		syscallarg(const char *) name;
	} */
	struct mqueue *mq;
	char *name;
	int error, refcnt = 0;

	/* Get the name from the user-space */
	name = kmem_zalloc(MQ_NAMELEN, KM_SLEEP);
	error = copyinstr(SCARG(uap, name), name, MQ_NAMELEN - 1, NULL);
	if (error) {
		kmem_free(name, MQ_NAMELEN);
		return error;
	}

	/* Lookup for this file */
	mutex_enter(&mqlist_mtx);
	mq = mqueue_lookup(name);
	if (mq == NULL) {
		error = ENOENT;
		goto error;
	}

	/* Check the permissions */
	if (mqueue_access(l, mq, VWRITE)) {
		mutex_exit(&mq->mq_mtx);
		error = EACCES;
		goto error;
	}

	/* Mark message queue as unlinking, before leaving the window */
	mq->mq_attrib.mq_flags |= MQ_UNLINK;

	/* Wake up all waiters, if there are such */
	cv_broadcast(&mq->mq_send_cv);
	cv_broadcast(&mq->mq_recv_cv);

	refcnt = mq->mq_refcnt;
	if (refcnt == 0)
		LIST_REMOVE(mq, mq_list);

	mutex_exit(&mq->mq_mtx);
error:
	mutex_exit(&mqlist_mtx);

	/*
	 * If there are no references - destroy the message
	 * queue, otherwise, the last mq_close() will do that.
	 */
	if (error == 0 && refcnt == 0)
		mqueue_destroy(mq);

	kmem_free(name, MQ_NAMELEN);
	return error;
}

/*
 * SysCtl.
 */

SYSCTL_SETUP(sysctl_mqueue_setup, "sysctl mqueue setup")
{
	const struct sysctlnode *node = NULL;

	sysctl_createv(clog, 0, NULL, NULL,
		CTLFLAG_PERMANENT,
		CTLTYPE_NODE, "kern", NULL,
		NULL, 0, NULL, 0,
		CTL_KERN, CTL_EOL);
	sysctl_createv(clog, 0, NULL, NULL,
		CTLFLAG_PERMANENT|CTLFLAG_IMMEDIATE,
		CTLTYPE_INT, "posix_msg",
		SYSCTL_DESCR("Version of IEEE Std 1003.1 and its "
			     "Message Passing option to which the "
			     "system attempts to conform"),
		NULL, _POSIX_MESSAGE_PASSING, NULL, 0,
		CTL_KERN, CTL_CREATE, CTL_EOL);
	sysctl_createv(clog, 0, NULL, &node,
		CTLFLAG_PERMANENT,
		CTLTYPE_NODE, "mqueue",
		SYSCTL_DESCR("Message queue options"),
		NULL, 0, NULL, 0,
		CTL_KERN, CTL_CREATE, CTL_EOL);

	if (node == NULL)
		return;

	sysctl_createv(clog, 0, &node, NULL,
		CTLFLAG_PERMANENT | CTLFLAG_READWRITE,
		CTLTYPE_INT, "mq_open_max",
		SYSCTL_DESCR("Maximal number of message queue descriptors "
			     "that process could open"),
		NULL, 0, &mq_open_max, 0,
		CTL_CREATE, CTL_EOL);
	sysctl_createv(clog, 0, &node, NULL,
		CTLFLAG_PERMANENT | CTLFLAG_READWRITE,
		CTLTYPE_INT, "mq_prio_max",
		SYSCTL_DESCR("Maximal priority of the message"),
		NULL, 0, &mq_prio_max, 0,
		CTL_CREATE, CTL_EOL);
	sysctl_createv(clog, 0, &node, NULL,
		CTLFLAG_PERMANENT | CTLFLAG_READWRITE,
		CTLTYPE_INT, "mq_max_msgsize",
		SYSCTL_DESCR("Maximal allowed size of the message"),
		NULL, 0, &mq_max_msgsize, 0,
		CTL_CREATE, CTL_EOL);
	sysctl_createv(clog, 0, &node, NULL,
		CTLFLAG_PERMANENT | CTLFLAG_READWRITE,
		CTLTYPE_INT, "mq_def_maxmsg",
		SYSCTL_DESCR("Default maximal message count"),
		NULL, 0, &mq_def_maxmsg, 0,
		CTL_CREATE, CTL_EOL);
}

/*
 * Debugging.
 */
#if defined(DDB)

void
mqueue_print_list(void (*pr)(const char *, ...))
{
	struct mqueue *mq;

	(*pr)("Global list of the message queues:\n");
	(*pr)("%20s %10s %8s %8s %3s %4s %4s %4s\n",
	    "Name", "Ptr", "Mode", "Flags",  "Ref",
	    "MaxMsg", "MsgSze", "CurMsg");
	LIST_FOREACH(mq, &mqueue_head, mq_list) {
		(*pr)("%20s %10p %8x %8x %3u %6lu %6lu %6lu\n",
		    mq->mq_name, mq, mq->mq_mode,
		    mq->mq_attrib.mq_flags, mq->mq_refcnt,
		    mq->mq_attrib.mq_maxmsg, mq->mq_attrib.mq_msgsize,
		    mq->mq_attrib.mq_curmsgs);
	}
}

#endif /* defined(DDB) */