/*
 * POSIX message queues filesystem for Linux.
 *
 * Copyright (C) 2003,2004  Krzysztof Benedyczak    (golbi@mat.uni.torun.pl)
 *                          Michal Wronski          (michal.wronski@gmail.com)
 *
 * Spinlocks:               Mohamed Abbas           (abbas.mohamed@intel.com)
 * Lockless receive & send, fd based notify:
 *                          Manfred Spraul          (manfred@colorfullife.com)
 *
 * Audit:                   George Wilson           (ltcgcw@us.ibm.com)
 *
 * This file is released under the GPL.
 */

#include <linux/capability.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/file.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/sysctl.h>
#include <linux/poll.h>
#include <linux/mqueue.h>
#include <linux/msg.h>
#include <linux/skbuff.h>
#include <linux/netlink.h>
#include <linux/syscalls.h>
#include <linux/audit.h>
#include <linux/signal.h>
#include <linux/mutex.h>
#include <linux/nsproxy.h>
#include <linux/pid.h>
#include <linux/ipc_namespace.h>
#include <linux/ima.h>

#include <net/sock.h>
#include "util.h"

#define MQUEUE_MAGIC    0x19800202
#define DIRENT_SIZE     20
#define FILENT_SIZE     80

#define SEND            0
#define RECV            1

#define STATE_NONE      0
#define STATE_PENDING   1
#define STATE_READY     2

struct ext_wait_queue {         /* queue of sleeping tasks */
        struct task_struct *task;
        struct list_head list;
        struct msg_msg *msg;    /* ptr of loaded message */
        int state;              /* one of STATE_* values */
};

struct mqueue_inode_info {
        spinlock_t lock;
        struct inode vfs_inode;
        wait_queue_head_t wait_q;

        struct msg_msg **messages;
        struct mq_attr attr;

        struct sigevent notify;
        struct pid* notify_owner;
        struct user_struct *user;       /* user who created, for accounting */
        struct sock *notify_sock;
        struct sk_buff *notify_cookie;

        /* for tasks waiting for free space and messages, respectively */
        struct ext_wait_queue e_wait_q[2];

        unsigned long qsize; /* size of queue in memory (sum of all msgs) */
};

static const struct inode_operations mqueue_dir_inode_operations;
static const struct file_operations mqueue_file_operations;
static const struct super_operations mqueue_super_ops;
static void remove_notification(struct mqueue_inode_info *info);

static struct kmem_cache *mqueue_inode_cachep;

static struct ctl_table_header * mq_sysctl_table;

static inline struct mqueue_inode_info *MQUEUE_I(struct inode *inode)
{
        return container_of(inode, struct mqueue_inode_info, vfs_inode);
}

/*
 * This routine should be called with the mq_lock held.
 */
static inline struct ipc_namespace *__get_ns_from_inode(struct inode *inode)
{
        return get_ipc_ns(inode->i_sb->s_fs_info);
}

static struct ipc_namespace *get_ns_from_inode(struct inode *inode)
{
        struct ipc_namespace *ns;

        spin_lock(&mq_lock);
        ns = __get_ns_from_inode(inode);
        spin_unlock(&mq_lock);
        return ns;
}

static struct inode *mqueue_get_inode(struct super_block *sb,
                struct ipc_namespace *ipc_ns, int mode,
                struct mq_attr *attr)
{
        struct user_struct *u = current_user();
        struct inode *inode;

        inode = new_inode(sb);
        if (inode) {
                inode->i_mode = mode;
                inode->i_uid = current_fsuid();
                inode->i_gid = current_fsgid();
                inode->i_mtime = inode->i_ctime = inode->i_atime =
                                CURRENT_TIME;

                if (S_ISREG(mode)) {
                        struct mqueue_inode_info *info;
                        struct task_struct *p = current;
                        unsigned long mq_bytes, mq_msg_tblsz;

                        inode->i_fop = &mqueue_file_operations;
                        inode->i_size = FILENT_SIZE;
                        /* mqueue specific info */
                        info = MQUEUE_I(inode);
                        spin_lock_init(&info->lock);
                        init_waitqueue_head(&info->wait_q);
                        INIT_LIST_HEAD(&info->e_wait_q[0].list);
                        INIT_LIST_HEAD(&info->e_wait_q[1].list);
                        info->messages = NULL;
                        info->notify_owner = NULL;
                        info->qsize = 0;
                        info->user = NULL;      /* set when all is ok */
                        memset(&info->attr, 0, sizeof(info->attr));
                        info->attr.mq_maxmsg = ipc_ns->mq_msg_max;
                        info->attr.mq_msgsize = ipc_ns->mq_msgsize_max;
                        if (attr) {
                                info->attr.mq_maxmsg = attr->mq_maxmsg;
                                info->attr.mq_msgsize = attr->mq_msgsize;
                        }
                        mq_msg_tblsz = info->attr.mq_maxmsg * sizeof(struct msg_msg *);
                        mq_bytes = (mq_msg_tblsz +
                                (info->attr.mq_maxmsg * info->attr.mq_msgsize));

                        spin_lock(&mq_lock);
                        if (u->mq_bytes + mq_bytes < u->mq_bytes ||
                            u->mq_bytes + mq_bytes >
                            p->signal->rlim[RLIMIT_MSGQUEUE].rlim_cur) {
                                spin_unlock(&mq_lock);
                                goto out_inode;
                        }
                        u->mq_bytes += mq_bytes;
                        spin_unlock(&mq_lock);

                        info->messages = kmalloc(mq_msg_tblsz, GFP_KERNEL);
                        if (!info->messages) {
                                spin_lock(&mq_lock);
                                u->mq_bytes -= mq_bytes;
                                spin_unlock(&mq_lock);
                                goto out_inode;
                        }
                        /* all is ok */
                        info->user = get_uid(u);
                } else if (S_ISDIR(mode)) {
                        inc_nlink(inode);
                        /* Some things misbehave if size == 0 on a directory */
                        inode->i_size = 2 * DIRENT_SIZE;
                        inode->i_op = &mqueue_dir_inode_operations;
                        inode->i_fop = &simple_dir_operations;
                }
        }
        return inode;
out_inode:
        make_bad_inode(inode);
        iput(inode);
        return NULL;
}

static int mqueue_fill_super(struct super_block *sb, void *data, int silent)
{
        struct inode *inode;
        struct ipc_namespace *ns = data;
        int error = 0;

        sb->s_blocksize = PAGE_CACHE_SIZE;
        sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
        sb->s_magic = MQUEUE_MAGIC;
        sb->s_op = &mqueue_super_ops;

        inode = mqueue_get_inode(sb, ns, S_IFDIR | S_ISVTX | S_IRWXUGO,
                                NULL);
        if (!inode) {
                error = -ENOMEM;
                goto out;
        }

        sb->s_root = d_alloc_root(inode);
        if (!sb->s_root) {
                iput(inode);
                error = -ENOMEM;
        }

out:
        return error;
}

static int mqueue_get_sb(struct file_system_type *fs_type,
                         int flags, const char *dev_name,
                         void *data, struct vfsmount *mnt)
{
        if (!(flags & MS_KERNMOUNT))
                data = current->nsproxy->ipc_ns;
        return get_sb_ns(fs_type, flags, data, mqueue_fill_super, mnt);
}

static void init_once(void *foo)
{
        struct mqueue_inode_info *p = (struct mqueue_inode_info *) foo;

        inode_init_once(&p->vfs_inode);
}

static struct inode *mqueue_alloc_inode(struct super_block *sb)
{
        struct mqueue_inode_info *ei;

        ei = kmem_cache_alloc(mqueue_inode_cachep, GFP_KERNEL);
        if (!ei)
                return NULL;
        return &ei->vfs_inode;
}

static void mqueue_destroy_inode(struct inode *inode)
{
        kmem_cache_free(mqueue_inode_cachep, MQUEUE_I(inode));
}

static void mqueue_delete_inode(struct inode *inode)
{
        struct mqueue_inode_info *info;
        struct user_struct *user;
        unsigned long mq_bytes;
        int i;
        struct ipc_namespace *ipc_ns;

        if (S_ISDIR(inode->i_mode)) {
                clear_inode(inode);
                return;
        }
        ipc_ns = get_ns_from_inode(inode);
        info = MQUEUE_I(inode);
        spin_lock(&info->lock);
        for (i = 0; i < info->attr.mq_curmsgs; i++)
                free_msg(info->messages[i]);
        kfree(info->messages);
        spin_unlock(&info->lock);

        clear_inode(inode);

        mq_bytes = (info->attr.mq_maxmsg * sizeof(struct msg_msg *) +
                   (info->attr.mq_maxmsg * info->attr.mq_msgsize));
        user = info->user;
        if (user) {
                spin_lock(&mq_lock);
                user->mq_bytes -= mq_bytes;
                /*
                 * get_ns_from_inode() ensures that the
                 * (ipc_ns = sb->s_fs_info) is either a valid ipc_ns
                 * to which we now hold a reference, or it is NULL.
                 * We can't put it here under mq_lock, though.
                 */
                if (ipc_ns)
                        ipc_ns->mq_queues_count--;
                spin_unlock(&mq_lock);
                free_uid(user);
        }
        if (ipc_ns)
                put_ipc_ns(ipc_ns);
}

static int mqueue_create(struct inode *dir, struct dentry *dentry,
                                int mode, struct nameidata *nd)
{
        struct inode *inode;
        struct mq_attr *attr = dentry->d_fsdata;
        int error;
        struct ipc_namespace *ipc_ns;

        spin_lock(&mq_lock);
        ipc_ns = __get_ns_from_inode(dir);
        if (!ipc_ns) {
                error = -EACCES;
                goto out_unlock;
        }
        if (ipc_ns->mq_queues_count >= ipc_ns->mq_queues_max &&
                        !capable(CAP_SYS_RESOURCE)) {
                error = -ENOSPC;
                goto out_unlock;
        }
        ipc_ns->mq_queues_count++;
        spin_unlock(&mq_lock);

        inode = mqueue_get_inode(dir->i_sb, ipc_ns, mode, attr);
        if (!inode) {
                error = -ENOMEM;
                spin_lock(&mq_lock);
                ipc_ns->mq_queues_count--;
                goto out_unlock;
        }

        put_ipc_ns(ipc_ns);
        dir->i_size += DIRENT_SIZE;
        dir->i_ctime = dir->i_mtime = dir->i_atime = CURRENT_TIME;

        d_instantiate(dentry, inode);
        dget(dentry);
        return 0;
out_unlock:
        spin_unlock(&mq_lock);
        if (ipc_ns)
                put_ipc_ns(ipc_ns);
        return error;
}

static int mqueue_unlink(struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = dentry->d_inode;

        dir->i_ctime = dir->i_mtime = dir->i_atime = CURRENT_TIME;
        dir->i_size -= DIRENT_SIZE;
        drop_nlink(inode);
        dput(dentry);
        return 0;
}

/*
*       This is routine for system read from queue file.
*       To avoid mess with doing here some sort of mq_receive we allow
*       to read only queue size & notification info (the only values
*       that are interesting from user point of view and aren't accessible
*       through std routines)
*/
static ssize_t mqueue_read_file(struct file *filp, char __user *u_data,
                                size_t count, loff_t *off)
{
        struct mqueue_inode_info *info = MQUEUE_I(filp->f_path.dentry->d_inode);
        char buffer[FILENT_SIZE];
        ssize_t ret;

        spin_lock(&info->lock);
        snprintf(buffer, sizeof(buffer),
                        "QSIZE:%-10lu NOTIFY:%-5d SIGNO:%-5d NOTIFY_PID:%-6d\n",
                        info->qsize,
                        info->notify_owner ? info->notify.sigev_notify : 0,
                        (info->notify_owner &&
                         info->notify.sigev_notify == SIGEV_SIGNAL) ?
                                info->notify.sigev_signo : 0,
                        pid_vnr(info->notify_owner));
        spin_unlock(&info->lock);
        buffer[sizeof(buffer)-1] = '\0';

        ret = simple_read_from_buffer(u_data, count, off, buffer,
                                strlen(buffer));
        if (ret <= 0)
                return ret;

        filp->f_path.dentry->d_inode->i_atime = filp->f_path.dentry->d_inode->i_ctime = CURRENT_TIME;
        return ret;
}

static int mqueue_flush_file(struct file *filp, fl_owner_t id)
{
        struct mqueue_inode_info *info = MQUEUE_I(filp->f_path.dentry->d_inode);

        spin_lock(&info->lock);
        if (task_tgid(current) == info->notify_owner)
                remove_notification(info);

        spin_unlock(&info->lock);
        return 0;
}

static unsigned int mqueue_poll_file(struct file *filp, struct poll_table_struct *poll_tab)
{
        struct mqueue_inode_info *info = MQUEUE_I(filp->f_path.dentry->d_inode);
        int retval = 0;

        poll_wait(filp, &info->wait_q, poll_tab);

        spin_lock(&info->lock);
        if (info->attr.mq_curmsgs)
                retval = POLLIN | POLLRDNORM;

        if (info->attr.mq_curmsgs < info->attr.mq_maxmsg)
                retval |= POLLOUT | POLLWRNORM;
        spin_unlock(&info->lock);

        return retval;
}

/* Adds current to info->e_wait_q[sr] before element with smaller prio */
static void wq_add(struct mqueue_inode_info *info, int sr,
                        struct ext_wait_queue *ewp)
{
        struct ext_wait_queue *walk;

        ewp->task = current;

        list_for_each_entry(walk, &info->e_wait_q[sr].list, list) {
                if (walk->task->static_prio <= current->static_prio) {
                        list_add_tail(&ewp->list, &walk->list);
                        return;
                }
        }
        list_add_tail(&ewp->list, &info->e_wait_q[sr].list);
}

/*
 * Puts current task to sleep. Caller must hold queue lock. After return
 * lock isn't held.
 * sr: SEND or RECV
 */
static int wq_sleep(struct mqueue_inode_info *info, int sr,
                        long timeout, struct ext_wait_queue *ewp)
{
        int retval;
        signed long time;

        wq_add(info, sr, ewp);

        for (;;) {
                set_current_state(TASK_INTERRUPTIBLE);

                spin_unlock(&info->lock);
                time = schedule_timeout(timeout);

                while (ewp->state == STATE_PENDING)
                        cpu_relax();

                if (ewp->state == STATE_READY) {
                        retval = 0;
                        goto out;
                }
                spin_lock(&info->lock);
                if (ewp->state == STATE_READY) {
                        retval = 0;
                        goto out_unlock;
                }
                if (signal_pending(current)) {
                        retval = -ERESTARTSYS;
                        break;
                }
                if (time == 0) {
                        retval = -ETIMEDOUT;
                        break;
                }
        }
        list_del(&ewp->list);
out_unlock:
        spin_unlock(&info->lock);
out:
        return retval;
}

/*
 * Returns waiting task that should be serviced first or NULL if none exists
 */
static struct ext_wait_queue *wq_get_first_waiter(
                struct mqueue_inode_info *info, int sr)
{
        struct list_head *ptr;

        ptr = info->e_wait_q[sr].list.prev;
        if (ptr == &info->e_wait_q[sr].list)
                return NULL;
        return list_entry(ptr, struct ext_wait_queue, list);
}

/* Auxiliary functions to manipulate messages' list */
static void msg_insert(struct msg_msg *ptr, struct mqueue_inode_info *info)
{
        int k;

        k = info->attr.mq_curmsgs - 1;
        while (k >= 0 && info->messages[k]->m_type >= ptr->m_type) {
                info->messages[k + 1] = info->messages[k];
                k--;
        }
        info->attr.mq_curmsgs++;
        info->qsize += ptr->m_ts;
        info->messages[k + 1] = ptr;
}

static inline struct msg_msg *msg_get(struct mqueue_inode_info *info)
{
        info->qsize -= info->messages[--info->attr.mq_curmsgs]->m_ts;
        return info->messages[info->attr.mq_curmsgs];
}

static inline void set_cookie(struct sk_buff *skb, char code)
{
        ((char*)skb->data)[NOTIFY_COOKIE_LEN-1] = code;
}

/*
 * The next function is only to split too long sys_mq_timedsend
 */
static void __do_notify(struct mqueue_inode_info *info)
{
        /* notification
         * invoked when there is registered process and there isn't process
         * waiting synchronously for message AND state of queue changed from
         * empty to not empty. Here we are sure that no one is waiting
         * synchronously. */
        if (info->notify_owner &&
            info->attr.mq_curmsgs == 1) {
                struct siginfo sig_i;
                switch (info->notify.sigev_notify) {
                case SIGEV_NONE:
                        break;
                case SIGEV_SIGNAL:
                        /* sends signal */

                        sig_i.si_signo = info->notify.sigev_signo;
                        sig_i.si_errno = 0;
                        sig_i.si_code = SI_MESGQ;
                        sig_i.si_value = info->notify.sigev_value;
                        sig_i.si_pid = task_tgid_nr_ns(current,
                                                ns_of_pid(info->notify_owner));
                        sig_i.si_uid = current_uid();

                        kill_pid_info(info->notify.sigev_signo,
                                      &sig_i, info->notify_owner);
                        break;
                case SIGEV_THREAD:
                        set_cookie(info->notify_cookie, NOTIFY_WOKENUP);
                        netlink_sendskb(info->notify_sock, info->notify_cookie);
                        break;
                }
                /* after notification unregisters process */
                put_pid(info->notify_owner);
                info->notify_owner = NULL;
        }
        wake_up(&info->wait_q);
}

static long prepare_timeout(struct timespec *p)
{
        struct timespec nowts;
        long timeout;

        if (p) {
                if (unlikely(p->tv_nsec < 0 || p->tv_sec < 0
                        || p->tv_nsec >= NSEC_PER_SEC))
                        return -EINVAL;
                nowts = CURRENT_TIME;
                /* first subtract as jiffies can't be too big */
                p->tv_sec -= nowts.tv_sec;
                if (p->tv_nsec < nowts.tv_nsec) {
                        p->tv_nsec += NSEC_PER_SEC;
                        p->tv_sec--;
                }
                p->tv_nsec -= nowts.tv_nsec;
                if (p->tv_sec < 0)
                        return 0;

                timeout = timespec_to_jiffies(p) + 1;
        } else
                return MAX_SCHEDULE_TIMEOUT;

        return timeout;
}

static void remove_notification(struct mqueue_inode_info *info)
{
        if (info->notify_owner != NULL &&
            info->notify.sigev_notify == SIGEV_THREAD) {
                set_cookie(info->notify_cookie, NOTIFY_REMOVED);
                netlink_sendskb(info->notify_sock, info->notify_cookie);
        }
        put_pid(info->notify_owner);
        info->notify_owner = NULL;
}

static int mq_attr_ok(struct ipc_namespace *ipc_ns, struct mq_attr *attr)
{
        if (attr->mq_maxmsg <= 0 || attr->mq_msgsize <= 0)
                return 0;
        if (capable(CAP_SYS_RESOURCE)) {
                if (attr->mq_maxmsg > HARD_MSGMAX)
                        return 0;
        } else {
                if (attr->mq_maxmsg > ipc_ns->mq_msg_max ||
                                attr->mq_msgsize > ipc_ns->mq_msgsize_max)
                        return 0;
        }
        /* check for overflow */
        if (attr->mq_msgsize > ULONG_MAX/attr->mq_maxmsg)
                return 0;
        if ((unsigned long)(attr->mq_maxmsg * attr->mq_msgsize) +
            (attr->mq_maxmsg * sizeof (struct msg_msg *)) <
            (unsigned long)(attr->mq_maxmsg * attr->mq_msgsize))
                return 0;
        return 1;
}

/*
 * Invoked when creating a new queue via sys_mq_open
 */
static struct file *do_create(struct ipc_namespace *ipc_ns, struct dentry *dir,
                        struct dentry *dentry, int oflag, mode_t mode,
                        struct mq_attr *attr)
{
        const struct cred *cred = current_cred();
        struct file *result;
        int ret;

        if (attr) {
                ret = -EINVAL;
                if (!mq_attr_ok(ipc_ns, attr))
                        goto out;
                /* store for use during create */
                dentry->d_fsdata = attr;
        }

        mode &= ~current_umask();
        ret = mnt_want_write(ipc_ns->mq_mnt);
        if (ret)
                goto out;
        ret = vfs_create(dir->d_inode, dentry, mode, NULL);
        dentry->d_fsdata = NULL;
        if (ret)
                goto out_drop_write;

        result = dentry_open(dentry, ipc_ns->mq_mnt, oflag, cred);
        /*
         * dentry_open() took a persistent mnt_want_write(),
         * so we can now drop this one.
         */
        mnt_drop_write(ipc_ns->mq_mnt);
        return result;

out_drop_write:
        mnt_drop_write(ipc_ns->mq_mnt);
out:
        dput(dentry);
        mntput(ipc_ns->mq_mnt);
        return ERR_PTR(ret);
}

/* Opens existing queue */
static struct file *do_open(struct ipc_namespace *ipc_ns,
                                struct dentry *dentry, int oflag)
{
        const struct cred *cred = current_cred();

        static const int oflag2acc[O_ACCMODE] = { MAY_READ, MAY_WRITE,
                                                  MAY_READ | MAY_WRITE };

        if ((oflag & O_ACCMODE) == (O_RDWR | O_WRONLY)) {
                dput(dentry);
                mntput(ipc_ns->mq_mnt);
                return ERR_PTR(-EINVAL);
        }

        if (inode_permission(dentry->d_inode, oflag2acc[oflag & O_ACCMODE])) {
                dput(dentry);
                mntput(ipc_ns->mq_mnt);
                return ERR_PTR(-EACCES);
        }

        return dentry_open(dentry, ipc_ns->mq_mnt, oflag, cred);
}

SYSCALL_DEFINE4(mq_open, const char __user *, u_name, int, oflag, mode_t, mode,
                struct mq_attr __user *, u_attr)
{
        struct dentry *dentry;
        struct file *filp;
        char *name;
        struct mq_attr attr;
        int fd, error;
        struct ipc_namespace *ipc_ns = current->nsproxy->ipc_ns;

        if (u_attr && copy_from_user(&attr, u_attr, sizeof(struct mq_attr)))
                return -EFAULT;

        audit_mq_open(oflag, mode, u_attr ? &attr : NULL);

        if (IS_ERR(name = getname(u_name)))
                return PTR_ERR(name);

        fd = get_unused_fd_flags(O_CLOEXEC);
        if (fd < 0)
                goto out_putname;

        mutex_lock(&ipc_ns->mq_mnt->mnt_root->d_inode->i_mutex);
        dentry = lookup_one_len(name, ipc_ns->mq_mnt->mnt_root, strlen(name));
        if (IS_ERR(dentry)) {
                error = PTR_ERR(dentry);
                goto out_err;
        }
        mntget(ipc_ns->mq_mnt);

        if (oflag & O_CREAT) {
                if (dentry->d_inode) {  /* entry already exists */
                        audit_inode(name, dentry);
                        error = -EEXIST;
                        if (oflag & O_EXCL)
                                goto out;
                        filp = do_open(ipc_ns, dentry, oflag);
                } else {
                        filp = do_create(ipc_ns, ipc_ns->mq_mnt->mnt_root,
                                                dentry, oflag, mode,
                                                u_attr ? &attr : NULL);
                }
        } else {
                error = -ENOENT;
                if (!dentry->d_inode)
                        goto out;
                audit_inode(name, dentry);
                filp = do_open(ipc_ns, dentry, oflag);
        }

        if (IS_ERR(filp)) {
                error = PTR_ERR(filp);
                goto out_putfd;
        }
        ima_counts_get(filp);

        fd_install(fd, filp);
        goto out_upsem;

out:
        dput(dentry);
        mntput(ipc_ns->mq_mnt);
out_putfd:
        put_unused_fd(fd);
out_err:
        fd = error;
out_upsem:
        mutex_unlock(&ipc_ns->mq_mnt->mnt_root->d_inode->i_mutex);
out_putname:
        putname(name);
        return fd;
}

SYSCALL_DEFINE1(mq_unlink, const char __user *, u_name)
{
        int err;
        char *name;
        struct dentry *dentry;
        struct inode *inode = NULL;
        struct ipc_namespace *ipc_ns = current->nsproxy->ipc_ns;

        name = getname(u_name);
        if (IS_ERR(name))
                return PTR_ERR(name);

        mutex_lock_nested(&ipc_ns->mq_mnt->mnt_root->d_inode->i_mutex,
                        I_MUTEX_PARENT);
        dentry = lookup_one_len(name, ipc_ns->mq_mnt->mnt_root, strlen(name));
        if (IS_ERR(dentry)) {
                err = PTR_ERR(dentry);
                goto out_unlock;
        }

        if (!dentry->d_inode) {
                err = -ENOENT;
                goto out_err;
        }

        inode = dentry->d_inode;
        if (inode)
                atomic_inc(&inode->i_count);
        err = mnt_want_write(ipc_ns->mq_mnt);
        if (err)
                goto out_err;
        err = vfs_unlink(dentry->d_parent->d_inode, dentry);
        mnt_drop_write(ipc_ns->mq_mnt);
out_err:
        dput(dentry);

out_unlock:
        mutex_unlock(&ipc_ns->mq_mnt->mnt_root->d_inode->i_mutex);
        putname(name);
        if (inode)
                iput(inode);

        return err;
}

/* Pipelined send and receive functions.
 *
 * If a receiver finds no waiting message, then it registers itself in the
 * list of waiting receivers. A sender checks that list before adding the new
 * message into the message array. If there is a waiting receiver, then it
 * bypasses the message array and directly hands the message over to the
 * receiver.
 * The receiver accepts the message and returns without grabbing the queue
 * spinlock. Therefore an intermediate STATE_PENDING state and memory barriers
 * are necessary. The same algorithm is used for sysv semaphores, see
 * ipc/sem.c for more details.
 *
 * The same algorithm is used for senders.
 */

/* pipelined_send() - send a message directly to the task waiting in
 * sys_mq_timedreceive() (without inserting message into a queue).
 */
static inline void pipelined_send(struct mqueue_inode_info *info,
                                  struct msg_msg *message,
                                  struct ext_wait_queue *receiver)
{
        receiver->msg = message;
        list_del(&receiver->list);
        receiver->state = STATE_PENDING;
        wake_up_process(receiver->task);
        smp_wmb();
        receiver->state = STATE_READY;
}

/* pipelined_receive() - if there is task waiting in sys_mq_timedsend()
 * gets its message and put to the queue (we have one free place for sure). */
static inline void pipelined_receive(struct mqueue_inode_info *info)
{
        struct ext_wait_queue *sender = wq_get_first_waiter(info, SEND);

        if (!sender) {
                /* for poll */
                wake_up_interruptible(&info->wait_q);
                return;
        }
        msg_insert(sender->msg, info);
        list_del(&sender->list);
        sender->state = STATE_PENDING;
        wake_up_process(sender->task);
        smp_wmb();
        sender->state = STATE_READY;
}

SYSCALL_DEFINE5(mq_timedsend, mqd_t, mqdes, const char __user *, u_msg_ptr,
                size_t, msg_len, unsigned int, msg_prio,
                const struct timespec __user *, u_abs_timeout)
{
        struct file *filp;
        struct inode *inode;
        struct ext_wait_queue wait;
        struct ext_wait_queue *receiver;
        struct msg_msg *msg_ptr;
        struct mqueue_inode_info *info;
        struct timespec ts, *p = NULL;
        long timeout;
        int ret;

        if (u_abs_timeout) {
                if (copy_from_user(&ts, u_abs_timeout, 
                                        sizeof(struct timespec)))
                        return -EFAULT;
                p = &ts;
        }

        if (unlikely(msg_prio >= (unsigned long) MQ_PRIO_MAX))
                return -EINVAL;

        audit_mq_sendrecv(mqdes, msg_len, msg_prio, p);
        timeout = prepare_timeout(p);

        ret = -EBADF;
        filp = fget(mqdes);
        if (unlikely(!filp))
                goto out;

        inode = filp->f_path.dentry->d_inode;
        if (unlikely(filp->f_op != &mqueue_file_operations))
                goto out_fput;
        info = MQUEUE_I(inode);
        audit_inode(NULL, filp->f_path.dentry);

        if (unlikely(!(filp->f_mode & FMODE_WRITE)))
                goto out_fput;

        if (unlikely(msg_len > info->attr.mq_msgsize)) {
                ret = -EMSGSIZE;
                goto out_fput;
        }

        /* First try to allocate memory, before doing anything with
         * existing queues. */
        msg_ptr = load_msg(u_msg_ptr, msg_len);
        if (IS_ERR(msg_ptr)) {
                ret = PTR_ERR(msg_ptr);
                goto out_fput;
        }
        msg_ptr->m_ts = msg_len;
        msg_ptr->m_type = msg_prio;

        spin_lock(&info->lock);

        if (info->attr.mq_curmsgs == info->attr.mq_maxmsg) {
                if (filp->f_flags & O_NONBLOCK) {
                        spin_unlock(&info->lock);
                        ret = -EAGAIN;
                } else if (unlikely(timeout < 0)) {
                        spin_unlock(&info->lock);
                        ret = timeout;
                } else {
                        wait.task = current;
                        wait.msg = (void *) msg_ptr;
                        wait.state = STATE_NONE;
                        ret = wq_sleep(info, SEND, timeout, &wait);
                }
                if (ret < 0)
                        free_msg(msg_ptr);
        } else {
                receiver = wq_get_first_waiter(info, RECV);
                if (receiver) {
                        pipelined_send(info, msg_ptr, receiver);
                } else {
                        /* adds message to the queue */
                        msg_insert(msg_ptr, info);
                        __do_notify(info);
                }
                inode->i_atime = inode->i_mtime = inode->i_ctime =
                                CURRENT_TIME;
                spin_unlock(&info->lock);
                ret = 0;
        }
out_fput:
        fput(filp);
out:
        return ret;
}

SYSCALL_DEFINE5(mq_timedreceive, mqd_t, mqdes, char __user *, u_msg_ptr,
                size_t, msg_len, unsigned int __user *, u_msg_prio,
                const struct timespec __user *, u_abs_timeout)
{
        long timeout;
        ssize_t ret;
        struct msg_msg *msg_ptr;
        struct file *filp;
        struct inode *inode;
        struct mqueue_inode_info *info;
        struct ext_wait_queue wait;
        struct timespec ts, *p = NULL;

        if (u_abs_timeout) {
                if (copy_from_user(&ts, u_abs_timeout, 
                                        sizeof(struct timespec)))
                        return -EFAULT;
                p = &ts;
        }

        audit_mq_sendrecv(mqdes, msg_len, 0, p);
        timeout = prepare_timeout(p);

        ret = -EBADF;
        filp = fget(mqdes);
        if (unlikely(!filp))
                goto out;

        inode = filp->f_path.dentry->d_inode;
        if (unlikely(filp->f_op != &mqueue_file_operations))
                goto out_fput;
        info = MQUEUE_I(inode);
        audit_inode(NULL, filp->f_path.dentry);

        if (unlikely(!(filp->f_mode & FMODE_READ)))
                goto out_fput;

        /* checks if buffer is big enough */
        if (unlikely(msg_len < info->attr.mq_msgsize)) {
                ret = -EMSGSIZE;
                goto out_fput;
        }

        spin_lock(&info->lock);
        if (info->attr.mq_curmsgs == 0) {
                if (filp->f_flags & O_NONBLOCK) {
                        spin_unlock(&info->lock);
                        ret = -EAGAIN;
                        msg_ptr = NULL;
                } else if (unlikely(timeout < 0)) {
                        spin_unlock(&info->lock);
                        ret = timeout;
                        msg_ptr = NULL;
                } else {
                        wait.task = current;
                        wait.state = STATE_NONE;
                        ret = wq_sleep(info, RECV, timeout, &wait);
                        msg_ptr = wait.msg;

                }
        } else {
                msg_ptr = msg_get(info);

                inode->i_atime = inode->i_mtime = inode->i_ctime =
                                CURRENT_TIME;

                /* There is now free space in queue. */
                pipelined_receive(info);
                spin_unlock(&info->lock);
                ret = 0;
        }
        if (ret == 0) {
                ret = msg_ptr->m_ts;

                if ((u_msg_prio && put_user(msg_ptr->m_type, u_msg_prio)) ||
                        store_msg(u_msg_ptr, msg_ptr, msg_ptr->m_ts)) {
                        ret = -EFAULT;
                }
                free_msg(msg_ptr);
        }
out_fput:
        fput(filp);
out:
        return ret;
}

/*
 * Notes: the case when user wants us to deregister (with NULL as pointer)
 * and he isn't currently owner of notification, will be silently discarded.
 * It isn't explicitly defined in the POSIX.
 */
SYSCALL_DEFINE2(mq_notify, mqd_t, mqdes,
                const struct sigevent __user *, u_notification)
{
        int ret;
        struct file *filp;
        struct sock *sock;
        struct inode *inode;
        struct sigevent notification;
        struct mqueue_inode_info *info;
        struct sk_buff *nc;

        if (u_notification) {
                if (copy_from_user(&notification, u_notification,
                                        sizeof(struct sigevent)))
                        return -EFAULT;
        }

        audit_mq_notify(mqdes, u_notification ? &notification : NULL);

        nc = NULL;
        sock = NULL;
        if (u_notification != NULL) {
                if (unlikely(notification.sigev_notify != SIGEV_NONE &&
                             notification.sigev_notify != SIGEV_SIGNAL &&
                             notification.sigev_notify != SIGEV_THREAD))
                        return -EINVAL;
                if (notification.sigev_notify == SIGEV_SIGNAL &&
                        !valid_signal(notification.sigev_signo)) {
                        return -EINVAL;
                }
                if (notification.sigev_notify == SIGEV_THREAD) {
                        long timeo;

                        /* create the notify skb */
                        nc = alloc_skb(NOTIFY_COOKIE_LEN, GFP_KERNEL);
                        ret = -ENOMEM;
                        if (!nc)
                                goto out;
                        ret = -EFAULT;
                        if (copy_from_user(nc->data,
                                        notification.sigev_value.sival_ptr,
                                        NOTIFY_COOKIE_LEN)) {
                                goto out;
                        }

                        /* TODO: add a header? */
                        skb_put(nc, NOTIFY_COOKIE_LEN);
                        /* and attach it to the socket */
retry:
                        filp = fget(notification.sigev_signo);
                        ret = -EBADF;
                        if (!filp)
                                goto out;
                        sock = netlink_getsockbyfilp(filp);
                        fput(filp);
                        if (IS_ERR(sock)) {
                                ret = PTR_ERR(sock);
                                sock = NULL;
                                goto out;
                        }

                        timeo = MAX_SCHEDULE_TIMEOUT;
                        ret = netlink_attachskb(sock, nc, &timeo, NULL);
                        if (ret == 1)
                                goto retry;
                        if (ret) {
                                sock = NULL;
                                nc = NULL;
                                goto out;
                        }
                }
        }

        ret = -EBADF;
        filp = fget(mqdes);
        if (!filp)
                goto out;

        inode = filp->f_path.dentry->d_inode;
        if (unlikely(filp->f_op != &mqueue_file_operations))
                goto out_fput;
        info = MQUEUE_I(inode);

        ret = 0;
        spin_lock(&info->lock);
        if (u_notification == NULL) {
                if (info->notify_owner == task_tgid(current)) {
                        remove_notification(info);
                        inode->i_atime = inode->i_ctime = CURRENT_TIME;
                }
        } else if (info->notify_owner != NULL) {
                ret = -EBUSY;
        } else {
                switch (notification.sigev_notify) {
                case SIGEV_NONE:
                        info->notify.sigev_notify = SIGEV_NONE;
                        break;
                case SIGEV_THREAD:
                        info->notify_sock = sock;
                        info->notify_cookie = nc;
                        sock = NULL;
                        nc = NULL;
                        info->notify.sigev_notify = SIGEV_THREAD;
                        break;
                case SIGEV_SIGNAL:
                        info->notify.sigev_signo = notification.sigev_signo;
                        info->notify.sigev_value = notification.sigev_value;
                        info->notify.sigev_notify = SIGEV_SIGNAL;
                        break;
                }

                info->notify_owner = get_pid(task_tgid(current));
                inode->i_atime = inode->i_ctime = CURRENT_TIME;
        }
        spin_unlock(&info->lock);
out_fput:
        fput(filp);
out:
        if (sock) {
                netlink_detachskb(sock, nc);
        } else if (nc) {
                dev_kfree_skb(nc);
        }
        return ret;
}

SYSCALL_DEFINE3(mq_getsetattr, mqd_t, mqdes,
                const struct mq_attr __user *, u_mqstat,
                struct mq_attr __user *, u_omqstat)
{
        int ret;
        struct mq_attr mqstat, omqstat;
        struct file *filp;
        struct inode *inode;
        struct mqueue_inode_info *info;

        if (u_mqstat != NULL) {
                if (copy_from_user(&mqstat, u_mqstat, sizeof(struct mq_attr)))
                        return -EFAULT;
                if (mqstat.mq_flags & (~O_NONBLOCK))
                        return -EINVAL;
        }

        ret = -EBADF;
        filp = fget(mqdes);
        if (!filp)
                goto out;

        inode = filp->f_path.dentry->d_inode;
        if (unlikely(filp->f_op != &mqueue_file_operations))
                goto out_fput;
        info = MQUEUE_I(inode);

        spin_lock(&info->lock);

        omqstat = info->attr;
        omqstat.mq_flags = filp->f_flags & O_NONBLOCK;
        if (u_mqstat) {
                audit_mq_getsetattr(mqdes, &mqstat);
                spin_lock(&filp->f_lock);
                if (mqstat.mq_flags & O_NONBLOCK)
                        filp->f_flags |= O_NONBLOCK;
                else
                        filp->f_flags &= ~O_NONBLOCK;
                spin_unlock(&filp->f_lock);

                inode->i_atime = inode->i_ctime = CURRENT_TIME;
        }

        spin_unlock(&info->lock);

        ret = 0;
        if (u_omqstat != NULL && copy_to_user(u_omqstat, &omqstat,
                                                sizeof(struct mq_attr)))
                ret = -EFAULT;

out_fput:
        fput(filp);
out:
        return ret;
}

static const struct inode_operations mqueue_dir_inode_operations = {
        .lookup = simple_lookup,
        .create = mqueue_create,
        .unlink = mqueue_unlink,
};

static const struct file_operations mqueue_file_operations = {
        .flush = mqueue_flush_file,
        .poll = mqueue_poll_file,
        .read = mqueue_read_file,
};

static const struct super_operations mqueue_super_ops = {
        .alloc_inode = mqueue_alloc_inode,
        .destroy_inode = mqueue_destroy_inode,
        .statfs = simple_statfs,
        .delete_inode = mqueue_delete_inode,
        .drop_inode = generic_delete_inode,
};

static struct file_system_type mqueue_fs_type = {
        .name = "mqueue",
        .get_sb = mqueue_get_sb,
        .kill_sb = kill_litter_super,
};

int mq_init_ns(struct ipc_namespace *ns)
{
        ns->mq_queues_count  = 0;
        ns->mq_queues_max    = DFLT_QUEUESMAX;
        ns->mq_msg_max       = DFLT_MSGMAX;
        ns->mq_msgsize_max   = DFLT_MSGSIZEMAX;

        ns->mq_mnt = kern_mount_data(&mqueue_fs_type, ns);
        if (IS_ERR(ns->mq_mnt)) {
                int err = PTR_ERR(ns->mq_mnt);
                ns->mq_mnt = NULL;
                return err;
        }
        return 0;
}

void mq_clear_sbinfo(struct ipc_namespace *ns)
{
        ns->mq_mnt->mnt_sb->s_fs_info = NULL;
}

void mq_put_mnt(struct ipc_namespace *ns)
{
        mntput(ns->mq_mnt);
}

static int __init init_mqueue_fs(void)
{
        int error;

        mqueue_inode_cachep = kmem_cache_create("mqueue_inode_cache",
                                sizeof(struct mqueue_inode_info), 0,
                                SLAB_HWCACHE_ALIGN, init_once);
        if (mqueue_inode_cachep == NULL)
                return -ENOMEM;

        /* ignore failues - they are not fatal */
        mq_sysctl_table = mq_register_sysctl_table();

        error = register_filesystem(&mqueue_fs_type);
        if (error)
                goto out_sysctl;

        spin_lock_init(&mq_lock);

        init_ipc_ns.mq_mnt = kern_mount_data(&mqueue_fs_type, &init_ipc_ns);
        if (IS_ERR(init_ipc_ns.mq_mnt)) {
                error = PTR_ERR(init_ipc_ns.mq_mnt);
                goto out_filesystem;
        }

        return 0;

out_filesystem:
        unregister_filesystem(&mqueue_fs_type);
out_sysctl:
        if (mq_sysctl_table)
                unregister_sysctl_table(mq_sysctl_table);
        kmem_cache_destroy(mqueue_inode_cachep);
        return error;
}

__initcall(init_mqueue_fs);