队列的意思应该大家都清楚，不过还有有一些细节的地方不知道，下面是一个队列的源码，因该说这是队列的一部分，不是全部。而且是linux中队列，其他各种OS中队列大同小异。
/*
* 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/fs_context.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/vmalloc.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/user_namespace.h>
#include <linux/slab.h>
#include <linux/sched/wake_q.h>
#include <linux/sched/signal.h>
#include <linux/sched/user.h>
#include <net/sock.h>
#include "util.h"
struct mqueue_fs_context {
struct ipc_namespace *ipc_ns;
};
#define MQUEUE_MAGIC 0x19800202
#define DIRENT_SIZE 20
#define FILENT_SIZE 80
#define SEND 0
#define RECV 1
#define STATE_NONE 0
#define STATE_READY 1
struct posix_msg_tree_node {
struct rb_node rb_node;
struct list_head msg_list;
int priority;
};
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 rb_root msg_tree;
struct rb_node *msg_tree_rightmost;
struct posix_msg_tree_node *node_cache;
struct mq_attr attr;
struct sigevent notify;
struct pid *notify_owner;
struct user_namespace *notify_user_ns;
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 struct file_system_type mqueue_fs_type;
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 const struct fs_context_operations mqueue_fs_context_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;
}
/* Auxiliary functions to manipulate messages' list */
static int msg_insert(struct msg_msg *msg, struct mqueue_inode_info *info)
{
struct rb_node **p, *parent = NULL;
struct posix_msg_tree_node *leaf;
bool rightmost = true;
p = &info->msg_tree.rb_node;
while (*p) {
parent = *p;
leaf = rb_entry(parent, struct posix_msg_tree_node, rb_node);
if (likely(leaf->priority == msg->m_type))
goto insert_msg;
else if (msg->m_type < leaf->priority) {
p = &(*p)->rb_left;
rightmost = false;
} else
p = &(*p)->rb_right;
}
if (info->node_cache) {
leaf = info->node_cache;
info->node_cache = NULL;
} else {
leaf = kmalloc(sizeof(*leaf), GFP_ATOMIC);
if (!leaf)
return -ENOMEM;
INIT_LIST_HEAD(&leaf->msg_list);
}
leaf->priority = msg->m_type;
if (rightmost)
info->msg_tree_rightmost = &leaf->rb_node;
rb_link_node(&leaf->rb_node, parent, p);
rb_insert_color(&leaf->rb_node, &info->msg_tree);
insert_msg:
info->attr.mq_curmsgs++;
info->qsize += msg->m_ts;
list_add_tail(&msg->m_list, &leaf->msg_list);
return 0;
}
static inline void msg_tree_erase(struct posix_msg_tree_node *leaf,
struct mqueue_inode_info *info)
{
struct rb_node *node = &leaf->rb_node;
if (info->msg_tree_rightmost == node)
info->msg_tree_rightmost = rb_prev(node);
rb_erase(node, &info->msg_tree);
if (info->node_cache) {
kfree(leaf);
} else {
info->node_cache = leaf;
}
}
static inline struct msg_msg *msg_get(struct mqueue_inode_info *info)
{
struct rb_node *parent = NULL;
struct posix_msg_tree_node *leaf;
struct msg_msg *msg;
try_again:
/*
* During insert, low priorities go to the left and high to the
* right. On receive, we want the highest priorities first, so
* walk all the way to the right.
*/
parent = info->msg_tree_rightmost;
if (!parent) {
if (info->attr.mq_curmsgs) {
pr_warn_once("Inconsistency in POSIX message queue, "
"no tree element, but supposedly messages "
"should exist!
");
info->attr.mq_curmsgs = 0;
}
return NULL;
}
leaf = rb_entry(parent, struct posix_msg_tree_node, rb_node);
if (unlikely(list_empty(&leaf->msg_list))) {
pr_warn_once("Inconsistency in POSIX message queue, "
"empty leaf node but we haven't implemented "
"lazy leaf delete!
");
msg_tree_erase(leaf, info);
goto try_again;
} else {
msg = list_first_entry(&leaf->msg_list,
struct msg_msg, m_list);
list_del(&msg->m_list);
if (list_empty(&leaf->msg_list)) {
msg_tree_erase(leaf, info);
}
}
info->attr.mq_curmsgs--;
info->qsize -= msg->m_ts;
return msg;
}
static struct inode *mqueue_get_inode(struct super_block *sb,
struct ipc_namespace *ipc_ns, umode_t mode,
struct mq_attr *attr)
{
struct user_struct *u = current_user();
struct inode *inode;
int ret = -ENOMEM;
inode = new_inode(sb);
if (!inode)
goto err;
inode->i_ino = get_next_ino();
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(inode);
if (S_ISREG(mode)) {
struct mqueue_inode_info *info;
unsigned long mq_bytes, mq_treesize;
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->notify_owner = NULL;
info->notify_user_ns = NULL;
info->qsize = 0;
info->user = NULL; /* set when all is ok */
info->msg_tree = RB_ROOT;
info->msg_tree_rightmost = NULL;
info->node_cache = NULL;
memset(&info->attr, 0, sizeof(info->attr));
info->attr.mq_maxmsg = min(ipc_ns->mq_msg_max,
ipc_ns->mq_msg_default);
info->attr.mq_msgsize = min(ipc_ns->mq_msgsize_max,
ipc_ns->mq_msgsize_default);
if (attr) {
info->attr.mq_maxmsg = attr->mq_maxmsg;
info->attr.mq_msgsize = attr->mq_msgsize;
}
/*
* We used to allocate a static array of pointers and account
* the size of that array as well as one msg_msg struct per
* possible message into the queue size. That's no longer
* accurate as the queue is now an rbtree and will grow and
* shrink depending on usage patterns. We can, however, still
* account one msg_msg struct per message, but the nodes are
* allocated depending on priority usage, and most programs
* only use one, or a handful, of priorities. However, since
* this is pinned memory, we need to assume worst case, so
* that means the min(mq_maxmsg, max_priorities) * struct
* posix_msg_tree_node.
*/
ret = -EINVAL;
if (info->attr.mq_maxmsg <= 0 || info->attr.mq_msgsize <= 0)
goto out_inode;
if (capable(CAP_SYS_RESOURCE)) {
if (info->attr.mq_maxmsg > HARD_MSGMAX ||
info->attr.mq_msgsize > HARD_MSGSIZEMAX)
goto out_inode;
} else {
if (info->attr.mq_maxmsg > ipc_ns->mq_msg_max ||
info->attr.mq_msgsize > ipc_ns->mq_msgsize_max)
goto out_inode;
}
ret = -EOVERFLOW;
/* check for overflow */
if (info->attr.mq_msgsize > ULONG_MAX/info->attr.mq_maxmsg)
goto out_inode;
mq_treesize = info->attr.mq_maxmsg * sizeof(struct msg_msg) +
min_t(unsigned int, info->attr.mq_maxmsg, MQ_PRIO_MAX) *
sizeof(struct posix_msg_tree_node);
mq_bytes = info->attr.mq_maxmsg * info->attr.mq_msgsize;
if (mq_bytes + mq_treesize < mq_bytes)
goto out_inode;
mq_bytes += mq_treesize;
spin_lock(&mq_lock);
if (u->mq_bytes + mq_bytes < u->mq_bytes ||
u->mq_bytes + mq_bytes > rlimit(RLIMIT_MSGQUEUE)) {
spin_unlock(&mq_lock);
/* mqueue_evict_inode() releases info->messages */
ret = -EMFILE;
goto out_inode;
}
u->mq_bytes += mq_bytes;
spin_unlock(&mq_lock);
/* 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:
iput(inode);
err:
return ERR_PTR(ret);
}
static int mqueue_fill_super(struct super_block *sb, struct fs_context *fc)
{
struct inode *inode;
struct ipc_namespace *ns = sb->s_fs_info;
sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
sb->s_blocksize = PAGE_SIZE;
sb->s_blocksize_bits = PAGE_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 (IS_ERR(inode))
return PTR_ERR(inode);
sb->s_root = d_make_root(inode);
if (!sb->s_root)
return -ENOMEM;
return 0;
}
static int mqueue_get_tree(struct fs_context *fc)
{
struct mqueue_fs_context *ctx = fc->fs_private;
return get_tree_keyed(fc, mqueue_fill_super, ctx->ipc_ns);
}
static void mqueue_fs_context_free(struct fs_context *fc)
{
struct mqueue_fs_context *ctx = fc->fs_private;
put_ipc_ns(ctx->ipc_ns);
kfree(ctx);
}
static int mqueue_init_fs_context(struct fs_context *fc)
{
struct mqueue_fs_context *ctx;
ctx = kzalloc(sizeof(struct mqueue_fs_context), GFP_KERNEL);
if (!ctx)
return -ENOMEM;
ctx->ipc_ns = get_ipc_ns(current->nsproxy->ipc_ns);
put_user_ns(fc->user_ns);
fc->user_ns = get_user_ns(ctx->ipc_ns->user_ns);
fc->fs_private = ctx;
fc->ops = &mqueue_fs_context_ops;
return 0;
}
static struct vfsmount *mq_create_mount(struct ipc_namespace *ns)
{
struct mqueue_fs_context *ctx;
struct fs_context *fc;
struct vfsmount *mnt;
fc = fs_context_for_mount(&mqueue_fs_type, SB_KERNMOUNT);
if (IS_ERR(fc))
return ERR_CAST(fc);
ctx = fc->fs_private;
put_ipc_ns(ctx->ipc_ns);
ctx->ipc_ns = get_ipc_ns(ns);
put_user_ns(fc->user_ns);
fc->user_ns = get_user_ns(ctx->ipc_ns->user_ns);
mnt = fc_mount(fc);
put_fs_context(fc);
return 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_free_inode(struct inode *inode)
{
kmem_cache_free(mqueue_inode_cachep, MQUEUE_I(inode));
}
static void mqueue_evict_inode(struct inode *inode)
{
struct mqueue_inode_info *info;
struct user_struct *user;
struct ipc_namespace *ipc_ns;
struct msg_msg *msg, *nmsg;
LIST_HEAD(tmp_msg);
clear_inode(inode);
if (S_ISDIR(inode->i_mode))
return;
ipc_ns = get_ns_from_inode(inode);
info = MQUEUE_I(inode);
spin_lock(&info->lock);
while ((msg = msg_get(info)) != NULL)
list_add_tail(&msg->m_list, &tmp_msg);
kfree(info->node_cache);
spin_unlock(&info->lock);
list_for_each_entry_safe(msg, nmsg, &tmp_msg, m_list) {
list_del(&msg->m_list);
free_msg(msg);
}
user = info->user;
if (user) {
unsigned long mq_bytes, mq_treesize;
/* Total amount of bytes accounted for the mqueue */
mq_treesize = info->attr.mq_maxmsg * sizeof(struct msg_msg) +
min_t(unsigned int, info->attr.mq_maxmsg, MQ_PRIO_MAX) *
sizeof(struct posix_msg_tree_node);
mq_bytes = mq_treesize + (info->attr.mq_maxmsg *
info->attr.mq_msgsize);
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_attr(struct dentry *dentry, umode_t mode, void *arg)
{
struct inode *dir = dentry->d_parent->d_inode;
struct inode *inode;
struct mq_attr *attr = arg;
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 (IS_ERR(inode)) {
error = PTR_ERR(inode);
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(dir);
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_create(struct inode *dir, struct dentry *dentry,
umode_t mode, bool excl)
{
return mqueue_create_attr(dentry, mode, NULL);
}
static int mqueue_unlink(struct inode *dir, struct dentry *dentry)
{
struct inode *inode = d_inode(dentry);
dir->i_ctime = dir->i_mtime = dir->i_atime = current_time(dir);
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(file_inode(filp));
char buffer[FILENT_SIZE];
ssize_t ret;
spin_lock(&info->lock);
snprintf(buffer, sizeof(buffer),
"QSIZE:%-10lu NOTIFY:%-5d SIGNO:%-5d NOTIFY_PID:%-6d
",
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] = ' ';
ret = simple_read_from_buffer(u_data, count, off, buffer,
strlen(buffer));
if (ret <= 0)
return ret;
file_inode(filp)->i_atime = file_inode(filp)->i_ctime = current_time(file_inode(filp));
return ret;
}
static int mqueue_flush_file(struct file *filp, fl_owner_t id)
{
struct mqueue_inode_info *info = MQUEUE_I(file_inode(filp));
spin_lock(&info->lock);
if (task_tgid(current) == info->notify_owner)
remove_notification(info);
spin_unlock(&info->lock);
return 0;
}
static __poll_t mqueue_poll_file(struct file *filp, struct poll_table_struct *poll_tab)
{
struct mqueue_inode_info *info = MQUEUE_I(file_inode(filp));
__poll_t retval = 0;
poll_wait(filp, &info->wait_q, poll_tab);
spin_lock(&info->lock);
if (info->attr.mq_curmsgs)
retval = EPOLLIN | EPOLLRDNORM;
if (info->attr.mq_curmsgs < info->attr.mq_maxmsg)
retval |= EPOLLOUT | EPOLLWRNORM;
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;
list_for_each_entry(walk, &info->e_wait_q[sr].list, list) {
if (walk->task->prio <= current->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,
ktime_t *timeout, struct ext_wait_queue *ewp)
__releases(&info->lock)
{
int retval;
signed long time;
wq_add(info, sr, ewp);
for (;;) {
__set_current_state(TASK_INTERRUPTIBLE);
spin_unlock(&info->lock);
time = schedule_hrtimeout_range_clock(timeout, 0,
HRTIMER_MODE_ABS, CLOCK_REALTIME);
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);
}
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 kernel_siginfo sig_i;
switch (info->notify.sigev_notify) {
case SIGEV_NONE:
break;
case SIGEV_SIGNAL:
/* sends signal */
clear_siginfo(&sig_i);
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;
/* map current pid/uid into info->owner's namespaces */
rcu_read_lock();
sig_i.si_pid = task_tgid_nr_ns(current,
ns_of_pid(info->notify_owner));
sig_i.si_uid = from_kuid_munged(info->notify_user_ns, current_uid());
rcu_read_unlock();
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);
put_user_ns(info->notify_user_ns);
info->notify_owner = NULL;
info->notify_user_ns = NULL;
}
wake_up(&info->wait_q);
}
static int prepare_timeout(const struct __kernel_timespec __user *u_abs_timeout,
struct timespec64 *ts)
{
if (get_timespec64(ts, u_abs_timeout))
return -EFAULT;
if (!timespec64_valid(ts))
return -EINVAL;
return 0;
}
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);
put_user_ns(info->notify_user_ns);
info->notify_owner = NULL;
info->notify_user_ns = NULL;
}
static int prepare_open(struct dentry *dentry, int oflag, int ro,
umode_t mode, struct filename *name,
struct mq_attr *attr)
{
static const int oflag2acc[O_ACCMODE] = { MAY_READ, MAY_WRITE,
MAY_READ | MAY_WRITE };
int acc;
if (d_really_is_negative(dentry)) {
if (!(oflag & O_CREAT))
return -ENOENT;
if (ro)
return ro;
audit_inode_parent_hidden(name, dentry->d_parent);
return vfs_mkobj(dentry, mode & ~current_umask(),
mqueue_create_attr, attr);
}
/* it already existed */
audit_inode(name, dentry, 0);
if ((oflag & (O_CREAT|O_EXCL)) == (O_CREAT|O_EXCL))
return -EEXIST;
if ((oflag & O_ACCMODE) == (O_RDWR | O_WRONLY))
return -EINVAL;
acc = oflag2acc[oflag & O_ACCMODE];
return inode_permission(d_inode(dentry), acc);
}
static int do_mq_open(const char __user *u_name, int oflag, umode_t mode,
struct mq_attr *attr)
{
struct vfsmount *mnt = current->nsproxy->ipc_ns->mq_mnt;
struct dentry *root = mnt->mnt_root;
struct filename *name;
struct path path;
int fd, error;
int ro;
audit_mq_open(oflag, mode, attr);
if (IS_ERR(name = getname(u_name)))
return PTR_ERR(name);
fd = get_unused_fd_flags(O_CLOEXEC);
if (fd < 0)
goto out_putname;
ro = mnt_want_write(mnt); /* we'll drop it in any case */
inode_lock(d_inode(root));
path.dentry = lookup_one_len(name->name, root, strlen(name->name));
if (IS_ERR(path.dentry)) {
error = PTR_ERR(path.dentry);
goto out_putfd;
}
path.mnt = mntget(mnt);
error = prepare_open(path.dentry, oflag, ro, mode, name, attr);
if (!error) {
struct file *file = dentry_open(&path, oflag, current_cred());
if (!IS_ERR(file))
fd_install(fd, file);
else
error = PTR_ERR(file);
}
path_put(&path);
out_putfd:
if (error) {
put_unused_fd(fd);
fd = error;
}
inode_unlock(d_inode(root));
if (!ro)
mnt_drop_write(mnt);
out_putname:
putname(name);
return fd;
}
SYSCALL_DEFINE4(mq_open, const char __user *, u_name, int, oflag, umode_t, mode,
struct mq_attr __user *, u_attr)
{
struct mq_attr attr;
if (u_attr && copy_from_user(&attr, u_attr, sizeof(struct mq_attr)))
return -EFAULT;
return do_mq_open(u_name, oflag, mode, u_attr ? &attr : NULL);
}
SYSCALL_DEFINE1(mq_unlink, const char __user *, u_name)
{
int err;
struct filename *name;
struct dentry *dentry;
struct inode *inode = NULL;
struct ipc_namespace *ipc_ns = current->nsproxy->ipc_ns;
struct vfsmount *mnt = ipc_ns->mq_mnt;
name = getname(u_name);
if (IS_ERR(name))
return PTR_ERR(name);
audit_inode_parent_hidden(name, mnt->mnt_root);
err = mnt_want_write(mnt);
if (err)
goto out_name;
inode_lock_nested(d_inode(mnt->mnt_root), I_MUTEX_PARENT);
dentry = lookup_one_len(name->name, mnt->mnt_root,
strlen(name->name));
if (IS_ERR(dentry)) {
err = PTR_ERR(dentry);
goto out_unlock;
}
inode = d_inode(dentry);
if (!inode) {
err = -ENOENT;
} else {
ihold(inode);
err = vfs_unlink(d_inode(dentry->d_parent), dentry, NULL);
}
dput(dentry);
out_unlock:
inode_unlock(d_inode(mnt->mnt_root));
if (inode)
iput(inode);
mnt_drop_write(mnt);
out_name:
putname(name);
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:
*
* - Set pointer to message.
* - Queue the receiver task for later wakeup (without the info->lock).
* - Update its state to STATE_READY. Now the receiver can continue.
* - Wake up the process after the lock is dropped. Should the process wake up
* before this wakeup (due to a timeout or a signal) it will either see
* STATE_READY and continue or acquire the lock to check the state again.
*
* 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 wake_q_head *wake_q,
struct mqueue_inode_info *info,
struct msg_msg *message,
struct ext_wait_queue *receiver)
{
receiver->msg = message;
list_del(&receiver->list);
wake_q_add(wake_q, receiver->task);
/*
* Rely on the implicit cmpxchg barrier from wake_q_add such
* that we can ensure that updating receiver->state is the last
* write operation: As once set, the receiver can continue,
* and if we don't have the reference count from the wake_q,
* yet, at that point we can later have a use-after-free
* condition and bogus wakeup.
*/
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 wake_q_head *wake_q,
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;
}
if (msg_insert(sender->msg, info))
return;
list_del(&sender->list);
wake_q_add(wake_q, sender->task);
sender->state = STATE_READY;
}
static int do_mq_timedsend(mqd_t mqdes, const char __user *u_msg_ptr,
size_t msg_len, unsigned int msg_prio,
struct timespec64 *ts)
{
struct fd f;
struct inode *inode;
struct ext_wait_queue wait;
struct ext_wait_queue *receiver;
struct msg_msg *msg_ptr;
struct mqueue_inode_info *info;
ktime_t expires, *timeout = NULL;
struct posix_msg_tree_node *new_leaf = NULL;
int ret = 0;
DEFINE_WAKE_Q(wake_q);
if (unlikely(msg_prio >= (unsigned long) MQ_PRIO_MAX))
return -EINVAL;
if (ts) {
expires = timespec64_to_ktime(*ts);
timeout = &expires;
}
audit_mq_sendrecv(mqdes, msg_len, msg_prio, ts);
f = fdget(mqdes);
if (unlikely(!f.file)) {
ret = -EBADF;
goto out;
}
inode = file_inode(f.file);
if (unlikely(f.file->f_op != &mqueue_file_operations)) {
ret = -EBADF;
goto out_fput;
}
info = MQUEUE_I(inode);
audit_file(f.file);
if (unlikely(!(f.file->f_mode & FMODE_WRITE))) {
ret = -EBADF;
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;
/*
* msg_insert really wants us to have a valid, spare node struct so
* it doesn't have to kmalloc a GFP_ATOMIC allocation, but it will
* fall back to that if necessary.
*/
if (!info->node_cache)
new_leaf = kmalloc(sizeof(*new_leaf), GFP_KERNEL);
spin_lock(&info->lock);
if (!info->node_cache && new_leaf) {
/* Save our speculative allocation into the cache */
INIT_LIST_HEAD(&new_leaf->msg_list);
info->node_cache = new_leaf;
new_leaf = NULL;
} else {
kfree(new_leaf);
}
if (info->attr.mq_curmsgs == info->attr.mq_maxmsg) {
if (f.file->f_flags & O_NONBLOCK) {
ret = -EAGAIN;
} else {
wait.task = current;
wait.msg = (void *) msg_ptr;
wait.state = STATE_NONE;
ret = wq_sleep(info, SEND, timeout, &wait);
/*
* wq_sleep must be called with info->lock held, and
* returns with the lock released
*/
goto out_free;
}
} else {
receiver = wq_get_first_waiter(info, RECV);
if (receiver) {
pipelined_send(&wake_q, info, msg_ptr, receiver);
} else {
/* adds message to the queue */
ret = msg_insert(msg_ptr, info);
if (ret)
goto out_unlock;
__do_notify(info);
}
inode->i_atime = inode->i_mtime = inode->i_ctime =
current_time(inode);
}
out_unlock:
spin_unlock(&info->lock);
wake_up_q(&wake_q);
out_free:
if (ret)
free_msg(msg_ptr);
out_fput:
fdput(f);
out:
return ret;
}
static int do_mq_timedreceive(mqd_t mqdes, char __user *u_msg_ptr,
size_t msg_len, unsigned int __user *u_msg_prio,
struct timespec64 *ts)
{
ssize_t ret;
struct msg_msg *msg_ptr;
struct fd f;
struct inode *inode;
struct mqueue_inode_info *info;
struct ext_wait_queue wait;
ktime_t expires, *timeout = NULL;
struct posix_msg_tree_node *new_leaf = NULL;
if (ts) {
expires = timespec64_to_ktime(*ts);
timeout = &expires;
}
audit_mq_sendrecv(mqdes, msg_len, 0, ts);
f = fdget(mqdes);
if (unlikely(!f.file)) {
ret = -EBADF;
goto out;
}
inode = file_inode(f.file);
if (unlikely(f.file->f_op != &mqueue_file_operations)) {
ret = -EBADF;
goto out_fput;
}
info = MQUEUE_I(inode);
audit_file(f.file);
if (unlikely(!(f.file->f_mode & FMODE_READ))) {
ret = -EBADF;
goto out_fput;
}
/* checks if buffer is big enough */
if (unlikely(msg_len < info->attr.mq_msgsize)) {
ret = -EMSGSIZE;
goto out_fput;
}
/*
* msg_insert really wants us to have a valid, spare node struct so
* it doesn't have to kmalloc a GFP_ATOMIC allocation, but it will
* fall back to that if necessary.
*/
if (!info->node_cache)
new_leaf = kmalloc(sizeof(*new_leaf), GFP_KERNEL);
spin_lock(&info->lock);
if (!info->node_cache && new_leaf) {
/* Save our speculative allocation into the cache */
INIT_LIST_HEAD(&new_leaf->msg_list);
info->node_cache = new_leaf;
} else {
kfree(new_leaf);
}
if (info->attr.mq_curmsgs == 0) {
if (f.file->f_flags & O_NONBLOCK) {
spin_unlock(&info->lock);
ret = -EAGAIN;
} else {
wait.task = current;
wait.state = STATE_NONE;
ret = wq_sleep(info, RECV, timeout, &wait);
msg_ptr = wait.msg;
}
} else {
DEFINE_WAKE_Q(wake_q);
msg_ptr = msg_get(info);
inode->i_atime = inode->i_mtime = inode->i_ctime =
current_time(inode);
/* There is now free space in queue. */
pipelined_receive(&wake_q, info);
spin_unlock(&info->lock);
wake_up_q(&wake_q);
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:
fdput(f);
out:
return ret;
}
SYSCALL_DEFINE5(mq_timedsend, mqd_t, mqdes, const char __user *, u_msg_ptr,
size_t, msg_len, unsigned int, msg_prio,
const struct __kernel_timespec __user *, u_abs_timeout)
{
struct timespec64 ts, *p = NULL;
if (u_abs_timeout) {
int res = prepare_timeout(u_abs_timeout, &ts);
if (res)
return res;
p = &ts;
}
return do_mq_timedsend(mqdes, u_msg_ptr, msg_len, msg_prio, p);
}
SYSCALL_DEFINE5(mq_timedreceive, mqd_t, mqdes, char __user *, u_msg_ptr,
size_t, msg_len, unsigned int __user *, u_msg_prio,
const struct __kernel_timespec __user *, u_abs_timeout)
{
struct timespec64 ts, *p = NULL;
if (u_abs_timeout) {
int res = prepare_timeout(u_abs_timeout, &ts);
if (res)
return res;
p = &ts;
}
return do_mq_timedreceive(mqdes, u_msg_ptr, msg_len, u_msg_prio, p);
}
/*
* 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.
*/
static int do_mq_notify(mqd_t mqdes, const struct sigevent *notification)
{
int ret;
struct fd f;
struct sock *sock;
struct inode *inode;
struct mqueue_inode_info *info;
struct sk_buff *nc;
audit_mq_notify(mqdes, notification);
nc = NULL;
sock = NULL;
if (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);
if (!nc)
return -ENOMEM;
if (copy_from_user(nc->data,
notification->sigev_value.sival_ptr,
NOTIFY_COOKIE_LEN)) {
ret = -EFAULT;
goto free_skb;
}
/* TODO: add a header? */
skb_put(nc, NOTIFY_COOKIE_LEN);
/* and attach it to the socket */
retry:
f = fdget(notification->sigev_signo);
if (!f.file) {
ret = -EBADF;
goto out;
}
sock = netlink_getsockbyfilp(f.file);
fdput(f);
if (IS_ERR(sock)) {
ret = PTR_ERR(sock);
goto free_skb;
}
timeo = MAX_SCHEDULE_TIMEOUT;
ret = netlink_attachskb(sock, nc, &timeo, NULL);
if (ret == 1) {
sock = NULL;
goto retry;
}
if (ret)
return ret;
}
}
f = fdget(mqdes);
if (!f.file) {
ret = -EBADF;
goto out;
}
inode = file_inode(f.file);
if (unlikely(f.file->f_op != &mqueue_file_operations)) {
ret = -EBADF;
goto out_fput;
}
info = MQUEUE_I(inode);
ret = 0;
spin_lock(&info->lock);
if (notification == NULL) {
if (info->notify_owner == task_tgid(current)) {
remove_notification(info);
inode->i_atime = inode->i_ctime = current_time(inode);
}
} 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));
info->notify_user_ns = get_user_ns(current_user_ns());
inode->i_atime = inode->i_ctime = current_time(inode);
}
spin_unlock(&info->lock);
out_fput:
fdput(f);
out:
if (sock)
netlink_detachskb(sock, nc);
else
free_skb:
dev_kfree_skb(nc);
return ret;
}
SYSCALL_DEFINE2(mq_notify, mqd_t, mqdes,
const struct sigevent __user *, u_notification)
{
struct sigevent n, *p = NULL;
if (u_notification) {
if (copy_from_user(&n, u_notification, sizeof(struct sigevent)))
return -EFAULT;
p = &n;
}
return do_mq_notify(mqdes, p);
}
static int do_mq_getsetattr(int mqdes, struct mq_attr *new, struct mq_attr *old)
{
struct fd f;
struct inode *inode;
struct mqueue_inode_info *info;
if (new && (new->mq_flags & (~O_NONBLOCK)))
return -EINVAL;
f = fdget(mqdes);
if (!f.file)
return -EBADF;
if (unlikely(f.file->f_op != &mqueue_file_operations)) {
fdput(f);
return -EBADF;
}
inode = file_inode(f.file);
info = MQUEUE_I(inode);
spin_lock(&info->lock);
if (old) {
*old = info->attr;
old->mq_flags = f.file->f_flags & O_NONBLOCK;
}
if (new) {
audit_mq_getsetattr(mqdes, new);
spin_lock(&f.file->f_lock);
if (new->mq_flags & O_NONBLOCK)
f.file->f_flags |= O_NONBLOCK;
else
f.file->f_flags &= ~O_NONBLOCK;
spin_unlock(&f.file->f_lock);
inode->i_atime = inode->i_ctime = current_time(inode);
}
spin_unlock(&info->lock);
fdput(f);
return 0;
}
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 mq_attr *new = NULL, *old = NULL;
if (u_mqstat) {
new = &mqstat;
if (copy_from_user(new, u_mqstat, sizeof(struct mq_attr)))
return -EFAULT;
}
if (u_omqstat)
old = &omqstat;
ret = do_mq_getsetattr(mqdes, new, old);
if (ret || !old)
return ret;
if (copy_to_user(u_omqstat, old, sizeof(struct mq_attr)))
return -EFAULT;
return 0;
}
#ifdef CONFIG_COMPAT
struct compat_mq_attr {
compat_long_t mq_flags; /* message queue flags */
compat_long_t mq_maxmsg; /* maximum number of messages */
compat_long_t mq_msgsize; /* maximum message size */
compat_long_t mq_curmsgs; /* number of messages currently queued */
compat_long_t __reserved[4]; /* ignored for input, zeroed for output */
};
static inline int get_compat_mq_attr(struct mq_attr *attr,
const struct compat_mq_attr __user *uattr)
{
struct compat_mq_attr v;
if (copy_from_user(&v, uattr, sizeof(*uattr)))
return -EFAULT;
memset(attr, 0, sizeof(*attr));
attr->mq_flags = v.mq_flags;
attr->mq_maxmsg = v.mq_maxmsg;
attr->mq_msgsize = v.mq_msgsize;
attr->mq_curmsgs = v.mq_curmsgs;
return 0;
}
static inline int put_compat_mq_attr(const struct mq_attr *attr,
struct compat_mq_attr __user *uattr)
{
struct compat_mq_attr v;
memset(&v, 0, sizeof(v));
v.mq_flags = attr->mq_flags;
v.mq_maxmsg = attr->mq_maxmsg;
v.mq_msgsize = attr->mq_msgsize;
v.mq_curmsgs = attr->mq_curmsgs;
if (copy_to_user(uattr, &v, sizeof(*uattr)))
return -EFAULT;
return 0;
}
COMPAT_SYSCALL_DEFINE4(mq_open, const char __user *, u_name,
int, oflag, compat_mode_t, mode,
struct compat_mq_attr __user *, u_attr)
{
struct mq_attr attr, *p = NULL;
if (u_attr && oflag & O_CREAT) {
p = &attr;
if (get_compat_mq_attr(&attr, u_attr))
return -EFAULT;
}
return do_mq_open(u_name, oflag, mode, p);
}
COMPAT_SYSCALL_DEFINE2(mq_notify, mqd_t, mqdes,
const struct compat_sigevent __user *, u_notification)
{
struct sigevent n, *p = NULL;
if (u_notification) {
if (get_compat_sigevent(&n, u_notification))
return -EFAULT;
if (n.sigev_notify == SIGEV_THREAD)
n.sigev_value.sival_ptr = compat_ptr(n.sigev_value.sival_int);
p = &n;
}
return do_mq_notify(mqdes, p);
}
COMPAT_SYSCALL_DEFINE3(mq_getsetattr, mqd_t, mqdes,
const struct compat_mq_attr __user *, u_mqstat,
struct compat_mq_attr __user *, u_omqstat)
{
int ret;
struct mq_attr mqstat, omqstat;
struct mq_attr *new = NULL, *old = NULL;
if (u_mqstat) {
new = &mqstat;
if (get_compat_mq_attr(new, u_mqstat))
return -EFAULT;
}
if (u_omqstat)
old = &omqstat;
ret = do_mq_getsetattr(mqdes, new, old);
if (ret || !old)
return ret;
if (put_compat_mq_attr(old, u_omqstat))
return -EFAULT;
return 0;
}
#endif
#ifdef CONFIG_COMPAT_32BIT_TIME
static int compat_prepare_timeout(const struct old_timespec32 __user *p,
struct timespec64 *ts)
{
if (get_old_timespec32(ts, p))
return -EFAULT;
if (!timespec64_valid(ts))
return -EINVAL;
return 0;
}
SYSCALL_DEFINE5(mq_timedsend_time32, mqd_t, mqdes,
const char __user *, u_msg_ptr,
unsigned int, msg_len, unsigned int, msg_prio,
const struct old_timespec32 __user *, u_abs_timeout)
{
struct timespec64 ts, *p = NULL;
if (u_abs_timeout) {
int res = compat_prepare_timeout(u_abs_timeout, &ts);
if (res)
return res;
p = &ts;
}
return do_mq_timedsend(mqdes, u_msg_ptr, msg_len, msg_prio, p);
}
SYSCALL_DEFINE5(mq_timedreceive_time32, mqd_t, mqdes,
char __user *, u_msg_ptr,
unsigned int, msg_len, unsigned int __user *, u_msg_prio,
const struct old_timespec32 __user *, u_abs_timeout)
{
struct timespec64 ts, *p = NULL;
if (u_abs_timeout) {
int res = compat_prepare_timeout(u_abs_timeout, &ts);
if (res)
return res;
p = &ts;
}
return do_mq_timedreceive(mqdes, u_msg_ptr, msg_len, u_msg_prio, p);
}
#endif
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,
.llseek = default_llseek,
};
static const struct super_operations mqueue_super_ops = {
.alloc_inode = mqueue_alloc_inode,
.free_inode = mqueue_free_inode,
.evict_inode = mqueue_evict_inode,
.statfs = simple_statfs,
};
static const struct fs_context_operations mqueue_fs_context_ops = {
.free = mqueue_fs_context_free,
.get_tree = mqueue_get_tree,
};
static struct file_system_type mqueue_fs_type = {
.name = "mqueue",
.init_fs_context = mqueue_init_fs_context,
.kill_sb = kill_litter_super,
.fs_flags = FS_USERNS_MOUNT,
};
int mq_init_ns(struct ipc_namespace *ns)
{
struct vfsmount *m;
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_msg_default = DFLT_MSG;
ns->mq_msgsize_default = DFLT_MSGSIZE;
m = mq_create_mount(ns);
if (IS_ERR(m))
return PTR_ERR(m);
ns->mq_mnt = m;
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)
{
kern_unmount(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|SLAB_ACCOUNT, init_once);
if (mqueue_inode_cachep == NULL)
return -ENOMEM;
/* ignore failures - 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);
error = mq_init_ns(&init_ipc_ns);
if (error)
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;
}
device_initcall(init_mqueue_fs);