Commit 36735a6a authored by Al Viro's avatar Al Viro
Browse files

mqueue: switch to on-demand creation of internal mount 



Instead of doing that upon each ipcns creation, we do that the first
time mq_open(2) or mqueue mount is done in an ipcns.  What's more,
doing that allows to get rid of mount_ns() use - we can go with
considerably cheaper mount_nodev(), avoiding the loop over all
mqueue superblock instances; ipcns->mq_mnt is used to locate preexisting
instance in O(1) time instead of O(instances) mount_ns() would've
cost us.

Based upon the version by Giuseppe Scrivano <gscrivan@redhat.com>; I've
added handling of userland mqueue mounts (original had been broken in
that area) and added a switch to mount_nodev().

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent a713fd7f

ipc/mqueue.c

+55 −19
Original line number Diff line number Diff line
@@ -325,8 +325,9 @@ err: 
static int mqueue_fill_super(struct super_block *sb, void *data, int silent)

{

	struct inode *inode;

	struct ipc_namespace *ns = sb->s_fs_info;

	struct ipc_namespace *ns = data;



	sb->s_fs_info = ns;

	sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;

	sb->s_blocksize = PAGE_SIZE;

	sb->s_blocksize_bits = PAGE_SHIFT;
@@ -343,18 +344,44 @@ static int mqueue_fill_super(struct super_block *sb, void *data, int silent) 
	return 0;

}



static struct file_system_type mqueue_fs_type;

/*

 * Return value is pinned only by reference in ->mq_mnt; it will

 * live until ipcns dies.  Caller does not need to drop it.

 */

static struct vfsmount *mq_internal_mount(void)

{

	struct ipc_namespace *ns = current->nsproxy->ipc_ns;

	struct vfsmount *m = ns->mq_mnt;

	if (m)

		return m;

	m = kern_mount_data(&mqueue_fs_type, ns);

	spin_lock(&mq_lock);

	if (unlikely(ns->mq_mnt)) {

		spin_unlock(&mq_lock);

		if (!IS_ERR(m))

			kern_unmount(m);

		return ns->mq_mnt;

	}

	if (!IS_ERR(m))

		ns->mq_mnt = m;

	spin_unlock(&mq_lock);

	return m;

}



static struct dentry *mqueue_mount(struct file_system_type *fs_type,

			 int flags, const char *dev_name,

			 void *data)

{

	struct ipc_namespace *ns;

	if (flags & SB_KERNMOUNT) {

		ns = data;

		data = NULL;

	} else {

		ns = current->nsproxy->ipc_ns;

	}

	return mount_ns(fs_type, flags, data, ns, ns->user_ns, mqueue_fill_super);

	struct vfsmount *m;

	if (flags & SB_KERNMOUNT)

		return mount_nodev(fs_type, flags, data, mqueue_fill_super);

	m = mq_internal_mount();

	if (IS_ERR(m))

		return ERR_CAST(m);

	atomic_inc(&m->mnt_sb->s_active);

	down_write(&m->mnt_sb->s_umount);

	return dget(m->mnt_root);

}



static void init_once(void *foo)
@@ -743,13 +770,16 @@ static int prepare_open(struct dentry *dentry, int oflag, int ro, 
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 vfsmount *mnt = mq_internal_mount();

	struct dentry *root;

	struct filename *name;

	struct path path;

	int fd, error;

	int ro;



	if (IS_ERR(mnt))

		return PTR_ERR(mnt);



	audit_mq_open(oflag, mode, attr);



	if (IS_ERR(name = getname(u_name)))
@@ -760,6 +790,7 @@ static int do_mq_open(const char __user *u_name, int oflag, umode_t mode, 
		goto out_putname;



	ro = mnt_want_write(mnt);	/* we'll drop it in any case */

	root = mnt->mnt_root;

	inode_lock(d_inode(root));

	path.dentry = lookup_one_len(name->name, root, strlen(name->name));

	if (IS_ERR(path.dentry)) {
@@ -808,6 +839,9 @@ SYSCALL_DEFINE1(mq_unlink, const char __user *, u_name) 
	struct ipc_namespace *ipc_ns = current->nsproxy->ipc_ns;

	struct vfsmount *mnt = ipc_ns->mq_mnt;



	if (!mnt)

		return -ENOENT;



	name = getname(u_name);

	if (IS_ERR(name))

		return PTR_ERR(name);
@@ -1534,28 +1568,26 @@ int mq_init_ns(struct ipc_namespace *ns) 
	ns->mq_msgsize_max   = DFLT_MSGSIZEMAX;

	ns->mq_msg_default   = DFLT_MSG;

	ns->mq_msgsize_default  = DFLT_MSGSIZE;



	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)

{

	if (ns->mq_mnt)

		ns->mq_mnt->mnt_sb->s_fs_info = NULL;

}



void mq_put_mnt(struct ipc_namespace *ns)

{

	if (ns->mq_mnt)

		kern_unmount(ns->mq_mnt);

}



static int __init init_mqueue_fs(void)

{

	struct vfsmount *m;

	int error;



	mqueue_inode_cachep = kmem_cache_create("mqueue_inode_cache",
@@ -1577,6 +1609,10 @@ static int __init init_mqueue_fs(void) 
	if (error)

		goto out_filesystem;



	m = kern_mount_data(&mqueue_fs_type, &init_ipc_ns);

	if (IS_ERR(m))

		goto out_filesystem;

	init_ipc_ns.mq_mnt = m;

	return 0;



out_filesystem:

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