autofs4: add miscellaneous device for ioctls

Add a miscellaneous device to the autofs4 module for routing ioctls.  This
provides the ability to obtain an ioctl file handle for an autofs mount
point that is possibly covered by another mount.

The actual problem with autofs is that it can't reconnect to existing
mounts.  Immediately one things of just adding the ability to remount
autofs file systems would solve it, but alas, that can't work.  This is
because autofs direct mounts and the implementation of "on demand mount
and expire" of nested mount trees have the file system mounted on top of
the mount trigger dentry.

To resolve this a miscellaneous device node for routing ioctl commands to
these mount points has been implemented in the autofs4 kernel module and a
library added to autofs.  This provides the ability to open a file
descriptor for these over mounted autofs mount points.

Please refer to Documentation/filesystems/autofs4-mount-control.txt for a
discussion of the problem, implementation alternatives considered and a
description of the interface.

[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: build fix]
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 915 insertions, 12 deletions

diff --git a/fs/autofs4/Makefile b/fs/autofs4/Makefile
index f2c3b79e94d..a811c1f7d9a 100644
--- a/fs/autofs4/Makefile
+++ b/fs/autofs4/Makefile
@@ -4,4 +4,4 @@
 
 obj-$(CONFIG_AUTOFS4_FS) += autofs4.o
 
-autofs4-objs := init.o inode.o root.o symlink.o waitq.o expire.o
+autofs4-objs := init.o inode.o root.o symlink.o waitq.o expire.o dev-ioctl.o
diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
index fa76d18be08..e0f16da00e5 100644
--- a/fs/autofs4/autofs_i.h
+++ b/fs/autofs4/autofs_i.h
@@ -14,6 +14,7 @@
 /* Internal header file for autofs */
 
 #include <linux/auto_fs4.h>
+#include <linux/auto_dev-ioctl.h>
 #include <linux/mutex.h>
 #include <linux/list.h>
 
@@ -21,6 +22,9 @@
 #define AUTOFS_IOC_FIRST     AUTOFS_IOC_READY
 #define AUTOFS_IOC_COUNT     32
 
+#define AUTOFS_DEV_IOCTL_IOC_FIRST	(AUTOFS_DEV_IOCTL_VERSION)
+#define AUTOFS_DEV_IOCTL_IOC_COUNT	(AUTOFS_IOC_COUNT - 11)
+
 #define AUTOFS_TYPE_TRIGGER	(AUTOFS_TYPE_DIRECT|AUTOFS_TYPE_OFFSET)
 
 #include <linux/kernel.h>
@@ -37,11 +41,27 @@
 /* #define DEBUG */
 
 #ifdef DEBUG
-#define DPRINTK(fmt,args...) do { printk(KERN_DEBUG "pid %d: %s: " fmt "\n" , current->pid , __func__ , ##args); } while(0)
+#define DPRINTK(fmt, args...)				\
+do {							\
+	printk(KERN_DEBUG "pid %d: %s: " fmt "\n",	\
+		current->pid, __func__, ##args);	\
+} while (0)
 #else
-#define DPRINTK(fmt,args...) do {} while(0)
+#define DPRINTK(fmt, args...) do {} while (0)
 #endif
 
+#define AUTOFS_WARN(fmt, args...)			\
+do {							\
+	printk(KERN_WARNING "pid %d: %s: " fmt "\n",	\
+		current->pid, __func__, ##args);	\
+} while (0)
+
+#define AUTOFS_ERROR(fmt, args...)			\
+do {							\
+	printk(KERN_ERR "pid %d: %s: " fmt "\n",	\
+		current->pid, __func__, ##args);	\
+} while (0)
+
 /* Unified info structure.  This is pointed to by both the dentry and
    inode structures.  Each file in the filesystem has an instance of this
    structure.  It holds a reference to the dentry, so dentries are never
@@ -170,6 +190,17 @@ int autofs4_expire_run(struct super_block *, struct vfsmount *,
 			struct autofs_packet_expire __user *);
 int autofs4_expire_multi(struct super_block *, struct vfsmount *,
 			struct autofs_sb_info *, int __user *);
+struct dentry *autofs4_expire_direct(struct super_block *sb,
+				     struct vfsmount *mnt,
+				     struct autofs_sb_info *sbi, int how);
+struct dentry *autofs4_expire_indirect(struct super_block *sb,
+				       struct vfsmount *mnt,
+				       struct autofs_sb_info *sbi, int how);
+
+/* Device node initialization */
+
+int autofs_dev_ioctl_init(void);
+void autofs_dev_ioctl_exit(void);
 
 /* Operations structures */
 
diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
new file mode 100644
index 00000000000..625abf5422e
--- /dev/null
+++ b/fs/autofs4/dev-ioctl.c
@@ -0,0 +1,863 @@
+/*
+ * Copyright 2008 Red Hat, Inc. All rights reserved.
+ * Copyright 2008 Ian Kent <raven@themaw.net>
+ *
+ * This file is part of the Linux kernel and is made available under
+ * the terms of the GNU General Public License, version 2, or at your
+ * option, any later version, incorporated herein by reference.
+ */
+
+#include <linux/module.h>
+#include <linux/vmalloc.h>
+#include <linux/miscdevice.h>
+#include <linux/init.h>
+#include <linux/wait.h>
+#include <linux/namei.h>
+#include <linux/fcntl.h>
+#include <linux/file.h>
+#include <linux/fdtable.h>
+#include <linux/sched.h>
+#include <linux/compat.h>
+#include <linux/syscalls.h>
+#include <linux/smp_lock.h>
+#include <linux/magic.h>
+#include <linux/dcache.h>
+#include <linux/uaccess.h>
+
+#include "autofs_i.h"
+
+/*
+ * This module implements an interface for routing autofs ioctl control
+ * commands via a miscellaneous device file.
+ *
+ * The alternate interface is needed because we need to be able open
+ * an ioctl file descriptor on an autofs mount that may be covered by
+ * another mount. This situation arises when starting automount(8)
+ * or other user space daemon which uses direct mounts or offset
+ * mounts (used for autofs lazy mount/umount of nested mount trees),
+ * which have been left busy at at service shutdown.
+ */
+
+#define AUTOFS_DEV_IOCTL_SIZE	sizeof(struct autofs_dev_ioctl)
+
+typedef int (*ioctl_fn)(struct file *, struct autofs_sb_info *,
+			struct autofs_dev_ioctl *);
+
+static int check_name(const char *name)
+{
+	if (!strchr(name, '/'))
+		return -EINVAL;
+	return 0;
+}
+
+/*
+ * Check a string doesn't overrun the chunk of
+ * memory we copied from user land.
+ */
+static int invalid_str(char *str, void *end)
+{
+	while ((void *) str <= end)
+		if (!*str++)
+			return 0;
+	return -EINVAL;
+}
+
+/*
+ * Check that the user compiled against correct version of autofs
+ * misc device code.
+ *
+ * As well as checking the version compatibility this always copies
+ * the kernel interface version out.
+ */
+static int check_dev_ioctl_version(int cmd, struct autofs_dev_ioctl *param)
+{
+	int err = 0;
+
+	if ((AUTOFS_DEV_IOCTL_VERSION_MAJOR != param->ver_major) ||
+	    (AUTOFS_DEV_IOCTL_VERSION_MINOR < param->ver_minor)) {
+		AUTOFS_WARN("ioctl control interface version mismatch: "
+		     "kernel(%u.%u), user(%u.%u), cmd(%d)",
+		     AUTOFS_DEV_IOCTL_VERSION_MAJOR,
+		     AUTOFS_DEV_IOCTL_VERSION_MINOR,
+		     param->ver_major, param->ver_minor, cmd);
+		err = -EINVAL;
+	}
+
+	/* Fill in the kernel version. */
+	param->ver_major = AUTOFS_DEV_IOCTL_VERSION_MAJOR;
+	param->ver_minor = AUTOFS_DEV_IOCTL_VERSION_MINOR;
+
+	return err;
+}
+
+/*
+ * Copy parameter control struct, including a possible path allocated
+ * at the end of the struct.
+ */
+static struct autofs_dev_ioctl *copy_dev_ioctl(struct autofs_dev_ioctl __user *in)
+{
+	struct autofs_dev_ioctl tmp, *ads;
+
+	if (copy_from_user(&tmp, in, sizeof(tmp)))
+		return ERR_PTR(-EFAULT);
+
+	if (tmp.size < sizeof(tmp))
+		return ERR_PTR(-EINVAL);
+
+	ads = kmalloc(tmp.size, GFP_KERNEL);
+	if (!ads)
+		return ERR_PTR(-ENOMEM);
+
+	if (copy_from_user(ads, in, tmp.size)) {
+		kfree(ads);
+		return ERR_PTR(-EFAULT);
+	}
+
+	return ads;
+}
+
+static inline void free_dev_ioctl(struct autofs_dev_ioctl *param)
+{
+	kfree(param);
+	return;
+}
+
+/*
+ * Check sanity of parameter control fields and if a path is present
+ * check that it has a "/" and is terminated.
+ */
+static int validate_dev_ioctl(int cmd, struct autofs_dev_ioctl *param)
+{
+	int err = -EINVAL;
+
+	if (check_dev_ioctl_version(cmd, param)) {
+		AUTOFS_WARN("invalid device control module version "
+		     "supplied for cmd(0x%08x)", cmd);
+		goto out;
+	}
+
+	if (param->size > sizeof(*param)) {
+		err = check_name(param->path);
+		if (err) {
+			AUTOFS_WARN("invalid path supplied for cmd(0x%08x)",
+				    cmd);
+			goto out;
+		}
+
+		err = invalid_str(param->path,
+				 (void *) ((size_t) param + param->size));
+		if (err) {
+			AUTOFS_WARN("invalid path supplied for cmd(0x%08x)",
+				    cmd);
+			goto out;
+		}
+	}
+
+	err = 0;
+out:
+	return err;
+}
+
+/*
+ * Get the autofs super block info struct from the file opened on
+ * the autofs mount point.
+ */
+static struct autofs_sb_info *autofs_dev_ioctl_sbi(struct file *f)
+{
+	struct autofs_sb_info *sbi = NULL;
+	struct inode *inode;
+
+	if (f) {
+		inode = f->f_path.dentry->d_inode;
+		sbi = autofs4_sbi(inode->i_sb);
+	}
+	return sbi;
+}
+
+/* Return autofs module protocol version */
+static int autofs_dev_ioctl_protover(struct file *fp,
+				     struct autofs_sb_info *sbi,
+				     struct autofs_dev_ioctl *param)
+{
+	param->arg1 = sbi->version;
+	return 0;
+}
+
+/* Return autofs module protocol sub version */
+static int autofs_dev_ioctl_protosubver(struct file *fp,
+					struct autofs_sb_info *sbi,
+					struct autofs_dev_ioctl *param)
+{
+	param->arg1 = sbi->sub_version;
+	return 0;
+}
+
+/*
+ * Walk down the mount stack looking for an autofs mount that
+ * has the requested device number (aka. new_encode_dev(sb->s_dev).
+ */
+static int autofs_dev_ioctl_find_super(struct nameidata *nd, dev_t devno)
+{
+	struct dentry *dentry;
+	struct inode *inode;
+	struct super_block *sb;
+	dev_t s_dev;
+	unsigned int err;
+
+	err = -ENOENT;
+
+	/* Lookup the dentry name at the base of our mount point */
+	dentry = d_lookup(nd->path.dentry, &nd->last);
+	if (!dentry)
+		goto out;
+
+	dput(nd->path.dentry);
+	nd->path.dentry = dentry;
+
+	/* And follow the mount stack looking for our autofs mount */
+	while (follow_down(&nd->path.mnt, &nd->path.dentry)) {
+		inode = nd->path.dentry->d_inode;
+		if (!inode)
+			break;
+
+		sb = inode->i_sb;
+		s_dev = new_encode_dev(sb->s_dev);
+		if (devno == s_dev) {
+			if (sb->s_magic == AUTOFS_SUPER_MAGIC) {
+				err = 0;
+				break;
+			}
+		}
+	}
+out:
+	return err;
+}
+
+/*
+ * Walk down the mount stack looking for an autofs mount that
+ * has the requested mount type (ie. indirect, direct or offset).
+ */
+static int autofs_dev_ioctl_find_sbi_type(struct nameidata *nd, unsigned int type)
+{
+	struct dentry *dentry;
+	struct autofs_info *ino;
+	unsigned int err;
+
+	err = -ENOENT;
+
+	/* Lookup the dentry name at the base of our mount point */
+	dentry = d_lookup(nd->path.dentry, &nd->last);
+	if (!dentry)
+		goto out;
+
+	dput(nd->path.dentry);
+	nd->path.dentry = dentry;
+
+	/* And follow the mount stack looking for our autofs mount */
+	while (follow_down(&nd->path.mnt, &nd->path.dentry)) {
+		ino = autofs4_dentry_ino(nd->path.dentry);
+		if (ino && ino->sbi->type & type) {
+			err = 0;
+			break;
+		}
+	}
+out:
+	return err;
+}
+
+static void autofs_dev_ioctl_fd_install(unsigned int fd, struct file *file)
+{
+	struct files_struct *files = current->files;
+	struct fdtable *fdt;
+
+	spin_lock(&files->file_lock);
+	fdt = files_fdtable(files);
+	BUG_ON(fdt->fd[fd] != NULL);
+	rcu_assign_pointer(fdt->fd[fd], file);
+	FD_SET(fd, fdt->close_on_exec);
+	spin_unlock(&files->file_lock);
+}
+
+
+/*
+ * Open a file descriptor on the autofs mount point corresponding
+ * to the given path and device number (aka. new_encode_dev(sb->s_dev)).
+ */
+static int autofs_dev_ioctl_open_mountpoint(const char *path, dev_t devid)
+{
+	struct file *filp;
+	struct nameidata nd;
+	int err, fd;
+
+	fd = get_unused_fd();
+	if (likely(fd >= 0)) {
+		/* Get nameidata of the parent directory */
+		err = path_lookup(path, LOOKUP_PARENT, &nd);
+		if (err)
+			goto out;
+
+		/*
+		 * Search down, within the parent, looking for an
+		 * autofs super block that has the device number
+		 * corresponding to the autofs fs we want to open.
+		 */
+		err = autofs_dev_ioctl_find_super(&nd, devid);
+		if (err) {
+			path_put(&nd.path);
+			goto out;
+		}
+
+		filp = dentry_open(nd.path.dentry, nd.path.mnt, O_RDONLY);
+		if (IS_ERR(filp)) {
+			err = PTR_ERR(filp);
+			goto out;
+		}
+
+		autofs_dev_ioctl_fd_install(fd, filp);
+	}
+
+	return fd;
+
+out:
+	put_unused_fd(fd);
+	return err;
+}
+
+/* Open a file descriptor on an autofs mount point */
+static int autofs_dev_ioctl_openmount(struct file *fp,
+				      struct autofs_sb_info *sbi,
+				      struct autofs_dev_ioctl *param)
+{
+	const char *path;
+	dev_t devid;
+	int err, fd;
+
+	/* param->path has already been checked */
+	if (!param->arg1)
+		return -EINVAL;
+
+	param->ioctlfd = -1;
+
+	path = param->path;
+	devid = param->arg1;
+
+	err = 0;
+	fd = autofs_dev_ioctl_open_mountpoint(path, devid);
+	if (unlikely(fd < 0)) {
+		err = fd;
+		goto out;
+	}
+
+	param->ioctlfd = fd;
+out:
+	return err;
+}
+
+/* Close file descriptor allocated above (user can also use close(2)). */
+static int autofs_dev_ioctl_closemount(struct file *fp,
+				       struct autofs_sb_info *sbi,
+				       struct autofs_dev_ioctl *param)
+{
+	return sys_close(param->ioctlfd);
+}
+
+/*
+ * Send "ready" status for an existing wait (either a mount or an expire
+ * request).
+ */
+static int autofs_dev_ioctl_ready(struct file *fp,
+				  struct autofs_sb_info *sbi,
+				  struct autofs_dev_ioctl *param)
+{
+	autofs_wqt_t token;
+
+	token = (autofs_wqt_t) param->arg1;
+	return autofs4_wait_release(sbi, token, 0);
+}
+
+/*
+ * Send "fail" status for an existing wait (either a mount or an expire
+ * request).
+ */
+static int autofs_dev_ioctl_fail(struct file *fp,
+				 struct autofs_sb_info *sbi,
+				 struct autofs_dev_ioctl *param)
+{
+	autofs_wqt_t token;
+	int status;
+
+	token = (autofs_wqt_t) param->arg1;
+	status = param->arg2 ? param->arg2 : -ENOENT;
+	return autofs4_wait_release(sbi, token, status);
+}
+
+/*
+ * Set the pipe fd for kernel communication to the daemon.
+ *
+ * Normally this is set at mount using an option but if we
+ * are reconnecting to a busy mount then we need to use this
+ * to tell the autofs mount about the new kernel pipe fd. In
+ * order to protect mounts against incorrectly setting the
+ * pipefd we also require that the autofs mount be catatonic.
+ *
+ * This also sets the process group id used to identify the
+ * controlling process (eg. the owning automount(8) daemon).
+ */
+static int autofs_dev_ioctl_setpipefd(struct file *fp,
+				      struct autofs_sb_info *sbi,
+				      struct autofs_dev_ioctl *param)
+{
+	int pipefd;
+	int err = 0;
+
+	if (param->arg1 == -1)
+		return -EINVAL;
+
+	pipefd = param->arg1;
+
+	mutex_lock(&sbi->wq_mutex);
+	if (!sbi->catatonic) {
+		mutex_unlock(&sbi->wq_mutex);
+		return -EBUSY;
+	} else {
+		struct file *pipe = fget(pipefd);
+		if (!pipe->f_op || !pipe->f_op->write) {
+			err = -EPIPE;
+			fput(pipe);
+			goto out;
+		}
+		sbi->oz_pgrp = task_pgrp_nr(current);
+		sbi->pipefd = pipefd;
+		sbi->pipe = pipe;
+		sbi->catatonic = 0;
+	}
+out:
+	mutex_unlock(&sbi->wq_mutex);
+	return err;
+}
+
+/*
+ * Make the autofs mount point catatonic, no longer responsive to
+ * mount requests. Also closes the kernel pipe file descriptor.
+ */
+static int autofs_dev_ioctl_catatonic(struct file *fp,
+				      struct autofs_sb_info *sbi,
+				      struct autofs_dev_ioctl *param)
+{
+	autofs4_catatonic_mode(sbi);
+	return 0;
+}
+
+/* Set the autofs mount timeout */
+static int autofs_dev_ioctl_timeout(struct file *fp,
+				    struct autofs_sb_info *sbi,
+				    struct autofs_dev_ioctl *param)
+{
+	unsigned long timeout;
+
+	timeout = param->arg1;
+	param->arg1 = sbi->exp_timeout / HZ;
+	sbi->exp_timeout = timeout * HZ;
+	return 0;
+}
+
+/*
+ * Return the uid and gid of the last request for the mount
+ *
+ * When reconstructing an autofs mount tree with active mounts
+ * we need to re-connect to mounts that may have used the original
+ * process uid and gid (or string variations of them) for mount
+ * lookups within the map entry.
+ */
+static int autofs_dev_ioctl_requester(struct file *fp,
+				      struct autofs_sb_info *sbi,
+				      struct autofs_dev_ioctl *param)
+{
+	struct autofs_info *ino;
+	struct nameidata nd;
+	const char *path;
+	dev_t devid;
+	int err = -ENOENT;
+
+	if (param->size <= sizeof(*param)) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	path = param->path;
+	devid = sbi->sb->s_dev;
+
+	param->arg1 = param->arg2 = -1;
+
+	/* Get nameidata of the parent directory */
+	err = path_lookup(path, LOOKUP_PARENT, &nd);
+	if (err)
+		goto out;
+
+	err = autofs_dev_ioctl_find_super(&nd, devid);
+	if (err)
+		goto out_release;
+
+	ino = autofs4_dentry_ino(nd.path.dentry);
+	if (ino) {
+		err = 0;
+		autofs4_expire_wait(nd.path.dentry);
+		spin_lock(&sbi->fs_lock);
+		param->arg1 = ino->uid;
+		param->arg2 = ino->gid;
+		spin_unlock(&sbi->fs_lock);
+	}
+
+out_release:
+	path_put(&nd.path);
+out:
+	return err;
+}
+
+/*
+ * Call repeatedly until it returns -EAGAIN, meaning there's nothing
+ * more that can be done.
+ */
+static int autofs_dev_ioctl_expire(struct file *fp,
+				   struct autofs_sb_info *sbi,
+				   struct autofs_dev_ioctl *param)
+{
+	struct dentry *dentry;
+	struct vfsmount *mnt;
+	int err = -EAGAIN;
+	int how;
+
+	how = param->arg1;
+	mnt = fp->f_path.mnt;
+
+	if (sbi->type & AUTOFS_TYPE_TRIGGER)
+		dentry = autofs4_expire_direct(sbi->sb, mnt, sbi, how);
+	else
+		dentry = autofs4_expire_indirect(sbi->sb, mnt, sbi, how);
+
+	if (dentry) {
+		struct autofs_info *ino = autofs4_dentry_ino(dentry);
+
+		/*
+		 * This is synchronous because it makes the daemon a
+		 * little easier
+		*/
+		err = autofs4_wait(sbi, dentry, NFY_EXPIRE);
+
+		spin_lock(&sbi->fs_lock);
+		if (ino->flags & AUTOFS_INF_MOUNTPOINT) {
+			ino->flags &= ~AUTOFS_INF_MOUNTPOINT;
+			sbi->sb->s_root->d_mounted++;
+		}
+		ino->flags &= ~AUTOFS_INF_EXPIRING;
+		complete_all(&ino->expire_complete);
+		spin_unlock(&sbi->fs_lock);
+		dput(dentry);
+	}
+
+	return err;
+}
+
+/* Check if autofs mount point is in use */
+static int autofs_dev_ioctl_askumount(struct file *fp,
+				      struct autofs_sb_info *sbi,
+				      struct autofs_dev_ioctl *param)
+{
+	param->arg1 = 0;
+	if (may_umount(fp->f_path.mnt))
+		param->arg1 = 1;
+	return 0;
+}
+
+/*
+ * Check if the given path is a mountpoint.
+ *
+ * If we are supplied with the file descriptor of an autofs
+ * mount we're looking for a specific mount. In this case
+ * the path is considered a mountpoint if it is itself a
+ * mountpoint or contains a mount, such as a multi-mount
+ * without a root mount. In this case we return 1 if the
+ * path is a mount point and the super magic of the covering
+ * mount if there is one or 0 if it isn't a mountpoint.
+ *
+ * If we aren't supplied with a file descriptor then we
+ * lookup the nameidata of the path and check if it is the
+ * root of a mount. If a type is given we are looking for
+ * a particular autofs mount and if we don't find a match
+ * we return fail. If the located nameidata path is the
+ * root of a mount we return 1 along with the super magic
+ * of the mount or 0 otherwise.
+ *
+ * In both cases the the device number (as returned by
+ * new_encode_dev()) is also returned.
+ */
+static int autofs_dev_ioctl_ismountpoint(struct file *fp,
+					 struct autofs_sb_info *sbi,
+					 struct autofs_dev_ioctl *param)
+{
+	struct nameidata nd;
+	const char *path;
+	unsigned int type;
+	int err = -ENOENT;
+
+	if (param->size <= sizeof(*param)) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	path = param->path;
+	type = param->arg1;
+
+	param->arg1 = 0;
+	param->arg2 = 0;
+
+	if (!fp || param->ioctlfd == -1) {
+		if (type == AUTOFS_TYPE_ANY) {
+			struct super_block *sb;
+
+			err = path_lookup(path, LOOKUP_FOLLOW, &nd);
+			if (err)
+				goto out;
+
+			sb = nd.path.dentry->d_sb;
+			param->arg1 = new_encode_dev(sb->s_dev);
+		} else {
+			struct autofs_info *ino;
+
+			err = path_lookup(path, LOOKUP_PARENT, &nd);
+			if (err)
+				goto out;
+
+			err = autofs_dev_ioctl_find_sbi_type(&nd, type);
+			if (err)
+				goto out_release;
+
+			ino = autofs4_dentry_ino(nd.path.dentry);
+			param->arg1 = autofs4_get_dev(ino->sbi);
+		}
+
+		err = 0;
+		if (nd.path.dentry->d_inode &&
+		    nd.path.mnt->mnt_root == nd.path.dentry) {
+			err = 1;
+			param->arg2 = nd.path.dentry->d_inode->i_sb->s_magic;
+		}
+	} else {
+		dev_t devid = new_encode_dev(sbi->sb->s_dev);
+
+		err = path_lookup(path, LOOKUP_PARENT, &nd);
+		if (err)
+			goto out;
+
+		err = autofs_dev_ioctl_find_super(&nd, devid);
+		if (err)
+			goto out_release;
+
+		param->arg1 = autofs4_get_dev(sbi);
+
+		err = have_submounts(nd.path.dentry);
+
+		if (nd.path.mnt->mnt_mountpoint != nd.path.mnt->mnt_root) {
+			if (follow_down(&nd.path.mnt, &nd.path.dentry)) {
+				struct inode *inode = nd.path.dentry->d_inode;
+				param->arg2 = inode->i_sb->s_magic;
+			}
+		}
+	}
+
+out_release:
+	path_put(&nd.path);
+out:
+	return err;
+}
+
+/*
+ * Our range of ioctl numbers isn't 0 based so we need to shift
+ * the array index by _IOC_NR(AUTOFS_CTL_IOC_FIRST) for the table
+ * lookup.
+ */
+#define cmd_idx(cmd)	(cmd - _IOC_NR(AUTOFS_DEV_IOCTL_IOC_FIRST))
+
+static ioctl_fn lookup_dev_ioctl(unsigned int cmd)
+{
+	static struct {
+		int cmd;
+		ioctl_fn fn;
+	} _ioctls[] = {
+		{cmd_idx(AUTOFS_DEV_IOCTL_VERSION_CMD), NULL},
+		{cmd_idx(AUTOFS_DEV_IOCTL_PROTOVER_CMD),
+			 autofs_dev_ioctl_protover},
+		{cmd_idx(AUTOFS_DEV_IOCTL_PROTOSUBVER_CMD),
+			 autofs_dev_ioctl_protosubver},
+		{cmd_idx(AUTOFS_DEV_IOCTL_OPENMOUNT_CMD),
+			 autofs_dev_ioctl_openmount},
+		{cmd_idx(AUTOFS_DEV_IOCTL_CLOSEMOUNT_CMD),
+			 autofs_dev_ioctl_closemount},
+		{cmd_idx(AUTOFS_DEV_IOCTL_READY_CMD),
+			 autofs_dev_ioctl_ready},
+		{cmd_idx(AUTOFS_DEV_IOCTL_FAIL_CMD),
+			 autofs_dev_ioctl_fail},
+		{cmd_idx(AUTOFS_DEV_IOCTL_SETPIPEFD_CMD),
+			 autofs_dev_ioctl_setpipefd},
+		{cmd_idx(AUTOFS_DEV_IOCTL_CATATONIC_CMD),
+			 autofs_dev_ioctl_catatonic},
+		{cmd_idx(AUTOFS_DEV_IOCTL_TIMEOUT_CMD),
+			 autofs_dev_ioctl_timeout},
+		{cmd_idx(AUTOFS_DEV_IOCTL_REQUESTER_CMD),
+			 autofs_dev_ioctl_requester},
+		{cmd_idx(AUTOFS_DEV_IOCTL_EXPIRE_CMD),
+			 autofs_dev_ioctl_expire},
+		{cmd_idx(AUTOFS_DEV_IOCTL_ASKUMOUNT_CMD),
+			 autofs_dev_ioctl_askumount},
+		{cmd_idx(AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD),
+			 autofs_dev_ioctl_ismountpoint}
+	};
+	unsigned int idx = cmd_idx(cmd);
+
+	return (idx >= ARRAY_SIZE(_ioctls)) ? NULL : _ioctls[idx].fn;
+}
+
+/* ioctl dispatcher */
+static int _autofs_dev_ioctl(unsigned int command, struct autofs_dev_ioctl __user *user)
+{
+	struct autofs_dev_ioctl *param;
+	struct file *fp;
+	struct autofs_sb_info *sbi;
+	unsigned int cmd_first, cmd;
+	ioctl_fn fn = NULL;
+	int err = 0;
+
+	/* only root can play with this */
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	cmd_first = _IOC_NR(AUTOFS_DEV_IOCTL_IOC_FIRST);
+	cmd = _IOC_NR(command);
+
+	if (_IOC_TYPE(command) != _IOC_TYPE(AUTOFS_DEV_IOCTL_IOC_FIRST) ||
+	    cmd - cmd_first >= AUTOFS_DEV_IOCTL_IOC_COUNT) {
+		return -ENOTTY;
+	}
+
+	/* Copy the parameters into kernel space. */
+	param = copy_dev_ioctl(user);
+	if (IS_ERR(param))
+		return PTR_ERR(param);
+
+	err = validate_dev_ioctl(command, param);
+	if (err)
+		goto out;
+
+	/* The validate routine above always sets the version */
+	if (cmd == AUTOFS_DEV_IOCTL_VERSION_CMD)
+		goto done;
+
+	fn = lookup_dev_ioctl(cmd);
+	if (!fn) {
+		AUTOFS_WARN("unknown command 0x%08x", command);
+		return -ENOTTY;
+	}
+
+	fp = NULL;
+	sbi = NULL;
+
+	/*
+	 * For obvious reasons the openmount can't have a file
+	 * descriptor yet. We don't take a reference to the
+	 * file during close to allow for immediate release.
+	 */
+	if (cmd != AUTOFS_DEV_IOCTL_OPENMOUNT_CMD &&
+	    cmd != AUTOFS_DEV_IOCTL_CLOSEMOUNT_CMD) {
+		fp = fget(param->ioctlfd);
+		if (!fp) {
+			if (cmd == AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD)
+				goto cont;
+			err = -EBADF;
+			goto out;
+		}
+
+		if (!fp->f_op) {
+			err = -ENOTTY;
+			fput(fp);
+			goto out;
+		}
+
+		sbi = autofs_dev_ioctl_sbi(fp);
+		if (!sbi || sbi->magic != AUTOFS_SBI_MAGIC) {
+			err = -EINVAL;
+			fput(fp);
+			goto out;
+		}
+
+		/*
+		 * Admin needs to be able to set the mount catatonic in
+		 * order to be able to perform the re-open.
+		 */
+		if (!autofs4_oz_mode(sbi) &&
+		    cmd != AUTOFS_DEV_IOCTL_CATATONIC_CMD) {
+			err = -EACCES;
+			fput(fp);
+			goto out;
+		}
+	}
+cont:
+	err = fn(fp, sbi, param);
+
+	if (fp)
+		fput(fp);
+done:
+	if (err >= 0 && copy_to_user(user, param, AUTOFS_DEV_IOCTL_SIZE))
+		err = -EFAULT;
+out:
+	free_dev_ioctl(param);
+	return err;
+}
+
+static long autofs_dev_ioctl(struct file *file, uint command, ulong u)
+{
+	int err;
+	err = _autofs_dev_ioctl(command, (struct autofs_dev_ioctl __user *) u);
+	return (long) err;
+}
+
+#ifdef CONFIG_COMPAT
+static long autofs_dev_ioctl_compat(struct file *file, uint command, ulong u)
+{
+	return (long) autofs_dev_ioctl(file, command, (ulong) compat_ptr(u));
+}
+#else
+#define autofs_dev_ioctl_compat NULL
+#endif
+
+static const struct file_operations _dev_ioctl_fops = {
+	.unlocked_ioctl	 = autofs_dev_ioctl,
+	.compat_ioctl = autofs_dev_ioctl_compat,
+	.owner	 = THIS_MODULE,
+};
+
+static struct miscdevice _autofs_dev_ioctl_misc = {
+	.minor 		= MISC_DYNAMIC_MINOR,
+	.name  		= AUTOFS_DEVICE_NAME,
+	.fops  		= &_dev_ioctl_fops
+};
+
+/* Register/deregister misc character device */
+int autofs_dev_ioctl_init(void)
+{
+	int r;
+
+	r = misc_register(&_autofs_dev_ioctl_misc);
+	if (r) {
+		AUTOFS_ERROR("misc_register failed for control device");
+		return r;
+	}
+
+	return 0;
+}
+
+void autofs_dev_ioctl_exit(void)
+{
+	misc_deregister(&_autofs_dev_ioctl_misc);
+	return;
+}
+
diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index e79dd09e12a..cde2f8e8935 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -244,10 +244,10 @@ cont:
 }
 
 /* Check if we can expire a direct mount (possibly a tree) */
-static struct dentry *autofs4_expire_direct(struct super_block *sb,
-					    struct vfsmount *mnt,
-					    struct autofs_sb_info *sbi,
-					    int how)
+struct dentry *autofs4_expire_direct(struct super_block *sb,
+				     struct vfsmount *mnt,
+				     struct autofs_sb_info *sbi,
+				     int how)
 {
 	unsigned long timeout;
 	struct dentry *root = dget(sb->s_root);
@@ -283,10 +283,10 @@ static struct dentry *autofs4_expire_direct(struct super_block *sb,
  *  - it is unused by any user process
  *  - it has been unused for exp_timeout time
  */
-static struct dentry *autofs4_expire_indirect(struct super_block *sb,
-					      struct vfsmount *mnt,
-					      struct autofs_sb_info *sbi,
-					      int how)
+struct dentry *autofs4_expire_indirect(struct super_block *sb,
+				       struct vfsmount *mnt,
+				       struct autofs_sb_info *sbi,
+				       int how)
 {
 	unsigned long timeout;
 	struct dentry *root = sb->s_root;
diff --git a/fs/autofs4/init.c b/fs/autofs4/init.c
index 723a1c5e361..9722e4bd895 100644
--- a/fs/autofs4/init.c
+++ b/fs/autofs4/init.c
@@ -29,11 +29,20 @@ static struct file_system_type autofs_fs_type = {
 
 static int __init init_autofs4_fs(void)
 {
-	return register_filesystem(&autofs_fs_type);
+	int err;
+
+	err = register_filesystem(&autofs_fs_type);
+	if (err)
+		return err;
+
+	autofs_dev_ioctl_init();
+
+	return err;
 }
 
 static void __exit exit_autofs4_fs(void)
 {
+	autofs_dev_ioctl_exit();
 	unregister_filesystem(&autofs_fs_type);
 }