VFS: Mountpoint file descriptor umount support

Index: linux-2.6.9-quilt/fs/mountfd.c
===================================================================
@@ -11,6 +11,8 @@
 
 #define VFSMOUNT(filp) ((struct vfsmount *)((filp)->private_data))
 
+extern int do_umount(struct vfsmount *mnt, int flags);
+
 static struct vfsmount *mfdfs_mnt;
 
 static void mfdfs_read_inode(struct inode *inode);

@@ -72,6 +74,18 @@ static int mfd_release(struct inode *ino
 	return 0;
 }
 
+static long mfd_umount(struct file *mountfilp, int flags)
+{
+	struct vfsmount *mnt;
+	int error;
+	
+	mnt = mntget(VFSMOUNT(mountfilp));
+
+	error = do_umount(mnt, flags);
+
+	return error;
+}
+
 static int mfd_ioctl(struct inode *inode, struct file *filp,
 		     unsigned int cmd, unsigned long arg);
 static struct file_operations mfd_file_ops = {

@@ -243,6 +257,12 @@ static int mfd_ioctl(struct inode *inode
 	switch (cmd) {
 	case MOUNTFD_IOC_GETDIRFD:
 		return mfd_getdirfd(filp);
+	case MOUNTFD_IOC_DETACH:
+		return mfd_umount(filp, MNT_DETACH);
+	case MOUNTFD_IOC_UNMOUNT:
+		return mfd_umount(filp, 0);
+	case MOUNTFD_IOC_FORCEDUNMOUNT:
+		return mfd_umount(filp, MNT_FORCE);
 	}
 	return -ENOTTY;
 }

Index: linux-2.6.9-quilt/fs/namespace.c
===================================================================
@@ -601,7 +601,7 @@ static void umount_tree(struct vfsmount 
 	spin_lock(&vfsmount_lock);
 }
 
-static int do_umount(struct vfsmount *mnt, int flags)
+int do_umount(struct vfsmount *mnt, int flags)
 {
 	struct super_block * sb = mnt->mnt_sb;
 	int retval;

Index: linux-2.6.9-quilt/include/linux/fs.h
===================================================================
@@ -214,7 +214,10 @@ extern int leases_enable, dir_notify_ena
 #define FIBMAP	   _IO(0x00,1)	/* bmap access */
 #define FIGETBSZ   _IO(0x00,2)	/* get the block size used for bmap */
 
-#define MOUNTFD_IOC_GETDIRFD _IO('p', 0xa0)
+#define MOUNTFD_IOC_GETDIRFD      _IO('p', 0xa0)
+#define MOUNTFD_IOC_UNMOUNT       _IO('p', 0xa1)
+#define MOUNTFD_IOC_DETACH        _IO('p', 0xa2)
+#define MOUNTFD_IOC_FORCEDUNMOUNT _IO('p', 0xa3)
 
 #ifdef __KERNEL__
 

Index: linux-2.6.9-quilt/fs/mountfd.c
===================================================================
@@ -5,6 +5,7 @@
 #include <linux/stat.h>
 #include <linux/init.h>
 #include <linux/security.h>
+#include <linux/namei.h>
 
 #define MFDFS_MAGIC 0x4A9F2E43
 #define MFDFS_ROOT_INO 1

@@ -251,6 +252,38 @@ out_filp:
 	return error;
 }
 
+static long mfd_attach(struct file *mountfilp, int dirfd)
+{
+	struct file *dir;
+	struct vfsmount *mnt;
+	struct nameidata nd;
+	int ret;
+
+	mnt = mntget(VFSMOUNT(mountfilp));
+
+	ret = -EBADF;
+	dir = fget(dirfd);
+	if (!dir)
+		goto out;
+
+	ret = -ENOTDIR;
+	if (!S_ISDIR(dir->f_dentry->d_inode->i_mode))
+		goto out2;
+
+	memset(&nd, 0, sizeof(nd));
+	nd.dentry = dget(dir->f_dentry);
+	nd.mnt = mntget(dir->f_vfsmnt);
+
+	ret = do_graft_mount(mnt, &nd);
+
+	path_release(&nd);
+out2:
+	put_filp(dir);
+out:
+	mntput(mnt);
+	return ret;
+}
+
 static int mfd_ioctl(struct inode *inode, struct file *filp,
 		     unsigned int cmd, unsigned long arg)
 {

@@ -263,6 +296,8 @@ static int mfd_ioctl(struct inode *inode
 		return mfd_umount(filp, 0);
 	case MOUNTFD_IOC_FORCEDUNMOUNT:
 		return mfd_umount(filp, MNT_FORCE);
+	case MOUNTFD_IOC_ATTACH:
+		return mfd_attach(filp, arg);
 	}
 	return -ENOTTY;
 }

Index: linux-2.6.9-quilt/include/linux/fs.h
===================================================================
@@ -218,6 +218,7 @@ extern int leases_enable, dir_notify_ena
 #define MOUNTFD_IOC_UNMOUNT       _IO('p', 0xa1)
 #define MOUNTFD_IOC_DETACH        _IO('p', 0xa2)
 #define MOUNTFD_IOC_FORCEDUNMOUNT _IO('p', 0xa3)
+#define MOUNTFD_IOC_ATTACH        _IOW('p', 0xa4, int)
 
 #ifdef __KERNEL__
 

Index: linux-2.6.9-quilt/include/linux/fs.h
===================================================================
@@ -219,6 +219,9 @@ extern int leases_enable, dir_notify_ena
 #define MOUNTFD_IOC_DETACH        _IO('p', 0xa2)
 #define MOUNTFD_IOC_FORCEDUNMOUNT _IO('p', 0xa3)
 #define MOUNTFD_IOC_ATTACH        _IOW('p', 0xa4, int)
+#define MOUNTFD_IOC_GETFIRSTCHILD _IO('p', 0xa5)
+/* TODO: change this interface to require the parent mfd as well */
+#define MOUNTFD_IOC_GETNEXTCHILD  _IO('p', 0xa6)
 
 #ifdef __KERNEL__
 

58 lines not on this page · raw message

Index: linux-2.6.9-quilt/fs/mountfd.c
===================================================================
@@ -160,6 +160,72 @@ static struct dentry *get_mfd_dentry(str
 	return dget(dentry);
 }
 
+static int mfd_read_fstype(struct vfsmount *mnt, char *buf)
+{
+	return scnprintf(buf, MOUNTFD_READSIZE-1, "%s", mnt->mnt_sb->s_type->name) + 1;
+}
+
+static int mfd_read_dev(struct vfsmount *mnt, char *buf)
+{
+	return scnprintf(buf, MOUNTFD_READSIZE-1, "%s", mnt->mnt_sb->s_id) + 1;
+}
+
+static int mfd_read_vfsoptions(struct vfsmount *mnt, char *buf)
+{
+	static struct vfs_info {
+		int flag;
+		char *str;
+	} vfs_info[] = {
+		{ MS_RDONLY, "ro" },
+		{ MS_DIRSYNC, "dirsync" },
+		{ MS_MANDLOCK, "mand" },
+		{ MS_NOATIME, "noatime" },
+		{ MS_NODIRATIME, "nodiratime" },
+		{ 0, NULL }
+	};
+	struct vfs_info *vfs_infop;
+	static struct mnt_info {
+		int flag;
+		char *str;
+	} mnt_info[] = {
+		{ MNT_NOSUID, "nosuid" },
+		{ MNT_NODEV, "nodev" },
+		{ MNT_NOEXEC, "noexec" },
+		{ 0, NULL }
+	};
+	struct mnt_info *mnt_infop;
+
+	char *p = buf;
+
+	int sb_flags = mnt->mnt_sb->s_flags;
+	int mnt_flags = mnt->mnt_flags;
+	int first = 0;
+
+	/*
+	 * Note: we skip length checks below because we assume we can't overrun
+	 * MOUNTFD_READSIZE.
+	 */
+
+	for (vfs_infop = vfs_info; vfs_infop->flag; vfs_infop++) {
+		if (sb_flags & vfs_infop->flag) {
+			if (first++)
+				*p++ = ',';
+			strcpy(p, vfs_infop->str);
+			p += strlen(vfs_infop->str);
+		}
+	}
+
+	for (mnt_infop = mnt_info; mnt_infop->flag; mnt_infop++) {
+		if (mnt_flags & mnt_infop->flag) {
+			if (first++)
+				*p++ = ',';
+			strcpy(p, mnt_infop->str);
+			p += strlen(mnt_infop->str);
+		}
+	}
+	return p - buf + 1;
+}
+
 static long open_mfd(struct vfsmount *mnt)
 {
 	struct file *file;

@@ -176,6 +242,7 @@ static long open_mfd(struct vfsmount *mn
 	if (fd < 0)
 		goto out_putfilp;
 
+	error = -ENOMEM;
 	file->private_data = mnt;
 	file->f_dentry = get_mfd_dentry(mnt);
 	if (IS_ERR(file->f_dentry)) {

@@ -326,9 +393,53 @@ static long mfd_nextchild(struct file *m
 	return ret;
 }
 
+static int mfd_ioctl_reads(struct inode *inode, struct file *filp,
+		     unsigned int cmd, unsigned long arg)
+{
+	char __user *user_buf = (char __user *)arg;
+	struct vfsmount *mnt;
+	char *buf;
+	int ret;
+
+	mnt = VFSMOUNT(filp);
+
+	buf = (char *)get_zeroed_page(GFP_KERNEL);
+	if (buf)
+		return -ENOMEM;
+	switch (cmd) {
+	/*
+	 * The following calls are expected to return the total number of bytes to write out, including '\0'.
+	 */
+	case MOUNTFD_IOC_GETDEV:
+		ret = mfd_read_dev(mnt, buf);
+		break;
+	case MOUNTFD_IOC_GETFSTYPE:
+		ret = mfd_read_fstype(mnt, buf);
+		break;
+	case MOUNTFD_IOC_GETVFSOPTIONS:
+		ret = mfd_read_vfsoptions(mnt, buf);
+		break;
+	case MOUNTFD_IOC_GETFSOPTIONS:
+		/* TODO: need super_block op that doesn't take a seq_file */
+		ret = -ENOSYS;
+		break;
+	default:
+		ret = -ENOTTY;
+	}
+
+	if (ret >= 0) {
+		if (copy_to_user(user_buf, buf, ret))
+			ret = -EFAULT;
+	}
+
+	free_page((unsigned long)buf);
+	return ret;
+}
+
 static int mfd_ioctl(struct inode *inode, struct file *filp,
 		     unsigned int cmd, unsigned long arg)
 {
+	int ret;
 	switch (cmd) {
 	case MOUNTFD_IOC_GETDIRFD:
 		return mfd_getdirfd(filp);

@@ -345,7 +456,8 @@ static int mfd_ioctl(struct inode *inode
 	case MOUNTFD_IOC_GETNEXTCHILD:
 		return mfd_nextchild(filp);
 	}
-	return -ENOTTY;
+	ret = mfd_ioctl_reads(inode, filp, cmd, arg);
+	return ret;
 }
 
 asmlinkage long sys_mountfd(int dirfd)

Index: linux-2.6.9-quilt/include/linux/fs.h
===================================================================
@@ -223,6 +223,12 @@ extern int leases_enable, dir_notify_ena
 /* TODO: change this interface to require the parent mfd as well */
 #define MOUNTFD_IOC_GETNEXTCHILD  _IO('p', 0xa6)
 
+#define MOUNTFD_READSIZE PAGE_SIZE
+#define MOUNTFD_IOC_GETDEV        _IOR('p', 0xa7, char [MOUNTFD_READSIZE])
+#define MOUNTFD_IOC_GETFSTYPE     _IOR('p', 0xa8, char [MOUNTFD_READSIZE])
+#define MOUNTFD_IOC_GETVFSOPTIONS _IOR('p', 0xa9, char [MOUNTFD_READSIZE])
+#define MOUNTFD_IOC_GETFSOPTIONS  _IOR('p', 0xaa, char [MOUNTFD_READSIZE])
+
 #ifdef __KERNEL__
 
 #include <linux/list.h>

Index: linux-2.6.9-quilt/include/linux/fs.h
===================================================================
@@ -228,6 +228,7 @@ extern int leases_enable, dir_notify_ena
 #define MOUNTFD_IOC_GETFSTYPE     _IOR('p', 0xa8, char [MOUNTFD_READSIZE])
 #define MOUNTFD_IOC_GETVFSOPTIONS _IOR('p', 0xa9, char [MOUNTFD_READSIZE])
 #define MOUNTFD_IOC_GETFSOPTIONS  _IOR('p', 0xaa, char [MOUNTFD_READSIZE])
+#define MOUNTFD_IOC_SETVFSEXPIRE  _IOW('p', 0xab, int)
 
 #ifdef __KERNEL__
 

Index: linux-2.6.9-quilt/fs/mountfd.c
===================================================================
@@ -393,6 +393,14 @@ static long mfd_nextchild(struct file *m
 	return ret;
 }
 
+static int mfd_vfsexpire(struct file *mountfilp, int arg)
+{
+	struct vfsmount *mnt;
+
+	mnt = VFSMOUNT(mountfilp);
+	return mnt_expire(mnt, arg);
+}
+
 static int mfd_ioctl_reads(struct inode *inode, struct file *filp,
 		     unsigned int cmd, unsigned long arg)
 {

@@ -455,6 +463,8 @@ static int mfd_ioctl(struct inode *inode
 		return mfd_firstchild(filp);
 	case MOUNTFD_IOC_GETNEXTCHILD:
 		return mfd_nextchild(filp);
+	case MOUNTFD_IOC_SETVFSEXPIRE:
+		return mfd_vfsexpire(filp, (int)arg);
 	}
 	ret = mfd_ioctl_reads(inode, filp, cmd, arg);
 	return ret;

Index: linux-2.6.9-quilt/kernel/kmod.c
===================================================================
@@ -140,17 +140,22 @@ EXPORT_SYMBOL(hotplug_path);
 
 struct subprocess_info {
 	struct completion *complete;
+	call_usermodehelper_cb_t cb;
+	void *cbdata;
+	int wait;
+	int retval;
+};
+
+struct simple_usermodehelper_info {
 	char *path;
 	char **argv;
 	char **envp;
-	int wait;
-	int retval;
 };
 
 /*
  * This is the task which runs the usermode application
  */
-static int ____call_usermodehelper(void *data)
+static int ____call_usermodehelper_cb(void *data)
 {
 	struct subprocess_info *sub_info = data;
 	int retval;

@@ -168,7 +173,7 @@ static int ____call_usermodehelper(void 
 
 	retval = -EPERM;
 	if (current->fs->root)
-		retval = execve(sub_info->path, sub_info->argv,sub_info->envp);
+		retval = (*sub_info->cb)(sub_info->cbdata);
 
 	/* Exec failed? */
 	sub_info->retval = retval;

@@ -190,7 +195,7 @@ static int wait_for_helper(void *data)
 	do_sigaction(SIGCHLD, &sa, (struct k_sigaction *)0);
 	allow_signal(SIGCHLD);
 
-	pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
+	pid = kernel_thread(____call_usermodehelper_cb, sub_info, SIGCHLD);
 	if (pid < 0) {
 		sub_info->retval = pid;
 	} else {

@@ -211,7 +216,7 @@ static int wait_for_helper(void *data)
 }
 
 /* This is run by khelper thread  */
-static void __call_usermodehelper(void *data)
+static void __call_usermodehelper_cb(void *data)
 {
 	struct subprocess_info *sub_info = data;
 	pid_t pid;

@@ -223,7 +228,7 @@ static void __call_usermodehelper(void *
 		pid = kernel_thread(wait_for_helper, sub_info,
 				    CLONE_FS | CLONE_FILES | SIGCHLD);
 	else
-		pid = kernel_thread(____call_usermodehelper, sub_info,
+		pid = kernel_thread(____call_usermodehelper_cb, sub_info,
 				    CLONE_VFORK | SIGCHLD);
 
 	if (pid < 0) {

@@ -234,12 +239,16 @@ static void __call_usermodehelper(void *
 }
 
 /**
- * call_usermodehelper - start a usermode application
- * @path: pathname for the application
- * @argv: null-terminated argument list
- * @envp: null-terminated environment list
+ * call_usermodehelper_cb - start a usermode application with a callback
+ * @cb: A user provided callback that will eventually execve.
+ * @cbdata: User supplied information that will be passed back to the callback.
  * @wait: wait for the application to finish and return status.
  *
+ * This call will do all the work required for setting up a usermode helper
+ * except perform the actual exec.  It is the caller's responsibility to
+ * provide a callback that will eventually exec.  This allows last minute
+ * changes to current.
+ *
  * Runs a user-space application.  The application is started
  * asynchronously if wait is not set, and runs as a child of keventd.
  * (ie. it runs with full root capabilities).

@@ -247,29 +256,62 @@ static void __call_usermodehelper(void *
  * Must be called from process context.  Returns a negative error code
  * if program was not execed successfully, or 0.
  */
-int call_usermodehelper(char *path, char **argv, char **envp, int wait)
+int call_usermodehelper_cb(call_usermodehelper_cb_t cb, void *cbdata, int wait)
 {
 	DECLARE_COMPLETION(done);
 	struct subprocess_info sub_info = {
 		.complete	= &done,
-		.path		= path,
-		.argv		= argv,
-		.envp		= envp,
+		.cb		= cb,
+		.cbdata		= cbdata,
 		.wait		= wait,
 		.retval		= 0,
 	};
-	DECLARE_WORK(work, __call_usermodehelper, &sub_info);
+	DECLARE_WORK(work, __call_usermodehelper_cb, &sub_info);
 
+	BUG_ON(!cb || !cbdata);
 	if (!khelper_wq)
 		return -EBUSY;
 
-	if (path[0] == '\0')
-		return 0;
-
 	queue_work(khelper_wq, &work);
 	wait_for_completion(&done);
 	return sub_info.retval;
 }
+EXPORT_SYMBOL(call_usermodehelper_cb);
+
+static int call_usermodehelper_simple(void *cbdata)
+{
+	struct simple_usermodehelper_info *info = cbdata;
+	return execve(info->path, info->argv, info->envp);
+}
+
+/**
+ * call_usermodehelper - start a usermode application
+ * @path: pathname for the application
+ * @argv: null-terminated argument list
+ * @envp: null-terminated environment list
+ * @wait: wait for the application to finish and return status.
+ *
+ * Runs a user-space application.  The application is started
+ * asynchronously if wait is not set, and runs as a child of keventd.
+ * (ie. it runs with full root capabilities).
+ *
+ * Must be called from process context.  Returns a negative error code
+ * if program was not execed successfully, or 0.
+ */
+
+int call_usermodehelper(char *path, char **argv, char **envp, int wait)
+{
+	struct simple_usermodehelper_info info = {
+		.path = path,
+		.argv = argv,
+		.envp = envp,
+	};
+	
+	if (path[0] == '\0')
+		return 0;
+
+	return call_usermodehelper_cb(call_usermodehelper_simple, &info, wait);
+}
 EXPORT_SYMBOL(call_usermodehelper);
 
 static __init int usermodehelper_init(void)

Index: linux-2.6.9-quilt/include/linux/kmod.h
===================================================================
@@ -34,6 +34,8 @@ static inline int request_module(const c
 #endif
 
 #define try_then_request_module(x, mod...) ((x) ?: (request_module(mod), (x)))
+typedef int (*call_usermodehelper_cb_t)(void *cbdata);
+extern int call_usermodehelper_cb(call_usermodehelper_cb_t cb, void *cbdata, int wait);
 extern int call_usermodehelper(char *path, char *argv[], char *envp[], int wait);
 
 #ifdef CONFIG_HOTPLUG

Index: linux-2.6.9-quilt/kernel/kmod.c
===================================================================
@@ -278,6 +278,13 @@ int call_usermodehelper_cb(call_usermode
 }
 EXPORT_SYMBOL(call_usermodehelper_cb);
 
+/* This is an ugly hack while the __KERNEL_SYSCALLS__ cleanup occurs */
+int call_usermodehelper_execve(char *path, char *argv[], char *envp[])
+{
+	return execve(path, argv, envp);
+}
+EXPORT_SYMBOL(call_usermodehelper_execve);
+
 static int call_usermodehelper_simple(void *cbdata)
 {
 	struct simple_usermodehelper_info *info = cbdata;

Index: linux-2.6.9-quilt/include/linux/kmod.h
===================================================================
@@ -36,6 +36,7 @@ static inline int request_module(const c
 #define try_then_request_module(x, mod...) ((x) ?: (request_module(mod), (x)))
 typedef int (*call_usermodehelper_cb_t)(void *cbdata);
 extern int call_usermodehelper_cb(call_usermodehelper_cb_t cb, void *cbdata, int wait);
+extern int call_usermodehelper_execve(char *path, char *argv[], char *envp[]);
 extern int call_usermodehelper(char *path, char *argv[], char *envp[], int wait);
 
 #ifdef CONFIG_HOTPLUG

Index: linux-2.6.9-quilt/fs/namespace.c
===================================================================
@@ -1733,3 +1733,4 @@ void __put_namespace(struct namespace *n
 	mntput(namespace->root);
 	kfree(namespace);
 }
+EXPORT_SYMBOL(__put_namespace);

Index: linux-2.6.9-quilt/fs/libfs.c
===================================================================
@@ -222,6 +222,7 @@ Enomem:
 	deactivate_super(s);
 	return ERR_PTR(-ENOMEM);
 }
+EXPORT_SYMBOL(get_sb_pseudo);
 
 int simple_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
 {

Index: linux-2.6.9-quilt/fs/namei.c
===================================================================
@@ -755,6 +755,7 @@ int fastcall link_path_walk(const char *
 
 		if (inode->i_op->follow_link) {
 			mntget(next.mnt);
+			nd->mnt = next.mnt;
 			err = do_follow_link(next.dentry, nd);
 			dput(next.dentry);
 			mntput(next.mnt);

@@ -809,6 +810,7 @@ last_component:
 		if ((lookup_flags & LOOKUP_FOLLOW)
 		    && inode && inode->i_op && inode->i_op->follow_link) {
 			mntget(next.mnt);
+			nd->mnt = next.mnt;
 			err = do_follow_link(next.dentry, nd);
 			dput(next.dentry);
 			mntput(next.mnt);

Index: linux-2.6.9-quilt/fs/open.c
===================================================================
@@ -121,7 +121,7 @@ asmlinkage long sys_statfs(const char __
 	struct nameidata nd;
 	int error;
 
-	error = user_path_walk(path, &nd);
+	error = user_path_walk_link(path, &nd);
 	if (!error) {
 		struct statfs tmp;
 		error = vfs_statfs_native(nd.dentry->d_inode->i_sb, &tmp);

@@ -140,7 +140,7 @@ asmlinkage long sys_statfs64(const char 
 
 	if (sz != sizeof(*buf))
 		return -EINVAL;
-	error = user_path_walk(path, &nd);
+	error = user_path_walk_link(path, &nd);
 	if (!error) {
 		struct statfs64 tmp;
 		error = vfs_statfs64(nd.dentry->d_inode->i_sb, &tmp);

Index: linux-2.6.9-quilt/include/linux/fs.h
===================================================================
@@ -735,6 +735,7 @@ extern int send_sigurg(struct fown_struc
 
 #define MNT_FORCE	0x00000001	/* Attempt to forcibily umount */
 #define MNT_DETACH	0x00000002	/* Just detach from the tree */
+#define MNT_NOFOLLOW    0x00000004      /* Do not follow symlinks */
 
 extern struct list_head super_blocks;
 extern spinlock_t sb_lock;

Index: linux-2.6.9-quilt/fs/namespace.c
===================================================================
@@ -693,8 +693,9 @@ asmlinkage long sys_umount(char __user *
 {
 	struct nameidata nd;
 	int retval;
+	int walk_flags = flags & MNT_NOFOLLOW ? 0 : LOOKUP_FOLLOW;
 
-	retval = __user_walk(name, LOOKUP_FOLLOW, &nd);
+	retval = __user_walk(name, walk_flags, &nd);
 	if (retval)
 		goto out;
 	retval = -EINVAL;

Index: linux-2.6.9-quilt/include/asm-i386/unistd.h
===================================================================
@@ -290,8 +290,9 @@
 #define __NR_mq_getsetattr	(__NR_mq_open+5)
 #define __NR_sys_kexec_load	283
 #define __NR_mountfd		300
+#define __NR_mnt_expire		301
 
-#define NR_syscalls 301
+#define NR_syscalls 302
 
 /* user-visible error numbers are in the range -1 - -124: see <asm-i386/errno.h> */
 

Index: linux-2.6.9-quilt/fs/namespace.c
===================================================================
@@ -1119,6 +1119,38 @@ static void bump_expiry_counter(struct v
 		parent->mnt_expiry_countdown = diff;
 }
 
+/* TESTING PURPOSES ONLY:  THIS IS NOT A REAL SYSCALL!! - IT WILL GO AWAY */
+asmlinkage int sys_mnt_expire(char __user *_path, int ticks)
+{
+	struct nameidata nd;
+	char *path;
+	int err;
+
+	path = getname(_path);
+	err = PTR_ERR(path);
+	if (IS_ERR(path))
+		goto out;
+
+	err = path_lookup(path, LOOKUP_FOLLOW|LOOKUP_DIRECTORY|LOOKUP_NOALT, &nd);
+	if (err)
+		goto out_name;
+
+	err = -EINVAL;
+	if (nd.mnt->mnt_root != nd.dentry)
+		goto out_nd;
+
+	err = -EBUSY;
+	if (!mnt_expire(nd.mnt, ticks))
+		err = 0;
+
+out_nd:
+	path_release(&nd);
+out_name:
+	putname(path);
+out:
+	return err;
+}
+
 /*
  * process a list of expirable mountpoints with the intent of discarding any
  * mountpoints that aren't in use and haven't been touched since last we came

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