mtdchar: kill persistently held vfsmount

... and mtdchar_notifier along with it; just have ->drop_inode() that
will unconditionally get evict them instead of dances on mtd device
removal and use simple_pin_fs() instead of kern_mount()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/mtd/mtdchar.c

@@ -39,7 +39,6 @@
 #include <asm/uaccess.h>
 
 static DEFINE_MUTEX(mtd_mutex);
-static struct vfsmount *mtd_inode_mnt __read_mostly;
 
 /*
  * Data structure to hold the pointer to the mtd device as well
@@ -75,7 +74,9 @@ static loff_t mtdchar_lseek(struct file *file, loff_t offset, int orig)
 	return -EINVAL;
 }
 
-
+static int count;
+static struct vfsmount *mnt;
+static struct file_system_type mtd_inodefs_type;
 
 static int mtdchar_open(struct inode *inode, struct file *file)
 {
@@ -92,6 +93,10 @@ static int mtdchar_open(struct inode *inode, struct file *file)
 	if ((file->f_mode & FMODE_WRITE) && (minor & 1))
 		return -EACCES;
 
+	ret = simple_pin_fs(&mtd_inodefs_type, &mnt, &count);
+	if (ret)
+		return ret;
+
 	mutex_lock(&mtd_mutex);
 	mtd = get_mtd_device(NULL, devnum);
 
@@ -106,7 +111,7 @@ static int mtdchar_open(struct inode *inode, struct file *file)
 		goto out;
 	}
 
-	mtd_ino = iget_locked(mtd_inode_mnt->mnt_sb, devnum);
+	mtd_ino = iget_locked(mnt->mnt_sb, devnum);
 	if (!mtd_ino) {
 		put_mtd_device(mtd);
 		ret = -ENOMEM;
@@ -141,6 +146,7 @@ static int mtdchar_open(struct inode *inode, struct file *file)
 
 out:
 	mutex_unlock(&mtd_mutex);
+	simple_release_fs(&mnt, &count);
 	return ret;
 } /* mtdchar_open */
 
@@ -162,6 +168,7 @@ static int mtdchar_close(struct inode *inode, struct file *file)
 	put_mtd_device(mtd);
 	file->private_data = NULL;
 	kfree(mfi);
+	simple_release_fs(&mnt, &count);
 
 	return 0;
 } /* mtdchar_close */
@@ -1175,10 +1182,15 @@ static const struct file_operations mtd_fops = {
 #endif
 };
 
+static const struct super_operations mtd_ops = {
+	.drop_inode = generic_delete_inode,
+	.statfs = simple_statfs,
+};
+
 static struct dentry *mtd_inodefs_mount(struct file_system_type *fs_type,
 				int flags, const char *dev_name, void *data)
 {
-	return mount_pseudo(fs_type, "mtd_inode:", NULL, NULL, MTD_INODE_FS_MAGIC);
+	return mount_pseudo(fs_type, "mtd_inode:", &mtd_ops, NULL, MTD_INODE_FS_MAGIC);
 }
 
 static struct file_system_type mtd_inodefs_type = {
@@ -1187,26 +1199,6 @@ static struct file_system_type mtd_inodefs_type = {
        .kill_sb = kill_anon_super,
 };
 
-static void mtdchar_notify_add(struct mtd_info *mtd)
-{
-}
-
-static void mtdchar_notify_remove(struct mtd_info *mtd)
-{
-	struct inode *mtd_ino = ilookup(mtd_inode_mnt->mnt_sb, mtd->index);
-
-	if (mtd_ino) {
-		/* Destroy the inode if it exists */
-		clear_nlink(mtd_ino);
-		iput(mtd_ino);
-	}
-}
-
-static struct mtd_notifier mtdchar_notifier = {
-	.add = mtdchar_notify_add,
-	.remove = mtdchar_notify_remove,
-};
-
 static int __init init_mtdchar(void)
 {
 	int ret;
@@ -1224,19 +1216,8 @@ static int __init init_mtdchar(void)
 		pr_notice("Can't register mtd_inodefs filesystem: %d\n", ret);
 		goto err_unregister_chdev;
 	}
-
-	mtd_inode_mnt = kern_mount(&mtd_inodefs_type);
-	if (IS_ERR(mtd_inode_mnt)) {
-		ret = PTR_ERR(mtd_inode_mnt);
-		pr_notice("Error mounting mtd_inodefs filesystem: %d\n", ret);
-		goto err_unregister_filesystem;
-	}
-	register_mtd_user(&mtdchar_notifier);
-
 	return ret;
 
-err_unregister_filesystem:
-	unregister_filesystem(&mtd_inodefs_type);
 err_unregister_chdev:
 	__unregister_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS, "mtd");
 	return ret;
@@ -1244,8 +1225,6 @@ static int __init init_mtdchar(void)
 
 static void __exit cleanup_mtdchar(void)
 {
-	unregister_mtd_user(&mtdchar_notifier);
-	kern_unmount(mtd_inode_mnt);
 	unregister_filesystem(&mtd_inodefs_type);
 	__unregister_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS, "mtd");
 }