[PATCH] dm: support ioctls on mapped devices: fix with fake file

The new ioctl code passes the wrong file pointer to the underlying device.
No file pointer is available so make a temporary fake one.

ioctl_by_bdev() does set_fs(KERNEL_DS) so it's for ioctls originating
within the kernel and unsuitable here.  We are processing ioctls that
originated in userspace and mapping them to different devices.  Fixing the
existing callers that pass a NULL file struct and consolidating the
fake_file users are separate matters to solve in later patches.
Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/md/dm-linear.c

@@ -104,8 +104,14 @@ static int linear_ioctl(struct dm_target *ti, struct inode *inode,
 {
 	struct linear_c *lc = (struct linear_c *) ti->private;
 	struct block_device *bdev = lc->dev->bdev;
+	struct file fake_file = {};
+	struct dentry fake_dentry = {};
 
-	return blkdev_driver_ioctl(bdev->bd_inode, filp, bdev->bd_disk, cmd, arg);
+	fake_file.f_mode = lc->dev->mode;
+	fake_file.f_dentry = &fake_dentry;
+	fake_dentry.d_inode = bdev->bd_inode;
+
+	return blkdev_driver_ioctl(bdev->bd_inode, &fake_file, bdev->bd_disk, cmd, arg);
 }
 
 static struct target_type linear_target = {

drivers/md/dm-mpath.c

@@ -1273,15 +1273,22 @@ static int multipath_ioctl(struct dm_target *ti, struct inode *inode,
 	struct multipath *m = (struct multipath *) ti->private;
 	struct block_device *bdev = NULL;
 	unsigned long flags;
+	struct file fake_file = {};
+	struct dentry fake_dentry = {};
 	int r = 0;
 
+	fake_file.f_dentry = &fake_dentry;
+
 	spin_lock_irqsave(&m->lock, flags);
 
 	if (!m->current_pgpath)
 		__choose_pgpath(m);
 
-	if (m->current_pgpath)
+	if (m->current_pgpath) {
 		bdev = m->current_pgpath->path.dev->bdev;
+		fake_dentry.d_inode = bdev->bd_inode;
+		fake_file.f_mode = m->current_pgpath->path.dev->mode;
+	}
 
 	if (m->queue_io)
 		r = -EAGAIN;
@@ -1290,8 +1297,8 @@ static int multipath_ioctl(struct dm_target *ti, struct inode *inode,
 
 	spin_unlock_irqrestore(&m->lock, flags);
 
-	return r ? : blkdev_driver_ioctl(bdev->bd_inode, filp, bdev->bd_disk,
-		     cmd, arg);
+	return r ? : blkdev_driver_ioctl(bdev->bd_inode, &fake_file,
+					 bdev->bd_disk, cmd, arg);
 }
 
 /*-----------------------------------------------------------------