Re: [PATCH 01/15] dm: support ioctls on mapped devices

[Andrew Morton <akpm@osdl.org>]

On Thu, 22 Jun 2006 16:17:21 +0100
Alasdair G Kergon <agk@redhat.com> wrote:

> On Thu, Jun 22, 2006 at 01:29:57AM -0700, Andrew Morton wrote:
> > OK.  I do think dm needs to remember /dev/sda's file* to get this right
> > though.  That's where the ->ioctl methods are.
> 
> > Oh dear.  raw_open() doesn't have a file* for the device.
>  
> Similar with device-mapper: in normal usage dm only sees major:minor.
> 
> Yes, the filp dm passes along is incorrect:
> 
> - return blkdev_driver_ioctl(bdev->bd_inode, filp, bdev->bd_disk, cmd, arg);
> + return blkdev_driver_ioctl(bdev->bd_inode, NULL, bdev->bd_disk, cmd, arg);
> 
> But should unlocked_ioctl become ?
> 
> - long (*unlocked_ioctl) (struct file *, unsigned, unsigned long);
> + long (*unlocked_ioctl) (struct inode *, struct file *, unsigned, unsigned long);
> 
> so it can be used for block devices?

Perhaps it should (have).  It's a bit nasty, but we do have at least two
internal callers who don't have a file*.

The alternative would be to cook up a fake file* like blkdev_get() does,
but we don't want to propagate that practice.

Oh well.  I suppose a lock_kernel() won't kill us.

> See also block/scsi_ioctl.c:201 verify_command()  [scsi_cmd_ioctl]
>          * file can be NULL from ioctl_by_bdev()...
> 
> Or should we be working towards eliminating interfaces that use device numbers?

If possible.  I guess that would require DM to track the devices with
file*'s or inode*'s or bdev*'s.  Which, I assume, would be non-trivial.