On Sat, Aug 25, 2018 at 12:47 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> Actually, I believe the intention was that fs developers don't need to worry
> about using file_inode() at all, because before the change we had:
>
> - file passed in to xfs f_op's and a_ops is either overlay file OR xfs file
> - file_inode() of either overlay/xfs file in xfs context is always xfs inode
> - file->f_path in xfs context, BTW, was overlay path and therefore,
> XFS_IOC_OPEN_BY_HANDLE was slightly broken in overlayfs over xfs,
> as were several other fs specific ioctls
>
> After stacked file operations change we should have the rules:
>
> 1. file passed in to xfs f_op's is always xfs file (*)
> 2. file passed in to xfs a_ops is always xfs file (**)
> 3. file_inode() of overlay file is an overlay inode
>
> (*) as explicit file argument or on iocb->ki_filp
> (**) as explicit file argument or on ->vm_file
>
> I believe that swapfile leaking an overlay file into xfs was an oversight,
> that is breaking rule #2.
Correct.
I believe the root cause is this
/* For O_DIRECT dentry_open() checks f_mapping->a_ops->direct_IO */
file->f_mapping = realfile->f_mapping;
in ovl_open(). So lets start with removing that. That should fix any
oopses related to this, but we'll have some other issues:
1) open(..., O_DIRECT) will return an error
This is easy to fix: add ovl_file_aops with a dummy ovl_direct_IO()
function that will never be called.
2) swapon() will return an error
First question that comes to mind: does anybody care? I wouldn't
think swapfiles would be an important feature for overlayfs, but we
did support them up till now, so removing support might cause a
regression somewhere out there. Unfortunate...
Thanks,
Miklos
