Re: ecryptfs

[Michael Halcrow <mhalcrow@us.ibm.com>]

On Mon, Aug 07, 2006 at 01:21:04PM -0400, Josef Sipek wrote:
> On Mon, Aug 07, 2006 at 11:31:15AM -0500, Michael Halcrow wrote:
> ...
> > Here is where I am thinking about going with crossing lower mount
> > points. This patch makes sure that there is a 1-to-1 mapping in
> > inode numbers between the stacked inodes and the lower inodes. It
> > maintains the association by modifying the struct inode to include
> > a back pointer from the lower inode to the stacked inode.
> 
> Do you maintain the inode numbers across mounts (of ecryptfs)? The
> patch doesn't look like it does.

Nope; this patch just aims to make sure that stacked and lower inodes
maintain a 1-to-1 relationship.

> > +		inode->i_private = NULL;
> > +#ifdef CONFIG_STACK_FS
> > +		inode->i_stacked_inode = NULL;
> > +#endif
> >  		inode->i_mapping = mapping;
> 
> Hrm. Looking at this made me think...This patch introduces pointers
> up the stack in the VFS. Would it make sense to introduce the down
> pointers as well, and make ecryptfs, et. al., depend on STACK_FS?
> This would clean up some of the use of private data. Of course these
> pointers (the up & down) make struct inode grow 8 bytes (on 32-bit
> systems).

I would say that using the existing private data pointer is a better
option than consuming more space in each and every inode struct.

Mike