Re: [PATCH v2 01/12] fs-verity: add a documentation file

[Eric Biggers]

On Mon, Dec 17, 2018 at 08:49:49AM -0800, Christoph Hellwig wrote:
> 
> > > Given that you alread use an ioctl as the interface what is the problem
> > > of passing this data through the ioctl?
> > 
> > Do you mean pass the verity metadata in a buffer?  That cannot work in general,
> > because it may be too large to fit into memory.
> 
> Have a pointer in the ioctl and do get_user_pages on it.

I don't see how that helps.  The Merkle tree can still be too large to fit in
memory.  In the worst case, it might not even fit in the address space.  And I
don't see how get_user_pages() helps either over just copy_from_user(); what are
you proposing to do with the pages after getting them, exactly?

- Eric