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

From: Eric Biggers
Date: Mon Dec 17 2018 - 13:32:10 EST

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