Re: [PATCH 0/5] bio: Direct IO: convert to pin_user_pages_fast()

[Al Viro <viro@xxxxxxxxxxxxxxxxxx>]

On Fri, Aug 21, 2020 at 09:20:54PM -0700, John Hubbard wrote:

> Direct IO behavior:
> 
>     ITER_IOVEC:
>         pin_user_pages_fast();
>         break;
> 
>     ITER_KVEC:    // already elevated page refcount, leave alone
>     ITER_BVEC:    // already elevated page refcount, leave alone
>     ITER_PIPE:    // just, no :)

Why?  What's wrong with splice to O_DIRECT file?