Re: [PATCH v6 03/34] iov_iter: Pass I/O direction into iov_iter_get_pages*()

[David Hildenbrand]

On 17.01.23 09:44, David Howells wrote:
> Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> > On Mon, Jan 16, 2023 at 11:08:24PM +0000, David Howells wrote:
> > > Define FOLL_SOURCE_BUF and FOLL_DEST_BUF to indicate to get_user_pages*()
> > > and iov_iter_get_pages*() how the buffer is intended to be used in an I/O
> > > operation.  Don't use READ and WRITE as a read I/O writes to memory and
> > > vice versa - which causes confusion.
> > >
> > > The direction is checked against the iterator's data_source.
> >
> > Why can't we use the existing FOLL_WRITE?
>
> Because FOLL_WRITE doesn't mean the same as WRITE:
>
>   (1) It looks like it should really be FOLL_CHECK_PTES_WRITABLE.  It's not
>       defined as being anything to do with the I/O.

Especially combined with FOLL_FORCE, this is not true.

--
Thanks,

David / dhildenb