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

[Al Viro]

On Mon, Jan 16, 2023 at 11:57:08PM -0800, Christoph Hellwig 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?

	I'm really not fond of passing FOLL_... stuff into iov_iter
primitives.  That space contains things like FOLL_PIN, which makes
no sense whatsoever for non-user-backed iterators; having the
callers pass it in makes them automatically dependent upon the
iov_iter flavour.