linux-kernel - Re: [PATCH v6 03/34] iov_iter: Pass I/O direction into iov_iter_get

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Date:   Tue, 17 Jan 2023 00:09:30 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v6 03/34] iov_iter: Pass I/O direction into
 iov_iter_get_pages*()

On Tue, Jan 17, 2023 at 09:07:48AM +0100, David Hildenbrand wrote:
> Agreed. What I understand, David considers that confusing when considering
> the I/O side of things.
> 
> I recall that there is
> 
> DMA_BIDIRECTIONAL -> FOLL_WRITE
> DMA_TO_DEVICE -> !FOLL_WRITE
> DMA_FROM_DEVICE -> FOLL_WRITE
> 
> that used different defines for a different API. Such terminology would be
> easier to get ... but then, again, not sure if we really need acronyms here.
> 
> We're pinning pages and FOLL_WRITE defines how we (pinning the page) are
> going to access these pages: R/O or R/W. So the read vs. write is never from
> the POC of the device (DMA read will write to the page).

Yes.  Maybe the name could be a little more verboe, FOLL_MEM_WRITE or
FOLL_WRITE_TO_MEM.  But I'd really prefer any renaming to be split from
logic changes.