linux-kernel - Re: [PATCH v8 02/10] iov_iter: Add a function to extract a page list from an iterator

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Date:   Tue, 24 Jan 2023 14:35:59 +0000
From:   David Howells <dhowells@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     dhowells@...hat.com, Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        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, Christoph Hellwig <hch@....de>,
        John Hubbard <jhubbard@...dia.com>, linux-mm@...ck.org
Subject: Re: [PATCH v8 02/10] iov_iter: Add a function to extract a page list from an iterator

David Hildenbrand <david@...hat.com> wrote:

> > +#define iov_iter_extract_mode(iter) (user_backed_iter(iter) ? FOLL_PIN : 0)
> > +
> 
> Does it make sense to move that to the patch where it is needed? (do we need
> it at all anymore?)

Yes, we need something.  Granted, there are now only two alternatives, not
three: either the pages are going to be pinned or they're not going to be
pinned, but I would rather have a specific function that tells you than just
use, say, user_backed_iter() to make it easier to adjust it later if we need
to - and easier to find the places where we need to adjust.

But if it's preferred we could require people to use user_backed_iter()
instead.

David