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Date: Thu, 22 Sep 2022 15:36:52 +0100 From: Al Viro <viro@...iv.linux.org.uk> To: Christoph Hellwig <hch@...radead.org> Cc: Jan Kara <jack@...e.cz>, John Hubbard <jhubbard@...dia.com>, Andrew Morton <akpm@...ux-foundation.org>, Jens Axboe <axboe@...nel.dk>, Miklos Szeredi <miklos@...redi.hu>, "Darrick J . Wong" <djwong@...nel.org>, Trond Myklebust <trond.myklebust@...merspace.com>, Anna Schumaker <anna@...nel.org>, David Hildenbrand <david@...hat.com>, Logan Gunthorpe <logang@...tatee.com>, linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org, linux-nfs@...r.kernel.org, linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2 4/7] iov_iter: new iov_iter_pin_pages*() routines On Thu, Sep 22, 2022 at 07:31:36AM -0700, Christoph Hellwig wrote: > On Wed, Sep 14, 2022 at 04:51:17AM +0100, Al Viro wrote: > > Unless I'm misreading Jan, the question is whether they should get or > > pin. > > And I think the answer is: inside ->read_iter or ->write_iter they > should neither get or pin. The callers of it need to pin the pages > if they are pagecache pages that can potentially be written to through > shared mappings, else a get would be enough. But the method instance > should not have to care and just be able to rely on the caller making > sure they do not go away. The interesting part, AFAICS, is where do we _unpin_ them and how do we keep track which pages (obtained from iov_iter_get_pages et.al.) need to be unpinned. > > I'm really tempted to slap > > if (WARN_ON(i->data_source)) > > return 0; > > into copy_to_iter() et.al., along with its opposite for copy_from_iter(). > > Ys, I think that would be useful. And we could use something more > descriptive than READ/WRITE to start with. See #work.iov_iter; done, but it took a bit of fixing the places that create iov_iter instances.
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