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Date: Tue, 4 Dec 2018 15:55:13 +0100
From: Christoph Hellwig <hch@lst.de>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, hch@lst.de
Subject: Re: [PATCH 24/27] block: implement bio helper to add iter kvec
 pages to bio
Message-ID: <20181204145513.GH3180@lst.de>
References: <20181130165646.27341-1-axboe@kernel.dk> <20181130165646.27341-25-axboe@kernel.dk> <20181130192102.GP2217@ZenIV.linux.org.uk>
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On Fri, Nov 30, 2018 at 07:21:02PM +0000, Al Viro wrote:
> On Fri, Nov 30, 2018 at 09:56:43AM -0700, Jens Axboe wrote:
> > For an ITER_KVEC, we can just iterate the iov and add the pages
> > to the bio directly.
> 
> > +		page = virt_to_page(kv->iov_base);
> > +		size = bio_add_page(bio, page, kv->iov_len,
> > +					offset_in_page(kv->iov_base));
> 
> Who said that you *can* do virt_to_page() on those?  E.g. vmalloc()'ed
> addresses are fine for ITER_KVEC, etc.

In this particular case the caller it seems the callers knows what kind
of pages we have, but we need to properly document this at the very least.

Note that in the completely generic case iov_base could also point to
memory without a struct page at all (e.g. ioremap()ed memory).