linux-kernel - Re: [RFC PATCH 2/7] block: convert bio_vec.bv_page to bv

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Message-ID: <20150317130254.GC4003@linux.intel.com>
Date:	Tue, 17 Mar 2015 09:02:54 -0400
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	axboe@...nel.dk, riel@...hat.com, linux-nvdimm@...1.01.org,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	linux-raid@...r.kernel.org, mgorman@...e.de, hch@...radead.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH 2/7] block: convert bio_vec.bv_page to bv_pfn

On Mon, Mar 16, 2015 at 11:05:33PM +0000, Al Viro wrote:
> > diff --git a/mm/iov_iter.c b/mm/iov_iter.c
> > index 827732047da1..be9a7c5b8703 100644
> > --- a/mm/iov_iter.c
> > +++ b/mm/iov_iter.c
> > @@ -61,7 +61,7 @@
> >  	__p = i->bvec;					\
> >  	__v.bv_len = min_t(size_t, n, __p->bv_len - skip);	\
> >  	if (likely(__v.bv_len)) {			\
> > -		__v.bv_page = __p->bv_page;		\
> > +		__v.bv_pfn = __p->bv_pfn;		\
> >  		__v.bv_offset = __p->bv_offset + skip; 	\
> >  		(void)(STEP);				\
> >  		skip += __v.bv_len;			\
> > @@ -72,7 +72,7 @@
> >  		__v.bv_len = min_t(size_t, n, __p->bv_len);	\
> >  		if (unlikely(!__v.bv_len))		\
> >  			continue;			\
> > -		__v.bv_page = __p->bv_page;		\
> > +		__v.bv_pfn = __p->bv_pfn;		\
> >  		__v.bv_offset = __p->bv_offset;		\
> >  		(void)(STEP);				\
> >  		skip = __v.bv_len;			\
> > @@ -369,7 +369,7 @@ size_t copy_to_iter(void *addr, size_t bytes, struct iov_iter *i)
> >  	iterate_and_advance(i, bytes, v,
> >  		__copy_to_user(v.iov_base, (from += v.iov_len) - v.iov_len,
> >  			       v.iov_len),
> > -		memcpy_to_page(v.bv_page, v.bv_offset,
> > +		memcpy_to_page(bvec_page(&v), v.bv_offset,
> 
> How had memcpy_to_page(NULL, ...) worked for you?

 static inline struct page *bvec_page(const struct bio_vec *bvec)
 {
-       return bvec->bv_page;
+       return pfn_to_page(bvec->bv_pfn.pfn);
 }

(yes, more work to be done here to make copy_to_iter work to a bvec that
is actually targetting a page-less address, but these are RFC patches
showing the direction we're heading in while keeping current code working)

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