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From: Kent Overstreet <kent.overstreet@gmail.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@fb.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	David Sterba <dsterba@suse.cz>, Huang Ying <ying.huang@intel.com>,
	linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	Theodore Ts'o <tytso@mit.edu>,
	"Darrick J . Wong" <darrick.wong@oracle.com>,
	Coly Li <colyli@suse.de>, Filipe Manana <fdmanana@gmail.com>,
	Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH V6 12/30] block: introduce bio_chunks()
Date: Wed, 13 Jun 2018 10:57:22 -0400	[thread overview]
Message-ID: <20180613145722.GA17340@kmo-pixel> (raw)
In-Reply-To: <20180613144741.GC4693@infradead.org>

On Wed, Jun 13, 2018 at 07:47:41AM -0700, Christoph Hellwig wrote:
> > +static inline unsigned bio_chunks(struct bio *bio)
> > +{
> > +	unsigned chunks = 0;
> > +	struct bio_vec bv;
> > +	struct bvec_iter iter;
> >  
> > -	return segs;
> > +	/*
> > +	 * We special case discard/write same/write zeroes, because they
> > +	 * interpret bi_size differently:
> > +	 */
> > +	switch (bio_op(bio)) {
> > +	case REQ_OP_DISCARD:
> > +	case REQ_OP_SECURE_ERASE:
> > +	case REQ_OP_WRITE_ZEROES:
> > +		return 0;
> > +	case REQ_OP_WRITE_SAME:
> > +		return 1;
> > +	default:
> > +		bio_for_each_chunk(bv, bio, iter)
> > +			chunks++;
> > +		return chunks;
> 
> Shouldn't this just return bio->bi_vcnt?

No.

bio->bi_vcnt is only for the owner of a bio (the code that originally allocated
it and filled it out) to use, and really the only legit use is
bio_for_each_segment_all() (iterating over segments without using bi_iter
because it's already been iterated to the end), and as a convenience thing for
bio_add_page.

Code that has a bio submitted to it can _not_ use bio->bi_vcnt, it's perfectly
legal for it to be 0 (and it is for e.g. bio splits).

  reply	other threads:[~2018-06-13 14:57 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-09 12:29 [PATCH V6 00/30] block: support multipage bvec Ming Lei
2018-06-09 12:29 ` [PATCH V6 01/30] block: simplify bio_check_pages_dirty Ming Lei
2018-06-09 12:29 ` [PATCH V6 02/30] block: bio_set_pages_dirty can't see NULL bv_page in a valid bio_vec Ming Lei
2018-06-09 12:29 ` [PATCH V6 03/30] block: use bio_add_page in bio_iov_iter_get_pages Ming Lei
2018-06-09 12:29 ` [PATCH V6 04/30] block: introduce multipage page bvec helpers Ming Lei
2018-06-09 12:29 ` [PATCH V6 05/30] block: introduce bio_for_each_chunk() Ming Lei
2018-06-09 12:29 ` [PATCH V6 06/30] block: use bio_for_each_chunk() to compute multipage bvec count Ming Lei
2018-06-09 12:29 ` [PATCH V6 07/30] block: use bio_for_each_chunk() to map sg Ming Lei
2018-06-09 12:29 ` [PATCH V6 08/30] block: introduce chunk_last_segment() Ming Lei
2018-06-11 17:19   ` Christoph Hellwig
2018-06-12  3:24     ` Ming Lei
2018-06-09 12:29 ` [PATCH V6 09/30] fs/buffer.c: use bvec iterator to truncate the bio Ming Lei
2018-06-09 12:29 ` [PATCH V6 10/30] btrfs: use chunk_last_segment to get bio's last page Ming Lei
2018-06-09 12:29 ` [PATCH V6 11/30] block: implement bio_pages_all() via bio_for_each_segment_all() Ming Lei
2018-06-13 14:44   ` Christoph Hellwig
2018-06-14  1:23     ` Ming Lei
2018-06-14  6:20       ` Christoph Hellwig
2018-06-09 12:29 ` [PATCH V6 12/30] block: introduce bio_chunks() Ming Lei
2018-06-13 14:47   ` Christoph Hellwig
2018-06-13 14:57     ` Kent Overstreet [this message]
2018-06-09 12:29 ` [PATCH V6 13/30] block: introduce rq_for_each_chunk() Ming Lei
2018-06-13 14:48   ` Christoph Hellwig
2018-06-14  1:52     ` Ming Lei
2018-06-09 12:29 ` [PATCH V6 14/30] block: loop: pass multipage chunks to iov_iter Ming Lei
2018-06-09 12:29 ` [PATCH V6 15/30] block: introduce bio_clone_chunk_bioset() Ming Lei
2018-06-13 14:56   ` Christoph Hellwig
2018-06-14  2:01     ` Ming Lei
2018-06-14  6:39       ` Christoph Hellwig
2018-06-14  7:28         ` Ming Lei
2018-06-09 12:30 ` [PATCH V6 16/30] dm: clone bio via bio_clone_chunk_bioset Ming Lei
2018-06-09 12:30 ` [PATCH V6 17/30] block: introduce bio_for_each_chunk_all and bio_for_each_chunk_segment_all Ming Lei
2018-06-09 12:30 ` [PATCH V6 18/30] block: convert to bio_for_each_chunk_segment_all() Ming Lei
2018-06-09 12:30 ` [PATCH V6 19/30] md/dm/bcache: conver to bio_for_each_chunk_segment_all and bio_for_each_chunk_all Ming Lei
2018-06-10 12:38   ` Coly Li
2018-06-13 14:57   ` Christoph Hellwig
2018-06-09 12:30 ` [PATCH V6 20/30] fs: conver to bio_for_each_chunk_segment_all() Ming Lei
2018-06-09 12:30 ` [PATCH V6 21/30] btrfs: conver to bio_for_each_chunk_segment_all Ming Lei
2018-06-09 12:30 ` [PATCH V6 22/30] ext4: " Ming Lei
2018-06-09 12:30 ` [PATCH V6 23/30] f2fs: " Ming Lei
2018-06-09 12:30 ` [PATCH V6 24/30] xfs: " Ming Lei
2018-06-09 12:30 ` [PATCH V6 25/30] exofs: " Ming Lei
2018-06-09 12:30 ` [PATCH V6 26/30] gfs2: " Ming Lei
2018-06-09 12:30 ` [PATCH V6 27/30] block: kill bio_for_each_segment_all() Ming Lei
2018-06-09 12:30 ` [PATCH V6 28/30] block: enable multipage bvecs Ming Lei
2018-06-09 12:30 ` [PATCH V6 29/30] block: always define BIO_MAX_PAGES as 256 Ming Lei
2018-06-09 12:30 ` [PATCH V6 30/30] block: document usage of bio iterator helpers Ming Lei
2018-06-15 15:43   ` Gi-Oh Kim
2018-06-11 16:48 ` [PATCH V6 00/30] block: support multipage bvec Christoph Hellwig
2018-06-12  3:42   ` Ming Lei
2018-06-13 14:42     ` Christoph Hellwig
2018-06-14  1:18       ` Ming Lei
2018-06-14  6:18         ` Christoph Hellwig
2018-06-13 14:59 ` Kent Overstreet
2018-06-14  1:20   ` Ming Lei
2018-06-15 12:59 ` Gi-Oh Kim
2018-06-21  1:17   ` Ming Lei
2018-06-21  8:40     ` Gi-Oh Kim

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