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Subject[PATCH V10 01/19] block: introduce multi-page page bvec helpers
Date
This patch introduces helpers of 'mp_bvec_iter_*' for multipage
bvec support.

The introduced helpers treate one bvec as real multi-page segment,
which may include more than one pages.

The existed helpers of bvec_iter_* are interfaces for supporting current
bvec iterator which is thought as single-page by drivers, fs, dm and
etc. These introduced helpers will build single-page bvec in flight, so
this way won't break current bio/bvec users, which needn't any change.

Cc: Dave Chinner <dchinner@redhat.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: dm-devel@redhat.com
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Cc: Shaohua Li <shli@kernel.org>
Cc: linux-raid@vger.kernel.org
Cc: linux-erofs@lists.ozlabs.org
Cc: David Sterba <dsterba@suse.com>
Cc: linux-btrfs@vger.kernel.org
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: linux-xfs@vger.kernel.org
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: linux-ext4@vger.kernel.org
Cc: Coly Li <colyli@suse.de>
Cc: linux-bcache@vger.kernel.org
Cc: Boaz Harrosh <ooo@electrozaur.com>
Cc: Bob Peterson <rpeterso@redhat.com>
Cc: cluster-devel@redhat.com
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
include/linux/bvec.h | 63 +++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 60 insertions(+), 3 deletions(-)

diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index 02c73c6aa805..8ef904a50577 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -23,6 +23,44 @@
#include <linux/kernel.h>
#include <linux/bug.h>
#include <linux/errno.h>
+#include <linux/mm.h>
+
+/*
+ * What is multi-page bvecs?
+ *
+ * - bvecs stored in bio->bi_io_vec is always multi-page(mp) style
+ *
+ * - bvec(struct bio_vec) represents one physically contiguous I/O
+ * buffer, now the buffer may include more than one pages after
+ * multi-page(mp) bvec is supported, and all these pages represented
+ * by one bvec is physically contiguous. Before mp support, at most
+ * one page is included in one bvec, we call it single-page(sp)
+ * bvec.
+ *
+ * - .bv_page of the bvec represents the 1st page in the mp bvec
+ *
+ * - .bv_offset of the bvec represents offset of the buffer in the bvec
+ *
+ * The effect on the current drivers/filesystem/dm/bcache/...:
+ *
+ * - almost everyone supposes that one bvec only includes one single
+ * page, so we keep the sp interface not changed, for example,
+ * bio_for_each_segment() still returns bvec with single page
+ *
+ * - bio_for_each_segment*() will be changed to return single-page
+ * bvec too
+ *
+ * - during iterating, iterator variable(struct bvec_iter) is always
+ * updated in multipage bvec style and that means bvec_iter_advance()
+ * is kept not changed
+ *
+ * - returned(copied) single-page bvec is built in flight by bvec
+ * helpers from the stored multipage bvec
+ *
+ * - In case that some components(such as iov_iter) need to support
+ * multi-page bvec, we introduce new helpers(mp_bvec_iter_*) for
+ * them.
+ */

/*
* was unsigned short, but we might as well be ready for > 64kB I/O pages
@@ -50,16 +88,35 @@ struct bvec_iter {
*/
#define __bvec_iter_bvec(bvec, iter) (&(bvec)[(iter).bi_idx])

-#define bvec_iter_page(bvec, iter) \
+#define mp_bvec_iter_page(bvec, iter) \
(__bvec_iter_bvec((bvec), (iter))->bv_page)

-#define bvec_iter_len(bvec, iter) \
+#define mp_bvec_iter_len(bvec, iter) \
min((iter).bi_size, \
__bvec_iter_bvec((bvec), (iter))->bv_len - (iter).bi_bvec_done)

-#define bvec_iter_offset(bvec, iter) \
+#define mp_bvec_iter_offset(bvec, iter) \
(__bvec_iter_bvec((bvec), (iter))->bv_offset + (iter).bi_bvec_done)

+#define mp_bvec_iter_page_idx(bvec, iter) \
+ (mp_bvec_iter_offset((bvec), (iter)) / PAGE_SIZE)
+
+/*
+ * <page, offset,length> of single-page(sp) segment.
+ *
+ * This helpers are for building sp bvec in flight.
+ */
+#define bvec_iter_offset(bvec, iter) \
+ (mp_bvec_iter_offset((bvec), (iter)) % PAGE_SIZE)
+
+#define bvec_iter_len(bvec, iter) \
+ min_t(unsigned, mp_bvec_iter_len((bvec), (iter)), \
+ (PAGE_SIZE - (bvec_iter_offset((bvec), (iter)))))
+
+#define bvec_iter_page(bvec, iter) \
+ nth_page(mp_bvec_iter_page((bvec), (iter)), \
+ mp_bvec_iter_page_idx((bvec), (iter)))
+
#define bvec_iter_bvec(bvec, iter) \
((struct bio_vec) { \
.bv_page = bvec_iter_page((bvec), (iter)), \
--
2.9.5
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