[Devel] [PATCH RHEL8 COMMIT] block: introduce multi-page bvec helpers

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-240.1.1.vz8.5.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-240.1.1.vz8.5.30
------>
commit 7d521b8602c953563d3f3ef968c916ea8eb51125
Author: Ming Lei <ming.lei at redhat.com>
Date:   Mon May 17 19:05:01 2021 +0300

    block: introduce multi-page bvec helpers
    
    ms commit 3d75ca0adef4
    
    This patch introduces helpers of 'mp_bvec_iter_*' for multi-page 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.
    
    Follows some multi-page bvec background:
    
    - bvecs stored in bio->bi_io_vec is always multi-page style
    
    - bvec(struct bio_vec) represents one physically contiguous I/O
    buffer, now the buffer may include more than one page after
    multi-page bvec is supported, and all these pages represented
    by one bvec is physically contiguous. Before multi-page bvec
    support, at most one page is included in one bvec, we call it
    single-page bvec.
    
    - .bv_page of the bvec points to the 1st page in the multi-page bvec
    
    - .bv_offset of the bvec is the 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 single-page bvec
    
    - bio_for_each_segment_all() will return single-page bvec too
    
    - during iterating, iterator variable(struct bvec_iter) is always
    updated in multi-page bvec style, and bvec_iter_advance() is kept
    not changed
    
    - returned(copied) single-page bvec is built in flight by bvec
    helpers from the stored multi-page bvec
    
    Reviewed-by: Christoph Hellwig <hch at lst.de>
    Reviewed-by: Omar Sandoval <osandov at fb.com>
    Signed-off-by: Ming Lei <ming.lei at redhat.com>
    Signed-off-by: Jens Axboe <axboe at kernel.dk>
    
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    
    =====================
    Patchset description:
    
    dm-ploop: Kill loop
    
    Intermediate patches can't be base for bisect.
    
    In scope of https://jira.sw.ru/browse/PSBM-123654
    
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 include/linux/bvec.h | 30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index 609f328707d2..a383d77d6e86 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -23,6 +23,7 @@
 #include <linux/kernel.h>
 #include <linux/bug.h>
 #include <linux/errno.h>
+#include <linux/mm.h>
 
 /*
  * was unsigned short, but we might as well be ready for > 64kB I/O pages
@@ -57,16 +58,39 @@ struct bvec_iter {
  */
 #define __bvec_iter_bvec(bvec, iter)	(&(bvec)[(iter).bi_idx])
 
-#define bvec_iter_page(bvec, iter)				\
+/* multi-page (mp_bvec) helpers */
+#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)
+
+#define mp_bvec_iter_bvec(bvec, iter)				\
+((struct bio_vec) {						\
+	.bv_page	= mp_bvec_iter_page((bvec), (iter)),	\
+	.bv_len		= mp_bvec_iter_len((bvec), (iter)),	\
+	.bv_offset	= mp_bvec_iter_offset((bvec), (iter)),	\
+})
+
+/* For building single-page 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)),	\