dm io: use bvec iterator helpers to implement .get_page and .next_page

Firstly we have mature bvec/bio iterator helper for iterate each
page in one bio, not necessary to reinvent a wheel to do that.

Secondly the coming multipage bvecs requires this patch.

Also add comments about the direct access to bvec table.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 24 insertions, 10 deletions

diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index 0bf1a12e35fe..03940bf36f6c 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -162,7 +162,10 @@ struct dpages {
                          struct page **p, unsigned long *len, unsigned *offset);
         void (*next_page)(struct dpages *dp);
 
-        unsigned context_u;
+        union {
+                unsigned context_u;
+                struct bvec_iter context_bi;
+        };
         void *context_ptr;
 
         void *vma_invalidate_address;
@@ -204,25 +207,36 @@ static void list_dp_init(struct dpages *dp, struct page_list *pl, unsigned offse
 static void bio_get_page(struct dpages *dp, struct page **p,
                          unsigned long *len, unsigned *offset)
 {
-        struct bio_vec *bvec = dp->context_ptr;
-        *p = bvec->bv_page;
-        *len = bvec->bv_len - dp->context_u;
-        *offset = bvec->bv_offset + dp->context_u;
+        struct bio_vec bvec = bvec_iter_bvec((struct bio_vec *)dp->context_ptr,
+                                             dp->context_bi);
+
+        *p = bvec.bv_page;
+        *len = bvec.bv_len;
+        *offset = bvec.bv_offset;
+
+        /* avoid figuring it out again in bio_next_page() */
+        dp->context_bi.bi_sector = (sector_t)bvec.bv_len;
 }
 
 static void bio_next_page(struct dpages *dp)
 {
-        struct bio_vec *bvec = dp->context_ptr;
-        dp->context_ptr = bvec + 1;
-        dp->context_u = 0;
+        unsigned int len = (unsigned int)dp->context_bi.bi_sector;
+
+        bvec_iter_advance((struct bio_vec *)dp->context_ptr,
+                          &dp->context_bi, len);
 }
 
 static void bio_dp_init(struct dpages *dp, struct bio *bio)
 {
         dp->get_page = bio_get_page;
         dp->next_page = bio_next_page;
-        dp->context_ptr = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
-        dp->context_u = bio->bi_iter.bi_bvec_done;
+
+        /*
+         * We just use bvec iterator to retrieve pages, so it is ok to
+         * access the bvec table directly here
+         */
+        dp->context_ptr = bio->bi_io_vec;
+        dp->context_bi = bio->bi_iter;
 }
 
 /*