block: introduce mp_bvec_last_segment()

BTRFS and guard_bio_eod() need to get the last singlepage segment
from one multipage bvec, so introduce this helper to make them happy.

Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index 0ae729b..21f76ba 100644 (file)
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -131,4 +131,26 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
        .bi_bvec_done   = 0,                                            \
 }
 
+/*
+ * Get the last single-page segment from the multi-page bvec and store it
+ * in @seg
+ */
+static inline void mp_bvec_last_segment(const struct bio_vec *bvec,
+                                       struct bio_vec *seg)
+{
+       unsigned total = bvec->bv_offset + bvec->bv_len;
+       unsigned last_page = (total - 1) / PAGE_SIZE;
+
+       seg->bv_page = nth_page(bvec->bv_page, last_page);
+
+       /* the whole segment is inside the last page */
+       if (bvec->bv_offset >= last_page * PAGE_SIZE) {
+               seg->bv_offset = bvec->bv_offset % PAGE_SIZE;
+               seg->bv_len = bvec->bv_len;
+       } else {
+               seg->bv_offset = 0;
+               seg->bv_len = total - last_page * PAGE_SIZE;
+       }
+}
+
 #endif /* __LINUX_BVEC_ITER_H */