From: Ming Lei ming.lei@redhat.com
commit 3d75ca0adef4280650c6690a0c4702a74a6f3c95 upstream.
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@lst.de Reviewed-by: Omar Sandoval osandov@fb.com Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Cc: Zubin Mithra zsm@chromium.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/bvec.h | 30 +++++++++++++++++++++++++++--- 1 file changed, 27 insertions(+), 3 deletions(-)
--- 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 @@ -52,16 +53,39 @@ 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)), \