block: Add bio_for_each_segment_all()

__bio_for_each_segment() iterates bvecs from the specified index
instead of bio->bv_idx. Currently, the only usage is to walk all the
bvecs after the bio has been advanced by specifying 0 index.

For immutable bvecs, we need to split these apart;
bio_for_each_segment() is going to have a different implementation.
This will also help document the intent of code that's using it -
bio_for_each_segment_all() is only legal to use for code that owns the
bio.

Signed-off-by: Kent Overstreet <[e-mail]>
CC: Jens Axboe <[e-mail]>
CC: Neil Brown <[e-mail]>
CC: Boaz Harrosh <[e-mail]>

drivers/block/rbd.c

···
 	/* Find first affected segment... */
 
 	resid = offset;
-	__bio_for_each_segment(bv, bio_src, idx, 0) {
+	bio_for_each_segment(bv, bio_src, idx) {
 		if (resid < bv->bv_len)
 			break;
 		resid -= bv->bv_len;

drivers/md/raid1.c

···
 			 * know the original bi_idx, so we just free
 			 * them all
 			 */
-			__bio_for_each_segment(bvec, mbio, j, 0)
+			bio_for_each_segment_all(bvec, mbio, j)
 				bvec->bv_page = r1_bio->behind_bvecs[j].bv_page;
 			if (test_bit(WriteMostly, &conf->mirrors[i].rdev->flags))
 				atomic_inc(&r1_bio->behind_remaining);

fs/bio.c

···
 	int iov_idx = 0;
 	unsigned int iov_off = 0;
 
-	__bio_for_each_segment(bvec, bio, i, 0) {
+	bio_for_each_segment_all(bvec, bio, i) {
 		char *bv_addr = page_address(bvec->bv_page);
 		unsigned int bv_len = iovecs[i].bv_len;
 
···
 	return bio;
 cleanup:
 	if (!map_data)
-		bio_for_each_segment(bvec, bio, i)
+		bio_for_each_segment_all(bvec, bio, i)
 			__free_page(bvec->bv_page);
 
 	bio_put(bio);
···
 	/*
 	 * make sure we dirty pages we wrote to
 	 */
-	__bio_for_each_segment(bvec, bio, i, 0) {
+	bio_for_each_segment_all(bvec, bio, i) {
 		if (bio_data_dir(bio) == READ)
 			set_page_dirty_lock(bvec->bv_page);
 
···
 	int i;
 	char *p = bmd->sgvecs[0].iov_base;
 
-	__bio_for_each_segment(bvec, bio, i, 0) {
+	bio_for_each_segment_all(bvec, bio, i) {
 		char *addr = page_address(bvec->bv_page);
 		int len = bmd->iovecs[i].bv_len;
 
···
 	if (!reading) {
 		void *p = data;
 
-		bio_for_each_segment(bvec, bio, i) {
+		bio_for_each_segment_all(bvec, bio, i) {
 			char *addr = page_address(bvec->bv_page);
 
 			memcpy(addr, p, bvec->bv_len);
···
 	if (index >= bio->bi_idx)
 		index = bio->bi_vcnt - 1;
 
-	__bio_for_each_segment(bv, bio, i, 0) {
+	bio_for_each_segment_all(bv, bio, i) {
 		if (i == index) {
 			if (offset > bv->bv_offset)
 				sectors += (offset - bv->bv_offset) / sector_sz;

fs/exofs/ore.c

···
 	struct bio_vec *bv;
 	unsigned i;
 
-	__bio_for_each_segment(bv, bio, i, 0) {
+	bio_for_each_segment_all(bv, bio, i) {
 		unsigned this_count = bv->bv_len;
 
 		if (likely(PAGE_SIZE == this_count))

fs/exofs/ore_raid.c

···
 		if (!bio)
 			continue;
 
-		__bio_for_each_segment(bv, bio, i, 0) {
+		bio_for_each_segment_all(bv, bio, i) {
 			struct page *page = bv->bv_page;
 
 			SetPageUptodate(page);

include/linux/bio.h

···
 #define bio_io_error(bio) bio_endio((bio), -EIO)
 
 /*
- * drivers should not use the __ version unless they _really_ want to
- * run through the entire bio and not just pending pieces
+ * drivers should not use the __ version unless they _really_ know what
+ * they're doing
  */
 #define __bio_for_each_segment(bvl, bio, i, start_idx)			\
 	for (bvl = bio_iovec_idx((bio), (start_idx)), i = (start_idx);	\
 	     i < (bio)->bi_vcnt;					\
 	     bvl++, i++)
 
+/*
+ * drivers should _never_ use the all version - the bio may have been split
+ * before it got to the driver and the driver won't own all of it
+ */
+#define bio_for_each_segment_all(bvl, bio, i)				\
+	for (i = 0;							\
+	     bvl = bio_iovec_idx((bio), (i)), i < (bio)->bi_vcnt;	\
+	     i++)
+
 #define bio_for_each_segment(bvl, bio, i)				\
-	__bio_for_each_segment(bvl, bio, i, (bio)->bi_idx)
+	for (i = (bio)->bi_idx;						\
+	     bvl = bio_iovec_idx((bio), (i)), i < (bio)->bi_vcnt;	\
+	     i++)
 
 /*
  * get a reference to a bio, so it won't disappear. the intended use is

mm/bounce.c

···
 	/*
 	 * free up bounce indirect pages used
 	 */
-	__bio_for_each_segment(bvec, bio, i, 0) {
+	bio_for_each_segment_all(bvec, bio, i) {
 		org_vec = bio_orig->bi_io_vec + i;
 		if (bvec->bv_page == org_vec->bv_page)
 			continue;