dm: bio list helpers

More bio_list helper functions for new targets (including dm-delay and
dm-loop) to manipulate lists of bios.

Signed-off-by: Heinz Mauelshagen <hjm@redhat.com>
Signed-off-by: Bryn Reeves <breeves@redhat.com>
Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: Heinz Mauelshagen

drivers/md/dm-bio-list.h

@@ -8,17 +8,43 @@
 #define DM_BIO_LIST_H
 
 #include <linux/bio.h>
+#include <linux/prefetch.h>
 
 struct bio_list {
 	struct bio *head;
 	struct bio *tail;
 };
 
+static inline int bio_list_empty(const struct bio_list *bl)
+{
+	return bl->head == NULL;
+}
+
+#define BIO_LIST_INIT { .head = NULL, .tail = NULL }
+
+#define BIO_LIST(bl) \
+	struct bio_list bl = BIO_LIST_INIT
+
 static inline void bio_list_init(struct bio_list *bl)
 {
 	bl->head = bl->tail = NULL;
 }
 
+#define bio_list_for_each(bio, bl) \
+	for (bio = (bl)->head; bio && ({ prefetch(bio->bi_next); 1; }); \
+	     bio = bio->bi_next)
+
+static inline unsigned bio_list_size(const struct bio_list *bl)
+{
+	unsigned sz = 0;
+	struct bio *bio;
+
+	bio_list_for_each(bio, bl)
+		sz++;
+
+	return sz;
+}
+
 static inline void bio_list_add(struct bio_list *bl, struct bio *bio)
 {
 	bio->bi_next = NULL;