So far bio list helpers always use .bi_next to traverse the list, we
will support to link bios by other bio field.

Prepare for such support by adding a macro so that users can define
another helpers for linking bios by other bio field.

Reviewed-by: Hannes Reinecke <h...@suse.de>
Signed-off-by: Ming Lei <ming....@redhat.com>
---
 include/linux/bio.h | 132 +++++++++++++++++++++++---------------------
 1 file changed, 68 insertions(+), 64 deletions(-)

diff --git a/include/linux/bio.h b/include/linux/bio.h
index d0246c92a6e8..619edd26a6c0 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -608,75 +608,11 @@ static inline unsigned bio_list_size(const struct 
bio_list *bl)
        return sz;
 }
 
-static inline void bio_list_add(struct bio_list *bl, struct bio *bio)
-{
-       bio->bi_next = NULL;
-
-       if (bl->tail)
-               bl->tail->bi_next = bio;
-       else
-               bl->head = bio;
-
-       bl->tail = bio;
-}
-
-static inline void bio_list_add_head(struct bio_list *bl, struct bio *bio)
-{
-       bio->bi_next = bl->head;
-
-       bl->head = bio;
-
-       if (!bl->tail)
-               bl->tail = bio;
-}
-
-static inline void bio_list_merge(struct bio_list *bl, struct bio_list *bl2)
-{
-       if (!bl2->head)
-               return;
-
-       if (bl->tail)
-               bl->tail->bi_next = bl2->head;
-       else
-               bl->head = bl2->head;
-
-       bl->tail = bl2->tail;
-}
-
-static inline void bio_list_merge_head(struct bio_list *bl,
-                                      struct bio_list *bl2)
-{
-       if (!bl2->head)
-               return;
-
-       if (bl->head)
-               bl2->tail->bi_next = bl->head;
-       else
-               bl->tail = bl2->tail;
-
-       bl->head = bl2->head;
-}
-
 static inline struct bio *bio_list_peek(struct bio_list *bl)
 {
        return bl->head;
 }
 
-static inline struct bio *bio_list_pop(struct bio_list *bl)
-{
-       struct bio *bio = bl->head;
-
-       if (bio) {
-               bl->head = bl->head->bi_next;
-               if (!bl->head)
-                       bl->tail = NULL;
-
-               bio->bi_next = NULL;
-       }
-
-       return bio;
-}
-
 static inline struct bio *bio_list_get(struct bio_list *bl)
 {
        struct bio *bio = bl->head;
@@ -686,6 +622,74 @@ static inline struct bio *bio_list_get(struct bio_list *bl)
        return bio;
 }
 
+#define BIO_LIST_HELPERS(_pre, link)                                   \
+                                                                       \
+static inline void _pre##_add(struct bio_list *bl, struct bio *bio)    \
+{                                                                      \
+       bio->bi_##link = NULL;                                          \
+                                                                       \
+       if (bl->tail)                                                   \
+               bl->tail->bi_##link = bio;                              \
+       else                                                            \
+               bl->head = bio;                                         \
+                                                                       \
+       bl->tail = bio;                                                 \
+}                                                                      \
+                                                                       \
+static inline void _pre##_add_head(struct bio_list *bl, struct bio *bio) \
+{                                                                      \
+       bio->bi_##link = bl->head;                                      \
+                                                                       \
+       bl->head = bio;                                                 \
+                                                                       \
+       if (!bl->tail)                                                  \
+               bl->tail = bio;                                         \
+}                                                                      \
+                                                                       \
+static inline void _pre##_merge(struct bio_list *bl, struct bio_list *bl2) \
+{                                                                      \
+       if (!bl2->head)                                                 \
+               return;                                                 \
+                                                                       \
+       if (bl->tail)                                                   \
+               bl->tail->bi_##link = bl2->head;                        \
+       else                                                            \
+               bl->head = bl2->head;                                   \
+                                                                       \
+       bl->tail = bl2->tail;                                           \
+}                                                                      \
+                                                                       \
+static inline void _pre##_merge_head(struct bio_list *bl,              \
+                                      struct bio_list *bl2)            \
+{                                                                      \
+       if (!bl2->head)                                                 \
+               return;                                                 \
+                                                                       \
+       if (bl->head)                                                   \
+               bl2->tail->bi_##link = bl->head;                        \
+       else                                                            \
+               bl->tail = bl2->tail;                                   \
+                                                                       \
+       bl->head = bl2->head;                                           \
+}                                                                      \
+                                                                       \
+static inline struct bio *_pre##_pop(struct bio_list *bl)              \
+{                                                                      \
+       struct bio *bio = bl->head;                                     \
+                                                                       \
+       if (bio) {                                                      \
+               bl->head = bl->head->bi_##link;                         \
+               if (!bl->head)                                          \
+                       bl->tail = NULL;                                \
+                                                                       \
+               bio->bi_##link = NULL;                                  \
+       }                                                               \
+                                                                       \
+       return bio;                                                     \
+}                                                                      \
+
+BIO_LIST_HELPERS(bio_list, next);
+
 /*
  * Increment chain count for the bio. Make sure the CHAIN flag update
  * is visible before the raised count.
-- 
2.29.2

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