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 <koverstreet@google.com>
CC: Jens Axboe <axboe@kernel.dk>
CC: Neil Brown <neilb@suse.de>
CC: Boaz Harrosh <bharrosh@panasas.com>

1 files changed, 14 insertions, 3 deletions

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 90d36c65cb70..be2efa09f9bf 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -137,16 +137,27 @@ static inline int bio_has_allocated_vec(struct bio *bio)
 #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