bio: add bvec_iter rewind API

Some ->bi_end_io handlers (for example: pi_verify or decrypt handlers)
need to know original data vector, but after bio traverse io-stack it may
be advanced, splited and relocated many times so it is hard to guess
original iterator. Let's add 'bi_done' conter which accounts number
of bytes iterator was advanced during it's evolution. Later end_io handler
may easily restore original iterator by rewinding iterator to
iter->bi_done.

Note: this change makes sizeof (struct bvec_iter) multiple to 8

Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
[hch: switched to true/false return]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/include/linux/bio.h b/include/linux/bio.h
index d5e8689f86b8c8c30cccc770f572820ebcdf4c8a..1eba19580185e4b9893a3cbc8156baa9dec89a2c 100644 (file)
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -165,14 +165,29 @@ static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter,
 {
        iter->bi_sector += bytes >> 9;
 
-       if (bio_no_advance_iter(bio))
+       if (bio_no_advance_iter(bio)) {
                iter->bi_size -= bytes;
-       else {
+               iter->bi_done += bytes;
+       } else {
                bvec_iter_advance(bio->bi_io_vec, iter, bytes);
                /* TODO: It is reasonable to complete bio with error here. */
        }
 }
 
+static inline bool bio_rewind_iter(struct bio *bio, struct bvec_iter *iter,
+               unsigned int bytes)
+{
+       iter->bi_sector -= bytes >> 9;
+
+       if (bio_no_advance_iter(bio)) {
+               iter->bi_size += bytes;
+               iter->bi_done -= bytes;
+               return true;
+       }
+
+       return bvec_iter_rewind(bio->bi_io_vec, iter, bytes);
+}
+
 #define __bio_for_each_segment(bvl, bio, iter, start)                  \
        for (iter = (start);                                            \
             (iter).bi_size &&                                          \

diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index de317b4c13c105ec5d3166f9705927994b3a1136..ec8a4d7af6bda55586bc0b0221b3dcfe6e5ab487 100644 (file)
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -40,6 +40,8 @@ struct bvec_iter {
 
        unsigned int            bi_idx;         /* current index into bvl_vec */
 
+       unsigned int            bi_done;        /* number of bytes completed */
+
        unsigned int            bi_bvec_done;   /* number of bytes completed in
                                                   current bvec */
 };
@@ -83,6 +85,7 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
                bytes -= len;
                iter->bi_size -= len;
                iter->bi_bvec_done += len;
+               iter->bi_done += len;
 
                if (iter->bi_bvec_done == __bvec_iter_bvec(bv, *iter)->bv_len) {
                        iter->bi_bvec_done = 0;
@@ -92,6 +95,30 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
        return true;
 }
 
+static inline bool bvec_iter_rewind(const struct bio_vec *bv,
+                                    struct bvec_iter *iter,
+                                    unsigned int bytes)
+{
+       while (bytes) {
+               unsigned len = min(bytes, iter->bi_bvec_done);
+
+               if (iter->bi_bvec_done == 0) {
+                       if (WARN_ONCE(iter->bi_idx == 0,
+                                     "Attempted to rewind iter beyond "
+                                     "bvec's boundaries\n")) {
+                               return false;
+                       }
+                       iter->bi_idx--;
+                       iter->bi_bvec_done = __bvec_iter_bvec(bv, *iter)->bv_len;
+                       continue;
+               }
+               bytes -= len;
+               iter->bi_size += len;
+               iter->bi_bvec_done -= len;
+       }
+       return true;
+}
+
 #define for_each_bvec(bvl, bio_vec, iter, start)                       \
        for (iter = (start);                                            \
             (iter).bi_size &&                                          \