block: drop request->hard_* and *nr_sectors

struct request has had a few different ways to represent some
properties of a request.  ->hard_* represent block layer's view of the
request progress (completion cursor) and the ones without the prefix
are supposed to represent the issue cursor and allowed to be updated
as necessary by the low level drivers.  The thing is that as block
layer supports partial completion, the two cursors really aren't
necessary and only cause confusion.  In addition, manual management of
request detail from low level drivers is cumbersome and error-prone at
the very least.

Another interesting duplicate fields are rq->[hard_]nr_sectors and
rq->{hard_cur|current}_nr_sectors against rq->data_len and
rq->bio->bi_size.  This is more convoluted than the hard_ case.

rq->[hard_]nr_sectors are initialized for requests with bio but
blk_rq_bytes() uses it only for !pc requests.  rq->data_len is
initialized for all request but blk_rq_bytes() uses it only for pc
requests.  This causes good amount of confusion throughout block layer
and its drivers and determining the request length has been a bit of
black magic which may or may not work depending on circumstances and
what the specific LLD is actually doing.

rq->{hard_cur|current}_nr_sectors represent the number of sectors in
the contiguous data area at the front.  This is mainly used by drivers
which transfers data by walking request segment-by-segment.  This
value always equals rq->bio->bi_size >> 9.  However, data length for
pc requests may not be multiple of 512 bytes and using this field
becomes a bit confusing.

In general, having multiple fields to represent the same property
leads only to confusion and subtle bugs.  With recent block low level
driver cleanups, no driver is accessing or manipulating these
duplicate fields directly.  Drop all the duplicates.  Now rq->sector
means the current sector, rq->data_len the current total length and
rq->bio->bi_size the current segment length.  Everything else is
defined in terms of these three and available only through accessors.

* blk_recalc_rq_sectors() is collapsed into blk_update_request() and
  now handles pc and fs requests equally other than rq->sector update.
  This means that now pc requests can use partial completion too (no
  in-kernel user yet tho).

* bio_cur_sectors() is replaced with bio_cur_bytes() as block layer
  now uses byte count as the primary data length.

* blk_rq_pos() is now guranteed to be always correct.  In-block users
  converted.

* blk_rq_bytes() is now guaranteed to be always valid as is
  blk_rq_sectors().  In-block users converted.

* blk_rq_sectors() is now guaranteed to equal blk_rq_bytes() >> 9.
  More convenient one is used.

* blk_rq_bytes() and blk_rq_cur_bytes() are now inlined and take const
  pointer to request.

[ Impact: API cleanup, single way to represent one property of a request ]

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

3 files changed, 20 insertions, 25 deletions

diff --git a/include/linux/bio.h b/include/linux/bio.h
index f37ca8c726ba..d30ec6f30dd7 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -218,12 +218,12 @@ struct bio {
 #define bio_sectors(bio)        ((bio)->bi_size >> 9)
 #define bio_empty_barrier(bio)  (bio_barrier(bio) && !bio_has_data(bio) && !bio_discard(bio))
 
-static inline unsigned int bio_cur_sectors(struct bio *bio)
+static inline unsigned int bio_cur_bytes(struct bio *bio)
 {
         if (bio->bi_vcnt)
-                return bio_iovec(bio)->bv_len >> 9;
+                return bio_iovec(bio)->bv_len;
         else /* dataless requests such as discard */
-                return bio->bi_size >> 9;
+                return bio->bi_size;
 }
 
 static inline void *bio_data(struct bio *bio)
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 4e5f85598728..ce2bf5efa9ba 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -166,19 +166,8 @@ struct request {
         enum rq_cmd_type_bits cmd_type;
         unsigned long atomic_flags;
 
-        /* Maintain bio traversal state for part by part I/O submission.
-         * hard_* are block layer internals, no driver should touch them!
-         */
-
-        sector_t sector;                /* next sector to submit */
-        sector_t hard_sector;           /* next sector to complete */
-        unsigned long nr_sectors;       /* no. of sectors left to submit */
-        unsigned long hard_nr_sectors;  /* no. of sectors left to complete */
-        /* no. of sectors left to submit in the current segment */
-        unsigned int current_nr_sectors;
-
-        /* no. of sectors left to complete in the current segment */
-        unsigned int hard_cur_sectors;
+        sector_t sector;        /* sector cursor */
+        unsigned int data_len;  /* total data len, don't access directly */
 
         struct bio *bio;
         struct bio *biotail;
@@ -226,7 +215,6 @@ struct request {
         unsigned char __cmd[BLK_MAX_CDB];
         unsigned char *cmd;
 
-        unsigned int data_len;
         unsigned int extra_len; /* length of alignment and padding */
         unsigned int sense_len;
         unsigned int resid_len; /* residual count */
@@ -840,20 +828,27 @@ extern void blkdev_dequeue_request(struct request *req);
  */
 static inline sector_t blk_rq_pos(const struct request *rq)
 {
-        return rq->hard_sector;
+        return rq->sector;
+}
+
+static inline unsigned int blk_rq_bytes(const struct request *rq)
+{
+        return rq->data_len;
 }
 
-extern unsigned int blk_rq_bytes(struct request *rq);
-extern unsigned int blk_rq_cur_bytes(struct request *rq);
+static inline int blk_rq_cur_bytes(const struct request *rq)
+{
+        return rq->bio ? bio_cur_bytes(rq->bio) : 0;
+}
 
 static inline unsigned int blk_rq_sectors(const struct request *rq)
 {
-        return rq->hard_nr_sectors;
+        return blk_rq_bytes(rq) >> 9;
 }
 
 static inline unsigned int blk_rq_cur_sectors(const struct request *rq)
 {
-        return rq->hard_cur_sectors;
+        return blk_rq_cur_bytes(rq) >> 9;
 }
 
 /*
@@ -928,7 +923,7 @@ static inline void blk_end_request_all(struct request *rq, int error)
  */
 static inline bool blk_end_request_cur(struct request *rq, int error)
 {
-        return blk_end_request(rq, error, rq->hard_cur_sectors << 9);
+        return blk_end_request(rq, error, blk_rq_cur_bytes(rq));
 }
 
 /**
@@ -981,7 +976,7 @@ static inline void __blk_end_request_all(struct request *rq, int error)
  */
 static inline bool __blk_end_request_cur(struct request *rq, int error)
 {
-        return __blk_end_request(rq, error, rq->hard_cur_sectors << 9);
+        return __blk_end_request(rq, error, blk_rq_cur_bytes(rq));
 }
 
 extern void blk_complete_request(struct request *);
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index c59b769f62b0..4e462878c9ca 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -171,7 +171,7 @@ enum {
         ELV_MQUEUE_MUST,
 };
 
-#define rq_end_sector(rq)       ((rq)->sector + (rq)->nr_sectors)
+#define rq_end_sector(rq)       (blk_rq_pos(rq) + blk_rq_sectors(rq))
 #define rb_entry_rq(node)       rb_entry((node), struct request, rb_node)
 
 /*