block: use the same failfast bits for bio and request

bio and request use the same set of failfast bits.  This patch makes
the following changes to simplify things.

* enumify BIO_RW* bits and reorder bits such that BIOS_RW_FAILFAST_*
  bits coincide with __REQ_FAILFAST_* bits.

* The above pushes BIO_RW_AHEAD out of sync with __REQ_FAILFAST_DEV
  but the matching is useless anyway.  init_request_from_bio() is
  responsible for setting FAILFAST bits on FS requests and non-FS
  requests never use BIO_RW_AHEAD.  Drop the code and comment from
  blk_rq_bio_prep().

* Define REQ_FAILFAST_MASK which is OR of all FAILFAST bits and
  simplify FAILFAST flags handling in init_request_from_bio().

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

3 files changed, 34 insertions, 32 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index e3299a77a0d8..4daae1ee2b23 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1111,17 +1111,13 @@ void init_request_from_bio(struct request *req, struct bio *bio)
         req->cmd_type = REQ_TYPE_FS;
 
         /*
-         * inherit FAILFAST from bio (for read-ahead, and explicit FAILFAST)
+         * Inherit FAILFAST from bio (for read-ahead, and explicit
+         * FAILFAST).  FAILFAST flags are identical for req and bio.
          */
         if (bio_rw_ahead(bio))
-                req->cmd_flags |= (REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT |
-                                   REQ_FAILFAST_DRIVER);
-        if (bio_failfast_dev(bio))
-                req->cmd_flags |= REQ_FAILFAST_DEV;
-        if (bio_failfast_transport(bio))
-                req->cmd_flags |= REQ_FAILFAST_TRANSPORT;
-        if (bio_failfast_driver(bio))
-                req->cmd_flags |= REQ_FAILFAST_DRIVER;
+                req->cmd_flags |= REQ_FAILFAST_MASK;
+        else
+                req->cmd_flags |= bio->bi_rw & REQ_FAILFAST_MASK;
 
         if (unlikely(bio_discard(bio))) {
                 req->cmd_flags |= REQ_DISCARD;
@@ -2239,9 +2235,8 @@ EXPORT_SYMBOL(__blk_end_request_cur);
 void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
                      struct bio *bio)
 {
-        /* Bit 0 (R/W) is identical in rq->cmd_flags and bio->bi_rw, and
-           we want BIO_RW_AHEAD (bit 1) to imply REQ_FAILFAST (bit 1). */
-        rq->cmd_flags |= (bio->bi_rw & 3);
+        /* Bit 0 (R/W) is identical in rq->cmd_flags and bio->bi_rw */
+        rq->cmd_flags |= bio->bi_rw & REQ_RW;
 
         if (bio_has_data(bio)) {
                 rq->nr_phys_segments = bio_phys_segments(q, bio);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 2892b710771c..a299ed38fcd7 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -142,37 +142,40 @@ struct bio {
  *
  * bit 0 -- data direction
  *      If not set, bio is a read from device. If set, it's a write to device.
- * bit 1 -- rw-ahead when set
- * bit 2 -- barrier
+ * bit 1 -- fail fast device errors
+ * bit 2 -- fail fast transport errors
+ * bit 3 -- fail fast driver errors
+ * bit 4 -- rw-ahead when set
+ * bit 5 -- barrier
  *      Insert a serialization point in the IO queue, forcing previously
  *      submitted IO to be completed before this one is issued.
- * bit 3 -- synchronous I/O hint.
- * bit 4 -- Unplug the device immediately after submitting this bio.
- * bit 5 -- metadata request
+ * bit 6 -- synchronous I/O hint.
+ * bit 7 -- Unplug the device immediately after submitting this bio.
+ * bit 8 -- metadata request
  *      Used for tracing to differentiate metadata and data IO. May also
  *      get some preferential treatment in the IO scheduler
- * bit 6 -- discard sectors
+ * bit 9 -- discard sectors
  *      Informs the lower level device that this range of sectors is no longer
  *      used by the file system and may thus be freed by the device. Used
  *      for flash based storage.
- * bit 7 -- fail fast device errors
- * bit 8 -- fail fast transport errors
- * bit 9 -- fail fast driver errors
  *      Don't want driver retries for any fast fail whatever the reason.
  * bit 10 -- Tell the IO scheduler not to wait for more requests after this
         one has been submitted, even if it is a SYNC request.
  */
-#define BIO_RW          0       /* Must match RW in req flags (blkdev.h) */
-#define BIO_RW_AHEAD    1       /* Must match FAILFAST in req flags */
-#define BIO_RW_BARRIER  2
-#define BIO_RW_SYNCIO   3
-#define BIO_RW_UNPLUG   4
-#define BIO_RW_META     5
-#define BIO_RW_DISCARD  6
-#define BIO_RW_FAILFAST_DEV             7
-#define BIO_RW_FAILFAST_TRANSPORT       8
-#define BIO_RW_FAILFAST_DRIVER          9
-#define BIO_RW_NOIDLE   10
+enum bio_rw_flags {
+        BIO_RW,
+        BIO_RW_FAILFAST_DEV,
+        BIO_RW_FAILFAST_TRANSPORT,
+        BIO_RW_FAILFAST_DRIVER,
+        /* above flags must match REQ_* */
+        BIO_RW_AHEAD,
+        BIO_RW_BARRIER,
+        BIO_RW_SYNCIO,
+        BIO_RW_UNPLUG,
+        BIO_RW_META,
+        BIO_RW_DISCARD,
+        BIO_RW_NOIDLE,
+};
 
 #define bio_rw_flagged(bio, flag)       ((bio)->bi_rw & (1 << (flag)))
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 69103e053c92..c3015736d814 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -93,6 +93,7 @@ enum rq_flag_bits {
         __REQ_FAILFAST_DEV,     /* no driver retries of device errors */
         __REQ_FAILFAST_TRANSPORT, /* no driver retries of transport errors */
         __REQ_FAILFAST_DRIVER,  /* no driver retries of driver errors */
+        /* above flags must match BIO_RW_* */
         __REQ_DISCARD,          /* request to discard sectors */
         __REQ_SORTED,           /* elevator knows about this request */
         __REQ_SOFTBARRIER,      /* may not be passed by ioscheduler */
@@ -143,6 +144,9 @@ enum rq_flag_bits {
 #define REQ_NOIDLE      (1 << __REQ_NOIDLE)
 #define REQ_IO_STAT     (1 << __REQ_IO_STAT)
 
+#define REQ_FAILFAST_MASK       (REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT | \
+                                 REQ_FAILFAST_DRIVER)
+
 #define BLK_MAX_CDB     16
 
 /*