dm request: extend target interface

This patch adds the following target interfaces for request-based dm.

  map_rq    : for mapping a request

  rq_end_io : for finishing a request

  busy      : for avoiding performance regression from bio-based dm.
              Target can tell dm core not to map requests now, and
              that may help requests in the block layer queue to be
              bigger by I/O merging.
              In bio-based dm, this behavior is done by device
              drivers managing the block layer queue.
              But in request-based dm, dm core has to do that
              since dm core manages the block layer queue.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 89ff2df..c1ba76c 100644 (file)
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -45,6 +45,8 @@ typedef void (*dm_dtr_fn) (struct dm_target *ti);
  */
 typedef int (*dm_map_fn) (struct dm_target *ti, struct bio *bio,
                          union map_info *map_context);
+typedef int (*dm_map_request_fn) (struct dm_target *ti, struct request *clone,
+                                 union map_info *map_context);
 
 /*
  * Returns:
@@ -57,6 +59,9 @@ typedef int (*dm_map_fn) (struct dm_target *ti, struct bio *bio,
 typedef int (*dm_endio_fn) (struct dm_target *ti,
                            struct bio *bio, int error,
                            union map_info *map_context);
+typedef int (*dm_request_endio_fn) (struct dm_target *ti,
+                                   struct request *clone, int error,
+                                   union map_info *map_context);
 
 typedef void (*dm_flush_fn) (struct dm_target *ti);
 typedef void (*dm_presuspend_fn) (struct dm_target *ti);
@@ -75,6 +80,13 @@ typedef int (*dm_ioctl_fn) (struct dm_target *ti, unsigned int cmd,
 typedef int (*dm_merge_fn) (struct dm_target *ti, struct bvec_merge_data *bvm,
                            struct bio_vec *biovec, int max_size);
 
+/*
+ * Returns:
+ *    0: The target can handle the next I/O immediately.
+ *    1: The target can't handle the next I/O immediately.
+ */
+typedef int (*dm_busy_fn) (struct dm_target *ti);
+
 void dm_error(const char *message);
 
 /*
@@ -107,7 +119,9 @@ struct target_type {
        dm_ctr_fn ctr;
        dm_dtr_fn dtr;
        dm_map_fn map;
+       dm_map_request_fn map_rq;
        dm_endio_fn end_io;
+       dm_request_endio_fn rq_end_io;
        dm_flush_fn flush;
        dm_presuspend_fn presuspend;
        dm_postsuspend_fn postsuspend;
@@ -117,6 +131,7 @@ struct target_type {
        dm_message_fn message;
        dm_ioctl_fn ioctl;
        dm_merge_fn merge;
+       dm_busy_fn busy;
 };
 
 struct io_restrictions {