[v4,1/5] block: add accounting for merged requests

diff --git a/block.c b/block.c
index d45e4dd..61412e9 100644
--- a/block.c
+++ b/block.c
@@ -4562,6 +4562,8 @@  static int multiwrite_merge(BlockDriverState *bs, BlockRequest *reqs,
         }
     }
 
+    block_acct_merge_done(&bs->stats, BLOCK_ACCT_WRITE, num_reqs - outidx - 1);
+
     return outidx + 1;
 }
 
diff --git a/block/accounting.c b/block/accounting.c
index 18102f0..01d594f 100644
--- a/block/accounting.c
+++ b/block/accounting.c
@@ -54,3 +54,10 @@  void block_acct_highest_sector(BlockAcctStats *stats, int64_t sector_num,
         stats->wr_highest_sector = sector_num + nb_sectors - 1;
     }
 }
+
+void block_acct_merge_done(BlockAcctStats *stats, enum BlockAcctType type,
+                      int num_requests)
+{
+    assert(type < BLOCK_MAX_IOTYPE);
+    stats->merged[type] += num_requests;
+}
diff --git a/block/qapi.c b/block/qapi.c
index 75c388e..d1a8917 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -335,6 +335,8 @@  static BlockStats *bdrv_query_stats(const BlockDriverState *bs,
     s->stats->wr_bytes = bs->stats.nr_bytes[BLOCK_ACCT_WRITE];
     s->stats->rd_operations = bs->stats.nr_ops[BLOCK_ACCT_READ];
     s->stats->wr_operations = bs->stats.nr_ops[BLOCK_ACCT_WRITE];
+    s->stats->rd_merged = bs->stats.merged[BLOCK_ACCT_READ];
+    s->stats->wr_merged = bs->stats.merged[BLOCK_ACCT_WRITE];
     s->stats->wr_highest_offset =
         bs->stats.wr_highest_sector * BDRV_SECTOR_SIZE;
     s->stats->flush_operations = bs->stats.nr_ops[BLOCK_ACCT_FLUSH];
diff --git a/hmp.c b/hmp.c
index 481be80..5a10154 100644
--- a/hmp.c
+++ b/hmp.c
@@ -474,6 +474,8 @@  void hmp_info_blockstats(Monitor *mon, const QDict *qdict)
                        " wr_total_time_ns=%" PRId64
                        " rd_total_time_ns=%" PRId64
                        " flush_total_time_ns=%" PRId64
+                       " rd_merged=%" PRId64
+                       " wr_merged=%" PRId64
                        "\n",
                        stats->value->stats->rd_bytes,
                        stats->value->stats->wr_bytes,
@@ -482,7 +484,9 @@  void hmp_info_blockstats(Monitor *mon, const QDict *qdict)
                        stats->value->stats->flush_operations,
                        stats->value->stats->wr_total_time_ns,
                        stats->value->stats->rd_total_time_ns,
-                       stats->value->stats->flush_total_time_ns);
+                       stats->value->stats->flush_total_time_ns,
+                       stats->value->stats->rd_merged,
+                       stats->value->stats->wr_merged);
     }
 
     qapi_free_BlockStatsList(stats_list);
diff --git a/include/block/accounting.h b/include/block/accounting.h
index 50b42b3..4c406cf 100644
--- a/include/block/accounting.h
+++ b/include/block/accounting.h
@@ -39,6 +39,7 @@  typedef struct BlockAcctStats {
     uint64_t nr_bytes[BLOCK_MAX_IOTYPE];
     uint64_t nr_ops[BLOCK_MAX_IOTYPE];
     uint64_t total_time_ns[BLOCK_MAX_IOTYPE];
+    uint64_t merged[BLOCK_MAX_IOTYPE];
     uint64_t wr_highest_sector;
 } BlockAcctStats;
 
@@ -53,5 +54,7 @@  void block_acct_start(BlockAcctStats *stats, BlockAcctCookie *cookie,
 void block_acct_done(BlockAcctStats *stats, BlockAcctCookie *cookie);
 void block_acct_highest_sector(BlockAcctStats *stats, int64_t sector_num,
                                unsigned int nb_sectors);
+void block_acct_merge_done(BlockAcctStats *stats, enum BlockAcctType type,
+                           int num_requests);
 
 #endif
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 80984d1..b7d9772 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -407,13 +407,20 @@ 
 #                     growable sparse files (like qcow2) that are used on top
 #                     of a physical device.
 #
+# @rd_merged: Number of read requests that have been merged into another
+#             request (Since 2.3).
+#
+# @wr_merged: Number of write requests that have been merged into another
+#             request (Since 2.3).
+#
 # Since: 0.14.0
 ##
 { 'type': 'BlockDeviceStats',
   'data': {'rd_bytes': 'int', 'wr_bytes': 'int', 'rd_operations': 'int',
            'wr_operations': 'int', 'flush_operations': 'int',
            'flush_total_time_ns': 'int', 'wr_total_time_ns': 'int',
-           'rd_total_time_ns': 'int', 'wr_highest_offset': 'int' } }
+           'rd_total_time_ns': 'int', 'wr_highest_offset': 'int',
+           'rd_merged': 'int', 'wr_merged': 'int' } }
 
 ##
 # @BlockStats:
diff --git a/qmp-commands.hx b/qmp-commands.hx
index c5f16dd..af3fd19 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -2303,6 +2303,10 @@  Each json-object contain the following:
     - "flush_total_time_ns": total time spend on cache flushes in nano-seconds (json-int)
     - "wr_highest_offset": Highest offset of a sector written since the
                            BlockDriverState has been opened (json-int)
+    - "rd_merged": number of read requests that have been merged into
+                   another request (json-int)
+    - "wr_merged": number of write requests that have been merged into
+                   another request (json-int)
 - "parent": Contains recursively the statistics of the underlying
             protocol (e.g. the host file for a qcow2 image). If there is
             no underlying protocol, this field is omitted
@@ -2326,6 +2330,8 @@  Example:
                   "rd_total_times_ns":3465673657
                   "flush_total_times_ns":49653
                   "flush_operations":61,
+                  "rd_merged":0,
+                  "wr_merged":0
                }
             },
             "stats":{
@@ -2337,7 +2343,9 @@  Example:
                "flush_operations":51,
                "wr_total_times_ns":313253456
                "rd_total_times_ns":3465673657
-               "flush_total_times_ns":49653
+               "flush_total_times_ns":49653,
+               "rd_merged":0,
+               "wr_merged":0
             }
          },
          {
@@ -2351,7 +2359,9 @@  Example:
                "flush_operations":0,
                "wr_total_times_ns":0
                "rd_total_times_ns":0
-               "flush_total_times_ns":0
+               "flush_total_times_ns":0,
+               "rd_merged":0,
+               "wr_merged":0
             }
          },
          {
@@ -2365,7 +2375,9 @@  Example:
                "flush_operations":0,
                "wr_total_times_ns":0
                "rd_total_times_ns":0
-               "flush_total_times_ns":0
+               "flush_total_times_ns":0,
+               "rd_merged":0,
+               "wr_merged":0
             }
          },
          {
@@ -2379,7 +2391,9 @@  Example:
                "flush_operations":0,
                "wr_total_times_ns":0
                "rd_total_times_ns":0
-               "flush_total_times_ns":0
+               "flush_total_times_ns":0,
+               "rd_merged":0,
+               "wr_merged":0
             }
          }
       ]