This can be used by management applications starting with a job in
background mode to determine when the switch to active mode should
happen.

While the same information is already there, as the job-agnostic
@offset, it's not clear to users what the value means for mirror: it's
documentet to be relative to @len only and @len is documented to be
able to change in both directions while the job runs.

Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
 block/mirror.c       | 6 ++++++
 qapi/block-core.json | 5 ++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/block/mirror.c b/block/mirror.c
index ac83309b82..e7b4905b70 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -86,6 +86,9 @@ typedef struct MirrorBlockJob {
     int64_t active_write_bytes_in_flight;
     bool prepared;
     bool in_drain;
+
+    /* Additional information intended for users (returned in mirror_query) */
+    int64_t data_sent;
 } MirrorBlockJob;
 
 typedef struct MirrorBDSOpaque {
@@ -215,6 +218,7 @@ static void coroutine_fn mirror_iteration_done(MirrorOp *op, int ret)
         }
         if (!s->initial_zeroing_ongoing) {
             job_progress_update(&s->common.job, op->bytes);
+            s->data_sent += op->bytes;
         }
     }
     qemu_iovec_destroy(&op->qiov);
@@ -1259,6 +1263,7 @@ static void mirror_query(BlockJob *job, BlockJobInfo *info)
 
     info->u.mirror = (BlockJobInfoMirror) {
         .actively_synced = s->actively_synced,
+        .data_sent       = s->data_sent,
         .remaining_dirty = bdrv_get_dirty_count(s->dirty_bitmap),
     };
 }
@@ -1384,6 +1389,7 @@ do_sync_target_write(MirrorBlockJob *job, MirrorMethod method,
     job->active_write_bytes_in_flight -= bytes;
     if (ret >= 0) {
         job_progress_update(&job->common.job, bytes);
+        job->data_sent += bytes;
     } else {
         BlockErrorAction action;
 
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 91594eace4..656be5ce2e 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1308,12 +1308,15 @@
 # @actively-synced: Whether the source is actively synced to the target, i.e.
 #                   same data and new writes are done synchronously to both.
 #
+# @data-sent: How much data was sent in total until now.
+#
 # @remaining-dirty: How much of the source is dirty relative to the target.
 #
 # Since 8.0
 ##
 { 'struct': 'BlockJobInfoMirror',
-  'data': { 'actively-synced': 'bool', 'remaining-dirty': 'int64' } }
+  'data': { 'actively-synced': 'bool', 'data-sent': 'int64',
+            'remaining-dirty': 'int64' } }
 
 ##
 # @BlockJobInfo:
-- 
2.30.2