[Qemu-block] [PATCH v2 6/7] mirror: efficiently zero out target

[Denis V. Lunev]

With a bdrv_co_write_zeroes method on a target BDS zeroes will not be placed
into the wire. Thus the target could be very efficiently zeroed out. This
is should be done with the largest chunk possible.

Signed-off-by: Denis V. Lunev <address@hidden>
Reviewed-by: Vladimir Sementsov-Ogievskiy<address@hidden>
CC: Stefan Hajnoczi <address@hidden>
CC: Fam Zheng <address@hidden>
CC: Kevin Wolf <address@hidden>
CC: Max Reitz <address@hidden>
CC: Jeff Cody <address@hidden>
CC: Eric Blake <address@hidden>
---
 block/mirror.c | 33 +++++++++++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index 7208023..4ecfbf1 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -526,8 +526,37 @@ static int mirror_dirty_init(MirrorBlockJob *s)
     last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
 
     if (base == NULL && !bdrv_has_zero_init(target_bs)) {
-        bdrv_set_dirty_bitmap(s->dirty_bitmap, 0, end);
-        return 0;
+        if (!bdrv_can_write_zeroes_with_unmap(target_bs)) {
+            bdrv_set_dirty_bitmap(s->dirty_bitmap, 0, end);
+            return 0;
+        }
+
+        for (sector_num = 0; sector_num < end; ) {
+            int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
+
+            int nb_sectors = QEMU_ALIGN_DOWN(INT_MAX, s->granularity);
+            nb_sectors = MIN(nb_sectors >> BDRV_SECTOR_BITS, end - sector_num);
+
+            if (now - last_pause_ns > SLICE_TIME) {
+                last_pause_ns = now;
+                block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, 0);
+            }
+
+            if (block_job_is_cancelled(&s->common)) {
+                return 0;
+            }
+
+            if (s->in_flight >= MAX_IN_FLIGHT) {
+                trace_mirror_yield(s, s->in_flight, s->buf_free_count, -1);
+                mirror_wait_for_io(s);
+                continue;
+            }
+
+            mirror_do_zero_or_discard(s, sector_num, nb_sectors, false);
+            sector_num += nb_sectors;
+        }
+
+        mirror_drain(s);
     }
 
     /* First part, loop on the sectors and initialize the dirty bitmap.  */
-- 
2.5.0