Re: [Qemu-devel] [PATCH v2 1/6] mirror: Discard target sectors if not allocated at source side

Re: [Qemu-devel] [PATCH v2 1/6] mirror: Discard target sectors if not allocated at source side

[wangxiaolong]

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[Qemu-devel] [PATCH v2 0/6] block: Mirror discarded sectors

[Fam Zheng]

v2: Fix typo and add Eric's rev-by in patch 3.
    Add patch 1 to discard target in mirror job. (Paolo)
    Add patch 6 to improve iotests.wait_ready. (John)

This fixes the mirror assert failure reported by wangxiaolong:

https://lists.gnu.org/archive/html/qemu-devel/2015-04/msg04458.html

The direct cause is that hbitmap code couldn't handle unset of bits *after*
iterator's current position. We could fix that, but the bdrv_reset_dirty() call
is more questionable:

Before, if guest discarded some sectors during migration, it could see
different data after moving to dest side, depending on block backends of the
src and the dest. This is IMO worse than mirroring the actual reading as done
in this series, because we don't know what the guest is doing.

For example if a guest first issues WRITE SAME to wipe out the area then issues
UNMAP to discard it, just to get rid of some sensitive data completely, we may
miss both operations and leave stale data on dest image.


Fam Zheng (6):
  mirror: Discard target sectors if not allocated at source side
  block: Fix dirty bitmap in bdrv_co_discard
  block: Remove bdrv_reset_dirty
  qemu-iotests: Make block job methods common
  qemu-iotests: Add test case for mirror with unmap
  iotests: Use event_wait in wait_ready

 block.c                       | 12 --------
 block/io.c                    |  4 +--
 block/mirror.c                | 12 ++++++--
 include/block/block_int.h     |  2 --
 tests/qemu-iotests/041        | 66 ++++++++++---------------------------------
 tests/qemu-iotests/131        | 59 ++++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/131.out    |  5 ++++
 tests/qemu-iotests/group      |  1 +
 tests/qemu-iotests/iotests.py | 23 +++++++++++++++
 9 files changed, 115 insertions(+), 69 deletions(-)
 create mode 100644 tests/qemu-iotests/131
 create mode 100644 tests/qemu-iotests/131.out

-- 
1.9.3

[Qemu-devel] [PATCH v2 1/6] mirror: Discard target sectors if not allocated at source side

[Fam Zheng]

If guest discards a source cluster during mirror, we would want to
discard target side as well.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/mirror.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index 58f391a..37a5b61 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -163,6 +163,7 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
     int64_t end, sector_num, next_chunk, next_sector, hbitmap_next_sector;
     uint64_t delay_ns = 0;
     MirrorOp *op;
+    int pnum;
 
     s->sector_num = hbitmap_iter_next(&s->hbi);
     if (s->sector_num < 0) {
@@ -289,8 +290,15 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
     s->in_flight++;
     s->sectors_in_flight += nb_sectors;
     trace_mirror_one_iteration(s, sector_num, nb_sectors);
-    bdrv_aio_readv(source, sector_num, &op->qiov, nb_sectors,
-                   mirror_read_complete, op);
+
+    if (!bdrv_is_allocated_above(source, NULL, sector_num,
+                                 nb_sectors, &pnum)) {
+        bdrv_aio_discard(s->target, sector_num, nb_sectors,
+                         mirror_write_complete, op);
+    } else {
+        bdrv_aio_readv(source, sector_num, &op->qiov, nb_sectors,
+                       mirror_read_complete, op);
+    }
     return delay_ns;
 }
 
-- 
1.9.3