[PATCH v2 12/19] block/block-copy: add write-unchanged mode

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

We are going to implement push backup with fleecing scheme. This means
that backup job will be a fleecing user and therefore will not need
separate copy-before-write filter. Instead it will consider source as
constant unchanged drive. Of course backup will want to unshare writes
on source for this case. But we want to do copy-before-write
operations. Still these operations may be considered as
write-unchanged. Add corresponding option to block-copy now, to use in
the following commit.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 include/block/block-copy.h | 3 ++-
 block/block-copy.c         | 9 ++++++---
 block/copy-before-write.c  | 2 +-
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/block/block-copy.h b/include/block/block-copy.h
index a11e1620f6..a66f81d314 100644
--- a/include/block/block-copy.h
+++ b/include/block/block-copy.h
@@ -25,7 +25,8 @@ typedef struct BlockCopyState BlockCopyState;
 typedef struct BlockCopyCallState BlockCopyCallState;
 
 BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
-                                     BdrvDirtyBitmap *bitmap, Error **errp);
+                                     BdrvDirtyBitmap *bitmap,
+                                     bool write_unchanged, Error **errp);
 
 /* Function should be called prior any actual copy request */
 void block_copy_set_copy_opts(BlockCopyState *s, bool use_copy_range,
diff --git a/block/block-copy.c b/block/block-copy.c
index 46e6a6736d..6d5d517ac6 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -279,7 +279,8 @@ void block_copy_set_copy_opts(BlockCopyState *s, bool use_copy_range,
                               bool compress)
 {
     /* Keep BDRV_REQ_SERIALISING set (or not set) in block_copy_state_new() */
-    s->write_flags = (s->write_flags & BDRV_REQ_SERIALISING) |
+    s->write_flags = (s->write_flags &
+                      (BDRV_REQ_SERIALISING | BDRV_REQ_WRITE_UNCHANGED)) |
         (compress ? BDRV_REQ_WRITE_COMPRESSED : 0);
 
     if (s->max_transfer < s->cluster_size) {
@@ -340,7 +341,8 @@ static int64_t block_copy_calculate_cluster_size(BlockDriverState *target,
 }
 
 BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
-                                     BdrvDirtyBitmap *bitmap, Error **errp)
+                                     BdrvDirtyBitmap *bitmap,
+                                     bool write_unchanged, Error **errp)
 {
     ERRP_GUARD();
     BlockCopyState *s;
@@ -393,7 +395,8 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
         .copy_bitmap = copy_bitmap,
         .cluster_size = cluster_size,
         .len = bdrv_dirty_bitmap_size(copy_bitmap),
-        .write_flags = (is_fleecing ? BDRV_REQ_SERIALISING : 0),
+        .write_flags = (is_fleecing ? BDRV_REQ_SERIALISING : 0) |
+            (write_unchanged ? BDRV_REQ_WRITE_UNCHANGED : 0),
         .mem = shres_create(BLOCK_COPY_MAX_MEM),
         .max_transfer = QEMU_ALIGN_DOWN(
                                     block_copy_max_transfer(source, target),
diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index 686a085861..7e4e4bf7d4 100644
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -212,7 +212,7 @@ static int cbw_open(BlockDriverState *bs, QDict *options, int flags,
             ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
              bs->file->bs->supported_zero_flags);
 
-    s->bcs = block_copy_state_new(bs->file, s->target, bitmap, errp);
+    s->bcs = block_copy_state_new(bs->file, s->target, bitmap, false, errp);
     if (!s->bcs) {
         error_prepend(errp, "Cannot create block-copy-state: ");
         return -EINVAL;
-- 
2.29.2