[PATCH v2 13/19] block/copy-before-write: use write-unchanged in fleecing mode

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

As announced in previous commit, we need use write-unchanged operations
for fleecing, so that fleecing client may unshare writes if needed.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/copy-before-write.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index 7e4e4bf7d4..91250cc634 100644
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -132,6 +132,8 @@ static void cbw_child_perm(BlockDriverState *bs, BdrvChild *c,
                            uint64_t perm, uint64_t shared,
                            uint64_t *nperm, uint64_t *nshared)
 {
+    BDRVCopyBeforeWriteState *s = bs->opaque;
+
     if (!(role & BDRV_CHILD_FILTERED)) {
         /*
          * Target child
@@ -142,7 +144,7 @@ static void cbw_child_perm(BlockDriverState *bs, BdrvChild *c,
          * only upfront.
          */
         *nshared = BLK_PERM_ALL & ~BLK_PERM_RESIZE;
-        *nperm = BLK_PERM_WRITE;
+        *nperm = s->fleecing ? BLK_PERM_WRITE_UNCHANGED : BLK_PERM_WRITE;
     } else {
         /* Source child */
         bdrv_default_perms(bs, c, role, reopen_queue,
@@ -212,7 +214,14 @@ 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, false, errp);
+    /*
+     * For fleecing scheme set parameter write_unchanged=true, as our
+     * copy-before-write operations will actually be write-unchanged. As well we
+     * take write-unchanged permission instead of write, which is important for
+     * backup with immutable_source=true to work as fleecing client.
+     */
+    s->bcs = block_copy_state_new(bs->file, s->target, bitmap,
+                                  is_fleecing_drv(unfiltered_target), errp);
     if (!s->bcs) {
         error_prepend(errp, "Cannot create block-copy-state: ");
         return -EINVAL;
-- 
2.29.2