[PATCH 14/21] block: add bdrv_attach_child_noperm() transaction action

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

The code partly duplicates bdrv_root_attach_child() and
bdrv_attach_child(). Still refactoring these two functions by renaming
them to *_common with new noperm argument is more complicating. When
all operations moved to new graph update paradigm (update permissions
only on updated graph) all duplications should leave.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block.c | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 90 insertions(+), 4 deletions(-)

diff --git a/block.c b/block.c
index 08501350b7..5f6ad1d016 100644
--- a/block.c
+++ b/block.c
@@ -2974,16 +2974,102 @@ BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
     return child;
 }
 
-static void bdrv_detach_child(BdrvChild *child)
+static void bdrv_remove_empty_child(BdrvChild *child)
 {
+    assert(!child->bs);
     QLIST_SAFE_REMOVE(child, next);
-
-    bdrv_replace_child(child, NULL);
-
     g_free(child->name);
     g_free(child);
 }
 
+typedef struct BdrvAttachChildNopermState {
+    BdrvChild *child;
+    AioContext *old_aio_context; /* NULL if not changed */
+} BdrvAttachChildNopermState;
+
+static void bdrv_attach_child_noperm_abort(void *opaque)
+{
+    BdrvAttachChildNopermState *s = opaque;
+    BlockDriverState *bs = s->child->bs;
+
+    bdrv_replace_child_noperm(s->child, NULL);
+    bdrv_remove_empty_child(s->child);
+
+    /*
+     * refcnt was positive prior to bdrv_ref() in bdrv_attach_child_noperm(),
+     * so bs should not be deleted now.
+     */
+    assert(bs->refcnt > 1);
+    bdrv_unref(bs);
+    if (s->old_aio_context) {
+        bdrv_try_set_aio_context(bs, s->old_aio_context, NULL);
+    }
+}
+
+static BdrvActionDrv bdrv_attach_child_noperm_drv = {
+    .abort = bdrv_attach_child_noperm_abort,
+    .clean = g_free,
+};
+
+__attribute__((unused))
+static BdrvChild *bdrv_attach_child_noperm(BlockDriverState *parent_bs,
+                                           BlockDriverState *child_bs,
+                                           const char *child_name,
+                                           BdrvChildRole child_role,
+                                           GSList **tran,
+                                           Error **errp)
+{
+    int ret;
+    BdrvChild *child;
+    uint64_t perm, shared_perm;
+    AioContext *parent_ctx = bdrv_get_aio_context(parent_bs);
+    AioContext *child_ctx = bdrv_get_aio_context(child_bs);
+    BdrvAttachChildNopermState *s;
+
+    if (child_ctx != parent_ctx) {
+        ret = bdrv_try_set_aio_context(child_bs, parent_ctx, errp);
+        if (ret < 0) {
+            return NULL;
+        }
+    }
+
+    bdrv_get_cumulative_perm(parent_bs, &perm, &shared_perm);
+
+    assert(parent_bs->drv);
+    bdrv_child_perm(parent_bs, child_bs, NULL, child_role, NULL,
+                    perm, shared_perm, &perm, &shared_perm);
+
+    child = g_new(BdrvChild, 1);
+    *child = (BdrvChild) {
+        .bs             = NULL,
+        .name           = g_strdup(child_name),
+        .klass          = &child_of_bds,
+        .role           = child_role,
+        .perm           = perm,
+        .shared_perm    = shared_perm,
+        .opaque         = parent_bs,
+    };
+    bdrv_ref(child_bs);
+    bdrv_replace_child_noperm(child, child_bs);
+
+    QLIST_INSERT_HEAD(&parent_bs->children, child, next);
+
+    s = g_new(BdrvAttachChildNopermState, 1);
+    *s = (BdrvAttachChildNopermState) {
+        .child = child,
+        .old_aio_context = child_ctx == parent_ctx ? NULL : child_ctx,
+    };
+    tran_prepend(tran, &bdrv_attach_child_noperm_drv, s);
+
+    return child;
+}
+
+static void bdrv_detach_child(BdrvChild *child)
+{
+    bdrv_replace_child(child, NULL);
+    bdrv_remove_empty_child(child);
+}
+
 /* Callers must ensure that child->frozen is false. */
 void bdrv_root_unref_child(BdrvChild *child)
 {
-- 
2.21.3