[Qemu-devel] [PATCH v2 08/11] block: simplify bdrv_drop_intermediate

[Fam Zheng <famz@redhat.com>]

bdrv_drop_intermediate used a local list to iterate through backing
chain and delete each BDS. It is simplified while adopting to refcount
mechanism.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block.c | 71 ++++++++++-------------------------------------------------------
 1 file changed, 11 insertions(+), 60 deletions(-)

diff --git a/block.c b/block.c
index 57a3876..499de22 100644
--- a/block.c
+++ b/block.c
@@ -2027,12 +2027,6 @@ BlockDriverState *bdrv_find_overlay(BlockDriverState *active,
     return overlay;
 }
 
-typedef struct BlkIntermediateStates {
-    BlockDriverState *bs;
-    QSIMPLEQ_ENTRY(BlkIntermediateStates) entry;
-} BlkIntermediateStates;
-
-
 /*
  * Drops images above 'base' up to and including 'top', and sets the image
  * above 'top' to have base as its backing file.
@@ -2062,15 +2056,9 @@ typedef struct BlkIntermediateStates {
 int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,
                            BlockDriverState *base)
 {
-    BlockDriverState *intermediate;
-    BlockDriverState *base_bs = NULL;
     BlockDriverState *new_top_bs = NULL;
-    BlkIntermediateStates *intermediate_state, *next;
     int ret = -EIO;
 
-    QSIMPLEQ_HEAD(states_to_delete, BlkIntermediateStates) states_to_delete;
-    QSIMPLEQ_INIT(&states_to_delete);
-
     if (!top->drv || !base->drv) {
         goto exit;
     }
@@ -2082,58 +2070,21 @@ int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,
         goto exit;
     }
 
-    /* special case of new_top_bs->backing_hd already pointing to base - nothing
-     * to do, no intermediate images */
-    if (new_top_bs->backing_hd == base) {
-        ret = 0;
-        goto exit;
-    }
-
-    intermediate = top;
-
-    /* now we will go down through the list, and add each BDS we find
-     * into our deletion queue, until we hit the 'base'
-     */
-    while (intermediate) {
-        intermediate_state = g_malloc0(sizeof(BlkIntermediateStates));
-        intermediate_state->bs = intermediate;
-        QSIMPLEQ_INSERT_TAIL(&states_to_delete, intermediate_state, entry);
-
-        if (intermediate->backing_hd == base) {
-            base_bs = intermediate->backing_hd;
-            break;
+    while (new_top_bs->backing_hd && new_top_bs->backing_hd != base) {
+        BlockDriverState *backing = new_top_bs->backing_hd;
+        if (backing == NULL) {
+            goto exit;
         }
-        intermediate = intermediate->backing_hd;
-    }
-    if (base_bs == NULL) {
-        /* something went wrong, we did not end at the base. safely
-         * unravel everything, and exit with error */
-        goto exit;
+        new_top_bs->backing_hd = backing->backing_hd;
+        /* break backing_hd chain before releasing bs, so we don't free all the
+         * way up the backing chain */
+        backing->backing_hd = NULL;
+        bdrv_unref(backing, false);
     }
 
-    /* success - we can delete the intermediate states, and link top->base */
-    ret = bdrv_change_backing_file(new_top_bs, base_bs->filename,
-                                   base_bs->drv ? base_bs->drv->format_name : "");
-    if (ret) {
-        goto exit;
-    }
-    if (new_top_bs->backing_hd) {
-        bdrv_unref(new_top_bs->backing_hd, false);
-    }
-    new_top_bs->backing_hd = base_bs;
-    bdrv_ref(base_bs, false);
-
-    QSIMPLEQ_FOREACH_SAFE(intermediate_state, &states_to_delete, entry, next) {
-        /* so that bdrv_close() does not recursively close the chain */
-        intermediate_state->bs->backing_hd = NULL;
-        bdrv_delete(intermediate_state->bs);
-    }
-    ret = 0;
-
+    ret = bdrv_change_backing_file(new_top_bs, base->filename,
+                                   base->drv ? base->drv->format_name : "");
 exit:
-    QSIMPLEQ_FOREACH_SAFE(intermediate_state, &states_to_delete, entry, next) {
-        g_free(intermediate_state);
-    }
     return ret;
 }
 
-- 
1.8.3.2