block: implement 'resize' callback for child_of_bds class

If a filtered child is resized, the size of the parent node is now
also refreshed (recursively for chains of filtered children).

For filter block drivers that do not implement .bdrv_co_getlength(),
this commit does not change the current behavior, because
bdrv_co_refresh_total_sectors() will used the current size via the
passed-in hint. This is the case for block drivers for (some) block
jobs, as well as copy-before-write.

Block jobs already set up a blocker preventing a QMP block_resize
operation while the job is running. That does not directly cover an
associated 'file' node of a 'raw' node, but resizing such a 'file'
node is already prevented too (backup, commit, mirror and stream were
checked).

The other case is copy-before-write. This commit does not change the
fact that the copy-before-write node still has the same size after its
filtered child is resized.

Block drivers that do implement .bdrv_co_getlength() and where
.is_filter is true, already returned the length of the file child, so
there is no change before and after this commit, with two exceptions:
1. preallocate can return an early data_end and otherwise queries the
   file child, but that special casing is not changed.
2. blkverify returns the length of the test file. This commit does not
   affect that behavior.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Message-ID: <20250917115509.401015-4-f.ebner@proxmox.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/block.c b/block.c
index 8848e9a7ed665a1bfbde2aba29e2c414f5bbe39b..cf08e64add769a9aadbc195e655a98b77e04cb73 100644 (file)
--- a/block.c
+++ b/block.c
@@ -1497,6 +1497,17 @@ static void GRAPH_WRLOCK bdrv_child_cb_detach(BdrvChild *child)
     }
 }
 
+static void coroutine_fn GRAPH_RDLOCK bdrv_child_cb_resize(BdrvChild *child)
+{
+    BlockDriverState *bs = child->opaque;
+
+    if (child->role & BDRV_CHILD_FILTERED) {
+        /* Best effort, ignore errors. */
+        bdrv_co_refresh_total_sectors(bs, bs->total_sectors);
+        bdrv_co_parent_cb_resize(bs);
+    }
+}
+
 static int bdrv_child_cb_update_filename(BdrvChild *c, BlockDriverState *base,
                                          const char *filename,
                                          bool backing_mask_protocol,
@@ -1529,6 +1540,7 @@ const BdrvChildClass child_of_bds = {
     .detach          = bdrv_child_cb_detach,
     .inactivate      = bdrv_child_cb_inactivate,
     .change_aio_ctx  = bdrv_child_cb_change_aio_ctx,
+    .resize          = bdrv_child_cb_resize,
     .update_filename = bdrv_child_cb_update_filename,
     .get_parent_aio_context = child_of_bds_get_parent_aio_context,
 };

diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h
index 8a3d427356e33c59c64db5d2ae38ffa1e0b7b814..c55b35da8e46547fec2035a28694e12fc2505382 100644 (file)
--- a/include/block/block_int-common.h
+++ b/include/block/block_int-common.h
@@ -1023,7 +1023,7 @@ struct BdrvChildClass {
     /*
      * Notifies the parent that the child was resized.
      */
-    void (*resize)(BdrvChild *child);
+    void GRAPH_RDLOCK_PTR (*resize)(BdrvChild *child);
 
     /*
      * Returns a name that is supposedly more useful for human users than the