diff mbox series

[v4,06/19] block: Add bdrv_recurse_can_replace()

Message ID 20200218103454.296704-7-mreitz@redhat.com
State New
Headers show
Series block: Fix check_to_replace_node() | expand

Commit Message

Max Reitz Feb. 18, 2020, 10:34 a.m. UTC 
After a couple of follow-up patches, this function will replace
bdrv_recurse_is_first_non_filter() in check_to_replace_node().

bdrv_recurse_is_first_non_filter() is both not sufficiently specific for
check_to_replace_node() (it allows cases that should not be allowed,
like replacing child nodes of quorum with dissenting data that have more
parents than just quorum), and it is too restrictive (it is perfectly
fine to replace filters).

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block.c                   | 38 ++++++++++++++++++++++++++++++++++++++
 include/block/block_int.h | 10 ++++++++++
 2 files changed, 48 insertions(+)
diff mbox series

Patch

diff --git a/block.c b/block.c
index f6731fa9be..553ccff216 100644
--- a/block.c
+++ b/block.c
@@ -6235,6 +6235,44 @@  bool bdrv_recurse_is_first_non_filter(BlockDriverState *bs,
     return false;
 }
 
+/*
+ * This function checks whether the given @to_replace is allowed to be
+ * replaced by a node that always shows the same data as @bs.  This is
+ * used for example to verify whether the mirror job can replace
+ * @to_replace by the target mirrored from @bs.
+ * To be replaceable, @bs and @to_replace may either be guaranteed to
+ * always show the same data (because they are only connected through
+ * filters), or some driver may allow replacing one of its children
+ * because it can guarantee that this child's data is not visible at
+ * all (for example, for dissenting quorum children that have no other
+ * parents).
+ */
+bool bdrv_recurse_can_replace(BlockDriverState *bs,
+                              BlockDriverState *to_replace)
+{
+    if (!bs || !bs->drv) {
+        return false;
+    }
+
+    if (bs == to_replace) {
+        return true;
+    }
+
+    /* See what the driver can do */
+    if (bs->drv->bdrv_recurse_can_replace) {
+        return bs->drv->bdrv_recurse_can_replace(bs, to_replace);
+    }
+
+    /* For filters without an own implementation, we can recurse on our own */
+    if (bs->drv->is_filter) {
+        BdrvChild *child = bs->file ?: bs->backing;
+        return bdrv_recurse_can_replace(child->bs, to_replace);
+    }
+
+    /* Safe default */
+    return false;
+}
+
 BlockDriverState *check_to_replace_node(BlockDriverState *parent_bs,
                                         const char *node_name, Error **errp)
 {
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 640fb82c78..eaefac210e 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -102,6 +102,13 @@  struct BlockDriver {
      */
     bool (*bdrv_recurse_is_first_non_filter)(BlockDriverState *bs,
                                              BlockDriverState *candidate);
+    /*
+     * Return true if @to_replace can be replaced by a BDS with the
+     * same data as @bs without it affecting @bs's behavior (that is,
+     * without it being visible to @bs's parents).
+     */
+    bool (*bdrv_recurse_can_replace)(BlockDriverState *bs,
+                                     BlockDriverState *to_replace);
 
     int (*bdrv_probe)(const uint8_t *buf, int buf_size, const char *filename);
     int (*bdrv_probe_device)(const char *filename);
@@ -1263,6 +1270,9 @@  void bdrv_format_default_perms(BlockDriverState *bs, BdrvChild *c,
                                uint64_t perm, uint64_t shared,
                                uint64_t *nperm, uint64_t *nshared);
 
+bool bdrv_recurse_can_replace(BlockDriverState *bs,
+                              BlockDriverState *to_replace);
+
 /*
  * Default implementation for drivers to pass bdrv_co_block_status() to
  * their file.