[Qemu-devel] [PATCH 2/2] block: commit and stream return an error when a subtree is found

[Benoît Canet]

In bdrv_find_backing_image when looking for the base BDS of a backing chain and
a BDS having a multiple children block driver is found return NULL and set an
error message.

This will hopefully remove any unwanted interference between stream, commit
and drivers like quorum.

CC: Jeff Cody <address@hidden>
Signed-off-by: Benoît Canet <address@hidden>
---
 block.c               | 17 +++++++++++++++--
 blockdev.c            | 18 ++++++++++++------
 include/block/block.h |  3 ++-
 3 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/block.c b/block.c
index d06dd51..ea86252 100644
--- a/block.c
+++ b/block.c
@@ -4339,9 +4339,13 @@ int bdrv_is_snapshot(BlockDriverState *bs)
 /* backing_file can either be relative, or absolute, or a protocol.  If it is
  * relative, it must be relative to the chain.  So, passing in bs->filename
  * from a BDS as backing_file should not be done, as that may be relative to
- * the CWD rather than the chain. */
+ * the CWD rather than the chain.
+ * If a multiple children BDS driver is found down the backing chain path then
+ * return NULL and set an error message.
+ */
 BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
-        const char *backing_file)
+                                          const char *backing_file,
+                                          Error **errp)
 {
     char *filename_full = NULL;
     char *backing_file_full = NULL;
@@ -4362,6 +4366,15 @@ BlockDriverState 
*bdrv_find_backing_image(BlockDriverState *bs,
 
     for (curr_bs = bs; curr_bs->backing_hd; curr_bs = curr_bs->backing_hd) {
 
+        /* If a BDS having a multiple children block driver is found then the
+         * function should fail.
+         */
+        if (curr_bs->drv && curr_bs->drv->supports_multiple_children) {
+            error_setg(errp, "multiple children block driver found down the "
+                             "backing chain");
+            break;
+        }
+
         /* If either of the filename paths is actually a protocol, then
          * compare unmodified paths; otherwise make paths relative */
         if (is_protocol || path_has_protocol(curr_bs->backing_file)) {
diff --git a/blockdev.c b/blockdev.c
index e919566..4c5c28e 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1894,9 +1894,11 @@ void qmp_block_stream(const char *device,
     }
 
     if (has_base) {
-        base_bs = bdrv_find_backing_image(bs, base);
+        base_bs = bdrv_find_backing_image(bs, base, errp);
         if (base_bs == NULL) {
-            error_set(errp, QERR_BASE_NOT_FOUND, base);
+            if (!*errp) {
+                error_set(errp, QERR_BASE_NOT_FOUND, base);
+            }
             return;
         }
         base_name = base;
@@ -1965,23 +1967,27 @@ void qmp_block_commit(const char *device,
 
     if (has_top && top) {
         if (strcmp(bs->filename, top) != 0) {
-            top_bs = bdrv_find_backing_image(bs, top);
+            top_bs = bdrv_find_backing_image(bs, top, errp);
         }
     }
 
     if (top_bs == NULL) {
-        error_setg(errp, "Top image file %s not found", top ? top : "NULL");
+        if (!*errp) {
+            error_setg(errp, "Top image file %s not found", top ? top : 
"NULL");
+        }
         return;
     }
 
     if (has_base && base) {
-        base_bs = bdrv_find_backing_image(top_bs, base);
+        base_bs = bdrv_find_backing_image(top_bs, base, errp);
     } else {
         base_bs = bdrv_find_base(top_bs);
     }
 
     if (base_bs == NULL) {
-        error_set(errp, QERR_BASE_NOT_FOUND, base ? base : "NULL");
+        if (!*errp) {
+            error_set(errp, QERR_BASE_NOT_FOUND, base ? base : "NULL");
+        }
         return;
     }
 
diff --git a/include/block/block.h b/include/block/block.h
index 8f4ad16..65cde65 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -272,7 +272,8 @@ int coroutine_fn bdrv_co_writev(BlockDriverState *bs, 
int64_t sector_num,
 int coroutine_fn bdrv_co_write_zeroes(BlockDriverState *bs, int64_t sector_num,
     int nb_sectors, BdrvRequestFlags flags);
 BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
-    const char *backing_file);
+                                          const char *backing_file,
+                                          Error **errp);
 int bdrv_get_backing_file_depth(BlockDriverState *bs);
 void bdrv_refresh_filename(BlockDriverState *bs);
 int bdrv_truncate(BlockDriverState *bs, int64_t offset);
-- 
2.1.0