[Qemu-devel] [PATCH v3 2/4] block: in commit, determine base image from the top image

[Jeff Cody]

This simplifies some code and error checking, and also fixes a bug.

bdrv_find_backing_image() should only be passed absolute filenames,
or filenames relative to the chain.  In the QMP message handler for
block commit, when looking up the base do so from the determined top
image, so we know it is reachable from top.

Signed-off-by: Jeff Cody <jc...@redhat.com>
---
 block/commit.c |  9 ---------
 blockdev.c     | 21 +++++++++++----------
 2 files changed, 11 insertions(+), 19 deletions(-)

diff --git a/block/commit.c b/block/commit.c
index 733c914..13d9e82 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -211,15 +211,6 @@ void commit_start(BlockDriverState *bs, BlockDriverState 
*base,
         return;
     }
 
-    /* top and base may be valid, but let's make sure that base is reachable
-     * from top */
-    if (bdrv_find_backing_image(top, base->filename) != base) {
-        error_setg(errp,
-                   "Base (%s) is not reachable from top (%s)",
-                   base->filename, top->filename);
-        return;
-    }
-
     overlay_bs = bdrv_find_overlay(bs, top);
 
     if (overlay_bs == NULL) {
diff --git a/blockdev.c b/blockdev.c
index 99828ad..46e4bbd 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1157,16 +1157,6 @@ void qmp_block_commit(const char *device,
         error_set(errp, QERR_DEVICE_NOT_FOUND, device);
         return;
     }
-    if (base && has_base) {
-        base_bs = bdrv_find_backing_image(bs, base);
-    } else {
-        base_bs = bdrv_find_base(bs);
-    }
-
-    if (base_bs == NULL) {
-        error_set(errp, QERR_BASE_NOT_FOUND, base ? base : "NULL");
-        return;
-    }
 
     /* default top_bs is the active layer */
     top_bs = bs;
@@ -1182,6 +1172,17 @@ void qmp_block_commit(const char *device,
         return;
     }
 
+    if (has_base && base) {
+        base_bs = bdrv_find_backing_image(top_bs, base);
+    } else {
+        base_bs = bdrv_find_base(top_bs);
+    }
+
+    if (base_bs == NULL) {
+        error_set(errp, QERR_BASE_NOT_FOUND, base ? base : "NULL");
+        return;
+    }
+
     commit_start(bs, base_bs, top_bs, speed, on_error, block_job_cb, bs,
                 &local_err);
     if (local_err != NULL) {
-- 
1.7.11.4