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Re: [Qemu-devel] [PATCH] dirty-bitmap: remove unnecessary return

From: Changlong Xie
Subject: Re: [Qemu-devel] [PATCH] dirty-bitmap: remove unnecessary return
Date: Fri, 1 Jul 2016 09:20:31 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 07/01/2016 02:18 AM, John Snow wrote:

On 06/30/2016 10:00 AM, Jeff Cody wrote:
On Thu, Jun 30, 2016 at 04:45:52PM +0800, Changlong Xie wrote:
On 06/30/2016 04:25 PM, Fam Zheng wrote:
On Thu, 06/30 16:01, Changlong Xie wrote:
Otherwise, we could never trigger assert(!bitmap->successor)

Signed-off-by: Changlong Xie <address@hidden>
  block/dirty-bitmap.c | 1 -
  1 file changed, 1 deletion(-)

diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
index 4902ca5..e9df5ac 100644
--- a/block/dirty-bitmap.c
+++ b/block/dirty-bitmap.c
@@ -131,7 +131,6 @@ int bdrv_dirty_bitmap_create_successor(BlockDriverState *bs,
      if (bdrv_dirty_bitmap_frozen(bitmap)) {
          error_setg(errp, "Cannot create a successor for a bitmap that is "
                     "currently frozen");
-        return -1;

This is wrong. Then we will always trigger assert for a frozen bitmap.

IMO, when it's a frozen bitmap, we will always return -1. So
"assert(!bitmap->successor)" is useless here, am i right?

I don't see a path where the assert could trigger, so I would agree that the
assert itself, while harmless, is not necessary (although it could be argued
it is in place in case the code above it changes in a way that does not
check bitmap->successor).


That doesn't mean we want to try and trigger an assert, however! :) The
error return is the proper error handling -- we don't expect that asserts
should ever be encountered QEMU, if one happens that is a sign of a bug.

Got it


The assert was indeed added to ensure that if the valid states of the
bitmap later expanded or changed, that the status checkers (e.g.
bdrv_dirty_bitmap_frozen()) were changed to match.

Thanks for all explanations. Although my brain always forces to think it's a redundant execution path, but since it's harmless, let's keep it.


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