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From 62c3dde0dcd04ce52e761beb66a3ec4aacd007e6 Mon Sep 17 00:00:00 2001
From: John Snow <>
Date: Wed, 18 Jul 2018 22:55:08 +0200
Subject: [PATCH 250/268] nbd/server: Fix dirty bitmap logic regression

RH-Author: John Snow <>
Message-id: <>
Patchwork-id: 81427
O-Subject: [RHEL-7.6 qemu-kvm-rhev PATCH 32/35] nbd/server: Fix dirty bitmap logic regression
Bugzilla: 1207657
RH-Acked-by: Eric Blake <>
RH-Acked-by: Stefan Hajnoczi <>
RH-Acked-by: Fam Zheng <>

From: Eric Blake <>

In my hurry to fix a build failure, I introduced a logic bug.
The assertion conditional is backwards, meaning that qemu will
now abort instead of reporting dirty bitmap status.

The bug can only be tickled by an NBD client using an exported
dirty bitmap (which is still an experimental QMP command), so
it's not the end of the world for supported usage (and neither
'make check' nor qemu-iotests fails); but it also shows that we
really want qemu-io support for reading dirty bitmaps if only
so that I can add iotests coverage to prevent future
brown-bag-of-shame events like this one.

Fixes: 45eb6fb6
Signed-off-by: Eric Blake <>
Message-Id: <>
(cherry picked from commit 7606c99a0421be7e9d984766fe239f7791a2fd9c)
Signed-off-by: John Snow <>
Signed-off-by: Miroslav Rezanina <>
 nbd/server.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/nbd/server.c b/nbd/server.c
index 50ac8bf..e52b76b 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1977,7 +1977,7 @@ static unsigned int bitmap_to_extents(BdrvDirtyBitmap *bitmap, uint64_t offset,
-    assert(offset > end);
+    assert(offset < end);
     *length = end - offset;
     return i;