From 231ea3db5b4c6b9de25fa62b2e6c39ebc4987a6f Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Fri, 18 Oct 2013 08:14:41 +0200
Subject: [PATCH 16/81] block: return BDRV_BLOCK_ZERO past end of backing file

RH-Author: Paolo Bonzini <pbonzini@redhat.com>
Message-id: <1382084091-16636-17-git-send-email-pbonzini@redhat.com>
Patchwork-id: 54999
O-Subject: [RHEL 7.0 qemu-kvm PATCH 16/26] block: return BDRV_BLOCK_ZERO past end of backing file
Bugzilla: 989646
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Max Reitz <mreitz@redhat.com>
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>

If the sectors are unallocated and we are past the end of the
backing file, they will read as zero.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit f0ad5712d5d15ff272b9e107910be4aae468fb3d)
---
 block.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 block.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index 00bc3b2..36a2f24 100644
--- a/block.c
+++ b/block.c
@@ -3068,8 +3068,16 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
         return ret;
     }
 
-    if (!(ret & BDRV_BLOCK_DATA) && bdrv_has_zero_init(bs)) {
-        ret |= BDRV_BLOCK_ZERO;
+    if (!(ret & BDRV_BLOCK_DATA)) {
+        if (bdrv_has_zero_init(bs)) {
+            ret |= BDRV_BLOCK_ZERO;
+        } else {
+            BlockDriverState *bs2 = bs->backing_hd;
+            int64_t length2 = bdrv_getlength(bs2);
+            if (length2 >= 0 && sector_num >= (length2 >> BDRV_SECTOR_BITS)) {
+                ret |= BDRV_BLOCK_ZERO;
+            }
+        }
     }
     return ret;
 }
-- 
1.7.1