Description of problem:
We have encountered a failure running qemu-img map on a file with multiple blocks.

Failure qemu-img map on FC28:

# rpm -qa | grep qemu
qemu-audio-alsa-2.12.0-0.5.rc1.fc28.x86_64
qemu-block-curl-2.12.0-0.5.rc1.fc28.x86_64
qemu-block-nfs-2.12.0-0.5.rc1.fc28.x86_64
qemu-ui-sdl-2.12.0-0.5.rc1.fc28.x86_64
qemu-img-2.12.0-0.5.rc1.fc28.x86_64
qemu-common-2.12.0-0.5.rc1.fc28.x86_64
qemu-audio-oss-2.12.0-0.5.rc1.fc28.x86_64
qemu-audio-sdl-2.12.0-0.5.rc1.fc28.x86_64
qemu-block-dmg-2.12.0-0.5.rc1.fc28.x86_64
qemu-block-iscsi-2.12.0-0.5.rc1.fc28.x86_64
qemu-block-rbd-2.12.0-0.5.rc1.fc28.x86_64
qemu-ui-gtk-2.12.0-0.5.rc1.fc28.x86_64
qemu-system-x86-core-2.12.0-0.5.rc1.fc28.x86_64
qemu-kvm-2.12.0-0.5.rc1.fc28.x86_64
libvirt-daemon-driver-qemu-4.2.0-1.fc28.x86_64
ipxe-roms-qemu-20170710-3.git0600d3ae.fc28.noarch
qemu-audio-pa-2.12.0-0.5.rc1.fc28.x86_64
qemu-block-gluster-2.12.0-0.5.rc1.fc28.x86_64
qemu-ui-curses-2.12.0-0.5.rc1.fc28.x86_64
qemu-system-x86-2.12.0-0.5.rc1.fc28.x86_64

[root@dhcp163-43 vdsm]# python
Python 2.7.15 (default, May 16 2018, 17:50:09) 
[GCC 8.1.1 20180502 (Red Hat 8.1.1-1)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import io
>>> filename = "/tmp/test2"
>>> with io.open(filename, "wb") as f:
...     f.write(b"x")
...     f.seek(16 * 1024)
...     f.write(b"x")
...     f.seek(42 * 1024)
...     f.write(b"x")
... 
1L
16384L
1L
43008L
1L
>>> 

Run the following command on that file:
    /usr/bin/qemu-img map --output json /tmp/test2

/usr/bin/qemu-img map --output json /tmp/test2
[{ "start": 0, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 0},
{ "start": 4096, "length": 12288, "depth": 0, "zero": true, "data": false, "offset": 4096},
{ "start": 16384, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 16384},
qemu-img: /builddir/build/BUILD/qemu-2.12.0-rc1/qemu-img.c:2680: get_block_status: Assertion `bytes' failed.
Aborted (core dumped)


A successful qemu-img map on FC27
# rpm -qa | grep qemu
qemu-system-x86-2.11.0-4.fc27.x86_64
qemu-guest-agent-2.11.0-4.fc27.x86_64
qemu-block-rbd-2.11.0-4.fc27.x86_64
qemu-img-2.11.0-4.fc27.x86_64
qemu-system-x86-core-2.11.0-4.fc27.x86_64
qemu-block-iscsi-2.11.0-4.fc27.x86_64
libvirt-daemon-driver-qemu-4.0.0-2.fc27.x86_64
ipxe-roms-qemu-20170710-3.git0600d3ae.fc27.noarch
qemu-sanity-check-nodeps-1.1.5-8.fc27.x86_64
qemu-kvm-2.11.0-4.fc27.x86_64
qemu-block-dmg-2.11.0-4.fc27.x86_64
qemu-common-2.11.0-4.fc27.x86_64
qemu-block-nfs-2.11.0-4.fc27.x86_64
qemu-block-ssh-2.11.0-4.fc27.x86_64
qemu-block-gluster-2.11.0-4.fc27.x86_64
qemu-block-curl-2.11.0-4.fc27.x86_64

Creating a file with the following python script:

>>> import io
>>> filename = "/tmp/test"
>>> with io.open(filename, "wb") as f:
...     f.write(b"x")
...     f.seek(16 * 1024)
...     f.write(b"x")
...     f.seek(42 * 1024)
...     f.write(b"x")
... 
1L
16384L
1L
43008L
1L

Run the following command on that file:
    /usr/bin/qemu-img map --output json /tmp/test

Output:
[{ "start": 0, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 0},
{ "start": 4096, "length": 12288, "depth": 0, "zero": true, "data": false, "offset": 4096},
{ "start": 16384, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 16384},
{ "start": 20480, "length": 20480, "depth": 0, "zero": true, "data": false, "offset": 20480},
{ "start": 40960, "length": 2560, "depth": 0, "zero": false, "data": true, "offset": 40960}]

Version-Release number of selected component (if applicable):


How reproducible:
100%

Steps to Reproduce:
1.
2.
3.

Actual results:


Expected results:


Additional info: