Comment 30 for bug 1847361

Still works:
$ apt install --reinstall qemu-block-extra
(this is like an upgrade to itself)

files match
root@f:~# md5sum /var/run/qemu/1_4.2-3ubuntu2~ppa4_/* /usr/lib/x86_64-linux-gnu/qemu/block*
e5fae910ca4c3c726ae0491a2cdab507 /var/run/qemu/1_4.2-3ubuntu2~ppa4_/block-curl.so
f780837ec4678eb783baecfab43fa2c1 /var/run/qemu/1_4.2-3ubuntu2~ppa4_/block-iscsi.so
34795eba24a8445621328562e0d953f2 /var/run/qemu/1_4.2-3ubuntu2~ppa4_/block-rbd.so
399dfc7f7912506ff96c3b96ed90a6eb /var/run/qemu/1_4.2-3ubuntu2~ppa4_/block-ssh.so
e5fae910ca4c3c726ae0491a2cdab507 /usr/lib/x86_64-linux-gnu/qemu/block-curl.so
f780837ec4678eb783baecfab43fa2c1 /usr/lib/x86_64-linux-gnu/qemu/block-iscsi.so
34795eba24a8445621328562e0d953f2 /usr/lib/x86_64-linux-gnu/qemu/block-rbd.so
399dfc7f7912506ff96c3b96ed90a6eb /usr/lib/x86_64-linux-gnu/qemu/block-ssh.so

Removing the original one to force fallback:
mv /usr/lib/x86_64-linux-gnu/qemu/block-curl.so /usr/lib/x86_64-linux-gnu/qemu/orig.block-curl.so.orig

root@f:~# lsof -p $(pidof qemu-system-x86_64) | grep block
<nothing>

Loading:
DEBUG: trying to load module: /usr/lib/x86_64-linux-gnu/qemu/block-curl.so
DEBUG: trying to load module: /usr/bin/../block-curl.so
DEBUG: trying to load module: /usr/bin/block-curl.so
DEBUG: trying to load module: /var/run/qemu/Debian_1_4.2-3ubuntu2~ppa4/block-curl.so

Two differences left:
1. the binary has the "Debian_" prefix. that is from Debian rules (silly) but easy to fix
   --with-pkgversion="Debian $(DEB_VERSION)"
   => Prepending that in our templating as well
2. The effective dir has a suffix _
     /var/run/qemu/1_4.2-3ubuntu2~ppa4_
   That is from PKGVERSION substitution, since we use the inverted set it replaces the EOL
   Using printf will not add that and behave in d/rules like the binary