[Virtio-fs] virtio-fs on zLinux (s390x)

[Gong Su]

Hi Stefan, I'm resending my questions to the list per your request.

Basically, I'm trying to see if I can get virtio-fs to work on zLinux.
Following the instructions on https://virtio-fs.gitlab.io/howto-qemu.html I
was able to compile all the pieces but when I tried to run qemu I realized
that it needs -numa option which isn't supported on s390x yet.

I have talked to Christian Borntraeger (whom I worked with on other
projects before) and he indicated that he had a plan to add -numa support
for s390x but currently is busy on other things.

So I'm trying to see if there are other ways for me to go forward without
having to wait for Christian. I see two options:

1. Merge virtiofsd into qemu itself. In the "Interchangeability" section of
the virtio-fs design page (https://virtio-fs.gitlab.io/design.html), it
mentioned that "It is also possible to forego vhost-user and emulate the
virtio-fs device directly inside the hypervisor, although this may result
in poor isolation and security." Since each guest typically gets its own
qemu process, maybe this is acceptable for some use cases. In exchange, you
get the benefit of not having to carve out a chunk of memory from /dev/shm
(and maybe simpler communication between virtiofsd and qemu).
2. Use something other than -numa to share memory between virtiofsd and
qemu that's supported on zLinux. I'm not entirely familiar with qemu so I
have no idea whether this is possible or not.

Thanks.
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