Researching `virtiofsd` Connection Persistence in QEMU

[Ashlok2003]

Hello Maintainers,

I am currently researching how virtiofsd maintains its connection with QEMU and whether it is possible to re-establish the connection without requiring a full restart of QEMU. Based on my understanding, virtiofsd establishes a persistent connection with QEMU via a UNIX domain socket. However, I have some questions regarding its behavior and potential reconnection mechanisms:

Key Questions:

1. Connection Persistence:

   • Once virtiofsd starts, does QEMU establish a strictly one-time connection with it?
   • Is there any built-in mechanism within QEMU to allow virtiofsd to reconnect without restarting the VM instance?

2. Failure Handling & Recovery:

   • If virtiofsd stops or crashes, what is the expected behavior in QEMU?
   • Are there any existing ways in QEMU to resume or reattach a new virtiofsd process to an already running VM?

3. Potential Workarounds:

   • From an architecture perspective, is there a reason why QEMU maintains a persistent connection to virtiofsd rather than a reconnectable session?
   • Are there specific limitations that prevent implementing a hot-reconnection mechanism within QEMU for virtiofsd?

My goal is to understand whether virtiofsd can be restarted independently of QEMU while keeping the VM's state intact. Any guidance, insights, or references to existing discussions on this topic would be greatly appreciated.

Thank you!