microsoft / microsoft/openvmm

storvsc: servicing/boot: write usermode storvsc client, rather than relying on kernel block device

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@juantian8seattle is already working on this.

Since Mar 10, 2026.

storage
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Description

Today OpenHCL uses the kernel's storvsc client for scenarios where OpenHCL uses synthetic storage from the Hyper-V host. This presents a few challenges:

  • It is expensive to map VTL0 addresses to the kernel on some architectures (arm64 specifically)
  • The kernel storage stack tries to discover the block devices, causing IO during boot and servicing operations
  • HCL must double buffer guest addresses if the IOs are not PAGE aligned
  • etc.

I'd like to evaluate using a usermode storvsc client instead.

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