Support live disk resizing for RAW images by tpressure · Pull Request #7476 · cloud-hypervisor/cloud-hypervisor

tpressure · 2025-11-13T14:43:48Z

Summary

This pull request introduces live disk resizing support for RAW images. This enhancement enables dynamic adjustment of disks while the guest is running. This is part of our cloud-hypervisor openstack enablement.

Testing

Ran our libvirt test suite.
Add integration test

vmm/src/api/mod.rs

src/bin/ch-remote.rs

rbradford

I'm kinda impressed that Linux works with this! Will need an integration test.

src/bin/ch-remote.rs

tpressure · 2025-11-13T19:19:47Z

I'm kinda impressed that Linux works with this! Will need an integration test.

I will have a look how these integration tests work soon.

russell-islam · 2025-11-14T00:06:08Z

Are we supporting both shrink and expanse? For expanse it is okay, but for shrink don't see a possibility of corruption?

tpressure · 2025-11-14T07:47:15Z

Are we supporting both shrink and expanse? For expanse it is okay, but for shrink don't see a possibility of corruption?

I tried to keep this compatible to qemu. If you shrink the disk, the guest has to play nice, i.e. the part that is shrinked must not be active at the time. There's also this comment in the qemu libvirt driver which basically states the same: https://gitlab.com/libvirt/libvirt/-/blob/master/src/qemu/qemu_driver.c?ref_type=heads#L9402

rbradford

Thanks! I have no problems in principal with the feature/PR. Please try and add an integration test.

src/bin/ch-remote.rs

virtio-devices/src/block.rs

block/src/async_io.rs

virtio-devices/src/block.rs

block/src/raw_async.rs

This change is a prerequisite for live disk resizing. Before this commit, the epoll-handler threads just got a copy of the sector size which we cannot update during runtime. On-behalf-of: SAP thomas.prescher@sap.com Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>

tpressure · 2025-12-15T07:58:23Z

I'm kinda impressed that Linux works with this! Will need an integration test.

@rbradford test has been added.

phip1611 · 2025-12-15T08:33:40Z

Please beware that since the latest QoL improvements (#7489), you can run cargo clippy locally fairly easy :)

phip1611 · 2025-12-15T08:48:23Z

TL;DR: Open question: disk resizing and byte-range OFD locks?!

One last question: Since we have #7494: How does this work together with disk locking using byte-ranges? The old range will remain locked but that will not correspond to the new size.

From a Cloud Hypervisor perspective, as the locks are just advisory and overlapping, we can keep the old lock as it will in any case prevent further Cloud Hypervisor instances from locking again. But technically, other software could see regions of the file being unlocked.

tpressure · 2025-12-16T13:56:39Z

TL;DR: Open question: disk resizing and byte-range OFD locks?!

One last question: Since we have #7494: How does this work together with disk locking using byte-ranges? The old range will remain locked but that will not correspond to the new size.

From a Cloud Hypervisor perspective, as the locks are just advisory and overlapping, we can keep the old lock as it will in any case prevent further Cloud Hypervisor instances from locking again. But technically, other software could see regions of the file being unlocked.

@phip1611 you are absolutely right. Would it be ok to do this in a follow-up PR?

phip1611 · 2025-12-16T14:28:35Z

@phip1611 you are absolutely right. Would it be ok to do this in a follow-up PR?

I think it would be sufficient to create a follow-up ticket. In fact, this also has some caveats. For example, next to this live resize functionality, in the static qcow2 case, the physical image can also grow transparently to the guest, if I'm not mistaken. No need to fix all of this here in this PR.

tpressure · 2025-12-16T14:31:18Z

@phip1611 you are absolutely right. Would it be ok to do this in a follow-up PR?

I think it would be sufficient to create a follow-up ticket. In fact, this also has some caveats. For example, next to this live resize functionality, in the static qcow2 case, the physical image can also grow transparently to the guest, if I'm not mistaken. No need to fix all of this here in this PR.

I've created #7569

rbradford

Just some nits.

virtio-devices/src/block.rs

vmm/src/device_manager.rs

Add basic infrastructure so resize events are propagated to the underlying disk implementation. On-behalf-of: SAP thomas.prescher@sap.com Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>

Support for resize events for raw_async disks. On-behalf-of: SAP thomas.prescher@sap.com Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>

Support disk resizing via ch-remote and REST api. On-behalf-of: SAP thomas.prescher@sap.com Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>

On-behalf-of: SAP thomas.prescher@sap.com Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>

This test verifies that we can grow and shrink disk images during runtime. On-behalf-of: SAP thomas.prescher@sap.com Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>

phip1611 · 2026-02-05T16:59:10Z

@weltling This is what I talked about in today's meeting. If you see a pragmatic way forward to enable this system call for QCOW2, it would be great! I'm however unsure if it would make sense.. you are the domain expert here.

tpressure requested a review from a team as a code owner November 13, 2025 14:43

tpressure force-pushed the disk_resize_upstream branch 4 times, most recently from 0086f70 to 0513eb9 Compare November 13, 2025 15:22

rbradford reviewed Nov 13, 2025

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tpressure force-pushed the disk_resize_upstream branch from 0513eb9 to 95c9352 Compare November 13, 2025 16:38

tpressure requested a review from rbradford November 13, 2025 17:40

tpressure force-pushed the disk_resize_upstream branch 8 times, most recently from 349270d to 3fe60fb Compare November 13, 2025 19:01

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tpressure force-pushed the disk_resize_upstream branch from 3fe60fb to c835bec Compare November 13, 2025 19:16

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sboeuf reviewed Nov 18, 2025

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tpressure force-pushed the disk_resize_upstream branch from c835bec to e2eb29f Compare December 15, 2025 07:43

tpressure force-pushed the disk_resize_upstream branch from e2eb29f to 29bcd60 Compare December 15, 2025 07:43

tpressure requested review from rbradford and sboeuf December 15, 2025 07:51

tpressure force-pushed the disk_resize_upstream branch from 29bcd60 to eecaf37 Compare December 15, 2025 07:53

tpressure force-pushed the disk_resize_upstream branch 2 times, most recently from a7bfb15 to 9440b87 Compare December 15, 2025 07:56

tpressure force-pushed the disk_resize_upstream branch from 9440b87 to d18e840 Compare December 15, 2025 08:22

tpressure force-pushed the disk_resize_upstream branch from d18e840 to 9456396 Compare December 15, 2025 08:36

tpressure mentioned this pull request Dec 16, 2025

Add support for disk resizing and byte-range OFD locks #7569

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tpressure added 5 commits December 16, 2025 20:58

vmm: disk resize infrastructure

8235f94

Add basic infrastructure so resize events are propagated to the underlying disk implementation. On-behalf-of: SAP thomas.prescher@sap.com Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>

block: raw_async: implement disk resizing

88393da

Support for resize events for raw_async disks. On-behalf-of: SAP thomas.prescher@sap.com Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>

ch-remote: support live disk resizing

58e95c4

Support disk resizing via ch-remote and REST api. On-behalf-of: SAP thomas.prescher@sap.com Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>

docs: update vm.resize-disk

9821d04

On-behalf-of: SAP thomas.prescher@sap.com Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>

tests: add live disk resize test

95d0235

This test verifies that we can grow and shrink disk images during runtime. On-behalf-of: SAP thomas.prescher@sap.com Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>

tpressure force-pushed the disk_resize_upstream branch from 9456396 to 95d0235 Compare December 16, 2025 19:59

tpressure requested a review from rbradford December 16, 2025 19:59

rbradford approved these changes Dec 17, 2025

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rbradford added this pull request to the merge queue Dec 17, 2025

Merged via the queue into cloud-hypervisor:main with commit 736813f Dec 17, 2025
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likebreath added this to Cloud Hypervisor Roadmap Dec 17, 2025

github-project-automation bot moved this to ✅ Done in Cloud Hypervisor Roadmap Dec 17, 2025

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