add virtio-balloon device

[iwinux]

The virtio-balloon device is added to the VM when --device virtio-balloon is specified. However, I'm not sure how to verify it's actually working inside the VM.

$ find /sys -iname '*balloon*'
/sys/kernel/btf/virtio_balloon
/sys/bus/virtio/drivers/virtio_balloon
/sys/module/virtio_balloon
/sys/module/virtio_balloon/drivers/virtio:virtio_balloon

---

TODOs:

• add test to vfkit/test/vm_test.go
• add doc to usage.md
• confirm behavior of adding multiple balloon device

[openshift-ci]

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[openshift-ci]

Hi @iwinux. Thanks for your PR.

I'm waiting for a crc-org member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[cfergeau]

However, I'm not sure how to verify it's actually working inside the VM.

https://developer.apple.com/documentation/virtualization/vzvirtiotraditionalmemoryballoondevice?language=objc has some explanations how to interact with the balloon device. I don't know if these properties are supported in Code-Hex/vz though

[cfergeau]

Looks good to me, thanks for the patch!

Can you also add a balloon test to

vfkit/test/vm_test.go

Lines 201 to 230 in 9c685bc

	var pciidTests = map[string]pciidTest{
	"virtio-net": {
	vendorID: 0x1af4, // Red Hat
	deviceID: 0x1041,
	createDev: func(_ *testing.T) (config.VirtioDevice, error) {
	return config.VirtioNetNew("")
	},
	},
	"virtio-serial": {
	vendorID: 0x1af4, // Red Hat
	deviceID: 0x1043,
	createDev: func(t *testing.T) (config.VirtioDevice, error) {
	return config.VirtioSerialNew(filepath.Join(t.TempDir(), "serial.log"))
	},
	},
	"virtio-rng": {
	vendorID: 0x1af4, // Red Hat
	deviceID: 0x1044,
	createDev: func(_ *testing.T) (config.VirtioDevice, error) {
	return config.VirtioRngNew()
	},
	},
	"virtio-fs": {
	vendorID: 0x1af4, // Red Hat
	deviceID: 0x105a,
	createDev: func(_ *testing.T) (config.VirtioDevice, error) {
	return config.VirtioFsNew("./", "vfkit-share-test")
	},
	},
	}

?
And adding it to the documentation would also be useful, for example before/after virtio-rng https://github.com/crc-org/vfkit/blob/main/doc/usage.md#random-number-generator

Documentation for the virtualization framework says that it's only allowed to have one virtio-balloon device at a time in a VM, do you know if we get an error if we pass --device virtio-balloon multiple times?

[iwinux]

https://developer.apple.com/documentation/virtualization/vzvirtiotraditionalmemoryballoondevice?language=objc has some explanations how to interact with the balloon device. I don't know if these properties are supported in Code-Hex/vz though

@cfergeau After reading the page I realize that this patch has only enabled the virtio-balloon device for guests, but hasn't utilized the device at the host side for memory allocation. The latter task seems a bit more complicated, should I leave it as a separate issue?

https://github.com/firecracker-microvm/firecracker/blob/main/docs/ballooning.md also provides some insights on how the device can be used.

[cfergeau]

The latter task seems a bit more complicated, should I leave it as a separate issue?

No objections to that, this definitely can be addressed later on, I was just trying to provide guidance as you were unsure how to test it.

[iwinux]

Passing --device virtio-balloon multiple times has no observable effects:

Output of vfkit:

INFO[0000] &{1 512    {[efi variable-store=efi.vars create] true}  [virtio-blk,path=alpine-virt-3.21.2-aarch64.iso virtio-fs,sharedDir=test,mountTag=test virtio-net,nat,mac=ca:fe:00:00:00:97 virtio-gpu,width=1920,height=1080 virtio-input,keyboard virtio-input,pointing virtio-rng virtio-balloon virtio-balloon virtio-balloon virtio-balloon virtio-balloon] none://  true } 
INFO[0000] boot parameters: &{EFIVariableStorePath:efi.vars CreateVariableStore:true} 
INFO[0000]                                              
INFO[0000] virtual machine parameters:                  
INFO[0000]      vCPUs: 1                                    
INFO[0000]      memory: 512 MiB                             
INFO[0000]                                              
INFO[0000] Adding virtio-blk device (imagePath: alpine-virt-3.21.2-aarch64.iso) 
INFO[0000] Adding virtio-fs device                      
INFO[0000] Adding virtio-net device (nat: true macAddress: [ca:fe:00:00:00:97]) 
INFO[0000] Adding virtio-gpu device                     
INFO[0000] Adding virtio-input keyboard device          
INFO[0000] Adding virtio-input pointing device          
INFO[0000] Adding virtio-rng device                     
INFO[0000] Adding virtio-balloon device                 
INFO[0000] Adding virtio-balloon device                 
INFO[0000] Adding virtio-balloon device                 
INFO[0000] Adding virtio-balloon device                 
INFO[0000] Adding virtio-balloon device

Output of lspci inside VM:

00:00.0 Host bridge: Apple Inc. Device 1a05
00:01.0 Ethernet controller: Red Hat, Inc. Virtio 1.0 network device (rev 01)
00:05.0 Mass storage controller: Red Hat, Inc. Virtio 1.0 block device (rev 01)
00:06.0 Mass storage controller: Red Hat, Inc. Virtio file system (rev 01)
00:07.0 Display controller: Red Hat, Inc. Virtio 1.0 GPU (rev 01)
00:08.0 Network and computing encryption device: Red Hat, Inc. Virtio 1.0 RNG (rev 01)
00:09.0 Memory controller: Red Hat, Inc. Virtio 1.0 memory balloon (rev 01)
00:0a.0 USB controller: Apple Inc. Device 1a06