Don't copy local image

[zeenix]

If the source image is local, instead of copying it over, use qemu-img command to create an image with the source image as backing image instead.

For crc, this reduces disk usage greatly (~ 9GB currently) and start up time by around 20 seconds on my very high-end system with an SSD.

This adds a runtime dependency on qemu-img command so we probably should check for that as part of CRC preflight checks.

Fixes #37.

[zeenix]

PTALA

[zeenix]

@praveenkumar PTALA

[cfergeau]

Couple of minor comments, but overall looks good to me.

Something that I was wondering during the review, should we create the overlay image in snc and ship it in the bundle? This has the advantage of not adding a qemu-img dependency on the libvirt machine driver (even if it's already there indirectly through libvirt). This would also mean we could try to use the overlay on macos too, where qemu-img is less likely to be present (but I don't know if hyperkit's qcow2 implementation supports that).

[cfergeau]

These 2 comments seem a bit redundant?

[zeenix]

How so?

[cfergeau]

I don't see much difference in meaning/information provided by
For local image on Linux, we can avoid copying by making use of base image through qemu-img and Local disk image so we can avoid copying by making use of backing image feature of qcow2
Both lines repeat "we are on linux, we have a local image, we can avoid the copy", and then you have 2 different ways of saying we are going to use an overlay instead of doing the copy.

[zeenix]

Something that I was wondering during the review, should we create the overlay image in snc and ship it in the bundle?

Would be worth investigating for sure but could we merge this now please?

[cfergeau]

I've tested this, but I had some permissions issues when trying to create the VM and start it. I believe this is caused by
pkg/crc/preflight/preflight_checks_common.go: err = os.MkdirAll(bundleDir, 0700), after changing ~/.crc/cache to 0755, it was fine. One way around it could be to create a hard link for the base image in ~/.crc/machines/crc/. Another way is to change crc :)

[cfergeau]

Could you add a full link in the commit log #37 ?
github unhelpfully shorten it, I mean have n explicit "Fixes https://github.com/ code-ready /machine-driver-libvirt/issues/37 " in the log. Easier to directly click on it when using git tools.

[zeenix]

Could you add a full link in the commit log #37 ?

Would GH be able to pick it up and resolve the issue automatically?

[cfergeau]

Could you add a full link in the commit log #37 ?

Would GH be able to pick it up and resolve the issue automatically?

Yes

[cfergeau]

On a machine with a rotating disk, this saves 2 minutes on startup time! (cold cache)

[praveenkumar]

where qemu-img is less likely to be present (but I don't know if hyperkit's qcow2 implementation supports that

@cfergeau I didn't try it out but it doesn't hurt to create as part of snc if that allow us the different format conversion without any issue.

[zeenix]

As discussed on slack, it turns out that with the hardlink approach, the source file in the cache directory will also change ownership to qemu user and after the first crc start and crc delete, the linking will not work any more because the link will be created by normal user.

So this means that we should first get #20 in since that would mean qemu process runs as active normal user and we won't have this problem.

[praveenkumar]

closing this since it is now fixed by #57