qemu driver: Add option to configure drive_interface

[bogue1979]

For QEMU the options -drive file=image.img and -drive file=image.img,if=ide are identical.
This change will use the second variant as default and allow to define an image file using the virtio driver inside of the VM.
Using this driver should improve the disk IO a lot.

[bogue1979]

Ping

[hashicorp-cla]

All committers have signed the CLA.

[tgross]

Hi @bogue1979! This looks great. I think the only thing that comes to mind here is being sure about the default behavior for QEMU. Do you know if ide is platform-specific behavior and that QEMU isn't doing something "smart" based on the available interfaces on the platform? I want to make sure we're not introducing a breaking change, and that we're not boxing ourselves in for future updates we have on the roadmap for expanding QEMU support beyond x86_64 platform.

The man page has this to say:

if=interface
This option defines on which type on interface the drive is connected. Available types are: ide, scsi, sd, mtd, floppy, pflash, virtio.

With nothing about the default.

[bogue1979]

Hi @bogue1979! This looks great. I think the only thing that comes to mind here is being sure about the default behavior for QEMU. Do you know if ide is platform-specific behavior and that QEMU isn't doing something "smart" based on the available interfaces on the platform? I want to make sure we're not introducing a breaking change, and that we're not boxing ourselves in for future updates we have on the roadmap for expanding QEMU support beyond x86_64 platform.

The man page has this to say:

if=interface
This option defines on which type on interface the drive is connected. Available types are: ide, scsi, sd, mtd, floppy, pflash, virtio.

With nothing about the default.

Honestly I have no possibility to test another architecture. When I run a VM only with file=image.img on linux_x64, qemu implicitly attaches a virtual ide disk. On the other side giving the option to explicitly configure the interface, any non default behaviour can be overriden within the nomad job file. I guess if another architecture does not understand the given ide interface updating the documentation should be sufficient.

[bogue1979]

@tgross
any news on this?

[tgross]

Sorry about the delayed follow-up @bogue1979. This looks pretty good.

You haven't made the PR editable by maintainers, so I'll also need you to add a changelog entry at .changelog/11864.txt with the following contents:

```release-note:improvement
qemu: Added option to configure `drive_interface`
```

Once that's done we can get this merged and shipped in the upcoming Nomad 1.3.2

[tgross]

LGTM! Thanks for your patience on this one @bogue1979 !

merge conflicts

[tgross]

Oops, sorry jumped the gun there @bogue1979. GitHub is saying there are some merge conflicts here. Might need to rebase on main.

[bogue1979]

Sorry I'm not really a developer and Git sometimes confuses me when it does not work as expected.

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