added VZNetworkBlockDeviceStorageDeviceAttachment

[saracen]

Further to Code-Hex#142, this adds VZNetworkBlockDeviceStorageDeviceAttachment support.

This PR lacks setting a delegate to monitor state changes to the attachment, mostly because I couldn't figure out the best way to integrate this and it would probably lead to a much larger PR. Hopefully that can be done in a follow-up.

I've updated the MacOS application to ease testing. You can serve an existing raw disk within the bundle directory with qemu-nbd:

qemu-nbd -k $(pwd)/source.sock -f raw -x export --cache=none disk.img

And then run:

./macOS -nbd-url "nbd+unix:///export?socket=source.sock"

The -install option also works well with this argument if you serve a disk created with qemu-img.

This is great news as it gives access to qemu's qcow2 format and linked disks functionality.

Relates to Code-Hex#143

[saracen]

Hey @AkihiroSuda,

I've copied this over from Code-Hex#156, changing how the string is initialized (as per cfergeau's comment). I haven't yet tested with this change though, as I've ran out of disk space to pull/install a new image 😄

[AkihiroSuda]

Thanks, but please sign the commit for DCO
https://github.com/apps/dco

(run git commit -a -s --amend, and make sure that the Signed-off-by: NAME <EMAIL> line with your real name is included in the commit message)

[saracen]

@AkihiroSuda All done. Looks like macos-15-large test job had problems, but log isn't showing for me as to why it took so long.

[AkihiroSuda]

Thanks