cargo xtask run fails to fetch edk2

[kraxel]

[INFO] downloading https://github.com/rust-osdev/ovmf-prebuilt/releases/download/edk2-stable202402-r1/edk2-stable202402-r1-bin.tar.xz
Error: remote request failed

Caused by:
    io: Peer disconnected

Trying to fetch the file with wget shows that github redirects to https://objects.githubusercontent.com/.... I think this is new, I can't remember having seen this before.

[kraxel]

Even when using --ovmf-code + --ovmf-vars xtask tries to fetch prebuild edk2.

[phip1611]

Good catch! Thanks.

1.) Probably we have to update the URL
2.) it shouldn't fetch when we provide OVMF as environmental variable

[nicholasbishop]

I think the download issue must have been a transient problem with github or the network; it seems to be working fine now.

I also checked on why it's downloading if you specify --ovmf-code + --ovmf-vars: it's because we need a third file, shell.efi. If you specify that one as well (with OVMF_SHELL, since there's no arg defined for it), the download is correctly skipped.

So I think the only thing we should maybe do here is add a --ovmf-shell arg, to make that 3rd dependency more discoverable in the help output.