Fix compilation of the xtask package under Windows

The qemu code makes use of some APIs from the `nix` crate, which causes
compilation to fail on Windows (native, not WSL). The qemu code can't be
easily made to work on Windows, but the rest of xtask should still work
fine building, running clippy, etc. Fix by adding `#![cfg(unix)]` to the
`qemu` module, as well as the `disk` and `net` modules that are only
used by the qemu code. Also changed the `run_vm_tests` action to panic
on non-Unix targets.

Author: nicholasbishop

xtask/Cargo.toml

@@ -6,6 +6,7 @@ publish = false
 
 [dependencies]
 anyhow = "1.0.51"
+cfg-if = "1.0.0"
 clap = { version = "3.0.13", features = ["derive"] }
 # The latest fatfs release (0.3.5) is old, use git instead to pick up some fixes.
 fatfs = { git = "https://github.com/rafalh/rust-fatfs.git", rev = "87fc1ed5074a32b4e0344fcdde77359ef9e75432" }

xtask/src/disk.rs

@@ -1,3 +1,5 @@
+#![cfg(unix)]
+
 use anyhow::Result;
 use fatfs::{Date, DateTime, FileSystem, FormatVolumeOptions, FsOptions, StdIoWrapper, Time};
 use mbrman::{MBRPartitionEntry, CHS, MBR};

xtask/src/main.rs

@@ -8,6 +8,7 @@ mod util;
 
 use anyhow::Result;
 use cargo::{Cargo, CargoAction, Feature, Package};
+use cfg_if::cfg_if;
 use clap::Parser;
 use opt::{Action, BuildOpt, ClippyOpt, DocOpt, MiriOpt, Opt, QemuOpt};
 use std::process::Command;
@@ -102,7 +103,13 @@ fn run_vm_tests(opt: &QemuOpt) -> Result<()> {
     };
     run_cmd(cargo.command()?)?;
 
-    qemu::run_qemu(*opt.target, opt)
+    cfg_if! {
+        if #[cfg(unix)] {
+            qemu::run_qemu(*opt.target, opt)
+        } else {
+            panic!("vm tests are only supported on unix targets");
+        }
+    }
 }
 
 /// Run unit tests and doctests on the host. Most of uefi-rs is tested

xtask/src/net.rs

@@ -1,3 +1,5 @@
+#![cfg(unix)]
+
 use std::net::UdpSocket;
 
 /// Start a thread that listens on UDP port 21572 and simulates a simple echo

xtask/src/qemu.rs

@@ -1,3 +1,5 @@
+#![cfg(unix)]
+
 use crate::arch::UefiArch;
 use crate::disk::{check_mbr_test_disk, create_mbr_test_disk};
 use crate::net;