context: Check if nested virt is supported before enabling

Cargo.toml

@@ -13,3 +13,5 @@ anyhow = "1.0.79"
 clap = { version = "4.5.0", features = ["derive"] }
 mac_address = "1.1.5"
 sysinfo = "0.31.4"
+log = "0.4.0"
+env_logger = "0.11.8"

src/context.rs

@@ -20,6 +20,7 @@ extern "C" {
     fn krun_set_vm_config(ctx_id: u32, num_vcpus: u8, ram_mib: u32) -> i32;
     fn krun_set_smbios_oem_strings(ctx_id: u32, oem_strings: *const *const c_char) -> i32;
     fn krun_set_nested_virt(ctx_id: u32, enabled: bool) -> i32;
+    fn krun_check_nested_virt() -> i32;
     fn krun_start_enter(ctx_id: u32) -> i32;
 }
 
@@ -40,6 +41,17 @@ impl TryFrom<Args> for KrunContext {
         // Start by setting up the desired log level for libkrun.
         unsafe { krun_set_log_level(args.krun_log_level) };
 
+        let log_level = match args.krun_log_level {
+            0 => "off",
+            1 => "error",
+            2 => "warn",
+            3 => "info",
+            4 => "debug",
+            _ => "trace",
+        };
+        env_logger::Builder::from_env(env_logger::Env::default().default_filter_or(log_level))
+            .init();
+
         // Create a new context in libkrun. Store identifier to later use to configure VM
         // resources and devices.
         let id = unsafe { krun_create_ctx() };
@@ -89,8 +101,16 @@ impl TryFrom<Args> for KrunContext {
 
         set_smbios_oem_strings(id, &args.oem_strings)?;
 
-        if args.nested && unsafe { krun_set_nested_virt(id, args.nested) } < 0 {
-            return Err(anyhow!("unable to set krun nested virtualization"));
+        if args.nested {
+            match unsafe { krun_check_nested_virt() } {
+                1 => {
+                    if unsafe { krun_set_nested_virt(id, args.nested) } < 0 {
+                        return Err(anyhow!("krun nested virtualization reported as supported, yet failed to enable"));
+                    }
+                }
+                0 => log::debug!("nested virtualization is not supported on this host. -n,--nested argument ignored"),
+                _ => return Err(anyhow!("unable to check nested virtualization is supported on this host")),
+            }
         }
 
         Ok(Self { id, args })