feature(krata): first pass on cpu hotplug support (#340)

* fix(runtime): adjust memory resources inside a transaction

* feature(krata): first pass on cpu hotplug support

crates/xen/xenclient/examples/boot.rs

@@ -27,6 +27,7 @@ async fn main() -> Result<()> {
         base: BaseDomainConfig {
             uuid: Uuid::new_v4(),
             max_vcpus: 1,
+            target_vcpus: 1,
             max_mem_mb: 512,
             target_mem_mb: 512,
             enable_iommu: true,

crates/xen/xenclient/src/tx.rs

@@ -194,7 +194,16 @@ impl ClientTransaction {
             self.tx.mkdir(&path).await?;
             self.tx.set_perms(&path, ro_perm).await?;
             let path = format!("{}/cpu/{}/availability", self.dom_path, i);
-            self.tx.write_string(&path, "online").await?;
+            self.tx
+                .write_string(
+                    &path,
+                    if i < base.target_vcpus {
+                        "online"
+                    } else {
+                        "offline"
+                    },
+                )
+                .await?;
             self.tx.set_perms(&path, ro_perm).await?;
         }
         Ok(())

crates/xen/xenplatform/src/domain.rs

@@ -9,6 +9,8 @@ use xencall::XenCall;
 
 use crate::error::Result;
 
+pub const XEN_EXTRA_MEMORY_KB: u64 = 2048;
+
 pub struct BaseDomainManager<P: BootSetupPlatform> {
     call: XenCall,
     pub platform: Arc<P>,
@@ -29,7 +31,7 @@ impl<P: BootSetupPlatform> BaseDomainManager<P> {
         let domid = self.call.create_domain(domain).await?;
         self.call.set_max_vcpus(domid, config.max_vcpus).await?;
         self.call
-            .set_max_mem(domid, (config.max_mem_mb * 1024) + 2048)
+            .set_max_mem(domid, (config.max_mem_mb * 1024) + XEN_EXTRA_MEMORY_KB)
             .await?;
         let loader = ElfImageLoader::load_file_kernel(&config.kernel)?;
         let platform = (*self.platform).clone();
@@ -64,6 +66,7 @@ pub struct BaseDomainConfig {
     pub uuid: Uuid,
     pub owner_domid: u32,
     pub max_vcpus: u32,
+    pub target_vcpus: u32,
     pub max_mem_mb: u64,
     pub target_mem_mb: u64,
     pub kernel: Vec<u8>,