feat(vmm): make the initramfs optional

Signed-off-by: Kuruyia <github@kuruyia.net>

src/vmm/src/args.rs

@@ -15,7 +15,7 @@ pub struct CliArguments {
 
     /// Path to the cpio archive to use as the initramfs.
     #[arg(short, long, env)]
-    pub initramfs: PathBuf,
+    pub initramfs: Option<PathBuf>,
 
     /// Number of virtual CPUs assigned to the guest.
     #[clap(short, long, env, default_value = "1")]

src/vmm/src/core/kernel.rs

@@ -126,10 +126,9 @@ fn load_initramfs(mem: &GuestMemoryMmap, start_addr: u64, data: Vec<u8>) -> Resu
 pub fn kernel_setup(
     guest_memory: &GuestMemoryMmap,
     kernel_path: PathBuf,
-    initramfs_path: PathBuf,
+    initramfs_path: Option<PathBuf>,
 ) -> Result<KernelLoaderResult> {
     let mut kernel_image = File::open(kernel_path).map_err(Error::IO)?;
-    let initramfs = fs::read(initramfs_path).map_err(Error::IO)?;
     let zero_page_addr = GuestAddress(ZEROPG_START);
 
     // Load the kernel into guest memory.
@@ -141,10 +140,6 @@ pub fn kernel_setup(
     )
     .map_err(Error::KernelLoad)?;
 
-    // Load the initramfs into guest memory.
-    let (initramfs_addr, initramfs_size) =
-        load_initramfs(guest_memory, kernel_load.kernel_end, initramfs)?;
-
     // Generate boot parameters.
     let mut bootparams = build_bootparams(guest_memory, GuestAddress(HIMEM_START))?;
 
@@ -163,9 +158,17 @@ pub fn kernel_setup(
     )
     .map_err(Error::KernelLoad)?;
 
-    // Add the initramfs to the boot parameters.
-    bootparams.hdr.ramdisk_image = initramfs_addr;
-    bootparams.hdr.ramdisk_size = initramfs_size;
+    // Handle the initramfs.
+    if let Some(initramfs_path) = initramfs_path {
+        // Load the initramfs into guest memory.
+        let initramfs = fs::read(initramfs_path).map_err(Error::IO)?;
+        let (initramfs_addr, initramfs_size) =
+            load_initramfs(guest_memory, kernel_load.kernel_end, initramfs)?;
+
+        // Add the initramfs to the boot parameters.
+        bootparams.hdr.ramdisk_image = initramfs_addr;
+        bootparams.hdr.ramdisk_size = initramfs_size;
+    }
 
     // Write the boot parameters in the zeropage.
     LinuxBootConfigurator::write_bootparams::<GuestMemoryMmap>(

src/vmm/src/core/vmm.rs

@@ -12,7 +12,7 @@ use std::io;
 use std::net::Ipv4Addr;
 use std::os::unix::io::AsRawFd;
 use std::os::unix::prelude::RawFd;
-use std::path::Path;
+use std::path::{Path, PathBuf};
 use std::sync::{Arc, Mutex};
 use std::thread;
 use tracing::info;
@@ -220,13 +220,13 @@ impl VMM {
         num_vcpus: u8,
         mem_size_mb: u32,
         kernel_path: &Path,
-        initramfs_path: &Path,
+        initramfs_path: &Option<PathBuf>,
     ) -> Result<()> {
         self.configure_memory(mem_size_mb)?;
         let kernel_load = kernel::kernel_setup(
             &self.guest_memory,
             kernel_path.to_path_buf(),
-            initramfs_path.to_path_buf(),
+            initramfs_path.clone(),
         )?;
         self.configure_io()?;
         self.configure_vcpus(num_vcpus, kernel_load)?;