Add --mbr-file option handling to VM builder

src/builders_v2/linux_vm/mod.rs

@@ -171,6 +171,9 @@ pub struct BuildOpts {
     /// Create image from scratch (don't use base VM image).
     pub from_scratch: bool,
 
+    /// MBR bootcode file.
+    pub mbr_file: Option<PathBuf>,
+
     /// Mount root filesystem as read-write.
     pub rw_root: bool,
 

src/commands/build.rs

@@ -144,10 +144,7 @@ pub struct BuildArgs {
 
     /// Path to MBR file.
     ///
-    /// If none provided, following paths will be tried:
-    /// - /usr/share/syslinux/mbr.bin
-    /// - /usr/lib/syslinux/mbr/mbr.bin
-    /// - /usr/lib/syslinux/bios/mbr.bin
+    /// If none provided, a number of default locations will be tried.
     #[arg(long, value_name = "FILE", value_hint = ValueHint::FilePath, verbatim_doc_comment)]
     pub mbr_file: Option<PathBuf>,
 
@@ -361,6 +358,7 @@ impl TryFrom<&BuildArgs> for linux_vm::LinuxVMBuildContext {
 
         let gen_base_img = opts.generate_base_image;
         let from_scratch = opts.from_scratch;
+        let mbr_file = opts.mbr_file.clone();
         let rw_root = opts.rw_root;
 
         let opts = linux_vm::BuildOpts {
@@ -371,6 +369,7 @@ impl TryFrom<&BuildArgs> for linux_vm::LinuxVMBuildContext {
             init_system_opts,
             fs_source,
             from_scratch,
+            mbr_file,
             rw_root,
             gen_base_img,
         };