mount: enable bind mounting folders from initrd

Author: KarlK90

src/cmdline.rs

@@ -14,6 +14,7 @@ pub struct CmdlineOptions {
     pub nfsroot: Option<String>,
     pub init: String,
     pub cleanup: bool,
+    pub bind_mount: Option<String>,
 }
 
 const SBIN_INIT: &str = "/sbin/init";
@@ -28,6 +29,7 @@ impl Default for CmdlineOptions {
             nfsroot: None,
             init: SBIN_INIT.into(),
             cleanup: true,
+            bind_mount: None,
         }
     }
 }
@@ -45,6 +47,7 @@ fn parse_option(key: &str, value: Option<&str>, options: &mut CmdlineOptions) ->
         "rw" => options.rootfsflags.remove(MsFlags::MS_RDONLY),
         "nfsroot" => options.nfsroot = Some(ensure_value(key, value)?.to_string()),
         "init" => options.init = ensure_value(key, value)?.into(),
+        "rsinit.bind" => options.bind_mount = Some(ensure_value(key, value)?.to_string()),
         _ => (),
     }
     Ok(())
@@ -236,4 +239,19 @@ mod tests {
 
         assert_eq!(options, expected);
     }
+
+    #[test]
+    fn test_rsinit_bind() {
+        let cmdline = "root=/dev/root rsinit.bind=/lib/modules\n";
+
+        let expected = CmdlineOptions {
+            root: Some("/dev/root".into()),
+            bind_mount: Some("/lib/modules".into()),
+            ..Default::default()
+        };
+
+        let options = parse_cmdline(cmdline).expect("failed");
+
+        assert_eq!(options, expected);
+    }
 }

src/main.rs

@@ -30,6 +30,8 @@ use systemd::{mount_systemd, shutdown};
 #[cfg(feature = "usb9pfs")]
 use usbg_9pfs::prepare_9pfs_gadget;
 
+use crate::mount::mount_bind;
+
 mod cmdline;
 #[cfg(feature = "dmverity")]
 mod dmverity;
@@ -96,6 +98,7 @@ fn start_root(options: &mut CmdlineOptions) -> Result<()> {
         unlink(exe.as_path())?;
     }
 
+    mount_bind(options)?;
     mount_move_special(options)?;
 
     chdir("/root")?;

src/mount.rs

@@ -4,7 +4,7 @@
 use std::fs::remove_dir;
 use std::path::Path;
 
-use log::debug;
+use log::{debug, error};
 use nix::mount::{mount, MsFlags};
 
 use crate::cmdline::CmdlineOptions;
@@ -105,3 +105,19 @@ pub fn mount_move_special(options: &CmdlineOptions) -> Result<()> {
     mount_move("/proc", "/root/proc", options.cleanup)?;
     Ok(())
 }
+
+pub fn mount_bind(options: &CmdlineOptions) -> Result<()> {
+    if let Some(src) = &options.bind_mount {
+        if !Path::new(src).exists() {
+            error!("Can't bind mount {} as it doesn't exist", *src);
+            return Ok(());
+        }
+
+        let dst = format!("/root{src}");
+
+        debug!("Bind mounting {src} to {dst}");
+
+        do_mount(Some(src), &dst, None, MsFlags::MS_BIND, None)?;
+    }
+    Ok(())
+}